Research ArticleAcid Corrosion Inhibition and Adsorption Behaviour of EthylHydroxyethyl Cellulose on Mild Steel Corrosion
I O Arukalam1 I O Madu1 N T Ijomah1 C M Ewulonu2 and G N Onyeagoro1
1 Department of Polymer and Textile Engineering Federal University of Technology PMB 1526 Owerri Nigeria2 Department of Polymer and Textile Engineering Nnamdi Azikiwe University PMB 5025 Awka Nigeria
Correspondence should be addressed to I O Arukalam innocentarukalamyahoocom
Received 21 December 2013 Accepted 5 February 2014 Published 13 March 2014
Academic Editor Jean-Francois Gohy
Copyright copy 2014 I O Arukalam et alThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
The corrosion inhibition of mild steel in 10M H2SO4solution by ethyl hydroxyethyl cellulose has been studied in relation to the
concentration of the additive using weight loss measurement EIS polarization and quantum chemical calculation techniquesThe results indicate that EHEC inhibited corrosion reaction in the acid medium and inhibition efficiency increased with EHECconcentration Further increase in inhibition efficiency is observed in the presence of iodide ions due to synergistic effectImpedance results reveal that EHEC is adsorbed on the corroding metal surface Adsorption followed a modified Langmuirisotherm with very high negative values of the free energy of adsorption (Δ119866ads) The polarization data indicate that the inhibitorwas of mixed type with predominant effect on the cathodic partial reaction The frontier molecular orbitals HOMO (the highestoccupiedmolecular orbital) and LUMO (the lowest unoccupiedmolecular orbital) as well as local reactivity of the EHECmoleculewere analyzed theoretically using the density functional theory to explain the adsorption characteristics at a molecular level Thetheoretical predictions showed good agreement with experimental results
1 Introduction
Organic compounds containing polar functional groups suchas nitrogen sulphur andor oxygen in a conjugated systemhave been reported to be effective as corrosion inhibitors forsteel [1ndash8] Some of the organic compounds are polymericin nature and therefore possess multiple active centres Thestudy of corrosion inhibition by polymers has been on theincrease in recent times Polymers are employed as corrosioninhibitors because the presence of many adsorption centreshelps them form complexes with metal ions The formedcomplexes were adsorbed on the metal surface to form abarrier film which separated the metal surface from thecorrosive agents present in the aggressive solution [9ndash14]The effectiveness of inhibition by the adsorbed inhibitorsystem will be determined by the energy released on formingthe metal-inhibitor bond compared to the correspondingchanges when the pure acid reacts with the metal [15]
Some authors have reported on the effectiveness ofpolymeric corrosion inhibitors [16ndash20] In their accounts the
inhibitive power of these polymers is related structurally tothe cyclic rings and heteroatoms which are the major activecentres of adsorption
In order to support experimental studies theoreticalcalculations are conducted in order to provide molecular-level understanding of the observed experimental behaviourThe major driving force of quantum chemical research is tounderstand and explain the functions of ethyl hydroxyethylcellulose in molecular forms Among quantum chemicalmethods for evaluation of corrosion inhibitors density func-tional theory (DFT) has shown significant promise [21ndash23]and appears to be adequate for pointing out the changesin electronic structure responsible for inhibitory action Thegeometry of the inhibitor is in ground state as well as thenature of their molecular orbitals HOMO (the highest occu-pied molecular orbital) and LUMO (the lowest unoccupiedmolecular orbital) that are involved in the properties ofactivity of inhibitors [24 25]
The present study presents the appraisal of inhibitivecapability of ethyl hydroxyethyl cellulose (EHEC) on mild
Hindawi Publishing CorporationJournal of MaterialsVolume 2014 Article ID 101709 11 pageshttpdxdoiorg1011552014101709
2 Journal of Materials
steel corrosion in 10MH2SO4solution using weight loss
measurements and quantum chemical calculations tech-niques
2 Materials and Methods
21 Sample Preparation Tests were performed on mild steelspecimens of the following percentage chemical compositionSi 002 C 005Mn 018 Cu 002 Cr 002 and the remainderFe This was machined into test coupons of dimensions 3 times2 times 005 cm and a small hole drilled at one end of thecoupon to enable suspension into the test solution in thebeaker The metal specimens were polished with fine emerypaper degreased and cleaned as described elsewhere [2627] EHEC sourced from Sigma Aldrich chemical companywas used without further purification at concentrations of05 10 15 20 and 25 gL Blank sulphuric acid solutionwas prepared in the concentration of 10MH
2SO4 The
potassium iodide KI from BDH Laboratory Supplies wasused 05 gL KI was prepared and added to each of thesolutions containing the additive
22 Weight Loss Measurements Weight loss experimentswere conducted on test coupons Tests were conducted undertotal immersion conditions in 200mL of test solutions atambient temperature 28plusmn1∘CThe pre-cleaned and weighedcoupons were suspended in beakers containing the solutionsusing glass rods and hooks All tests were made in aeratedsolutions and were run three times to ensure reproducibilityTo determine weight loss with respect to time the couponswere retrieved from test solutions at 24 h intervals progres-sively for 120 h (5 days) At the end of the tests the weightloss was taken to be the mean value of the difference betweenthe initial and final weights of the coupons for the threedeterminations at a given time The corrosion rates of mildsteel in 10MH
2SO4solution and the acid solution containing
the additive EHEC were calculated from the expression
Corrosion rate 119877119888(mmy) = [
87 600Δ119882
120588119860119905] (1)
whereΔ119882 120588 119860 119905 areweight loss in gram density ofmild steelin gcm3 surface of the test coupon in cm2 and time periodof exposure in the test solution in hour respectively
23 Electrochemical Experiments Electrochemical experi-ments were performed using a VERSASTAT 3 AdvancedElectrochemical System operated with V3 Studio electro-chemical software A conventional three-electrode glass cellwas used for the experiments Test coupons with 1 cm2exposed surface area were used as working electrode and agraphite rod as counterelectrodeThe reference electrode wasa saturated calomel electrode (SCE) which was connectedvia Lugginrsquos capillary The working electrode was immersedin a test solution for 30 minutes to attain a stable opencircuit potential prior to electrochemical measurements Allexperiments were undertaken in 300mL of stagnant aeratedsolutions at 29 plusmn 1∘C Each test was run in triplicate to
verify the reproducibility of the systems Electrochemicalimpedance spectroscopy (EIS) measurements were madeat corrosion potentials (119864corr) over a frequency range of100 kHzndash10mHz with a signal amplitude perturbation of5mV Spectra analyses were performed using Zsimpwinsoftware Potentiodynamic polarization studies were carriedout in the potential range minus250 to +250mV at a scan rate of033mV sminus1
All theoretical quantum chemical calculations were per-formed using the density functional theory (DFT) electronicstructure programs Forcite and DMol3 as contained in theMaterials Studio 40 software
3 Results and Discussion
31 Corrosion Rates The corrosion rates of metals and alloysin aggressive solutions can be determined using differentelectrochemical and nonelectrochemical techniques Themechanism of anodic dissolution of iron in acidic solutionscorresponds to [28]
Fe +OHlArrrArr FeOHads + 119890minus (2a)
FeOHads 997888rarr FeOH+ + 119890minus (2b)
FeOH+ +H+ lArrrArr F2+ +H2O (2c)
As a consequence of these reactions including the highsolubility of the corrosion products the metal loses weightin the solution The results of the gravimetric determinationof mild steel corrosion rate as a function of time andconcentration of the additive are given in Table 1
These results show that the corrosion rate of mild steelin 10MH
2SO4decreases with time in systems with additive
and the blank acid solution The effects of addition ofdifferent concentrations of EHEC on corrosion rates in theacid solution after 5 days of exposure are shown in Table 1EHEC is observed to reduce the corrosion rate at the studiedconcentration of 05 gL EHEC indicating inhibition of thecorrosion reaction This effect becomes more pronouncedwith increasing concentration of the inhibitor which suggeststhat the inhibition process is sensitive to the concentration(amount) of the additive present
32 Inhibition Efficiency A quantitative evaluation of theeffect of EHEC on mild steel corrosion in 10M H
2SO4solu-
tion was achieved from appraisal of the inhibition efficiency(119868) given by
119868 = [1 minus119877cinh119877 cblk
] times 100 (3)
where 119877cinh and 119877cblk are the corrosion rates in inhibited anduninhibited solutions respectively The values obtained forthe inhibition efficiency are given in Table 2
The plots show that 119868 increased progressively with con-centration of the additive (Figure 1) Following the observedtrend of inhibition organic inhibitors are known to decreasemetal dissolution by forming a protective adsorption film
Journal of Materials 3
Table 1 Calculated values of corrosion rate of mild steel in 10M H2SO4 in the absence and presence of EHEC and KI
which blocks the metal surface separating it from the corro-sive medium [29ndash32] Consequently in inhibited solutionsthe corrosion rate is indicative of the number of free cor-roding sites remaining after some sites have been effectivelyblocked by inhibitor adsorption It has been suggested [3334] however that anions such as Clminus Iminus SO
4
2minus and S2minus mayalso participate in forming reaction intermediates on thecorroding metal surface which either inhibit or stimulatecorrosion It is important to recognize that the suppressionor stimulation of the dissolution process is initiated by thespecific adsorption of anion on the metal surface
33 Effect ofHalide IonAddition To further clarify themodesof inhibitor adsorption experiments were conducted in thepresence of iodide ions which are strongly adsorbed onthe surface of mild steel in acidic solution and facilitateadsorption of organic cation-type inhibitors by acting asintermediate bridges between the positive end of the organiccation and the positively charged metal surface Specificadsorption of iodide ions on the metal surface leads torecharging the electrical double layer [35] The inhibitor isthen drawn into the double layer by electrostatic interaction
with the adsorbed Iminus ions forming ion pairs on the metalsurface which increases the degree of surface coverage
Iminussol 997888rarr Iminusads (4a)
Iminusads + Inh+sol 997888rarr [Iminus minus Inh+]ads (4b)
Thus an improvement of 119868 on addition of KI is anindication of the participation of protonated inhibitor speciesin the adsorption process (Figure 2) Table 2 illustrates theeffect of addition of 05 gL KI to the different concentrationsof EHEC on the corrosion of mild steel in 10MH
2SO4
solution
34 Adsorption Consideration Basic parameters which aredescriptors of the nature and modes of adsorption of organicinhibitor on the corroding metal surface can be provided byadsorption isotherms which depend on the degree of surfacecoverage 120579 The observed inhibition of the corrosion of mildsteel in 10MH
2SO4solution indicates high degree of surface
coverage From a theoretical perspective the adsorptionroute is regarded as a substitution process between theorganic inhibitor in the aqueous solution (Inhsol) and water
4 Journal of Materials
05 10 15 20 25
42
44
46
48
50
52
54
56
Day 1Day 2Day 3
Day 4Day 5
Inhi
bitio
n effi
cien
cy I
()
Concentration of inhibitor C (gL)
Figure 1 Variation of inhibition efficiency with concentration ofEHEC
molecules adsorbed at the metal surface (H2Oads) as follows
[36ndash38]
Inh(sol) + 119909H2O(ads) lArrrArr Inh
(ads) + 119909H2O(sol) (5)
where 119909 represents the number of water molecules replacedby one molecule of adsorbed inhibitor The adsorption bondstrength is dependent on the composition of the metal andcorrodent inhibitor structure concentration and orienta-tion as well as temperature Since EHEC can be protonated inthe presence of strong acids it is quite necessary to considerboth cationic and molecular species when discussing theadsorption process of EHEC Figure 3 shows the plot of119862120579 versus 119862 to be linear which is in agreement with theLangmuir equation [39]
119862
120579=
119899
119870ads+ 119899119862 (6)
where 119862 is the concentration of inhibitor and 119870ads is theequilibrium constant for the adsorption-desorption process
In general 119870ads represents the adsorption power ofthe inhibitor molecule on the metal surface The positivevalues confirm the adsorbability of EHEC on the metalsurface The linear plots obtained in Figure 3 suggest thatEHEC adsorption from 10MH
2SO4solution followed the
Langmuir isotherm though the isothermparameters indicatesome deviations from ideal Langmuir behaviour The slopedeviates from unity (see 119899 values in Table 3) with nonzerointercept on the 119910-axis which could be traced to somelimitations in the underlying assumptions The results in factimply that each EHEC molecule occupies 119899 active corrosionsites on the mild steel surface in 10M H
2SO4solution
The free energy of adsorption (Δ119866ads) obtained from (7)which is evaluated from 119870ads obtained from intercepts of theLangmuir plots is given in Table 3
where 119877 and 119879 are the universal gas constant and absolutetemperature respectively The other parameter retains itsprevious meaning The large negative Δ119866ads values impliedthat the adsorption of EHEC on the mild steel surface wasfavourable from thermodynamics point of view and indicatedthat the inhibitor was strongly adsorbed covering bothanodic and cathodic regions
In addition it is important to note that adsorption freeenergy values of minus20 kJmolminus1 or less negative are associatedwith an electrostatic interaction between charged moleculesand charged metal surface (physical adsorption) On theother hand adsorption free energy values of minus40Kjmolminus1 ormore negative values involve charge sharing or transfer fromthe inhibitor molecules to the metal surface to form a co-ordinate covalent bond (chemical adsorption) [40]
35 Impedance Measurements Electrochemical impedancespectroscopy analyses provide insight into the kinetics ofelectrode processes as well as the surface characteristicsof the electrochemical system of interest Figure 4 presentsthe impedance spectra measured at 119864corr after 30minutesof immersion and exemplified the Nyquist plots obtainedfor mild steel in 10MH
2SO4solution in the absence and
presence of EHEC and EHEC + KI The observed increase inthe impedance parameters in inhibited solutions is associatedwith the corrosion inhibiting effect of EHEC The Nyquistplots for all systems generally have the form of only onedepressed semicircle corresponding to one time constantalthough a slight sign of low-frequency inductive behaviourcan be discerned The depression of the capacitance semicir-cle with centre below the real axis suggests a distribution ofthe capacitance due to inhomogeneities associated with theelectrode surface
The presence of a single time constant may be attributedto the short exposure time in the corrosive medium whichis not adequate to reveal degradation of the substrate [41]A polarization resistance (119877
119901) can be extracted from the
intercept of the low-frequency loop at the real axis ofimpedance (119885re) in the Nyquist plots since the inductiveloop is negligible The value of 119877
119901is very close to that of
the charge transfer resistance 119877ct which can be extractedfrom the diameter of the semicircle [41 42] The impedancespectra for theNyquist plotswere thus adequately analyzed bybeing fit to the equivalent circuit model119877
119904(119876dl119877ct) which has
been previously used to model the mild steelacid solutioninterface [41 43]
The values of the impedance parameters derived fromthe Nyquist plots using the selected equivalent circuit model119877119904(119876dl119877ct) are given in Table 4 The terms 119876dl and 119899
respectively represent the magnitude and exponent of theconstant phase element (CPE) of the double layer The CPEwith impedance given by 119885CPE = 119876minus1(119895119908)
minus119899 where 119895 isan imaginary number and 119908 is the angular frequency in
Journal of Materials 5
1 2 3 4 50
102030405060708090
100
Time (days)
05 gL EHEC05 gL EHEC + KI
1 2 3 4 50
102030405060708090
100
Time (days)
10 gL EHEC10 gL EHEC + KI
1 2 3 4 50
102030405060708090
100
Time (days)
15 gL EHEC15 gL EHEC + KI
1 2 3 4 50
102030405060708090
100
Time (days)
20 gL EHEC20 gL EHEC + KI
1 2 3 4 50
102030405060708090
100
Time (days)
25 gL EHEC25 gL EHEC + KI
Inhi
bitio
n effi
cien
cy I
()
Inhi
bitio
n effi
cien
cy I
()
Inhi
bitio
n effi
cien
cy I
()
Inhi
bitio
n effi
cien
cy I
()
Inhi
bitio
n effi
cien
cy I
()
Figure 2 Synergistic effect between KI and EHEC on the variation of inhibition efficiency with time
rads is used in place of a capacitor to compensate for thedeviations from ideal dielectric behaviour associated withthe nonhomogeneity of the electrode surface Introductionof EHEC into the acid corrodent leads to an increase in 119877ctand a reduction of119876dl indicating a hindering of the corrosionreaction The decrease in 119876dl values which normally resultsfrom a decrease in the dielectric constant andor an increasein the double layer thickness is due to inhibitor adsorption onthe metalelectrolyte interface [44] This implies that EHECreduces the corrosion rate of themild steel specimen by virtueof adsorption on the metalelectrolyte interface a fact thathas been previously established A quantitative measure ofthe protective effect can be obtained by comparing the values
of the charge transfer resistance in the absence (119877ct) andpresence of inhibitor (119877ctinh) as follows
119868 = [1 minus119877ct119877ctinh
] times 100 (8)
where (119877ctinh) and 119877ct are the charge transfer resistance forinhibited and uninhibited systems respectively
The double layer capacitance values of the systems werealso examined and calculated using the expression
119862dl =1
2120587119891max119877ct (9)
where 119891max is the maximum frequency The obtained valuesof 119862dl are presented in Table 4
6 Journal of Materials
05 10 15 20 25
10
15
20
25
30
35
40
45
50
Day 1Day 2Day 3
Day 4Day 5
C120579
(gL
)
C (gL)
Figure 3 Langmuir isotherm for EHEC adsorption on mild steelsurface in 10MH
2SO4
0 20 40 60 80 100 120 140
0102030405060708090
100110120130140
Blank25 gL EHEC25 gL EHEC + KI
Zim
(Ω)
Zre (Ω)
Figure 4 Nyquist impedance spectra of mild steel corrosion in10MH
2SO4in the absence and presence of EHEC and EHEC + KI
Lower double layer capacitance suggests reduced electriccharge stored which is a consequence of increased adsorp-tion layer that acted as a dielectric constant The increasein 119877ct values in inhibited systems which corresponds to anincrease in the diameter of the Nyquist semicircle confirmsthat the corrosion inhibiting effect of EHEC and EHEC + KIand is much more pronounced in the latter system implyingthat KI synergistically enhanced the corrosion inhibitingeffect of EHEC In other words lower 119862dl values correspond
to reduced double layer capacitance which according to theHelmholtzmodel (10) results fromadecrease in the dielectricconstant (120576) or an increase in the interfacial layer thickness(120575)
119862dl =120576120576119900119860
120575 (10)
where 120576 is the dielectric constant of the medium 120576119900is the
vacuum permittivity 119860 is the electrode area and 120575 is thethickness of the interfacial layer
Since adsorption of an organic inhibitor on a metalsurface involves the replacement of adsorbedwatermoleculeson the surface the smaller dielectric constant of the organicmolecule compared towater aswell as the increased thicknessof interfacial layer due to inhibitor adsorption acted simulta-neously to reduce the double layer capacitanceThis providesexperimental evidence of adsorption of EHEC on mild steelsurface The significantly lower 119862dl value of the EHEC + KIsystem supports the assertion that the iodide ion significantlyenhances adsorption of EHEC on the metalsolution inter-face
36 Polarization Measurements Figure 5 shows the polar-ization curves of mild steel dissolution in 10MH
2SO4
solution in the absence and presence of EHEC and EHEC+ KI Introduction of EHEC and EHEC + KI into the acidsolutionwas observed to shift the corrosion potentials of bothinhibited systems slightly in the negative direction and inboth cases inhibited the anodic metal dissolution reactionas well as the cathodic hydrogen evolution reaction Sincethe 119864corr is not altered significantly the implication is thatthe corrosion inhibition process is under mixed control withpredominant cathodic effect In addition following observa-tions in Figure 5 both cathodic and anodic partial reactionsare affected as evident in decrease in the corrosion currentdensities This implies that EHEC functioned as a mixed-type inhibitor for both systems However marked cathodicpartial hydrogen evolution reaction is discerned Moresodocumented report [45] has it that when displacement in119864corr is gt85mV the inhibitor can be regarded as a cathodicor anodic type inhibitor and if the displacement in 119864corris lt85mV the inhibitor can be seen as mixed type In thepresent study the displacement in the corrosion potential(119864corr) in the presence of EHEC and EHEC + KI shifted952 and 2075mV respectively in the cathodic directioncompared to the blank which is a confirmation that theinhibitor acts as a mixed-type inhibitor with predominantcathodic effect
Journal of Materials 7
Table 4 Impedance and polarization parameters for mild steel in 05M H2SO4 in the presence and absence of EHEC and EHEC + KI
System Impedance data Polarization data119877ct 119899 IE 119862dl (uF cm
minus2) times 10minus3 119864corr (mV (SCE)) 119877119901(Ω cm2) IE
Inhibition efficiency was calculated from the polarizationdata as follows
119868 = [1 minus119877119901
119877119901
inh] times 100 (11)
where 119877119901and 119877
119901
inh are polarization resistance for uninhib-ited and inhibited systems respectivelyThe calculated valuesare given in Table 4 Observations from Table 4 show thatthe inhibition efficiencies obtained from both impedanceand polarization results are comparable The data confirmthe consistency of EHEC and EHEC + KI at the prevailingexperimental condition
The cooperative effect between EHEC and KI in hin-dering the corrosion of mild steel in 10MH
2SO4solution
is also evident in both the Nyquist and Tafel polarizationplots Addition of KI resulted in a significant increase in thediameter of the Nyquist semicircle and hence an increase in119877ct as well as 119868 and a decrease in the corrosion currentdensity of the Tafel polarization curves The presence ofiodide ions shifts 119864corr more in the cathodic direction andfurther decreases the anodic and cathodic reaction kineticsThe mechanism of this synergistic effect has been describedin detail in some reports [46] The iodide ions are stronglychemisorbed on the corrodingmild steel surface and facilitateEHEC adsorption by acting as intermediate bridges betweenthe positively charged metal surface and EHEC cations Thisstabilizes the adsorption of EHEC on the mild steel surfaceleading to higher surface coverage To account for the aboveobservations it is necessary to recognize that the process ofadsorption of an organic inhibitor on a corroding metal sur-face depends on factors such as the nature and surface chargeon the metal in the corrosive medium as well as the inhibitorstructure Consequently more iodide ions are adsorbed onmild steel which presents a more positive surface giving riseto increased synergistic interactions with protonated EHECspecies and hence higher inhibition efficiencies
E versus SCE (V)minus08 minus07 minus06 minus05 minus04 minus03 minus02
001
1E minus 3
1E minus 4
1E minus 5
1E minus 6
Blank25 gL EHEC25 gL EHEC + KI
i(A
cmminus2)
Figure 5 Polarization curves ofmild steel corrosion in 10MH2SO4
in the absence and presence of EHEC and EHEC + KI
37 Quantum Chemical Calculations The inhibition effec-tiveness of inhibitors has been reported to correlate with thequantum chemical parameters such as HOMO (the highestoccupied molecular orbital) LUMO (the lowest unoccupiedmolecular orbital) and the energy gap between the LUMOand HOMO (Δ119864 = 119864LUMO minus 119864HOMO) [47ndash49] A high119864HOMO (less negative) is associated with the capacity of amolecule to donate electrons to an appropriated acceptorwith empty molecular orbital that facilitated the adsorptionprocess and therefore indicated good performance of thecorrosion inhibitor [50] 119864LUMO corresponds to a tendencyfor electron acceptance Based on this the calculated dif-ference Δ119864 demonstrates inherent electron donating abilityand measures the interaction of the inhibitor molecule withthe metal surface
According to the frontier molecular orbital theory ofchemical reactivity transition of electrons is due to aninteraction between the frontier orbitals HOMOand LUMOof reacting species The energy of HOMO is directly relatedto the ionization potential and characterizes the susceptibilityof the molecule toward attack by electrophiles The energyof LUMO is directly related to the electron affinity andcharacterizes the susceptibility of the molecule toward attackby nucleophile The lower the values of 119864LUMO the strongerthe electron accepting ability of the molecule
8 Journal of Materials
(a) Optimized structure (b) Total electron density
(c) HOMO orbital (d) LUMO orbital
(e) Fukui function for nucleophilic attack (f) Fukui function for electrophilic attack
Figure 6 Electronic properties of ethyl hydroxyethyl cellulose (EHEC) [C grey H white O red]
The electronic structure of EHEC the distribution offrontier molecular orbital and Fukui indices have beenmod-eled in order to establish the active sites as well as local reac-tivity of the inhibitingmoleculesThis was achieved using theDFT electronic structure programs Forcite and DMol3 andusing a Mulliken population analysis Electronic parametersfor the simulation include restricted spin polarization usingtheDNDbasis set as the PerdewWang (PW) local correlationdensity functional The geometry optimized structures ofEHEC HOMO and LUMOorbitals Fukui functions and thetotal electron density are presented in Figure 6 In the EHEC
molecule theHOMOorbital is saturated around the aromaticnucleus which is the region of highest electron density andoften the site at which electrophiles attack and represents theactive centres with the utmost ability to bond to the metalsurface The LUMO orbital is saturated around the ethoxyfunction and represents the site at which nucleophilic attackoccurs
Local reactivity was analyzed by means of the Fukuiindices to assess the active regions in terms of nucleophilicand electrophilic behaviour Thus the site for nucleophilicattack will be the place where the value of 119891+ is maximum In
Journal of Materials 9
turn the site for electrophilic attack is controlled by the valueof 119891minus The values of 119864HOMO 119864LUMO Δ119864 and Fukui functionsare given inTable 5Higher values of119864HOMO indicate a greaterdisposition of a molecule to donate electrons to a metalsurface In the same way low values of the energy of the gapΔ119864 will afford good inhibition efficiency since the energyrequired to remove an electron from the last occupied orbitalwill be minimized [51] The above descriptors howeversuggest that EHEC possessed good inhibiting potential Thisis in agreement with the experimental findings
4 Conclusions
Ethyl hydroxyethyl cellulose was found to be an effectiveinhibitor of mild steel in 10MH
2SO4solution and its inhibi-
tion efficiency increased with increasing concentration Thecorrosion process is inhibited by adsorption of EHEC on themild steel surface following themodified Langmuir isothermThe inhibiting action is attributed to general adsorption ofboth protonated and molecular species of the additive on thecathodic and anodic sites on the corrodingmild steel surfaceIn addition corrosion inhibition is due to the formationof a chemisorbed film on the mild steel surface The EISmeasurement confirmed the adsorption of EHEC and EHEC+ KI on the mild steel surface Polarization studies showedthat EHEC and EHEC + KI were mixed-type inhibitorsystems with predominant cathodic effect The theoreticalstudy demonstrated that the inhibition efficiency is related tomolecular structure of inhibitor whereby increase in 119864HOMOand decrease in 119864LUMO favoured inhibition efficiency
Conflict of Interests
Theauthors hereby declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors are grateful to Udemmadu Tochukwu andOchiogu Valentine for assistance in carrying out some mea-surements
References
[1] E E Oguzie Y Li and F H Wang ldquoEffect of ascorbic acidon mild steel dissolution in sulphuric acid solution investigatedby electrochemical polarization and surface probe techniquesrdquoJournal of Applied Electrochemistry vol 37 no 10 pp 1183ndash11902007
[2] L G da Trindade and R S Goncalves ldquoEvidence of caffeineadsorption on a low-carbon steel surface in ethanolrdquo CorrosionScience vol 51 no 8 pp 1578ndash1583 2009
[3] F Bentiss M Outirite M Traisnel et al ldquoImprovementof corrosion resistance of carbon steel in hydrochloric acidmedium by 36-bis(3-pyridyl)pyridazinerdquo International Journalof Electrochemical Science vol 7 no 2 pp 1699ndash1723 2012
[4] S M A Shibli and V S Saji ldquoCo-inhibition characteristicsof sodium tungstate with potassium iodate on mild steelcorrosionrdquoCorrosion Science vol 47 no 9 pp 2213ndash2224 2005
[5] E E Oguzie C Unaegbu C N Ogukwe B N Okolue and AI Onuchukwu ldquoInhibition of mild steel corrosion in sulphuricacid using indigo dye and synergistic halide additivesrdquoMateri-als Chemistry and Physics vol 84 no 2-3 pp 363ndash368 2004
[6] V Kumpawat U Garg and R K Tak ldquoCorrosion inhibitionof aluminium in acid media by naturally occurring plantArtocarpus heterophyllus and Acacia senegalrdquo Journal of IndianCouncil of Chemists vol 26 no 1 pp 82ndash84 2009
[7] IA Akpan and N O Offiong ldquoEffect of ethanolamine andethylamine on the entropy content of the corrosion ofmild steelin tetraoxosulphate (VI) acid solutionrdquoChemistry andMaterialsResearch vol 2 no 7 pp 40ndash47 2012
[8] M Kissi M Bouklah B Hammouti and M BenkaddourldquoEstablishment of equivalent circuits from electrochemicalimpedance spectroscopy study of corrosion inhibition of steelby pyrazine in sulphuric acidic solutionrdquo Applied SurfaceScience vol 252 no 12 pp 4190ndash4197 2006
[9] S Rajendran S P Sridevi N Anthony A J Amalraj andM Sundaravadivelu ldquoCorrosion behaviour of carbon steel inpolyvinyl alcoholrdquo Anti-Corrosion Methods and Materials vol52 no 2 pp 102ndash107 2005
[10] B Qian J Wang M Zheng and B Hou ldquoSynergistic effect ofpolyaspartic acid and iodide ion on corrosion inhibition ofmildsteel in H
[11] D A Arthur A Jonathan P O Ameh and C Anya ldquoAreview on the assessment of polymeric materials used ascorrosion inhibitor of metals and alloysrdquo International Journalof Industrial Chemistry vol 4 article 2 pp 1ndash9 2013
[12] S A Umoren Y Li and F H Wang ldquoEffect of polyacrylicacid on the corrosion behaviour of aluminium in sulphuric acidsolutionrdquo Journal of Solid State Electrochemistry vol 14 no 12pp 2293ndash2305 2010
[13] S Banerjee A Mishra M M Singh B Maiti B Ray andP Maiti ldquoHighly efficient polyurethane ionomer corrosioninhibitor the effect of chain structurerdquo RSCAdvances vol 1 no2 pp 199ndash210 2011
[14] A K Dubey and G Singh ldquoCorrosion inhibition of mild steelin sulphuric acid solution by using polyethylene glycol methylether (PEGME)rdquo Portugaliae Electrochimica Acta vol 25 no 2pp 221ndash235 2007
[15] E E Oguzie S G Wang Y Li and F H Wang ldquoInfluenceof iron microstructure on corrosion inhibitor performance inacidic mediardquoThe Journal of Physical Chemistry C vol 113 no19 pp 8420ndash8429 2009
[16] S A Umoren E E Ebenso P C Okafor and O OgbobeldquoWater-soluble polymers as corrosion inhibitorsrdquo Pigment ampResin Technology vol 35 no 6 pp 346ndash352 2006
[17] S A Umoren and I B Obot ldquoPolyvinylpyrollidone andpolyacrylamide as corrosion inhibitors for mild steel in acidicmediumrdquo Surface Review and Letters vol 15 no 3 pp 277ndash2842008
[18] H Ashassi-Sorkhabi and N Ghalebsaz-Jeddi ldquoInhibition effectof polyethylene glycol on the corrosion of carbon steel insulphuric acidrdquoMaterials Chemistry and Physics vol 92 no 2-3pp 480ndash486 2005
[19] A Yurt V Butun and B Duran ldquoEffect of themolecular weightand structure of some novel water-soluble triblock copolymerson the electrochemical behaviour of mild steelrdquo MaterialsChemistry and Physics vol 105 no 1 pp 114ndash121 2007
10 Journal of Materials
[20] S A Umoren ldquoPolymers as corrosion inhibitors for metals indifferent mediamdasha reviewrdquo The Open Corrosion Journal vol 2pp 175ndash188 2009
[21] K F Khaled ldquoCorrosion control of copper in nitric acidsolutions using some amino acidsmdasha combined experimentaland theoretical studyrdquo Corrosion Science vol 52 no 10 pp3225ndash3234 2010
[22] E E Oguzie C O Akalezi C K Enenebeaku and J N AnekeldquoCorrosion inhibition and adsorption behavior of malachitegreen dye on aluminum corrosionrdquoChemical Engineering Com-munications vol 198 no 1 pp 46ndash60 2011
[23] J Cruz T Pandiyan and E Garcia-Ochoa ldquoA new inhibitor formild carbon steel electrochemical and DFT studiesrdquo Journal ofElectroanalytical Chemistry vol 583 no 1 pp 8ndash16 2005
[24] J Cruz R Martinez J Genesca and E Garcia-OchoaldquoExperimental and theoretical study of 1-(2-ethylamino)-2-methylimidazoline as an inhibitor of carbon steel corrosion inacid mediardquo Journal of Electroanalytical Chemistry vol 566 no1 pp 111ndash121 2004
[25] E E Oguzie Y Li S G Wang and F Wang ldquoUnderstandingcorrosion inhibition mechanismsmdashexperimental and theoreti-cal approachrdquo RSC Advances vol 1 no 5 pp 866ndash873 2011
[26] A Kumar A Sankara M Kumaravel and S RameshkumarldquoClitoria ternateamdashextracts as corrosion inhibitor for mild steelin acid mediumrdquo International Journal of Engineering Researchand Development vol 8 no 5 pp 64ndash67 2013
[27] E E Oguzie G N Onuoha and A I Onuchukwu ldquoInhibitorymechanism of mild steel corrosion in 2M sulphuric acidsolution by methylene blue dyerdquo Materials Chemistry andPhysics vol 89 no 2-3 pp 305ndash311 2005
[28] E E Oguzie C K Enenebeaku C O Akalezi S C Okoro AA Ayuk and E N Ejike ldquoAdsorption and corrosion-inhibitingeffect ofDacryodis edulis extract on low-carbon-steel corrosionin acidic mediardquo Journal of Colloid and Interface Science vol349 no 1 pp 283ndash292 2010
[29] E E Oguzie ldquoCorrosion inhibition of aluminium in acidicand alkaline media by Sansevieria trifasciata extractrdquo CorrosionScience vol 49 no 3 pp 1527ndash1539 2007
[30] S A Umoren I B Obot and E E Ebenso ldquoCorrosioninhibition of aluminium using exudate gum from Pachylobusedulis in the presence of halide ions in HClrdquo E-Journal ofChemistry vol 5 no 2 pp 355ndash364 2008
[31] P C Okafor E E Ebenso and U J Ekpe ldquoAzadirachta indicaextracts as corrosion inhibitor for mild steel in acid mediumrdquoInternational Journal of Electrochemical Science vol 5 no 7 pp978ndash993 2010
[32] M Lebrini F Robert A Lecente and C Roos ldquoCorrosioninhibition of C38 steel in 1M hydrochloric acid medium byalkaloids extract from Oxandra asbeckii plant rdquo CorrosionScience vol 53 no 2 pp 687ndash695 2011
[33] E E Oguzie ldquoInfluence of halide ions on the inhibitive effect ofcongo red dye on the corrosion of mild steel in sulphuric acidsolutionrdquoMaterials Chemistry and Physics vol 87 no 1 pp 212ndash217 2004
[34] E E Oguzie ldquoInhibition of acid corrosion of mild steel byTelfaria occidentalis extractrdquo Pigment amp Resin Technology vol34 no 6 pp 321ndash326 2005
[35] E E Oguzie V O Njoku C K Enenebeaku C O Akalezi andC Obi ldquoEffect of hexamethylpararosaniline chloride (crystalviolet) on mild steel corrosion in acidic mediardquo CorrosionScience vol 50 no 12 pp 3480ndash3486 2008
[36] M A Ameer E Khamis and G al-Senani ldquoEffect of temper-ature on stability of adsorbed inhibitors on steel in phosphoricacid solutionrdquo Journal of Applied Electrochemistry vol 32 no 2pp 149ndash156 2002
[37] P C Okafor E E Oguzie G E Iniama M E Ikpi and U JEkpe ldquoCorrosion inhibition properties of thiosemicarbazoneand semicarbazone derivatives in concentrated acid environ-mentrdquoGlobal Journal of Pure and Applied Sciences vol 14 no 1pp 89ndash96 2008
[38] I B Obot ldquoSynergistic effect of nizoral and iodide ions on thecorrosion inhibition of mild steel in sulphuric acid solutionrdquoPortugaliae ElectrochimicaActa vol 27 no 5 pp 539ndash553 2009
[39] N O Eddy S A Odoemelam and A O Odiongenyi ldquoEthanolextract of musa species peels as a green corrosion inhibitor formild steel kinetics adsorption and thermodynamic consider-ationsrdquo Electronic Journal of Environmental Agricultural andFood Chemistry vol 8 no 4 pp 243ndash255 2009
[40] M H Hussin and M J Kassim ldquoThe corrosion inhibition andadsorption behavior of Uncaria gambir extract on mild steel in1M HClrdquo Materials Chemistry and Physics vol 125 no 3 pp461ndash468 2010
[41] V K W Grips V E Selvi H C Barshilia and K S RajamldquoEffect of electroless nickel interlayer on the electrochemicalbehavior of single layer CrN TiN TiAlN coatings and nanolay-ered TiAlNCrN multilayer coatings prepared by reactive dcmagnetron sputteringrdquo Electrochimica Acta vol 51 no 17 pp3461ndash3468 2006
[42] E E Oguzie ldquoStudies on the inhibitive effect ofOccimum viridisextract on the acid corrosion of mild steelrdquoMaterials Chemistryand Physics vol 99 no 2-3 pp 441ndash446 2006
[43] B Wang M Du J Zhang and C J Gao ldquoElectrochemical andsurface analysis studies on corrosion inhibition of Q235 steelby imidazoline derivative against CO
2corrosionrdquo Corrosion
Science vol 53 no 1 pp 353ndash361 2011[44] G Mu and X Li ldquoInhibition of cold rolled steel corrosion
by Tween-20 in sulfuric acid weight loss electrochemical andAFM approaches rdquo Journal of Colloid and Interface Science vol289 no 1 pp 184ndash192 2005
[45] A K Satapathy G Gunasekaran S C Sahoo K Amit and PV Rodrigues ldquoCorrosion inhibition by Justicia gendarussa plantextract in hydrochloric acid solutionrdquoCorrosion Science vol 51no 12 pp 2848ndash2856 2009
[46] E E Oguzie Y Li and F H Wang ldquoCorrosion inhibition andadsorption behavior of methionine on mild steel in sulfuricacid and synergistic effect of iodide ionrdquo Journal of Colloid andInterface Science vol 310 no 1 pp 90ndash98 2007
[47] L M Rodrıguez-Valdez W Villamisar M Casales et alldquoComputational simulations of themolecular structure and cor-rosion properties of amidoethyl aminoethyl and hydroxyethylimidazolines inhibitorsrdquo Corrosion Science vol 48 no 12 pp4053ndash4064 2006
[48] H Ju Z P Kai and Y Li ldquoAminic nitrogen-bearing polydentateSchiff base compounds as corrosion inhibitors for iron in acidicmedia a quantum chemical calculationrdquo Corrosion Science vol50 no 3 pp 865ndash871 2008
[49] L M Rodrıguez-Valdez A Martınez-Villafane and DGlossman-Mitnik ldquoComputational simulation of themolecularstructure and properties of heterocyclic organic compoundswith possible corrosion inhibition propertiesrdquo Journal ofMolecular Structure THEOCHEM vol 713 no 1ndash3 pp 65ndash702005
Journal of Materials 11
[50] K F Khaled ldquoMolecular simulation quantum chemical calcu-lations and electrochemical studies for inhibition of mild steelby triazolesrdquo Electrochimica Acta vol 53 no 9 pp 3484ndash34922008
[51] R M Issa M K Awad and F M Atlam ldquoQuantum chemicalstudies on the inhibition of corrosion of copper surface bysubstituted uracilsrdquo Applied Surface Science vol 255 no 5 pp2433ndash2441 2008
steel corrosion in 10MH2SO4solution using weight loss
measurements and quantum chemical calculations tech-niques
2 Materials and Methods
21 Sample Preparation Tests were performed on mild steelspecimens of the following percentage chemical compositionSi 002 C 005Mn 018 Cu 002 Cr 002 and the remainderFe This was machined into test coupons of dimensions 3 times2 times 005 cm and a small hole drilled at one end of thecoupon to enable suspension into the test solution in thebeaker The metal specimens were polished with fine emerypaper degreased and cleaned as described elsewhere [2627] EHEC sourced from Sigma Aldrich chemical companywas used without further purification at concentrations of05 10 15 20 and 25 gL Blank sulphuric acid solutionwas prepared in the concentration of 10MH
2SO4 The
potassium iodide KI from BDH Laboratory Supplies wasused 05 gL KI was prepared and added to each of thesolutions containing the additive
22 Weight Loss Measurements Weight loss experimentswere conducted on test coupons Tests were conducted undertotal immersion conditions in 200mL of test solutions atambient temperature 28plusmn1∘CThe pre-cleaned and weighedcoupons were suspended in beakers containing the solutionsusing glass rods and hooks All tests were made in aeratedsolutions and were run three times to ensure reproducibilityTo determine weight loss with respect to time the couponswere retrieved from test solutions at 24 h intervals progres-sively for 120 h (5 days) At the end of the tests the weightloss was taken to be the mean value of the difference betweenthe initial and final weights of the coupons for the threedeterminations at a given time The corrosion rates of mildsteel in 10MH
2SO4solution and the acid solution containing
the additive EHEC were calculated from the expression
Corrosion rate 119877119888(mmy) = [
87 600Δ119882
120588119860119905] (1)
whereΔ119882 120588 119860 119905 areweight loss in gram density ofmild steelin gcm3 surface of the test coupon in cm2 and time periodof exposure in the test solution in hour respectively
23 Electrochemical Experiments Electrochemical experi-ments were performed using a VERSASTAT 3 AdvancedElectrochemical System operated with V3 Studio electro-chemical software A conventional three-electrode glass cellwas used for the experiments Test coupons with 1 cm2exposed surface area were used as working electrode and agraphite rod as counterelectrodeThe reference electrode wasa saturated calomel electrode (SCE) which was connectedvia Lugginrsquos capillary The working electrode was immersedin a test solution for 30 minutes to attain a stable opencircuit potential prior to electrochemical measurements Allexperiments were undertaken in 300mL of stagnant aeratedsolutions at 29 plusmn 1∘C Each test was run in triplicate to
verify the reproducibility of the systems Electrochemicalimpedance spectroscopy (EIS) measurements were madeat corrosion potentials (119864corr) over a frequency range of100 kHzndash10mHz with a signal amplitude perturbation of5mV Spectra analyses were performed using Zsimpwinsoftware Potentiodynamic polarization studies were carriedout in the potential range minus250 to +250mV at a scan rate of033mV sminus1
All theoretical quantum chemical calculations were per-formed using the density functional theory (DFT) electronicstructure programs Forcite and DMol3 as contained in theMaterials Studio 40 software
3 Results and Discussion
31 Corrosion Rates The corrosion rates of metals and alloysin aggressive solutions can be determined using differentelectrochemical and nonelectrochemical techniques Themechanism of anodic dissolution of iron in acidic solutionscorresponds to [28]
Fe +OHlArrrArr FeOHads + 119890minus (2a)
FeOHads 997888rarr FeOH+ + 119890minus (2b)
FeOH+ +H+ lArrrArr F2+ +H2O (2c)
As a consequence of these reactions including the highsolubility of the corrosion products the metal loses weightin the solution The results of the gravimetric determinationof mild steel corrosion rate as a function of time andconcentration of the additive are given in Table 1
These results show that the corrosion rate of mild steelin 10MH
2SO4decreases with time in systems with additive
and the blank acid solution The effects of addition ofdifferent concentrations of EHEC on corrosion rates in theacid solution after 5 days of exposure are shown in Table 1EHEC is observed to reduce the corrosion rate at the studiedconcentration of 05 gL EHEC indicating inhibition of thecorrosion reaction This effect becomes more pronouncedwith increasing concentration of the inhibitor which suggeststhat the inhibition process is sensitive to the concentration(amount) of the additive present
32 Inhibition Efficiency A quantitative evaluation of theeffect of EHEC on mild steel corrosion in 10M H
2SO4solu-
tion was achieved from appraisal of the inhibition efficiency(119868) given by
119868 = [1 minus119877cinh119877 cblk
] times 100 (3)
where 119877cinh and 119877cblk are the corrosion rates in inhibited anduninhibited solutions respectively The values obtained forthe inhibition efficiency are given in Table 2
The plots show that 119868 increased progressively with con-centration of the additive (Figure 1) Following the observedtrend of inhibition organic inhibitors are known to decreasemetal dissolution by forming a protective adsorption film
Journal of Materials 3
Table 1 Calculated values of corrosion rate of mild steel in 10M H2SO4 in the absence and presence of EHEC and KI
which blocks the metal surface separating it from the corro-sive medium [29ndash32] Consequently in inhibited solutionsthe corrosion rate is indicative of the number of free cor-roding sites remaining after some sites have been effectivelyblocked by inhibitor adsorption It has been suggested [3334] however that anions such as Clminus Iminus SO
4
2minus and S2minus mayalso participate in forming reaction intermediates on thecorroding metal surface which either inhibit or stimulatecorrosion It is important to recognize that the suppressionor stimulation of the dissolution process is initiated by thespecific adsorption of anion on the metal surface
33 Effect ofHalide IonAddition To further clarify themodesof inhibitor adsorption experiments were conducted in thepresence of iodide ions which are strongly adsorbed onthe surface of mild steel in acidic solution and facilitateadsorption of organic cation-type inhibitors by acting asintermediate bridges between the positive end of the organiccation and the positively charged metal surface Specificadsorption of iodide ions on the metal surface leads torecharging the electrical double layer [35] The inhibitor isthen drawn into the double layer by electrostatic interaction
with the adsorbed Iminus ions forming ion pairs on the metalsurface which increases the degree of surface coverage
Iminussol 997888rarr Iminusads (4a)
Iminusads + Inh+sol 997888rarr [Iminus minus Inh+]ads (4b)
Thus an improvement of 119868 on addition of KI is anindication of the participation of protonated inhibitor speciesin the adsorption process (Figure 2) Table 2 illustrates theeffect of addition of 05 gL KI to the different concentrationsof EHEC on the corrosion of mild steel in 10MH
2SO4
solution
34 Adsorption Consideration Basic parameters which aredescriptors of the nature and modes of adsorption of organicinhibitor on the corroding metal surface can be provided byadsorption isotherms which depend on the degree of surfacecoverage 120579 The observed inhibition of the corrosion of mildsteel in 10MH
2SO4solution indicates high degree of surface
coverage From a theoretical perspective the adsorptionroute is regarded as a substitution process between theorganic inhibitor in the aqueous solution (Inhsol) and water
4 Journal of Materials
05 10 15 20 25
42
44
46
48
50
52
54
56
Day 1Day 2Day 3
Day 4Day 5
Inhi
bitio
n effi
cien
cy I
()
Concentration of inhibitor C (gL)
Figure 1 Variation of inhibition efficiency with concentration ofEHEC
molecules adsorbed at the metal surface (H2Oads) as follows
[36ndash38]
Inh(sol) + 119909H2O(ads) lArrrArr Inh
(ads) + 119909H2O(sol) (5)
where 119909 represents the number of water molecules replacedby one molecule of adsorbed inhibitor The adsorption bondstrength is dependent on the composition of the metal andcorrodent inhibitor structure concentration and orienta-tion as well as temperature Since EHEC can be protonated inthe presence of strong acids it is quite necessary to considerboth cationic and molecular species when discussing theadsorption process of EHEC Figure 3 shows the plot of119862120579 versus 119862 to be linear which is in agreement with theLangmuir equation [39]
119862
120579=
119899
119870ads+ 119899119862 (6)
where 119862 is the concentration of inhibitor and 119870ads is theequilibrium constant for the adsorption-desorption process
In general 119870ads represents the adsorption power ofthe inhibitor molecule on the metal surface The positivevalues confirm the adsorbability of EHEC on the metalsurface The linear plots obtained in Figure 3 suggest thatEHEC adsorption from 10MH
2SO4solution followed the
Langmuir isotherm though the isothermparameters indicatesome deviations from ideal Langmuir behaviour The slopedeviates from unity (see 119899 values in Table 3) with nonzerointercept on the 119910-axis which could be traced to somelimitations in the underlying assumptions The results in factimply that each EHEC molecule occupies 119899 active corrosionsites on the mild steel surface in 10M H
2SO4solution
The free energy of adsorption (Δ119866ads) obtained from (7)which is evaluated from 119870ads obtained from intercepts of theLangmuir plots is given in Table 3
where 119877 and 119879 are the universal gas constant and absolutetemperature respectively The other parameter retains itsprevious meaning The large negative Δ119866ads values impliedthat the adsorption of EHEC on the mild steel surface wasfavourable from thermodynamics point of view and indicatedthat the inhibitor was strongly adsorbed covering bothanodic and cathodic regions
In addition it is important to note that adsorption freeenergy values of minus20 kJmolminus1 or less negative are associatedwith an electrostatic interaction between charged moleculesand charged metal surface (physical adsorption) On theother hand adsorption free energy values of minus40Kjmolminus1 ormore negative values involve charge sharing or transfer fromthe inhibitor molecules to the metal surface to form a co-ordinate covalent bond (chemical adsorption) [40]
35 Impedance Measurements Electrochemical impedancespectroscopy analyses provide insight into the kinetics ofelectrode processes as well as the surface characteristicsof the electrochemical system of interest Figure 4 presentsthe impedance spectra measured at 119864corr after 30minutesof immersion and exemplified the Nyquist plots obtainedfor mild steel in 10MH
2SO4solution in the absence and
presence of EHEC and EHEC + KI The observed increase inthe impedance parameters in inhibited solutions is associatedwith the corrosion inhibiting effect of EHEC The Nyquistplots for all systems generally have the form of only onedepressed semicircle corresponding to one time constantalthough a slight sign of low-frequency inductive behaviourcan be discerned The depression of the capacitance semicir-cle with centre below the real axis suggests a distribution ofthe capacitance due to inhomogeneities associated with theelectrode surface
The presence of a single time constant may be attributedto the short exposure time in the corrosive medium whichis not adequate to reveal degradation of the substrate [41]A polarization resistance (119877
119901) can be extracted from the
intercept of the low-frequency loop at the real axis ofimpedance (119885re) in the Nyquist plots since the inductiveloop is negligible The value of 119877
119901is very close to that of
the charge transfer resistance 119877ct which can be extractedfrom the diameter of the semicircle [41 42] The impedancespectra for theNyquist plotswere thus adequately analyzed bybeing fit to the equivalent circuit model119877
119904(119876dl119877ct) which has
been previously used to model the mild steelacid solutioninterface [41 43]
The values of the impedance parameters derived fromthe Nyquist plots using the selected equivalent circuit model119877119904(119876dl119877ct) are given in Table 4 The terms 119876dl and 119899
respectively represent the magnitude and exponent of theconstant phase element (CPE) of the double layer The CPEwith impedance given by 119885CPE = 119876minus1(119895119908)
minus119899 where 119895 isan imaginary number and 119908 is the angular frequency in
Journal of Materials 5
1 2 3 4 50
102030405060708090
100
Time (days)
05 gL EHEC05 gL EHEC + KI
1 2 3 4 50
102030405060708090
100
Time (days)
10 gL EHEC10 gL EHEC + KI
1 2 3 4 50
102030405060708090
100
Time (days)
15 gL EHEC15 gL EHEC + KI
1 2 3 4 50
102030405060708090
100
Time (days)
20 gL EHEC20 gL EHEC + KI
1 2 3 4 50
102030405060708090
100
Time (days)
25 gL EHEC25 gL EHEC + KI
Inhi
bitio
n effi
cien
cy I
()
Inhi
bitio
n effi
cien
cy I
()
Inhi
bitio
n effi
cien
cy I
()
Inhi
bitio
n effi
cien
cy I
()
Inhi
bitio
n effi
cien
cy I
()
Figure 2 Synergistic effect between KI and EHEC on the variation of inhibition efficiency with time
rads is used in place of a capacitor to compensate for thedeviations from ideal dielectric behaviour associated withthe nonhomogeneity of the electrode surface Introductionof EHEC into the acid corrodent leads to an increase in 119877ctand a reduction of119876dl indicating a hindering of the corrosionreaction The decrease in 119876dl values which normally resultsfrom a decrease in the dielectric constant andor an increasein the double layer thickness is due to inhibitor adsorption onthe metalelectrolyte interface [44] This implies that EHECreduces the corrosion rate of themild steel specimen by virtueof adsorption on the metalelectrolyte interface a fact thathas been previously established A quantitative measure ofthe protective effect can be obtained by comparing the values
of the charge transfer resistance in the absence (119877ct) andpresence of inhibitor (119877ctinh) as follows
119868 = [1 minus119877ct119877ctinh
] times 100 (8)
where (119877ctinh) and 119877ct are the charge transfer resistance forinhibited and uninhibited systems respectively
The double layer capacitance values of the systems werealso examined and calculated using the expression
119862dl =1
2120587119891max119877ct (9)
where 119891max is the maximum frequency The obtained valuesof 119862dl are presented in Table 4
6 Journal of Materials
05 10 15 20 25
10
15
20
25
30
35
40
45
50
Day 1Day 2Day 3
Day 4Day 5
C120579
(gL
)
C (gL)
Figure 3 Langmuir isotherm for EHEC adsorption on mild steelsurface in 10MH
2SO4
0 20 40 60 80 100 120 140
0102030405060708090
100110120130140
Blank25 gL EHEC25 gL EHEC + KI
Zim
(Ω)
Zre (Ω)
Figure 4 Nyquist impedance spectra of mild steel corrosion in10MH
2SO4in the absence and presence of EHEC and EHEC + KI
Lower double layer capacitance suggests reduced electriccharge stored which is a consequence of increased adsorp-tion layer that acted as a dielectric constant The increasein 119877ct values in inhibited systems which corresponds to anincrease in the diameter of the Nyquist semicircle confirmsthat the corrosion inhibiting effect of EHEC and EHEC + KIand is much more pronounced in the latter system implyingthat KI synergistically enhanced the corrosion inhibitingeffect of EHEC In other words lower 119862dl values correspond
to reduced double layer capacitance which according to theHelmholtzmodel (10) results fromadecrease in the dielectricconstant (120576) or an increase in the interfacial layer thickness(120575)
119862dl =120576120576119900119860
120575 (10)
where 120576 is the dielectric constant of the medium 120576119900is the
vacuum permittivity 119860 is the electrode area and 120575 is thethickness of the interfacial layer
Since adsorption of an organic inhibitor on a metalsurface involves the replacement of adsorbedwatermoleculeson the surface the smaller dielectric constant of the organicmolecule compared towater aswell as the increased thicknessof interfacial layer due to inhibitor adsorption acted simulta-neously to reduce the double layer capacitanceThis providesexperimental evidence of adsorption of EHEC on mild steelsurface The significantly lower 119862dl value of the EHEC + KIsystem supports the assertion that the iodide ion significantlyenhances adsorption of EHEC on the metalsolution inter-face
36 Polarization Measurements Figure 5 shows the polar-ization curves of mild steel dissolution in 10MH
2SO4
solution in the absence and presence of EHEC and EHEC+ KI Introduction of EHEC and EHEC + KI into the acidsolutionwas observed to shift the corrosion potentials of bothinhibited systems slightly in the negative direction and inboth cases inhibited the anodic metal dissolution reactionas well as the cathodic hydrogen evolution reaction Sincethe 119864corr is not altered significantly the implication is thatthe corrosion inhibition process is under mixed control withpredominant cathodic effect In addition following observa-tions in Figure 5 both cathodic and anodic partial reactionsare affected as evident in decrease in the corrosion currentdensities This implies that EHEC functioned as a mixed-type inhibitor for both systems However marked cathodicpartial hydrogen evolution reaction is discerned Moresodocumented report [45] has it that when displacement in119864corr is gt85mV the inhibitor can be regarded as a cathodicor anodic type inhibitor and if the displacement in 119864corris lt85mV the inhibitor can be seen as mixed type In thepresent study the displacement in the corrosion potential(119864corr) in the presence of EHEC and EHEC + KI shifted952 and 2075mV respectively in the cathodic directioncompared to the blank which is a confirmation that theinhibitor acts as a mixed-type inhibitor with predominantcathodic effect
Journal of Materials 7
Table 4 Impedance and polarization parameters for mild steel in 05M H2SO4 in the presence and absence of EHEC and EHEC + KI
System Impedance data Polarization data119877ct 119899 IE 119862dl (uF cm
minus2) times 10minus3 119864corr (mV (SCE)) 119877119901(Ω cm2) IE
Inhibition efficiency was calculated from the polarizationdata as follows
119868 = [1 minus119877119901
119877119901
inh] times 100 (11)
where 119877119901and 119877
119901
inh are polarization resistance for uninhib-ited and inhibited systems respectivelyThe calculated valuesare given in Table 4 Observations from Table 4 show thatthe inhibition efficiencies obtained from both impedanceand polarization results are comparable The data confirmthe consistency of EHEC and EHEC + KI at the prevailingexperimental condition
The cooperative effect between EHEC and KI in hin-dering the corrosion of mild steel in 10MH
2SO4solution
is also evident in both the Nyquist and Tafel polarizationplots Addition of KI resulted in a significant increase in thediameter of the Nyquist semicircle and hence an increase in119877ct as well as 119868 and a decrease in the corrosion currentdensity of the Tafel polarization curves The presence ofiodide ions shifts 119864corr more in the cathodic direction andfurther decreases the anodic and cathodic reaction kineticsThe mechanism of this synergistic effect has been describedin detail in some reports [46] The iodide ions are stronglychemisorbed on the corrodingmild steel surface and facilitateEHEC adsorption by acting as intermediate bridges betweenthe positively charged metal surface and EHEC cations Thisstabilizes the adsorption of EHEC on the mild steel surfaceleading to higher surface coverage To account for the aboveobservations it is necessary to recognize that the process ofadsorption of an organic inhibitor on a corroding metal sur-face depends on factors such as the nature and surface chargeon the metal in the corrosive medium as well as the inhibitorstructure Consequently more iodide ions are adsorbed onmild steel which presents a more positive surface giving riseto increased synergistic interactions with protonated EHECspecies and hence higher inhibition efficiencies
E versus SCE (V)minus08 minus07 minus06 minus05 minus04 minus03 minus02
001
1E minus 3
1E minus 4
1E minus 5
1E minus 6
Blank25 gL EHEC25 gL EHEC + KI
i(A
cmminus2)
Figure 5 Polarization curves ofmild steel corrosion in 10MH2SO4
in the absence and presence of EHEC and EHEC + KI
37 Quantum Chemical Calculations The inhibition effec-tiveness of inhibitors has been reported to correlate with thequantum chemical parameters such as HOMO (the highestoccupied molecular orbital) LUMO (the lowest unoccupiedmolecular orbital) and the energy gap between the LUMOand HOMO (Δ119864 = 119864LUMO minus 119864HOMO) [47ndash49] A high119864HOMO (less negative) is associated with the capacity of amolecule to donate electrons to an appropriated acceptorwith empty molecular orbital that facilitated the adsorptionprocess and therefore indicated good performance of thecorrosion inhibitor [50] 119864LUMO corresponds to a tendencyfor electron acceptance Based on this the calculated dif-ference Δ119864 demonstrates inherent electron donating abilityand measures the interaction of the inhibitor molecule withthe metal surface
According to the frontier molecular orbital theory ofchemical reactivity transition of electrons is due to aninteraction between the frontier orbitals HOMOand LUMOof reacting species The energy of HOMO is directly relatedto the ionization potential and characterizes the susceptibilityof the molecule toward attack by electrophiles The energyof LUMO is directly related to the electron affinity andcharacterizes the susceptibility of the molecule toward attackby nucleophile The lower the values of 119864LUMO the strongerthe electron accepting ability of the molecule
8 Journal of Materials
(a) Optimized structure (b) Total electron density
(c) HOMO orbital (d) LUMO orbital
(e) Fukui function for nucleophilic attack (f) Fukui function for electrophilic attack
Figure 6 Electronic properties of ethyl hydroxyethyl cellulose (EHEC) [C grey H white O red]
The electronic structure of EHEC the distribution offrontier molecular orbital and Fukui indices have beenmod-eled in order to establish the active sites as well as local reac-tivity of the inhibitingmoleculesThis was achieved using theDFT electronic structure programs Forcite and DMol3 andusing a Mulliken population analysis Electronic parametersfor the simulation include restricted spin polarization usingtheDNDbasis set as the PerdewWang (PW) local correlationdensity functional The geometry optimized structures ofEHEC HOMO and LUMOorbitals Fukui functions and thetotal electron density are presented in Figure 6 In the EHEC
molecule theHOMOorbital is saturated around the aromaticnucleus which is the region of highest electron density andoften the site at which electrophiles attack and represents theactive centres with the utmost ability to bond to the metalsurface The LUMO orbital is saturated around the ethoxyfunction and represents the site at which nucleophilic attackoccurs
Local reactivity was analyzed by means of the Fukuiindices to assess the active regions in terms of nucleophilicand electrophilic behaviour Thus the site for nucleophilicattack will be the place where the value of 119891+ is maximum In
Journal of Materials 9
turn the site for electrophilic attack is controlled by the valueof 119891minus The values of 119864HOMO 119864LUMO Δ119864 and Fukui functionsare given inTable 5Higher values of119864HOMO indicate a greaterdisposition of a molecule to donate electrons to a metalsurface In the same way low values of the energy of the gapΔ119864 will afford good inhibition efficiency since the energyrequired to remove an electron from the last occupied orbitalwill be minimized [51] The above descriptors howeversuggest that EHEC possessed good inhibiting potential Thisis in agreement with the experimental findings
4 Conclusions
Ethyl hydroxyethyl cellulose was found to be an effectiveinhibitor of mild steel in 10MH
2SO4solution and its inhibi-
tion efficiency increased with increasing concentration Thecorrosion process is inhibited by adsorption of EHEC on themild steel surface following themodified Langmuir isothermThe inhibiting action is attributed to general adsorption ofboth protonated and molecular species of the additive on thecathodic and anodic sites on the corrodingmild steel surfaceIn addition corrosion inhibition is due to the formationof a chemisorbed film on the mild steel surface The EISmeasurement confirmed the adsorption of EHEC and EHEC+ KI on the mild steel surface Polarization studies showedthat EHEC and EHEC + KI were mixed-type inhibitorsystems with predominant cathodic effect The theoreticalstudy demonstrated that the inhibition efficiency is related tomolecular structure of inhibitor whereby increase in 119864HOMOand decrease in 119864LUMO favoured inhibition efficiency
Conflict of Interests
Theauthors hereby declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors are grateful to Udemmadu Tochukwu andOchiogu Valentine for assistance in carrying out some mea-surements
References
[1] E E Oguzie Y Li and F H Wang ldquoEffect of ascorbic acidon mild steel dissolution in sulphuric acid solution investigatedby electrochemical polarization and surface probe techniquesrdquoJournal of Applied Electrochemistry vol 37 no 10 pp 1183ndash11902007
[2] L G da Trindade and R S Goncalves ldquoEvidence of caffeineadsorption on a low-carbon steel surface in ethanolrdquo CorrosionScience vol 51 no 8 pp 1578ndash1583 2009
[3] F Bentiss M Outirite M Traisnel et al ldquoImprovementof corrosion resistance of carbon steel in hydrochloric acidmedium by 36-bis(3-pyridyl)pyridazinerdquo International Journalof Electrochemical Science vol 7 no 2 pp 1699ndash1723 2012
[4] S M A Shibli and V S Saji ldquoCo-inhibition characteristicsof sodium tungstate with potassium iodate on mild steelcorrosionrdquoCorrosion Science vol 47 no 9 pp 2213ndash2224 2005
[5] E E Oguzie C Unaegbu C N Ogukwe B N Okolue and AI Onuchukwu ldquoInhibition of mild steel corrosion in sulphuricacid using indigo dye and synergistic halide additivesrdquoMateri-als Chemistry and Physics vol 84 no 2-3 pp 363ndash368 2004
[6] V Kumpawat U Garg and R K Tak ldquoCorrosion inhibitionof aluminium in acid media by naturally occurring plantArtocarpus heterophyllus and Acacia senegalrdquo Journal of IndianCouncil of Chemists vol 26 no 1 pp 82ndash84 2009
[7] IA Akpan and N O Offiong ldquoEffect of ethanolamine andethylamine on the entropy content of the corrosion ofmild steelin tetraoxosulphate (VI) acid solutionrdquoChemistry andMaterialsResearch vol 2 no 7 pp 40ndash47 2012
[8] M Kissi M Bouklah B Hammouti and M BenkaddourldquoEstablishment of equivalent circuits from electrochemicalimpedance spectroscopy study of corrosion inhibition of steelby pyrazine in sulphuric acidic solutionrdquo Applied SurfaceScience vol 252 no 12 pp 4190ndash4197 2006
[9] S Rajendran S P Sridevi N Anthony A J Amalraj andM Sundaravadivelu ldquoCorrosion behaviour of carbon steel inpolyvinyl alcoholrdquo Anti-Corrosion Methods and Materials vol52 no 2 pp 102ndash107 2005
[10] B Qian J Wang M Zheng and B Hou ldquoSynergistic effect ofpolyaspartic acid and iodide ion on corrosion inhibition ofmildsteel in H
[11] D A Arthur A Jonathan P O Ameh and C Anya ldquoAreview on the assessment of polymeric materials used ascorrosion inhibitor of metals and alloysrdquo International Journalof Industrial Chemistry vol 4 article 2 pp 1ndash9 2013
[12] S A Umoren Y Li and F H Wang ldquoEffect of polyacrylicacid on the corrosion behaviour of aluminium in sulphuric acidsolutionrdquo Journal of Solid State Electrochemistry vol 14 no 12pp 2293ndash2305 2010
[13] S Banerjee A Mishra M M Singh B Maiti B Ray andP Maiti ldquoHighly efficient polyurethane ionomer corrosioninhibitor the effect of chain structurerdquo RSCAdvances vol 1 no2 pp 199ndash210 2011
[14] A K Dubey and G Singh ldquoCorrosion inhibition of mild steelin sulphuric acid solution by using polyethylene glycol methylether (PEGME)rdquo Portugaliae Electrochimica Acta vol 25 no 2pp 221ndash235 2007
[15] E E Oguzie S G Wang Y Li and F H Wang ldquoInfluenceof iron microstructure on corrosion inhibitor performance inacidic mediardquoThe Journal of Physical Chemistry C vol 113 no19 pp 8420ndash8429 2009
[16] S A Umoren E E Ebenso P C Okafor and O OgbobeldquoWater-soluble polymers as corrosion inhibitorsrdquo Pigment ampResin Technology vol 35 no 6 pp 346ndash352 2006
[17] S A Umoren and I B Obot ldquoPolyvinylpyrollidone andpolyacrylamide as corrosion inhibitors for mild steel in acidicmediumrdquo Surface Review and Letters vol 15 no 3 pp 277ndash2842008
[18] H Ashassi-Sorkhabi and N Ghalebsaz-Jeddi ldquoInhibition effectof polyethylene glycol on the corrosion of carbon steel insulphuric acidrdquoMaterials Chemistry and Physics vol 92 no 2-3pp 480ndash486 2005
[19] A Yurt V Butun and B Duran ldquoEffect of themolecular weightand structure of some novel water-soluble triblock copolymerson the electrochemical behaviour of mild steelrdquo MaterialsChemistry and Physics vol 105 no 1 pp 114ndash121 2007
10 Journal of Materials
[20] S A Umoren ldquoPolymers as corrosion inhibitors for metals indifferent mediamdasha reviewrdquo The Open Corrosion Journal vol 2pp 175ndash188 2009
[21] K F Khaled ldquoCorrosion control of copper in nitric acidsolutions using some amino acidsmdasha combined experimentaland theoretical studyrdquo Corrosion Science vol 52 no 10 pp3225ndash3234 2010
[22] E E Oguzie C O Akalezi C K Enenebeaku and J N AnekeldquoCorrosion inhibition and adsorption behavior of malachitegreen dye on aluminum corrosionrdquoChemical Engineering Com-munications vol 198 no 1 pp 46ndash60 2011
[23] J Cruz T Pandiyan and E Garcia-Ochoa ldquoA new inhibitor formild carbon steel electrochemical and DFT studiesrdquo Journal ofElectroanalytical Chemistry vol 583 no 1 pp 8ndash16 2005
[24] J Cruz R Martinez J Genesca and E Garcia-OchoaldquoExperimental and theoretical study of 1-(2-ethylamino)-2-methylimidazoline as an inhibitor of carbon steel corrosion inacid mediardquo Journal of Electroanalytical Chemistry vol 566 no1 pp 111ndash121 2004
[25] E E Oguzie Y Li S G Wang and F Wang ldquoUnderstandingcorrosion inhibition mechanismsmdashexperimental and theoreti-cal approachrdquo RSC Advances vol 1 no 5 pp 866ndash873 2011
[26] A Kumar A Sankara M Kumaravel and S RameshkumarldquoClitoria ternateamdashextracts as corrosion inhibitor for mild steelin acid mediumrdquo International Journal of Engineering Researchand Development vol 8 no 5 pp 64ndash67 2013
[27] E E Oguzie G N Onuoha and A I Onuchukwu ldquoInhibitorymechanism of mild steel corrosion in 2M sulphuric acidsolution by methylene blue dyerdquo Materials Chemistry andPhysics vol 89 no 2-3 pp 305ndash311 2005
[28] E E Oguzie C K Enenebeaku C O Akalezi S C Okoro AA Ayuk and E N Ejike ldquoAdsorption and corrosion-inhibitingeffect ofDacryodis edulis extract on low-carbon-steel corrosionin acidic mediardquo Journal of Colloid and Interface Science vol349 no 1 pp 283ndash292 2010
[29] E E Oguzie ldquoCorrosion inhibition of aluminium in acidicand alkaline media by Sansevieria trifasciata extractrdquo CorrosionScience vol 49 no 3 pp 1527ndash1539 2007
[30] S A Umoren I B Obot and E E Ebenso ldquoCorrosioninhibition of aluminium using exudate gum from Pachylobusedulis in the presence of halide ions in HClrdquo E-Journal ofChemistry vol 5 no 2 pp 355ndash364 2008
[31] P C Okafor E E Ebenso and U J Ekpe ldquoAzadirachta indicaextracts as corrosion inhibitor for mild steel in acid mediumrdquoInternational Journal of Electrochemical Science vol 5 no 7 pp978ndash993 2010
[32] M Lebrini F Robert A Lecente and C Roos ldquoCorrosioninhibition of C38 steel in 1M hydrochloric acid medium byalkaloids extract from Oxandra asbeckii plant rdquo CorrosionScience vol 53 no 2 pp 687ndash695 2011
[33] E E Oguzie ldquoInfluence of halide ions on the inhibitive effect ofcongo red dye on the corrosion of mild steel in sulphuric acidsolutionrdquoMaterials Chemistry and Physics vol 87 no 1 pp 212ndash217 2004
[34] E E Oguzie ldquoInhibition of acid corrosion of mild steel byTelfaria occidentalis extractrdquo Pigment amp Resin Technology vol34 no 6 pp 321ndash326 2005
[35] E E Oguzie V O Njoku C K Enenebeaku C O Akalezi andC Obi ldquoEffect of hexamethylpararosaniline chloride (crystalviolet) on mild steel corrosion in acidic mediardquo CorrosionScience vol 50 no 12 pp 3480ndash3486 2008
[36] M A Ameer E Khamis and G al-Senani ldquoEffect of temper-ature on stability of adsorbed inhibitors on steel in phosphoricacid solutionrdquo Journal of Applied Electrochemistry vol 32 no 2pp 149ndash156 2002
[37] P C Okafor E E Oguzie G E Iniama M E Ikpi and U JEkpe ldquoCorrosion inhibition properties of thiosemicarbazoneand semicarbazone derivatives in concentrated acid environ-mentrdquoGlobal Journal of Pure and Applied Sciences vol 14 no 1pp 89ndash96 2008
[38] I B Obot ldquoSynergistic effect of nizoral and iodide ions on thecorrosion inhibition of mild steel in sulphuric acid solutionrdquoPortugaliae ElectrochimicaActa vol 27 no 5 pp 539ndash553 2009
[39] N O Eddy S A Odoemelam and A O Odiongenyi ldquoEthanolextract of musa species peels as a green corrosion inhibitor formild steel kinetics adsorption and thermodynamic consider-ationsrdquo Electronic Journal of Environmental Agricultural andFood Chemistry vol 8 no 4 pp 243ndash255 2009
[40] M H Hussin and M J Kassim ldquoThe corrosion inhibition andadsorption behavior of Uncaria gambir extract on mild steel in1M HClrdquo Materials Chemistry and Physics vol 125 no 3 pp461ndash468 2010
[41] V K W Grips V E Selvi H C Barshilia and K S RajamldquoEffect of electroless nickel interlayer on the electrochemicalbehavior of single layer CrN TiN TiAlN coatings and nanolay-ered TiAlNCrN multilayer coatings prepared by reactive dcmagnetron sputteringrdquo Electrochimica Acta vol 51 no 17 pp3461ndash3468 2006
[42] E E Oguzie ldquoStudies on the inhibitive effect ofOccimum viridisextract on the acid corrosion of mild steelrdquoMaterials Chemistryand Physics vol 99 no 2-3 pp 441ndash446 2006
[43] B Wang M Du J Zhang and C J Gao ldquoElectrochemical andsurface analysis studies on corrosion inhibition of Q235 steelby imidazoline derivative against CO
2corrosionrdquo Corrosion
Science vol 53 no 1 pp 353ndash361 2011[44] G Mu and X Li ldquoInhibition of cold rolled steel corrosion
by Tween-20 in sulfuric acid weight loss electrochemical andAFM approaches rdquo Journal of Colloid and Interface Science vol289 no 1 pp 184ndash192 2005
[45] A K Satapathy G Gunasekaran S C Sahoo K Amit and PV Rodrigues ldquoCorrosion inhibition by Justicia gendarussa plantextract in hydrochloric acid solutionrdquoCorrosion Science vol 51no 12 pp 2848ndash2856 2009
[46] E E Oguzie Y Li and F H Wang ldquoCorrosion inhibition andadsorption behavior of methionine on mild steel in sulfuricacid and synergistic effect of iodide ionrdquo Journal of Colloid andInterface Science vol 310 no 1 pp 90ndash98 2007
[47] L M Rodrıguez-Valdez W Villamisar M Casales et alldquoComputational simulations of themolecular structure and cor-rosion properties of amidoethyl aminoethyl and hydroxyethylimidazolines inhibitorsrdquo Corrosion Science vol 48 no 12 pp4053ndash4064 2006
[48] H Ju Z P Kai and Y Li ldquoAminic nitrogen-bearing polydentateSchiff base compounds as corrosion inhibitors for iron in acidicmedia a quantum chemical calculationrdquo Corrosion Science vol50 no 3 pp 865ndash871 2008
[49] L M Rodrıguez-Valdez A Martınez-Villafane and DGlossman-Mitnik ldquoComputational simulation of themolecularstructure and properties of heterocyclic organic compoundswith possible corrosion inhibition propertiesrdquo Journal ofMolecular Structure THEOCHEM vol 713 no 1ndash3 pp 65ndash702005
Journal of Materials 11
[50] K F Khaled ldquoMolecular simulation quantum chemical calcu-lations and electrochemical studies for inhibition of mild steelby triazolesrdquo Electrochimica Acta vol 53 no 9 pp 3484ndash34922008
[51] R M Issa M K Awad and F M Atlam ldquoQuantum chemicalstudies on the inhibition of corrosion of copper surface bysubstituted uracilsrdquo Applied Surface Science vol 255 no 5 pp2433ndash2441 2008
which blocks the metal surface separating it from the corro-sive medium [29ndash32] Consequently in inhibited solutionsthe corrosion rate is indicative of the number of free cor-roding sites remaining after some sites have been effectivelyblocked by inhibitor adsorption It has been suggested [3334] however that anions such as Clminus Iminus SO
4
2minus and S2minus mayalso participate in forming reaction intermediates on thecorroding metal surface which either inhibit or stimulatecorrosion It is important to recognize that the suppressionor stimulation of the dissolution process is initiated by thespecific adsorption of anion on the metal surface
33 Effect ofHalide IonAddition To further clarify themodesof inhibitor adsorption experiments were conducted in thepresence of iodide ions which are strongly adsorbed onthe surface of mild steel in acidic solution and facilitateadsorption of organic cation-type inhibitors by acting asintermediate bridges between the positive end of the organiccation and the positively charged metal surface Specificadsorption of iodide ions on the metal surface leads torecharging the electrical double layer [35] The inhibitor isthen drawn into the double layer by electrostatic interaction
with the adsorbed Iminus ions forming ion pairs on the metalsurface which increases the degree of surface coverage
Iminussol 997888rarr Iminusads (4a)
Iminusads + Inh+sol 997888rarr [Iminus minus Inh+]ads (4b)
Thus an improvement of 119868 on addition of KI is anindication of the participation of protonated inhibitor speciesin the adsorption process (Figure 2) Table 2 illustrates theeffect of addition of 05 gL KI to the different concentrationsof EHEC on the corrosion of mild steel in 10MH
2SO4
solution
34 Adsorption Consideration Basic parameters which aredescriptors of the nature and modes of adsorption of organicinhibitor on the corroding metal surface can be provided byadsorption isotherms which depend on the degree of surfacecoverage 120579 The observed inhibition of the corrosion of mildsteel in 10MH
2SO4solution indicates high degree of surface
coverage From a theoretical perspective the adsorptionroute is regarded as a substitution process between theorganic inhibitor in the aqueous solution (Inhsol) and water
4 Journal of Materials
05 10 15 20 25
42
44
46
48
50
52
54
56
Day 1Day 2Day 3
Day 4Day 5
Inhi
bitio
n effi
cien
cy I
()
Concentration of inhibitor C (gL)
Figure 1 Variation of inhibition efficiency with concentration ofEHEC
molecules adsorbed at the metal surface (H2Oads) as follows
[36ndash38]
Inh(sol) + 119909H2O(ads) lArrrArr Inh
(ads) + 119909H2O(sol) (5)
where 119909 represents the number of water molecules replacedby one molecule of adsorbed inhibitor The adsorption bondstrength is dependent on the composition of the metal andcorrodent inhibitor structure concentration and orienta-tion as well as temperature Since EHEC can be protonated inthe presence of strong acids it is quite necessary to considerboth cationic and molecular species when discussing theadsorption process of EHEC Figure 3 shows the plot of119862120579 versus 119862 to be linear which is in agreement with theLangmuir equation [39]
119862
120579=
119899
119870ads+ 119899119862 (6)
where 119862 is the concentration of inhibitor and 119870ads is theequilibrium constant for the adsorption-desorption process
In general 119870ads represents the adsorption power ofthe inhibitor molecule on the metal surface The positivevalues confirm the adsorbability of EHEC on the metalsurface The linear plots obtained in Figure 3 suggest thatEHEC adsorption from 10MH
2SO4solution followed the
Langmuir isotherm though the isothermparameters indicatesome deviations from ideal Langmuir behaviour The slopedeviates from unity (see 119899 values in Table 3) with nonzerointercept on the 119910-axis which could be traced to somelimitations in the underlying assumptions The results in factimply that each EHEC molecule occupies 119899 active corrosionsites on the mild steel surface in 10M H
2SO4solution
The free energy of adsorption (Δ119866ads) obtained from (7)which is evaluated from 119870ads obtained from intercepts of theLangmuir plots is given in Table 3
where 119877 and 119879 are the universal gas constant and absolutetemperature respectively The other parameter retains itsprevious meaning The large negative Δ119866ads values impliedthat the adsorption of EHEC on the mild steel surface wasfavourable from thermodynamics point of view and indicatedthat the inhibitor was strongly adsorbed covering bothanodic and cathodic regions
In addition it is important to note that adsorption freeenergy values of minus20 kJmolminus1 or less negative are associatedwith an electrostatic interaction between charged moleculesand charged metal surface (physical adsorption) On theother hand adsorption free energy values of minus40Kjmolminus1 ormore negative values involve charge sharing or transfer fromthe inhibitor molecules to the metal surface to form a co-ordinate covalent bond (chemical adsorption) [40]
35 Impedance Measurements Electrochemical impedancespectroscopy analyses provide insight into the kinetics ofelectrode processes as well as the surface characteristicsof the electrochemical system of interest Figure 4 presentsthe impedance spectra measured at 119864corr after 30minutesof immersion and exemplified the Nyquist plots obtainedfor mild steel in 10MH
2SO4solution in the absence and
presence of EHEC and EHEC + KI The observed increase inthe impedance parameters in inhibited solutions is associatedwith the corrosion inhibiting effect of EHEC The Nyquistplots for all systems generally have the form of only onedepressed semicircle corresponding to one time constantalthough a slight sign of low-frequency inductive behaviourcan be discerned The depression of the capacitance semicir-cle with centre below the real axis suggests a distribution ofthe capacitance due to inhomogeneities associated with theelectrode surface
The presence of a single time constant may be attributedto the short exposure time in the corrosive medium whichis not adequate to reveal degradation of the substrate [41]A polarization resistance (119877
119901) can be extracted from the
intercept of the low-frequency loop at the real axis ofimpedance (119885re) in the Nyquist plots since the inductiveloop is negligible The value of 119877
119901is very close to that of
the charge transfer resistance 119877ct which can be extractedfrom the diameter of the semicircle [41 42] The impedancespectra for theNyquist plotswere thus adequately analyzed bybeing fit to the equivalent circuit model119877
119904(119876dl119877ct) which has
been previously used to model the mild steelacid solutioninterface [41 43]
The values of the impedance parameters derived fromthe Nyquist plots using the selected equivalent circuit model119877119904(119876dl119877ct) are given in Table 4 The terms 119876dl and 119899
respectively represent the magnitude and exponent of theconstant phase element (CPE) of the double layer The CPEwith impedance given by 119885CPE = 119876minus1(119895119908)
minus119899 where 119895 isan imaginary number and 119908 is the angular frequency in
Journal of Materials 5
1 2 3 4 50
102030405060708090
100
Time (days)
05 gL EHEC05 gL EHEC + KI
1 2 3 4 50
102030405060708090
100
Time (days)
10 gL EHEC10 gL EHEC + KI
1 2 3 4 50
102030405060708090
100
Time (days)
15 gL EHEC15 gL EHEC + KI
1 2 3 4 50
102030405060708090
100
Time (days)
20 gL EHEC20 gL EHEC + KI
1 2 3 4 50
102030405060708090
100
Time (days)
25 gL EHEC25 gL EHEC + KI
Inhi
bitio
n effi
cien
cy I
()
Inhi
bitio
n effi
cien
cy I
()
Inhi
bitio
n effi
cien
cy I
()
Inhi
bitio
n effi
cien
cy I
()
Inhi
bitio
n effi
cien
cy I
()
Figure 2 Synergistic effect between KI and EHEC on the variation of inhibition efficiency with time
rads is used in place of a capacitor to compensate for thedeviations from ideal dielectric behaviour associated withthe nonhomogeneity of the electrode surface Introductionof EHEC into the acid corrodent leads to an increase in 119877ctand a reduction of119876dl indicating a hindering of the corrosionreaction The decrease in 119876dl values which normally resultsfrom a decrease in the dielectric constant andor an increasein the double layer thickness is due to inhibitor adsorption onthe metalelectrolyte interface [44] This implies that EHECreduces the corrosion rate of themild steel specimen by virtueof adsorption on the metalelectrolyte interface a fact thathas been previously established A quantitative measure ofthe protective effect can be obtained by comparing the values
of the charge transfer resistance in the absence (119877ct) andpresence of inhibitor (119877ctinh) as follows
119868 = [1 minus119877ct119877ctinh
] times 100 (8)
where (119877ctinh) and 119877ct are the charge transfer resistance forinhibited and uninhibited systems respectively
The double layer capacitance values of the systems werealso examined and calculated using the expression
119862dl =1
2120587119891max119877ct (9)
where 119891max is the maximum frequency The obtained valuesof 119862dl are presented in Table 4
6 Journal of Materials
05 10 15 20 25
10
15
20
25
30
35
40
45
50
Day 1Day 2Day 3
Day 4Day 5
C120579
(gL
)
C (gL)
Figure 3 Langmuir isotherm for EHEC adsorption on mild steelsurface in 10MH
2SO4
0 20 40 60 80 100 120 140
0102030405060708090
100110120130140
Blank25 gL EHEC25 gL EHEC + KI
Zim
(Ω)
Zre (Ω)
Figure 4 Nyquist impedance spectra of mild steel corrosion in10MH
2SO4in the absence and presence of EHEC and EHEC + KI
Lower double layer capacitance suggests reduced electriccharge stored which is a consequence of increased adsorp-tion layer that acted as a dielectric constant The increasein 119877ct values in inhibited systems which corresponds to anincrease in the diameter of the Nyquist semicircle confirmsthat the corrosion inhibiting effect of EHEC and EHEC + KIand is much more pronounced in the latter system implyingthat KI synergistically enhanced the corrosion inhibitingeffect of EHEC In other words lower 119862dl values correspond
to reduced double layer capacitance which according to theHelmholtzmodel (10) results fromadecrease in the dielectricconstant (120576) or an increase in the interfacial layer thickness(120575)
119862dl =120576120576119900119860
120575 (10)
where 120576 is the dielectric constant of the medium 120576119900is the
vacuum permittivity 119860 is the electrode area and 120575 is thethickness of the interfacial layer
Since adsorption of an organic inhibitor on a metalsurface involves the replacement of adsorbedwatermoleculeson the surface the smaller dielectric constant of the organicmolecule compared towater aswell as the increased thicknessof interfacial layer due to inhibitor adsorption acted simulta-neously to reduce the double layer capacitanceThis providesexperimental evidence of adsorption of EHEC on mild steelsurface The significantly lower 119862dl value of the EHEC + KIsystem supports the assertion that the iodide ion significantlyenhances adsorption of EHEC on the metalsolution inter-face
36 Polarization Measurements Figure 5 shows the polar-ization curves of mild steel dissolution in 10MH
2SO4
solution in the absence and presence of EHEC and EHEC+ KI Introduction of EHEC and EHEC + KI into the acidsolutionwas observed to shift the corrosion potentials of bothinhibited systems slightly in the negative direction and inboth cases inhibited the anodic metal dissolution reactionas well as the cathodic hydrogen evolution reaction Sincethe 119864corr is not altered significantly the implication is thatthe corrosion inhibition process is under mixed control withpredominant cathodic effect In addition following observa-tions in Figure 5 both cathodic and anodic partial reactionsare affected as evident in decrease in the corrosion currentdensities This implies that EHEC functioned as a mixed-type inhibitor for both systems However marked cathodicpartial hydrogen evolution reaction is discerned Moresodocumented report [45] has it that when displacement in119864corr is gt85mV the inhibitor can be regarded as a cathodicor anodic type inhibitor and if the displacement in 119864corris lt85mV the inhibitor can be seen as mixed type In thepresent study the displacement in the corrosion potential(119864corr) in the presence of EHEC and EHEC + KI shifted952 and 2075mV respectively in the cathodic directioncompared to the blank which is a confirmation that theinhibitor acts as a mixed-type inhibitor with predominantcathodic effect
Journal of Materials 7
Table 4 Impedance and polarization parameters for mild steel in 05M H2SO4 in the presence and absence of EHEC and EHEC + KI
System Impedance data Polarization data119877ct 119899 IE 119862dl (uF cm
minus2) times 10minus3 119864corr (mV (SCE)) 119877119901(Ω cm2) IE
Inhibition efficiency was calculated from the polarizationdata as follows
119868 = [1 minus119877119901
119877119901
inh] times 100 (11)
where 119877119901and 119877
119901
inh are polarization resistance for uninhib-ited and inhibited systems respectivelyThe calculated valuesare given in Table 4 Observations from Table 4 show thatthe inhibition efficiencies obtained from both impedanceand polarization results are comparable The data confirmthe consistency of EHEC and EHEC + KI at the prevailingexperimental condition
The cooperative effect between EHEC and KI in hin-dering the corrosion of mild steel in 10MH
2SO4solution
is also evident in both the Nyquist and Tafel polarizationplots Addition of KI resulted in a significant increase in thediameter of the Nyquist semicircle and hence an increase in119877ct as well as 119868 and a decrease in the corrosion currentdensity of the Tafel polarization curves The presence ofiodide ions shifts 119864corr more in the cathodic direction andfurther decreases the anodic and cathodic reaction kineticsThe mechanism of this synergistic effect has been describedin detail in some reports [46] The iodide ions are stronglychemisorbed on the corrodingmild steel surface and facilitateEHEC adsorption by acting as intermediate bridges betweenthe positively charged metal surface and EHEC cations Thisstabilizes the adsorption of EHEC on the mild steel surfaceleading to higher surface coverage To account for the aboveobservations it is necessary to recognize that the process ofadsorption of an organic inhibitor on a corroding metal sur-face depends on factors such as the nature and surface chargeon the metal in the corrosive medium as well as the inhibitorstructure Consequently more iodide ions are adsorbed onmild steel which presents a more positive surface giving riseto increased synergistic interactions with protonated EHECspecies and hence higher inhibition efficiencies
E versus SCE (V)minus08 minus07 minus06 minus05 minus04 minus03 minus02
001
1E minus 3
1E minus 4
1E minus 5
1E minus 6
Blank25 gL EHEC25 gL EHEC + KI
i(A
cmminus2)
Figure 5 Polarization curves ofmild steel corrosion in 10MH2SO4
in the absence and presence of EHEC and EHEC + KI
37 Quantum Chemical Calculations The inhibition effec-tiveness of inhibitors has been reported to correlate with thequantum chemical parameters such as HOMO (the highestoccupied molecular orbital) LUMO (the lowest unoccupiedmolecular orbital) and the energy gap between the LUMOand HOMO (Δ119864 = 119864LUMO minus 119864HOMO) [47ndash49] A high119864HOMO (less negative) is associated with the capacity of amolecule to donate electrons to an appropriated acceptorwith empty molecular orbital that facilitated the adsorptionprocess and therefore indicated good performance of thecorrosion inhibitor [50] 119864LUMO corresponds to a tendencyfor electron acceptance Based on this the calculated dif-ference Δ119864 demonstrates inherent electron donating abilityand measures the interaction of the inhibitor molecule withthe metal surface
According to the frontier molecular orbital theory ofchemical reactivity transition of electrons is due to aninteraction between the frontier orbitals HOMOand LUMOof reacting species The energy of HOMO is directly relatedto the ionization potential and characterizes the susceptibilityof the molecule toward attack by electrophiles The energyof LUMO is directly related to the electron affinity andcharacterizes the susceptibility of the molecule toward attackby nucleophile The lower the values of 119864LUMO the strongerthe electron accepting ability of the molecule
8 Journal of Materials
(a) Optimized structure (b) Total electron density
(c) HOMO orbital (d) LUMO orbital
(e) Fukui function for nucleophilic attack (f) Fukui function for electrophilic attack
Figure 6 Electronic properties of ethyl hydroxyethyl cellulose (EHEC) [C grey H white O red]
The electronic structure of EHEC the distribution offrontier molecular orbital and Fukui indices have beenmod-eled in order to establish the active sites as well as local reac-tivity of the inhibitingmoleculesThis was achieved using theDFT electronic structure programs Forcite and DMol3 andusing a Mulliken population analysis Electronic parametersfor the simulation include restricted spin polarization usingtheDNDbasis set as the PerdewWang (PW) local correlationdensity functional The geometry optimized structures ofEHEC HOMO and LUMOorbitals Fukui functions and thetotal electron density are presented in Figure 6 In the EHEC
molecule theHOMOorbital is saturated around the aromaticnucleus which is the region of highest electron density andoften the site at which electrophiles attack and represents theactive centres with the utmost ability to bond to the metalsurface The LUMO orbital is saturated around the ethoxyfunction and represents the site at which nucleophilic attackoccurs
Local reactivity was analyzed by means of the Fukuiindices to assess the active regions in terms of nucleophilicand electrophilic behaviour Thus the site for nucleophilicattack will be the place where the value of 119891+ is maximum In
Journal of Materials 9
turn the site for electrophilic attack is controlled by the valueof 119891minus The values of 119864HOMO 119864LUMO Δ119864 and Fukui functionsare given inTable 5Higher values of119864HOMO indicate a greaterdisposition of a molecule to donate electrons to a metalsurface In the same way low values of the energy of the gapΔ119864 will afford good inhibition efficiency since the energyrequired to remove an electron from the last occupied orbitalwill be minimized [51] The above descriptors howeversuggest that EHEC possessed good inhibiting potential Thisis in agreement with the experimental findings
4 Conclusions
Ethyl hydroxyethyl cellulose was found to be an effectiveinhibitor of mild steel in 10MH
2SO4solution and its inhibi-
tion efficiency increased with increasing concentration Thecorrosion process is inhibited by adsorption of EHEC on themild steel surface following themodified Langmuir isothermThe inhibiting action is attributed to general adsorption ofboth protonated and molecular species of the additive on thecathodic and anodic sites on the corrodingmild steel surfaceIn addition corrosion inhibition is due to the formationof a chemisorbed film on the mild steel surface The EISmeasurement confirmed the adsorption of EHEC and EHEC+ KI on the mild steel surface Polarization studies showedthat EHEC and EHEC + KI were mixed-type inhibitorsystems with predominant cathodic effect The theoreticalstudy demonstrated that the inhibition efficiency is related tomolecular structure of inhibitor whereby increase in 119864HOMOand decrease in 119864LUMO favoured inhibition efficiency
Conflict of Interests
Theauthors hereby declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors are grateful to Udemmadu Tochukwu andOchiogu Valentine for assistance in carrying out some mea-surements
References
[1] E E Oguzie Y Li and F H Wang ldquoEffect of ascorbic acidon mild steel dissolution in sulphuric acid solution investigatedby electrochemical polarization and surface probe techniquesrdquoJournal of Applied Electrochemistry vol 37 no 10 pp 1183ndash11902007
[2] L G da Trindade and R S Goncalves ldquoEvidence of caffeineadsorption on a low-carbon steel surface in ethanolrdquo CorrosionScience vol 51 no 8 pp 1578ndash1583 2009
[3] F Bentiss M Outirite M Traisnel et al ldquoImprovementof corrosion resistance of carbon steel in hydrochloric acidmedium by 36-bis(3-pyridyl)pyridazinerdquo International Journalof Electrochemical Science vol 7 no 2 pp 1699ndash1723 2012
[4] S M A Shibli and V S Saji ldquoCo-inhibition characteristicsof sodium tungstate with potassium iodate on mild steelcorrosionrdquoCorrosion Science vol 47 no 9 pp 2213ndash2224 2005
[5] E E Oguzie C Unaegbu C N Ogukwe B N Okolue and AI Onuchukwu ldquoInhibition of mild steel corrosion in sulphuricacid using indigo dye and synergistic halide additivesrdquoMateri-als Chemistry and Physics vol 84 no 2-3 pp 363ndash368 2004
[6] V Kumpawat U Garg and R K Tak ldquoCorrosion inhibitionof aluminium in acid media by naturally occurring plantArtocarpus heterophyllus and Acacia senegalrdquo Journal of IndianCouncil of Chemists vol 26 no 1 pp 82ndash84 2009
[7] IA Akpan and N O Offiong ldquoEffect of ethanolamine andethylamine on the entropy content of the corrosion ofmild steelin tetraoxosulphate (VI) acid solutionrdquoChemistry andMaterialsResearch vol 2 no 7 pp 40ndash47 2012
[8] M Kissi M Bouklah B Hammouti and M BenkaddourldquoEstablishment of equivalent circuits from electrochemicalimpedance spectroscopy study of corrosion inhibition of steelby pyrazine in sulphuric acidic solutionrdquo Applied SurfaceScience vol 252 no 12 pp 4190ndash4197 2006
[9] S Rajendran S P Sridevi N Anthony A J Amalraj andM Sundaravadivelu ldquoCorrosion behaviour of carbon steel inpolyvinyl alcoholrdquo Anti-Corrosion Methods and Materials vol52 no 2 pp 102ndash107 2005
[10] B Qian J Wang M Zheng and B Hou ldquoSynergistic effect ofpolyaspartic acid and iodide ion on corrosion inhibition ofmildsteel in H
[11] D A Arthur A Jonathan P O Ameh and C Anya ldquoAreview on the assessment of polymeric materials used ascorrosion inhibitor of metals and alloysrdquo International Journalof Industrial Chemistry vol 4 article 2 pp 1ndash9 2013
[12] S A Umoren Y Li and F H Wang ldquoEffect of polyacrylicacid on the corrosion behaviour of aluminium in sulphuric acidsolutionrdquo Journal of Solid State Electrochemistry vol 14 no 12pp 2293ndash2305 2010
[13] S Banerjee A Mishra M M Singh B Maiti B Ray andP Maiti ldquoHighly efficient polyurethane ionomer corrosioninhibitor the effect of chain structurerdquo RSCAdvances vol 1 no2 pp 199ndash210 2011
[14] A K Dubey and G Singh ldquoCorrosion inhibition of mild steelin sulphuric acid solution by using polyethylene glycol methylether (PEGME)rdquo Portugaliae Electrochimica Acta vol 25 no 2pp 221ndash235 2007
[15] E E Oguzie S G Wang Y Li and F H Wang ldquoInfluenceof iron microstructure on corrosion inhibitor performance inacidic mediardquoThe Journal of Physical Chemistry C vol 113 no19 pp 8420ndash8429 2009
[16] S A Umoren E E Ebenso P C Okafor and O OgbobeldquoWater-soluble polymers as corrosion inhibitorsrdquo Pigment ampResin Technology vol 35 no 6 pp 346ndash352 2006
[17] S A Umoren and I B Obot ldquoPolyvinylpyrollidone andpolyacrylamide as corrosion inhibitors for mild steel in acidicmediumrdquo Surface Review and Letters vol 15 no 3 pp 277ndash2842008
[18] H Ashassi-Sorkhabi and N Ghalebsaz-Jeddi ldquoInhibition effectof polyethylene glycol on the corrosion of carbon steel insulphuric acidrdquoMaterials Chemistry and Physics vol 92 no 2-3pp 480ndash486 2005
[19] A Yurt V Butun and B Duran ldquoEffect of themolecular weightand structure of some novel water-soluble triblock copolymerson the electrochemical behaviour of mild steelrdquo MaterialsChemistry and Physics vol 105 no 1 pp 114ndash121 2007
10 Journal of Materials
[20] S A Umoren ldquoPolymers as corrosion inhibitors for metals indifferent mediamdasha reviewrdquo The Open Corrosion Journal vol 2pp 175ndash188 2009
[21] K F Khaled ldquoCorrosion control of copper in nitric acidsolutions using some amino acidsmdasha combined experimentaland theoretical studyrdquo Corrosion Science vol 52 no 10 pp3225ndash3234 2010
[22] E E Oguzie C O Akalezi C K Enenebeaku and J N AnekeldquoCorrosion inhibition and adsorption behavior of malachitegreen dye on aluminum corrosionrdquoChemical Engineering Com-munications vol 198 no 1 pp 46ndash60 2011
[23] J Cruz T Pandiyan and E Garcia-Ochoa ldquoA new inhibitor formild carbon steel electrochemical and DFT studiesrdquo Journal ofElectroanalytical Chemistry vol 583 no 1 pp 8ndash16 2005
[24] J Cruz R Martinez J Genesca and E Garcia-OchoaldquoExperimental and theoretical study of 1-(2-ethylamino)-2-methylimidazoline as an inhibitor of carbon steel corrosion inacid mediardquo Journal of Electroanalytical Chemistry vol 566 no1 pp 111ndash121 2004
[25] E E Oguzie Y Li S G Wang and F Wang ldquoUnderstandingcorrosion inhibition mechanismsmdashexperimental and theoreti-cal approachrdquo RSC Advances vol 1 no 5 pp 866ndash873 2011
[26] A Kumar A Sankara M Kumaravel and S RameshkumarldquoClitoria ternateamdashextracts as corrosion inhibitor for mild steelin acid mediumrdquo International Journal of Engineering Researchand Development vol 8 no 5 pp 64ndash67 2013
[27] E E Oguzie G N Onuoha and A I Onuchukwu ldquoInhibitorymechanism of mild steel corrosion in 2M sulphuric acidsolution by methylene blue dyerdquo Materials Chemistry andPhysics vol 89 no 2-3 pp 305ndash311 2005
[28] E E Oguzie C K Enenebeaku C O Akalezi S C Okoro AA Ayuk and E N Ejike ldquoAdsorption and corrosion-inhibitingeffect ofDacryodis edulis extract on low-carbon-steel corrosionin acidic mediardquo Journal of Colloid and Interface Science vol349 no 1 pp 283ndash292 2010
[29] E E Oguzie ldquoCorrosion inhibition of aluminium in acidicand alkaline media by Sansevieria trifasciata extractrdquo CorrosionScience vol 49 no 3 pp 1527ndash1539 2007
[30] S A Umoren I B Obot and E E Ebenso ldquoCorrosioninhibition of aluminium using exudate gum from Pachylobusedulis in the presence of halide ions in HClrdquo E-Journal ofChemistry vol 5 no 2 pp 355ndash364 2008
[31] P C Okafor E E Ebenso and U J Ekpe ldquoAzadirachta indicaextracts as corrosion inhibitor for mild steel in acid mediumrdquoInternational Journal of Electrochemical Science vol 5 no 7 pp978ndash993 2010
[32] M Lebrini F Robert A Lecente and C Roos ldquoCorrosioninhibition of C38 steel in 1M hydrochloric acid medium byalkaloids extract from Oxandra asbeckii plant rdquo CorrosionScience vol 53 no 2 pp 687ndash695 2011
[33] E E Oguzie ldquoInfluence of halide ions on the inhibitive effect ofcongo red dye on the corrosion of mild steel in sulphuric acidsolutionrdquoMaterials Chemistry and Physics vol 87 no 1 pp 212ndash217 2004
[34] E E Oguzie ldquoInhibition of acid corrosion of mild steel byTelfaria occidentalis extractrdquo Pigment amp Resin Technology vol34 no 6 pp 321ndash326 2005
[35] E E Oguzie V O Njoku C K Enenebeaku C O Akalezi andC Obi ldquoEffect of hexamethylpararosaniline chloride (crystalviolet) on mild steel corrosion in acidic mediardquo CorrosionScience vol 50 no 12 pp 3480ndash3486 2008
[36] M A Ameer E Khamis and G al-Senani ldquoEffect of temper-ature on stability of adsorbed inhibitors on steel in phosphoricacid solutionrdquo Journal of Applied Electrochemistry vol 32 no 2pp 149ndash156 2002
[37] P C Okafor E E Oguzie G E Iniama M E Ikpi and U JEkpe ldquoCorrosion inhibition properties of thiosemicarbazoneand semicarbazone derivatives in concentrated acid environ-mentrdquoGlobal Journal of Pure and Applied Sciences vol 14 no 1pp 89ndash96 2008
[38] I B Obot ldquoSynergistic effect of nizoral and iodide ions on thecorrosion inhibition of mild steel in sulphuric acid solutionrdquoPortugaliae ElectrochimicaActa vol 27 no 5 pp 539ndash553 2009
[39] N O Eddy S A Odoemelam and A O Odiongenyi ldquoEthanolextract of musa species peels as a green corrosion inhibitor formild steel kinetics adsorption and thermodynamic consider-ationsrdquo Electronic Journal of Environmental Agricultural andFood Chemistry vol 8 no 4 pp 243ndash255 2009
[40] M H Hussin and M J Kassim ldquoThe corrosion inhibition andadsorption behavior of Uncaria gambir extract on mild steel in1M HClrdquo Materials Chemistry and Physics vol 125 no 3 pp461ndash468 2010
[41] V K W Grips V E Selvi H C Barshilia and K S RajamldquoEffect of electroless nickel interlayer on the electrochemicalbehavior of single layer CrN TiN TiAlN coatings and nanolay-ered TiAlNCrN multilayer coatings prepared by reactive dcmagnetron sputteringrdquo Electrochimica Acta vol 51 no 17 pp3461ndash3468 2006
[42] E E Oguzie ldquoStudies on the inhibitive effect ofOccimum viridisextract on the acid corrosion of mild steelrdquoMaterials Chemistryand Physics vol 99 no 2-3 pp 441ndash446 2006
[43] B Wang M Du J Zhang and C J Gao ldquoElectrochemical andsurface analysis studies on corrosion inhibition of Q235 steelby imidazoline derivative against CO
2corrosionrdquo Corrosion
Science vol 53 no 1 pp 353ndash361 2011[44] G Mu and X Li ldquoInhibition of cold rolled steel corrosion
by Tween-20 in sulfuric acid weight loss electrochemical andAFM approaches rdquo Journal of Colloid and Interface Science vol289 no 1 pp 184ndash192 2005
[45] A K Satapathy G Gunasekaran S C Sahoo K Amit and PV Rodrigues ldquoCorrosion inhibition by Justicia gendarussa plantextract in hydrochloric acid solutionrdquoCorrosion Science vol 51no 12 pp 2848ndash2856 2009
[46] E E Oguzie Y Li and F H Wang ldquoCorrosion inhibition andadsorption behavior of methionine on mild steel in sulfuricacid and synergistic effect of iodide ionrdquo Journal of Colloid andInterface Science vol 310 no 1 pp 90ndash98 2007
[47] L M Rodrıguez-Valdez W Villamisar M Casales et alldquoComputational simulations of themolecular structure and cor-rosion properties of amidoethyl aminoethyl and hydroxyethylimidazolines inhibitorsrdquo Corrosion Science vol 48 no 12 pp4053ndash4064 2006
[48] H Ju Z P Kai and Y Li ldquoAminic nitrogen-bearing polydentateSchiff base compounds as corrosion inhibitors for iron in acidicmedia a quantum chemical calculationrdquo Corrosion Science vol50 no 3 pp 865ndash871 2008
[49] L M Rodrıguez-Valdez A Martınez-Villafane and DGlossman-Mitnik ldquoComputational simulation of themolecularstructure and properties of heterocyclic organic compoundswith possible corrosion inhibition propertiesrdquo Journal ofMolecular Structure THEOCHEM vol 713 no 1ndash3 pp 65ndash702005
Journal of Materials 11
[50] K F Khaled ldquoMolecular simulation quantum chemical calcu-lations and electrochemical studies for inhibition of mild steelby triazolesrdquo Electrochimica Acta vol 53 no 9 pp 3484ndash34922008
[51] R M Issa M K Awad and F M Atlam ldquoQuantum chemicalstudies on the inhibition of corrosion of copper surface bysubstituted uracilsrdquo Applied Surface Science vol 255 no 5 pp2433ndash2441 2008
Figure 1 Variation of inhibition efficiency with concentration ofEHEC
molecules adsorbed at the metal surface (H2Oads) as follows
[36ndash38]
Inh(sol) + 119909H2O(ads) lArrrArr Inh
(ads) + 119909H2O(sol) (5)
where 119909 represents the number of water molecules replacedby one molecule of adsorbed inhibitor The adsorption bondstrength is dependent on the composition of the metal andcorrodent inhibitor structure concentration and orienta-tion as well as temperature Since EHEC can be protonated inthe presence of strong acids it is quite necessary to considerboth cationic and molecular species when discussing theadsorption process of EHEC Figure 3 shows the plot of119862120579 versus 119862 to be linear which is in agreement with theLangmuir equation [39]
119862
120579=
119899
119870ads+ 119899119862 (6)
where 119862 is the concentration of inhibitor and 119870ads is theequilibrium constant for the adsorption-desorption process
In general 119870ads represents the adsorption power ofthe inhibitor molecule on the metal surface The positivevalues confirm the adsorbability of EHEC on the metalsurface The linear plots obtained in Figure 3 suggest thatEHEC adsorption from 10MH
2SO4solution followed the
Langmuir isotherm though the isothermparameters indicatesome deviations from ideal Langmuir behaviour The slopedeviates from unity (see 119899 values in Table 3) with nonzerointercept on the 119910-axis which could be traced to somelimitations in the underlying assumptions The results in factimply that each EHEC molecule occupies 119899 active corrosionsites on the mild steel surface in 10M H
2SO4solution
The free energy of adsorption (Δ119866ads) obtained from (7)which is evaluated from 119870ads obtained from intercepts of theLangmuir plots is given in Table 3
where 119877 and 119879 are the universal gas constant and absolutetemperature respectively The other parameter retains itsprevious meaning The large negative Δ119866ads values impliedthat the adsorption of EHEC on the mild steel surface wasfavourable from thermodynamics point of view and indicatedthat the inhibitor was strongly adsorbed covering bothanodic and cathodic regions
In addition it is important to note that adsorption freeenergy values of minus20 kJmolminus1 or less negative are associatedwith an electrostatic interaction between charged moleculesand charged metal surface (physical adsorption) On theother hand adsorption free energy values of minus40Kjmolminus1 ormore negative values involve charge sharing or transfer fromthe inhibitor molecules to the metal surface to form a co-ordinate covalent bond (chemical adsorption) [40]
35 Impedance Measurements Electrochemical impedancespectroscopy analyses provide insight into the kinetics ofelectrode processes as well as the surface characteristicsof the electrochemical system of interest Figure 4 presentsthe impedance spectra measured at 119864corr after 30minutesof immersion and exemplified the Nyquist plots obtainedfor mild steel in 10MH
2SO4solution in the absence and
presence of EHEC and EHEC + KI The observed increase inthe impedance parameters in inhibited solutions is associatedwith the corrosion inhibiting effect of EHEC The Nyquistplots for all systems generally have the form of only onedepressed semicircle corresponding to one time constantalthough a slight sign of low-frequency inductive behaviourcan be discerned The depression of the capacitance semicir-cle with centre below the real axis suggests a distribution ofthe capacitance due to inhomogeneities associated with theelectrode surface
The presence of a single time constant may be attributedto the short exposure time in the corrosive medium whichis not adequate to reveal degradation of the substrate [41]A polarization resistance (119877
119901) can be extracted from the
intercept of the low-frequency loop at the real axis ofimpedance (119885re) in the Nyquist plots since the inductiveloop is negligible The value of 119877
119901is very close to that of
the charge transfer resistance 119877ct which can be extractedfrom the diameter of the semicircle [41 42] The impedancespectra for theNyquist plotswere thus adequately analyzed bybeing fit to the equivalent circuit model119877
119904(119876dl119877ct) which has
been previously used to model the mild steelacid solutioninterface [41 43]
The values of the impedance parameters derived fromthe Nyquist plots using the selected equivalent circuit model119877119904(119876dl119877ct) are given in Table 4 The terms 119876dl and 119899
respectively represent the magnitude and exponent of theconstant phase element (CPE) of the double layer The CPEwith impedance given by 119885CPE = 119876minus1(119895119908)
minus119899 where 119895 isan imaginary number and 119908 is the angular frequency in
Journal of Materials 5
1 2 3 4 50
102030405060708090
100
Time (days)
05 gL EHEC05 gL EHEC + KI
1 2 3 4 50
102030405060708090
100
Time (days)
10 gL EHEC10 gL EHEC + KI
1 2 3 4 50
102030405060708090
100
Time (days)
15 gL EHEC15 gL EHEC + KI
1 2 3 4 50
102030405060708090
100
Time (days)
20 gL EHEC20 gL EHEC + KI
1 2 3 4 50
102030405060708090
100
Time (days)
25 gL EHEC25 gL EHEC + KI
Inhi
bitio
n effi
cien
cy I
()
Inhi
bitio
n effi
cien
cy I
()
Inhi
bitio
n effi
cien
cy I
()
Inhi
bitio
n effi
cien
cy I
()
Inhi
bitio
n effi
cien
cy I
()
Figure 2 Synergistic effect between KI and EHEC on the variation of inhibition efficiency with time
rads is used in place of a capacitor to compensate for thedeviations from ideal dielectric behaviour associated withthe nonhomogeneity of the electrode surface Introductionof EHEC into the acid corrodent leads to an increase in 119877ctand a reduction of119876dl indicating a hindering of the corrosionreaction The decrease in 119876dl values which normally resultsfrom a decrease in the dielectric constant andor an increasein the double layer thickness is due to inhibitor adsorption onthe metalelectrolyte interface [44] This implies that EHECreduces the corrosion rate of themild steel specimen by virtueof adsorption on the metalelectrolyte interface a fact thathas been previously established A quantitative measure ofthe protective effect can be obtained by comparing the values
of the charge transfer resistance in the absence (119877ct) andpresence of inhibitor (119877ctinh) as follows
119868 = [1 minus119877ct119877ctinh
] times 100 (8)
where (119877ctinh) and 119877ct are the charge transfer resistance forinhibited and uninhibited systems respectively
The double layer capacitance values of the systems werealso examined and calculated using the expression
119862dl =1
2120587119891max119877ct (9)
where 119891max is the maximum frequency The obtained valuesof 119862dl are presented in Table 4
6 Journal of Materials
05 10 15 20 25
10
15
20
25
30
35
40
45
50
Day 1Day 2Day 3
Day 4Day 5
C120579
(gL
)
C (gL)
Figure 3 Langmuir isotherm for EHEC adsorption on mild steelsurface in 10MH
2SO4
0 20 40 60 80 100 120 140
0102030405060708090
100110120130140
Blank25 gL EHEC25 gL EHEC + KI
Zim
(Ω)
Zre (Ω)
Figure 4 Nyquist impedance spectra of mild steel corrosion in10MH
2SO4in the absence and presence of EHEC and EHEC + KI
Lower double layer capacitance suggests reduced electriccharge stored which is a consequence of increased adsorp-tion layer that acted as a dielectric constant The increasein 119877ct values in inhibited systems which corresponds to anincrease in the diameter of the Nyquist semicircle confirmsthat the corrosion inhibiting effect of EHEC and EHEC + KIand is much more pronounced in the latter system implyingthat KI synergistically enhanced the corrosion inhibitingeffect of EHEC In other words lower 119862dl values correspond
to reduced double layer capacitance which according to theHelmholtzmodel (10) results fromadecrease in the dielectricconstant (120576) or an increase in the interfacial layer thickness(120575)
119862dl =120576120576119900119860
120575 (10)
where 120576 is the dielectric constant of the medium 120576119900is the
vacuum permittivity 119860 is the electrode area and 120575 is thethickness of the interfacial layer
Since adsorption of an organic inhibitor on a metalsurface involves the replacement of adsorbedwatermoleculeson the surface the smaller dielectric constant of the organicmolecule compared towater aswell as the increased thicknessof interfacial layer due to inhibitor adsorption acted simulta-neously to reduce the double layer capacitanceThis providesexperimental evidence of adsorption of EHEC on mild steelsurface The significantly lower 119862dl value of the EHEC + KIsystem supports the assertion that the iodide ion significantlyenhances adsorption of EHEC on the metalsolution inter-face
36 Polarization Measurements Figure 5 shows the polar-ization curves of mild steel dissolution in 10MH
2SO4
solution in the absence and presence of EHEC and EHEC+ KI Introduction of EHEC and EHEC + KI into the acidsolutionwas observed to shift the corrosion potentials of bothinhibited systems slightly in the negative direction and inboth cases inhibited the anodic metal dissolution reactionas well as the cathodic hydrogen evolution reaction Sincethe 119864corr is not altered significantly the implication is thatthe corrosion inhibition process is under mixed control withpredominant cathodic effect In addition following observa-tions in Figure 5 both cathodic and anodic partial reactionsare affected as evident in decrease in the corrosion currentdensities This implies that EHEC functioned as a mixed-type inhibitor for both systems However marked cathodicpartial hydrogen evolution reaction is discerned Moresodocumented report [45] has it that when displacement in119864corr is gt85mV the inhibitor can be regarded as a cathodicor anodic type inhibitor and if the displacement in 119864corris lt85mV the inhibitor can be seen as mixed type In thepresent study the displacement in the corrosion potential(119864corr) in the presence of EHEC and EHEC + KI shifted952 and 2075mV respectively in the cathodic directioncompared to the blank which is a confirmation that theinhibitor acts as a mixed-type inhibitor with predominantcathodic effect
Journal of Materials 7
Table 4 Impedance and polarization parameters for mild steel in 05M H2SO4 in the presence and absence of EHEC and EHEC + KI
System Impedance data Polarization data119877ct 119899 IE 119862dl (uF cm
minus2) times 10minus3 119864corr (mV (SCE)) 119877119901(Ω cm2) IE
Inhibition efficiency was calculated from the polarizationdata as follows
119868 = [1 minus119877119901
119877119901
inh] times 100 (11)
where 119877119901and 119877
119901
inh are polarization resistance for uninhib-ited and inhibited systems respectivelyThe calculated valuesare given in Table 4 Observations from Table 4 show thatthe inhibition efficiencies obtained from both impedanceand polarization results are comparable The data confirmthe consistency of EHEC and EHEC + KI at the prevailingexperimental condition
The cooperative effect between EHEC and KI in hin-dering the corrosion of mild steel in 10MH
2SO4solution
is also evident in both the Nyquist and Tafel polarizationplots Addition of KI resulted in a significant increase in thediameter of the Nyquist semicircle and hence an increase in119877ct as well as 119868 and a decrease in the corrosion currentdensity of the Tafel polarization curves The presence ofiodide ions shifts 119864corr more in the cathodic direction andfurther decreases the anodic and cathodic reaction kineticsThe mechanism of this synergistic effect has been describedin detail in some reports [46] The iodide ions are stronglychemisorbed on the corrodingmild steel surface and facilitateEHEC adsorption by acting as intermediate bridges betweenthe positively charged metal surface and EHEC cations Thisstabilizes the adsorption of EHEC on the mild steel surfaceleading to higher surface coverage To account for the aboveobservations it is necessary to recognize that the process ofadsorption of an organic inhibitor on a corroding metal sur-face depends on factors such as the nature and surface chargeon the metal in the corrosive medium as well as the inhibitorstructure Consequently more iodide ions are adsorbed onmild steel which presents a more positive surface giving riseto increased synergistic interactions with protonated EHECspecies and hence higher inhibition efficiencies
E versus SCE (V)minus08 minus07 minus06 minus05 minus04 minus03 minus02
001
1E minus 3
1E minus 4
1E minus 5
1E minus 6
Blank25 gL EHEC25 gL EHEC + KI
i(A
cmminus2)
Figure 5 Polarization curves ofmild steel corrosion in 10MH2SO4
in the absence and presence of EHEC and EHEC + KI
37 Quantum Chemical Calculations The inhibition effec-tiveness of inhibitors has been reported to correlate with thequantum chemical parameters such as HOMO (the highestoccupied molecular orbital) LUMO (the lowest unoccupiedmolecular orbital) and the energy gap between the LUMOand HOMO (Δ119864 = 119864LUMO minus 119864HOMO) [47ndash49] A high119864HOMO (less negative) is associated with the capacity of amolecule to donate electrons to an appropriated acceptorwith empty molecular orbital that facilitated the adsorptionprocess and therefore indicated good performance of thecorrosion inhibitor [50] 119864LUMO corresponds to a tendencyfor electron acceptance Based on this the calculated dif-ference Δ119864 demonstrates inherent electron donating abilityand measures the interaction of the inhibitor molecule withthe metal surface
According to the frontier molecular orbital theory ofchemical reactivity transition of electrons is due to aninteraction between the frontier orbitals HOMOand LUMOof reacting species The energy of HOMO is directly relatedto the ionization potential and characterizes the susceptibilityof the molecule toward attack by electrophiles The energyof LUMO is directly related to the electron affinity andcharacterizes the susceptibility of the molecule toward attackby nucleophile The lower the values of 119864LUMO the strongerthe electron accepting ability of the molecule
8 Journal of Materials
(a) Optimized structure (b) Total electron density
(c) HOMO orbital (d) LUMO orbital
(e) Fukui function for nucleophilic attack (f) Fukui function for electrophilic attack
Figure 6 Electronic properties of ethyl hydroxyethyl cellulose (EHEC) [C grey H white O red]
The electronic structure of EHEC the distribution offrontier molecular orbital and Fukui indices have beenmod-eled in order to establish the active sites as well as local reac-tivity of the inhibitingmoleculesThis was achieved using theDFT electronic structure programs Forcite and DMol3 andusing a Mulliken population analysis Electronic parametersfor the simulation include restricted spin polarization usingtheDNDbasis set as the PerdewWang (PW) local correlationdensity functional The geometry optimized structures ofEHEC HOMO and LUMOorbitals Fukui functions and thetotal electron density are presented in Figure 6 In the EHEC
molecule theHOMOorbital is saturated around the aromaticnucleus which is the region of highest electron density andoften the site at which electrophiles attack and represents theactive centres with the utmost ability to bond to the metalsurface The LUMO orbital is saturated around the ethoxyfunction and represents the site at which nucleophilic attackoccurs
Local reactivity was analyzed by means of the Fukuiindices to assess the active regions in terms of nucleophilicand electrophilic behaviour Thus the site for nucleophilicattack will be the place where the value of 119891+ is maximum In
Journal of Materials 9
turn the site for electrophilic attack is controlled by the valueof 119891minus The values of 119864HOMO 119864LUMO Δ119864 and Fukui functionsare given inTable 5Higher values of119864HOMO indicate a greaterdisposition of a molecule to donate electrons to a metalsurface In the same way low values of the energy of the gapΔ119864 will afford good inhibition efficiency since the energyrequired to remove an electron from the last occupied orbitalwill be minimized [51] The above descriptors howeversuggest that EHEC possessed good inhibiting potential Thisis in agreement with the experimental findings
4 Conclusions
Ethyl hydroxyethyl cellulose was found to be an effectiveinhibitor of mild steel in 10MH
2SO4solution and its inhibi-
tion efficiency increased with increasing concentration Thecorrosion process is inhibited by adsorption of EHEC on themild steel surface following themodified Langmuir isothermThe inhibiting action is attributed to general adsorption ofboth protonated and molecular species of the additive on thecathodic and anodic sites on the corrodingmild steel surfaceIn addition corrosion inhibition is due to the formationof a chemisorbed film on the mild steel surface The EISmeasurement confirmed the adsorption of EHEC and EHEC+ KI on the mild steel surface Polarization studies showedthat EHEC and EHEC + KI were mixed-type inhibitorsystems with predominant cathodic effect The theoreticalstudy demonstrated that the inhibition efficiency is related tomolecular structure of inhibitor whereby increase in 119864HOMOand decrease in 119864LUMO favoured inhibition efficiency
Conflict of Interests
Theauthors hereby declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors are grateful to Udemmadu Tochukwu andOchiogu Valentine for assistance in carrying out some mea-surements
References
[1] E E Oguzie Y Li and F H Wang ldquoEffect of ascorbic acidon mild steel dissolution in sulphuric acid solution investigatedby electrochemical polarization and surface probe techniquesrdquoJournal of Applied Electrochemistry vol 37 no 10 pp 1183ndash11902007
[2] L G da Trindade and R S Goncalves ldquoEvidence of caffeineadsorption on a low-carbon steel surface in ethanolrdquo CorrosionScience vol 51 no 8 pp 1578ndash1583 2009
[3] F Bentiss M Outirite M Traisnel et al ldquoImprovementof corrosion resistance of carbon steel in hydrochloric acidmedium by 36-bis(3-pyridyl)pyridazinerdquo International Journalof Electrochemical Science vol 7 no 2 pp 1699ndash1723 2012
[4] S M A Shibli and V S Saji ldquoCo-inhibition characteristicsof sodium tungstate with potassium iodate on mild steelcorrosionrdquoCorrosion Science vol 47 no 9 pp 2213ndash2224 2005
[5] E E Oguzie C Unaegbu C N Ogukwe B N Okolue and AI Onuchukwu ldquoInhibition of mild steel corrosion in sulphuricacid using indigo dye and synergistic halide additivesrdquoMateri-als Chemistry and Physics vol 84 no 2-3 pp 363ndash368 2004
[6] V Kumpawat U Garg and R K Tak ldquoCorrosion inhibitionof aluminium in acid media by naturally occurring plantArtocarpus heterophyllus and Acacia senegalrdquo Journal of IndianCouncil of Chemists vol 26 no 1 pp 82ndash84 2009
[7] IA Akpan and N O Offiong ldquoEffect of ethanolamine andethylamine on the entropy content of the corrosion ofmild steelin tetraoxosulphate (VI) acid solutionrdquoChemistry andMaterialsResearch vol 2 no 7 pp 40ndash47 2012
[8] M Kissi M Bouklah B Hammouti and M BenkaddourldquoEstablishment of equivalent circuits from electrochemicalimpedance spectroscopy study of corrosion inhibition of steelby pyrazine in sulphuric acidic solutionrdquo Applied SurfaceScience vol 252 no 12 pp 4190ndash4197 2006
[9] S Rajendran S P Sridevi N Anthony A J Amalraj andM Sundaravadivelu ldquoCorrosion behaviour of carbon steel inpolyvinyl alcoholrdquo Anti-Corrosion Methods and Materials vol52 no 2 pp 102ndash107 2005
[10] B Qian J Wang M Zheng and B Hou ldquoSynergistic effect ofpolyaspartic acid and iodide ion on corrosion inhibition ofmildsteel in H
[11] D A Arthur A Jonathan P O Ameh and C Anya ldquoAreview on the assessment of polymeric materials used ascorrosion inhibitor of metals and alloysrdquo International Journalof Industrial Chemistry vol 4 article 2 pp 1ndash9 2013
[12] S A Umoren Y Li and F H Wang ldquoEffect of polyacrylicacid on the corrosion behaviour of aluminium in sulphuric acidsolutionrdquo Journal of Solid State Electrochemistry vol 14 no 12pp 2293ndash2305 2010
[13] S Banerjee A Mishra M M Singh B Maiti B Ray andP Maiti ldquoHighly efficient polyurethane ionomer corrosioninhibitor the effect of chain structurerdquo RSCAdvances vol 1 no2 pp 199ndash210 2011
[14] A K Dubey and G Singh ldquoCorrosion inhibition of mild steelin sulphuric acid solution by using polyethylene glycol methylether (PEGME)rdquo Portugaliae Electrochimica Acta vol 25 no 2pp 221ndash235 2007
[15] E E Oguzie S G Wang Y Li and F H Wang ldquoInfluenceof iron microstructure on corrosion inhibitor performance inacidic mediardquoThe Journal of Physical Chemistry C vol 113 no19 pp 8420ndash8429 2009
[16] S A Umoren E E Ebenso P C Okafor and O OgbobeldquoWater-soluble polymers as corrosion inhibitorsrdquo Pigment ampResin Technology vol 35 no 6 pp 346ndash352 2006
[17] S A Umoren and I B Obot ldquoPolyvinylpyrollidone andpolyacrylamide as corrosion inhibitors for mild steel in acidicmediumrdquo Surface Review and Letters vol 15 no 3 pp 277ndash2842008
[18] H Ashassi-Sorkhabi and N Ghalebsaz-Jeddi ldquoInhibition effectof polyethylene glycol on the corrosion of carbon steel insulphuric acidrdquoMaterials Chemistry and Physics vol 92 no 2-3pp 480ndash486 2005
[19] A Yurt V Butun and B Duran ldquoEffect of themolecular weightand structure of some novel water-soluble triblock copolymerson the electrochemical behaviour of mild steelrdquo MaterialsChemistry and Physics vol 105 no 1 pp 114ndash121 2007
10 Journal of Materials
[20] S A Umoren ldquoPolymers as corrosion inhibitors for metals indifferent mediamdasha reviewrdquo The Open Corrosion Journal vol 2pp 175ndash188 2009
[21] K F Khaled ldquoCorrosion control of copper in nitric acidsolutions using some amino acidsmdasha combined experimentaland theoretical studyrdquo Corrosion Science vol 52 no 10 pp3225ndash3234 2010
[22] E E Oguzie C O Akalezi C K Enenebeaku and J N AnekeldquoCorrosion inhibition and adsorption behavior of malachitegreen dye on aluminum corrosionrdquoChemical Engineering Com-munications vol 198 no 1 pp 46ndash60 2011
[23] J Cruz T Pandiyan and E Garcia-Ochoa ldquoA new inhibitor formild carbon steel electrochemical and DFT studiesrdquo Journal ofElectroanalytical Chemistry vol 583 no 1 pp 8ndash16 2005
[24] J Cruz R Martinez J Genesca and E Garcia-OchoaldquoExperimental and theoretical study of 1-(2-ethylamino)-2-methylimidazoline as an inhibitor of carbon steel corrosion inacid mediardquo Journal of Electroanalytical Chemistry vol 566 no1 pp 111ndash121 2004
[25] E E Oguzie Y Li S G Wang and F Wang ldquoUnderstandingcorrosion inhibition mechanismsmdashexperimental and theoreti-cal approachrdquo RSC Advances vol 1 no 5 pp 866ndash873 2011
[26] A Kumar A Sankara M Kumaravel and S RameshkumarldquoClitoria ternateamdashextracts as corrosion inhibitor for mild steelin acid mediumrdquo International Journal of Engineering Researchand Development vol 8 no 5 pp 64ndash67 2013
[27] E E Oguzie G N Onuoha and A I Onuchukwu ldquoInhibitorymechanism of mild steel corrosion in 2M sulphuric acidsolution by methylene blue dyerdquo Materials Chemistry andPhysics vol 89 no 2-3 pp 305ndash311 2005
[28] E E Oguzie C K Enenebeaku C O Akalezi S C Okoro AA Ayuk and E N Ejike ldquoAdsorption and corrosion-inhibitingeffect ofDacryodis edulis extract on low-carbon-steel corrosionin acidic mediardquo Journal of Colloid and Interface Science vol349 no 1 pp 283ndash292 2010
[29] E E Oguzie ldquoCorrosion inhibition of aluminium in acidicand alkaline media by Sansevieria trifasciata extractrdquo CorrosionScience vol 49 no 3 pp 1527ndash1539 2007
[30] S A Umoren I B Obot and E E Ebenso ldquoCorrosioninhibition of aluminium using exudate gum from Pachylobusedulis in the presence of halide ions in HClrdquo E-Journal ofChemistry vol 5 no 2 pp 355ndash364 2008
[31] P C Okafor E E Ebenso and U J Ekpe ldquoAzadirachta indicaextracts as corrosion inhibitor for mild steel in acid mediumrdquoInternational Journal of Electrochemical Science vol 5 no 7 pp978ndash993 2010
[32] M Lebrini F Robert A Lecente and C Roos ldquoCorrosioninhibition of C38 steel in 1M hydrochloric acid medium byalkaloids extract from Oxandra asbeckii plant rdquo CorrosionScience vol 53 no 2 pp 687ndash695 2011
[33] E E Oguzie ldquoInfluence of halide ions on the inhibitive effect ofcongo red dye on the corrosion of mild steel in sulphuric acidsolutionrdquoMaterials Chemistry and Physics vol 87 no 1 pp 212ndash217 2004
[34] E E Oguzie ldquoInhibition of acid corrosion of mild steel byTelfaria occidentalis extractrdquo Pigment amp Resin Technology vol34 no 6 pp 321ndash326 2005
[35] E E Oguzie V O Njoku C K Enenebeaku C O Akalezi andC Obi ldquoEffect of hexamethylpararosaniline chloride (crystalviolet) on mild steel corrosion in acidic mediardquo CorrosionScience vol 50 no 12 pp 3480ndash3486 2008
[36] M A Ameer E Khamis and G al-Senani ldquoEffect of temper-ature on stability of adsorbed inhibitors on steel in phosphoricacid solutionrdquo Journal of Applied Electrochemistry vol 32 no 2pp 149ndash156 2002
[37] P C Okafor E E Oguzie G E Iniama M E Ikpi and U JEkpe ldquoCorrosion inhibition properties of thiosemicarbazoneand semicarbazone derivatives in concentrated acid environ-mentrdquoGlobal Journal of Pure and Applied Sciences vol 14 no 1pp 89ndash96 2008
[38] I B Obot ldquoSynergistic effect of nizoral and iodide ions on thecorrosion inhibition of mild steel in sulphuric acid solutionrdquoPortugaliae ElectrochimicaActa vol 27 no 5 pp 539ndash553 2009
[39] N O Eddy S A Odoemelam and A O Odiongenyi ldquoEthanolextract of musa species peels as a green corrosion inhibitor formild steel kinetics adsorption and thermodynamic consider-ationsrdquo Electronic Journal of Environmental Agricultural andFood Chemistry vol 8 no 4 pp 243ndash255 2009
[40] M H Hussin and M J Kassim ldquoThe corrosion inhibition andadsorption behavior of Uncaria gambir extract on mild steel in1M HClrdquo Materials Chemistry and Physics vol 125 no 3 pp461ndash468 2010
[41] V K W Grips V E Selvi H C Barshilia and K S RajamldquoEffect of electroless nickel interlayer on the electrochemicalbehavior of single layer CrN TiN TiAlN coatings and nanolay-ered TiAlNCrN multilayer coatings prepared by reactive dcmagnetron sputteringrdquo Electrochimica Acta vol 51 no 17 pp3461ndash3468 2006
[42] E E Oguzie ldquoStudies on the inhibitive effect ofOccimum viridisextract on the acid corrosion of mild steelrdquoMaterials Chemistryand Physics vol 99 no 2-3 pp 441ndash446 2006
[43] B Wang M Du J Zhang and C J Gao ldquoElectrochemical andsurface analysis studies on corrosion inhibition of Q235 steelby imidazoline derivative against CO
2corrosionrdquo Corrosion
Science vol 53 no 1 pp 353ndash361 2011[44] G Mu and X Li ldquoInhibition of cold rolled steel corrosion
by Tween-20 in sulfuric acid weight loss electrochemical andAFM approaches rdquo Journal of Colloid and Interface Science vol289 no 1 pp 184ndash192 2005
[45] A K Satapathy G Gunasekaran S C Sahoo K Amit and PV Rodrigues ldquoCorrosion inhibition by Justicia gendarussa plantextract in hydrochloric acid solutionrdquoCorrosion Science vol 51no 12 pp 2848ndash2856 2009
[46] E E Oguzie Y Li and F H Wang ldquoCorrosion inhibition andadsorption behavior of methionine on mild steel in sulfuricacid and synergistic effect of iodide ionrdquo Journal of Colloid andInterface Science vol 310 no 1 pp 90ndash98 2007
[47] L M Rodrıguez-Valdez W Villamisar M Casales et alldquoComputational simulations of themolecular structure and cor-rosion properties of amidoethyl aminoethyl and hydroxyethylimidazolines inhibitorsrdquo Corrosion Science vol 48 no 12 pp4053ndash4064 2006
[48] H Ju Z P Kai and Y Li ldquoAminic nitrogen-bearing polydentateSchiff base compounds as corrosion inhibitors for iron in acidicmedia a quantum chemical calculationrdquo Corrosion Science vol50 no 3 pp 865ndash871 2008
[49] L M Rodrıguez-Valdez A Martınez-Villafane and DGlossman-Mitnik ldquoComputational simulation of themolecularstructure and properties of heterocyclic organic compoundswith possible corrosion inhibition propertiesrdquo Journal ofMolecular Structure THEOCHEM vol 713 no 1ndash3 pp 65ndash702005
Journal of Materials 11
[50] K F Khaled ldquoMolecular simulation quantum chemical calcu-lations and electrochemical studies for inhibition of mild steelby triazolesrdquo Electrochimica Acta vol 53 no 9 pp 3484ndash34922008
[51] R M Issa M K Awad and F M Atlam ldquoQuantum chemicalstudies on the inhibition of corrosion of copper surface bysubstituted uracilsrdquo Applied Surface Science vol 255 no 5 pp2433ndash2441 2008
Figure 2 Synergistic effect between KI and EHEC on the variation of inhibition efficiency with time
rads is used in place of a capacitor to compensate for thedeviations from ideal dielectric behaviour associated withthe nonhomogeneity of the electrode surface Introductionof EHEC into the acid corrodent leads to an increase in 119877ctand a reduction of119876dl indicating a hindering of the corrosionreaction The decrease in 119876dl values which normally resultsfrom a decrease in the dielectric constant andor an increasein the double layer thickness is due to inhibitor adsorption onthe metalelectrolyte interface [44] This implies that EHECreduces the corrosion rate of themild steel specimen by virtueof adsorption on the metalelectrolyte interface a fact thathas been previously established A quantitative measure ofthe protective effect can be obtained by comparing the values
of the charge transfer resistance in the absence (119877ct) andpresence of inhibitor (119877ctinh) as follows
119868 = [1 minus119877ct119877ctinh
] times 100 (8)
where (119877ctinh) and 119877ct are the charge transfer resistance forinhibited and uninhibited systems respectively
The double layer capacitance values of the systems werealso examined and calculated using the expression
119862dl =1
2120587119891max119877ct (9)
where 119891max is the maximum frequency The obtained valuesof 119862dl are presented in Table 4
6 Journal of Materials
05 10 15 20 25
10
15
20
25
30
35
40
45
50
Day 1Day 2Day 3
Day 4Day 5
C120579
(gL
)
C (gL)
Figure 3 Langmuir isotherm for EHEC adsorption on mild steelsurface in 10MH
2SO4
0 20 40 60 80 100 120 140
0102030405060708090
100110120130140
Blank25 gL EHEC25 gL EHEC + KI
Zim
(Ω)
Zre (Ω)
Figure 4 Nyquist impedance spectra of mild steel corrosion in10MH
2SO4in the absence and presence of EHEC and EHEC + KI
Lower double layer capacitance suggests reduced electriccharge stored which is a consequence of increased adsorp-tion layer that acted as a dielectric constant The increasein 119877ct values in inhibited systems which corresponds to anincrease in the diameter of the Nyquist semicircle confirmsthat the corrosion inhibiting effect of EHEC and EHEC + KIand is much more pronounced in the latter system implyingthat KI synergistically enhanced the corrosion inhibitingeffect of EHEC In other words lower 119862dl values correspond
to reduced double layer capacitance which according to theHelmholtzmodel (10) results fromadecrease in the dielectricconstant (120576) or an increase in the interfacial layer thickness(120575)
119862dl =120576120576119900119860
120575 (10)
where 120576 is the dielectric constant of the medium 120576119900is the
vacuum permittivity 119860 is the electrode area and 120575 is thethickness of the interfacial layer
Since adsorption of an organic inhibitor on a metalsurface involves the replacement of adsorbedwatermoleculeson the surface the smaller dielectric constant of the organicmolecule compared towater aswell as the increased thicknessof interfacial layer due to inhibitor adsorption acted simulta-neously to reduce the double layer capacitanceThis providesexperimental evidence of adsorption of EHEC on mild steelsurface The significantly lower 119862dl value of the EHEC + KIsystem supports the assertion that the iodide ion significantlyenhances adsorption of EHEC on the metalsolution inter-face
36 Polarization Measurements Figure 5 shows the polar-ization curves of mild steel dissolution in 10MH
2SO4
solution in the absence and presence of EHEC and EHEC+ KI Introduction of EHEC and EHEC + KI into the acidsolutionwas observed to shift the corrosion potentials of bothinhibited systems slightly in the negative direction and inboth cases inhibited the anodic metal dissolution reactionas well as the cathodic hydrogen evolution reaction Sincethe 119864corr is not altered significantly the implication is thatthe corrosion inhibition process is under mixed control withpredominant cathodic effect In addition following observa-tions in Figure 5 both cathodic and anodic partial reactionsare affected as evident in decrease in the corrosion currentdensities This implies that EHEC functioned as a mixed-type inhibitor for both systems However marked cathodicpartial hydrogen evolution reaction is discerned Moresodocumented report [45] has it that when displacement in119864corr is gt85mV the inhibitor can be regarded as a cathodicor anodic type inhibitor and if the displacement in 119864corris lt85mV the inhibitor can be seen as mixed type In thepresent study the displacement in the corrosion potential(119864corr) in the presence of EHEC and EHEC + KI shifted952 and 2075mV respectively in the cathodic directioncompared to the blank which is a confirmation that theinhibitor acts as a mixed-type inhibitor with predominantcathodic effect
Journal of Materials 7
Table 4 Impedance and polarization parameters for mild steel in 05M H2SO4 in the presence and absence of EHEC and EHEC + KI
System Impedance data Polarization data119877ct 119899 IE 119862dl (uF cm
minus2) times 10minus3 119864corr (mV (SCE)) 119877119901(Ω cm2) IE
Inhibition efficiency was calculated from the polarizationdata as follows
119868 = [1 minus119877119901
119877119901
inh] times 100 (11)
where 119877119901and 119877
119901
inh are polarization resistance for uninhib-ited and inhibited systems respectivelyThe calculated valuesare given in Table 4 Observations from Table 4 show thatthe inhibition efficiencies obtained from both impedanceand polarization results are comparable The data confirmthe consistency of EHEC and EHEC + KI at the prevailingexperimental condition
The cooperative effect between EHEC and KI in hin-dering the corrosion of mild steel in 10MH
2SO4solution
is also evident in both the Nyquist and Tafel polarizationplots Addition of KI resulted in a significant increase in thediameter of the Nyquist semicircle and hence an increase in119877ct as well as 119868 and a decrease in the corrosion currentdensity of the Tafel polarization curves The presence ofiodide ions shifts 119864corr more in the cathodic direction andfurther decreases the anodic and cathodic reaction kineticsThe mechanism of this synergistic effect has been describedin detail in some reports [46] The iodide ions are stronglychemisorbed on the corrodingmild steel surface and facilitateEHEC adsorption by acting as intermediate bridges betweenthe positively charged metal surface and EHEC cations Thisstabilizes the adsorption of EHEC on the mild steel surfaceleading to higher surface coverage To account for the aboveobservations it is necessary to recognize that the process ofadsorption of an organic inhibitor on a corroding metal sur-face depends on factors such as the nature and surface chargeon the metal in the corrosive medium as well as the inhibitorstructure Consequently more iodide ions are adsorbed onmild steel which presents a more positive surface giving riseto increased synergistic interactions with protonated EHECspecies and hence higher inhibition efficiencies
E versus SCE (V)minus08 minus07 minus06 minus05 minus04 minus03 minus02
001
1E minus 3
1E minus 4
1E minus 5
1E minus 6
Blank25 gL EHEC25 gL EHEC + KI
i(A
cmminus2)
Figure 5 Polarization curves ofmild steel corrosion in 10MH2SO4
in the absence and presence of EHEC and EHEC + KI
37 Quantum Chemical Calculations The inhibition effec-tiveness of inhibitors has been reported to correlate with thequantum chemical parameters such as HOMO (the highestoccupied molecular orbital) LUMO (the lowest unoccupiedmolecular orbital) and the energy gap between the LUMOand HOMO (Δ119864 = 119864LUMO minus 119864HOMO) [47ndash49] A high119864HOMO (less negative) is associated with the capacity of amolecule to donate electrons to an appropriated acceptorwith empty molecular orbital that facilitated the adsorptionprocess and therefore indicated good performance of thecorrosion inhibitor [50] 119864LUMO corresponds to a tendencyfor electron acceptance Based on this the calculated dif-ference Δ119864 demonstrates inherent electron donating abilityand measures the interaction of the inhibitor molecule withthe metal surface
According to the frontier molecular orbital theory ofchemical reactivity transition of electrons is due to aninteraction between the frontier orbitals HOMOand LUMOof reacting species The energy of HOMO is directly relatedto the ionization potential and characterizes the susceptibilityof the molecule toward attack by electrophiles The energyof LUMO is directly related to the electron affinity andcharacterizes the susceptibility of the molecule toward attackby nucleophile The lower the values of 119864LUMO the strongerthe electron accepting ability of the molecule
8 Journal of Materials
(a) Optimized structure (b) Total electron density
(c) HOMO orbital (d) LUMO orbital
(e) Fukui function for nucleophilic attack (f) Fukui function for electrophilic attack
Figure 6 Electronic properties of ethyl hydroxyethyl cellulose (EHEC) [C grey H white O red]
The electronic structure of EHEC the distribution offrontier molecular orbital and Fukui indices have beenmod-eled in order to establish the active sites as well as local reac-tivity of the inhibitingmoleculesThis was achieved using theDFT electronic structure programs Forcite and DMol3 andusing a Mulliken population analysis Electronic parametersfor the simulation include restricted spin polarization usingtheDNDbasis set as the PerdewWang (PW) local correlationdensity functional The geometry optimized structures ofEHEC HOMO and LUMOorbitals Fukui functions and thetotal electron density are presented in Figure 6 In the EHEC
molecule theHOMOorbital is saturated around the aromaticnucleus which is the region of highest electron density andoften the site at which electrophiles attack and represents theactive centres with the utmost ability to bond to the metalsurface The LUMO orbital is saturated around the ethoxyfunction and represents the site at which nucleophilic attackoccurs
Local reactivity was analyzed by means of the Fukuiindices to assess the active regions in terms of nucleophilicand electrophilic behaviour Thus the site for nucleophilicattack will be the place where the value of 119891+ is maximum In
Journal of Materials 9
turn the site for electrophilic attack is controlled by the valueof 119891minus The values of 119864HOMO 119864LUMO Δ119864 and Fukui functionsare given inTable 5Higher values of119864HOMO indicate a greaterdisposition of a molecule to donate electrons to a metalsurface In the same way low values of the energy of the gapΔ119864 will afford good inhibition efficiency since the energyrequired to remove an electron from the last occupied orbitalwill be minimized [51] The above descriptors howeversuggest that EHEC possessed good inhibiting potential Thisis in agreement with the experimental findings
4 Conclusions
Ethyl hydroxyethyl cellulose was found to be an effectiveinhibitor of mild steel in 10MH
2SO4solution and its inhibi-
tion efficiency increased with increasing concentration Thecorrosion process is inhibited by adsorption of EHEC on themild steel surface following themodified Langmuir isothermThe inhibiting action is attributed to general adsorption ofboth protonated and molecular species of the additive on thecathodic and anodic sites on the corrodingmild steel surfaceIn addition corrosion inhibition is due to the formationof a chemisorbed film on the mild steel surface The EISmeasurement confirmed the adsorption of EHEC and EHEC+ KI on the mild steel surface Polarization studies showedthat EHEC and EHEC + KI were mixed-type inhibitorsystems with predominant cathodic effect The theoreticalstudy demonstrated that the inhibition efficiency is related tomolecular structure of inhibitor whereby increase in 119864HOMOand decrease in 119864LUMO favoured inhibition efficiency
Conflict of Interests
Theauthors hereby declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors are grateful to Udemmadu Tochukwu andOchiogu Valentine for assistance in carrying out some mea-surements
References
[1] E E Oguzie Y Li and F H Wang ldquoEffect of ascorbic acidon mild steel dissolution in sulphuric acid solution investigatedby electrochemical polarization and surface probe techniquesrdquoJournal of Applied Electrochemistry vol 37 no 10 pp 1183ndash11902007
[2] L G da Trindade and R S Goncalves ldquoEvidence of caffeineadsorption on a low-carbon steel surface in ethanolrdquo CorrosionScience vol 51 no 8 pp 1578ndash1583 2009
[3] F Bentiss M Outirite M Traisnel et al ldquoImprovementof corrosion resistance of carbon steel in hydrochloric acidmedium by 36-bis(3-pyridyl)pyridazinerdquo International Journalof Electrochemical Science vol 7 no 2 pp 1699ndash1723 2012
[4] S M A Shibli and V S Saji ldquoCo-inhibition characteristicsof sodium tungstate with potassium iodate on mild steelcorrosionrdquoCorrosion Science vol 47 no 9 pp 2213ndash2224 2005
[5] E E Oguzie C Unaegbu C N Ogukwe B N Okolue and AI Onuchukwu ldquoInhibition of mild steel corrosion in sulphuricacid using indigo dye and synergistic halide additivesrdquoMateri-als Chemistry and Physics vol 84 no 2-3 pp 363ndash368 2004
[6] V Kumpawat U Garg and R K Tak ldquoCorrosion inhibitionof aluminium in acid media by naturally occurring plantArtocarpus heterophyllus and Acacia senegalrdquo Journal of IndianCouncil of Chemists vol 26 no 1 pp 82ndash84 2009
[7] IA Akpan and N O Offiong ldquoEffect of ethanolamine andethylamine on the entropy content of the corrosion ofmild steelin tetraoxosulphate (VI) acid solutionrdquoChemistry andMaterialsResearch vol 2 no 7 pp 40ndash47 2012
[8] M Kissi M Bouklah B Hammouti and M BenkaddourldquoEstablishment of equivalent circuits from electrochemicalimpedance spectroscopy study of corrosion inhibition of steelby pyrazine in sulphuric acidic solutionrdquo Applied SurfaceScience vol 252 no 12 pp 4190ndash4197 2006
[9] S Rajendran S P Sridevi N Anthony A J Amalraj andM Sundaravadivelu ldquoCorrosion behaviour of carbon steel inpolyvinyl alcoholrdquo Anti-Corrosion Methods and Materials vol52 no 2 pp 102ndash107 2005
[10] B Qian J Wang M Zheng and B Hou ldquoSynergistic effect ofpolyaspartic acid and iodide ion on corrosion inhibition ofmildsteel in H
[11] D A Arthur A Jonathan P O Ameh and C Anya ldquoAreview on the assessment of polymeric materials used ascorrosion inhibitor of metals and alloysrdquo International Journalof Industrial Chemistry vol 4 article 2 pp 1ndash9 2013
[12] S A Umoren Y Li and F H Wang ldquoEffect of polyacrylicacid on the corrosion behaviour of aluminium in sulphuric acidsolutionrdquo Journal of Solid State Electrochemistry vol 14 no 12pp 2293ndash2305 2010
[13] S Banerjee A Mishra M M Singh B Maiti B Ray andP Maiti ldquoHighly efficient polyurethane ionomer corrosioninhibitor the effect of chain structurerdquo RSCAdvances vol 1 no2 pp 199ndash210 2011
[14] A K Dubey and G Singh ldquoCorrosion inhibition of mild steelin sulphuric acid solution by using polyethylene glycol methylether (PEGME)rdquo Portugaliae Electrochimica Acta vol 25 no 2pp 221ndash235 2007
[15] E E Oguzie S G Wang Y Li and F H Wang ldquoInfluenceof iron microstructure on corrosion inhibitor performance inacidic mediardquoThe Journal of Physical Chemistry C vol 113 no19 pp 8420ndash8429 2009
[16] S A Umoren E E Ebenso P C Okafor and O OgbobeldquoWater-soluble polymers as corrosion inhibitorsrdquo Pigment ampResin Technology vol 35 no 6 pp 346ndash352 2006
[17] S A Umoren and I B Obot ldquoPolyvinylpyrollidone andpolyacrylamide as corrosion inhibitors for mild steel in acidicmediumrdquo Surface Review and Letters vol 15 no 3 pp 277ndash2842008
[18] H Ashassi-Sorkhabi and N Ghalebsaz-Jeddi ldquoInhibition effectof polyethylene glycol on the corrosion of carbon steel insulphuric acidrdquoMaterials Chemistry and Physics vol 92 no 2-3pp 480ndash486 2005
[19] A Yurt V Butun and B Duran ldquoEffect of themolecular weightand structure of some novel water-soluble triblock copolymerson the electrochemical behaviour of mild steelrdquo MaterialsChemistry and Physics vol 105 no 1 pp 114ndash121 2007
10 Journal of Materials
[20] S A Umoren ldquoPolymers as corrosion inhibitors for metals indifferent mediamdasha reviewrdquo The Open Corrosion Journal vol 2pp 175ndash188 2009
[21] K F Khaled ldquoCorrosion control of copper in nitric acidsolutions using some amino acidsmdasha combined experimentaland theoretical studyrdquo Corrosion Science vol 52 no 10 pp3225ndash3234 2010
[22] E E Oguzie C O Akalezi C K Enenebeaku and J N AnekeldquoCorrosion inhibition and adsorption behavior of malachitegreen dye on aluminum corrosionrdquoChemical Engineering Com-munications vol 198 no 1 pp 46ndash60 2011
[23] J Cruz T Pandiyan and E Garcia-Ochoa ldquoA new inhibitor formild carbon steel electrochemical and DFT studiesrdquo Journal ofElectroanalytical Chemistry vol 583 no 1 pp 8ndash16 2005
[24] J Cruz R Martinez J Genesca and E Garcia-OchoaldquoExperimental and theoretical study of 1-(2-ethylamino)-2-methylimidazoline as an inhibitor of carbon steel corrosion inacid mediardquo Journal of Electroanalytical Chemistry vol 566 no1 pp 111ndash121 2004
[25] E E Oguzie Y Li S G Wang and F Wang ldquoUnderstandingcorrosion inhibition mechanismsmdashexperimental and theoreti-cal approachrdquo RSC Advances vol 1 no 5 pp 866ndash873 2011
[26] A Kumar A Sankara M Kumaravel and S RameshkumarldquoClitoria ternateamdashextracts as corrosion inhibitor for mild steelin acid mediumrdquo International Journal of Engineering Researchand Development vol 8 no 5 pp 64ndash67 2013
[27] E E Oguzie G N Onuoha and A I Onuchukwu ldquoInhibitorymechanism of mild steel corrosion in 2M sulphuric acidsolution by methylene blue dyerdquo Materials Chemistry andPhysics vol 89 no 2-3 pp 305ndash311 2005
[28] E E Oguzie C K Enenebeaku C O Akalezi S C Okoro AA Ayuk and E N Ejike ldquoAdsorption and corrosion-inhibitingeffect ofDacryodis edulis extract on low-carbon-steel corrosionin acidic mediardquo Journal of Colloid and Interface Science vol349 no 1 pp 283ndash292 2010
[29] E E Oguzie ldquoCorrosion inhibition of aluminium in acidicand alkaline media by Sansevieria trifasciata extractrdquo CorrosionScience vol 49 no 3 pp 1527ndash1539 2007
[30] S A Umoren I B Obot and E E Ebenso ldquoCorrosioninhibition of aluminium using exudate gum from Pachylobusedulis in the presence of halide ions in HClrdquo E-Journal ofChemistry vol 5 no 2 pp 355ndash364 2008
[31] P C Okafor E E Ebenso and U J Ekpe ldquoAzadirachta indicaextracts as corrosion inhibitor for mild steel in acid mediumrdquoInternational Journal of Electrochemical Science vol 5 no 7 pp978ndash993 2010
[32] M Lebrini F Robert A Lecente and C Roos ldquoCorrosioninhibition of C38 steel in 1M hydrochloric acid medium byalkaloids extract from Oxandra asbeckii plant rdquo CorrosionScience vol 53 no 2 pp 687ndash695 2011
[33] E E Oguzie ldquoInfluence of halide ions on the inhibitive effect ofcongo red dye on the corrosion of mild steel in sulphuric acidsolutionrdquoMaterials Chemistry and Physics vol 87 no 1 pp 212ndash217 2004
[34] E E Oguzie ldquoInhibition of acid corrosion of mild steel byTelfaria occidentalis extractrdquo Pigment amp Resin Technology vol34 no 6 pp 321ndash326 2005
[35] E E Oguzie V O Njoku C K Enenebeaku C O Akalezi andC Obi ldquoEffect of hexamethylpararosaniline chloride (crystalviolet) on mild steel corrosion in acidic mediardquo CorrosionScience vol 50 no 12 pp 3480ndash3486 2008
[36] M A Ameer E Khamis and G al-Senani ldquoEffect of temper-ature on stability of adsorbed inhibitors on steel in phosphoricacid solutionrdquo Journal of Applied Electrochemistry vol 32 no 2pp 149ndash156 2002
[37] P C Okafor E E Oguzie G E Iniama M E Ikpi and U JEkpe ldquoCorrosion inhibition properties of thiosemicarbazoneand semicarbazone derivatives in concentrated acid environ-mentrdquoGlobal Journal of Pure and Applied Sciences vol 14 no 1pp 89ndash96 2008
[38] I B Obot ldquoSynergistic effect of nizoral and iodide ions on thecorrosion inhibition of mild steel in sulphuric acid solutionrdquoPortugaliae ElectrochimicaActa vol 27 no 5 pp 539ndash553 2009
[39] N O Eddy S A Odoemelam and A O Odiongenyi ldquoEthanolextract of musa species peels as a green corrosion inhibitor formild steel kinetics adsorption and thermodynamic consider-ationsrdquo Electronic Journal of Environmental Agricultural andFood Chemistry vol 8 no 4 pp 243ndash255 2009
[40] M H Hussin and M J Kassim ldquoThe corrosion inhibition andadsorption behavior of Uncaria gambir extract on mild steel in1M HClrdquo Materials Chemistry and Physics vol 125 no 3 pp461ndash468 2010
[41] V K W Grips V E Selvi H C Barshilia and K S RajamldquoEffect of electroless nickel interlayer on the electrochemicalbehavior of single layer CrN TiN TiAlN coatings and nanolay-ered TiAlNCrN multilayer coatings prepared by reactive dcmagnetron sputteringrdquo Electrochimica Acta vol 51 no 17 pp3461ndash3468 2006
[42] E E Oguzie ldquoStudies on the inhibitive effect ofOccimum viridisextract on the acid corrosion of mild steelrdquoMaterials Chemistryand Physics vol 99 no 2-3 pp 441ndash446 2006
[43] B Wang M Du J Zhang and C J Gao ldquoElectrochemical andsurface analysis studies on corrosion inhibition of Q235 steelby imidazoline derivative against CO
2corrosionrdquo Corrosion
Science vol 53 no 1 pp 353ndash361 2011[44] G Mu and X Li ldquoInhibition of cold rolled steel corrosion
by Tween-20 in sulfuric acid weight loss electrochemical andAFM approaches rdquo Journal of Colloid and Interface Science vol289 no 1 pp 184ndash192 2005
[45] A K Satapathy G Gunasekaran S C Sahoo K Amit and PV Rodrigues ldquoCorrosion inhibition by Justicia gendarussa plantextract in hydrochloric acid solutionrdquoCorrosion Science vol 51no 12 pp 2848ndash2856 2009
[46] E E Oguzie Y Li and F H Wang ldquoCorrosion inhibition andadsorption behavior of methionine on mild steel in sulfuricacid and synergistic effect of iodide ionrdquo Journal of Colloid andInterface Science vol 310 no 1 pp 90ndash98 2007
[47] L M Rodrıguez-Valdez W Villamisar M Casales et alldquoComputational simulations of themolecular structure and cor-rosion properties of amidoethyl aminoethyl and hydroxyethylimidazolines inhibitorsrdquo Corrosion Science vol 48 no 12 pp4053ndash4064 2006
[48] H Ju Z P Kai and Y Li ldquoAminic nitrogen-bearing polydentateSchiff base compounds as corrosion inhibitors for iron in acidicmedia a quantum chemical calculationrdquo Corrosion Science vol50 no 3 pp 865ndash871 2008
[49] L M Rodrıguez-Valdez A Martınez-Villafane and DGlossman-Mitnik ldquoComputational simulation of themolecularstructure and properties of heterocyclic organic compoundswith possible corrosion inhibition propertiesrdquo Journal ofMolecular Structure THEOCHEM vol 713 no 1ndash3 pp 65ndash702005
Journal of Materials 11
[50] K F Khaled ldquoMolecular simulation quantum chemical calcu-lations and electrochemical studies for inhibition of mild steelby triazolesrdquo Electrochimica Acta vol 53 no 9 pp 3484ndash34922008
[51] R M Issa M K Awad and F M Atlam ldquoQuantum chemicalstudies on the inhibition of corrosion of copper surface bysubstituted uracilsrdquo Applied Surface Science vol 255 no 5 pp2433ndash2441 2008
Figure 3 Langmuir isotherm for EHEC adsorption on mild steelsurface in 10MH
2SO4
0 20 40 60 80 100 120 140
0102030405060708090
100110120130140
Blank25 gL EHEC25 gL EHEC + KI
Zim
(Ω)
Zre (Ω)
Figure 4 Nyquist impedance spectra of mild steel corrosion in10MH
2SO4in the absence and presence of EHEC and EHEC + KI
Lower double layer capacitance suggests reduced electriccharge stored which is a consequence of increased adsorp-tion layer that acted as a dielectric constant The increasein 119877ct values in inhibited systems which corresponds to anincrease in the diameter of the Nyquist semicircle confirmsthat the corrosion inhibiting effect of EHEC and EHEC + KIand is much more pronounced in the latter system implyingthat KI synergistically enhanced the corrosion inhibitingeffect of EHEC In other words lower 119862dl values correspond
to reduced double layer capacitance which according to theHelmholtzmodel (10) results fromadecrease in the dielectricconstant (120576) or an increase in the interfacial layer thickness(120575)
119862dl =120576120576119900119860
120575 (10)
where 120576 is the dielectric constant of the medium 120576119900is the
vacuum permittivity 119860 is the electrode area and 120575 is thethickness of the interfacial layer
Since adsorption of an organic inhibitor on a metalsurface involves the replacement of adsorbedwatermoleculeson the surface the smaller dielectric constant of the organicmolecule compared towater aswell as the increased thicknessof interfacial layer due to inhibitor adsorption acted simulta-neously to reduce the double layer capacitanceThis providesexperimental evidence of adsorption of EHEC on mild steelsurface The significantly lower 119862dl value of the EHEC + KIsystem supports the assertion that the iodide ion significantlyenhances adsorption of EHEC on the metalsolution inter-face
36 Polarization Measurements Figure 5 shows the polar-ization curves of mild steel dissolution in 10MH
2SO4
solution in the absence and presence of EHEC and EHEC+ KI Introduction of EHEC and EHEC + KI into the acidsolutionwas observed to shift the corrosion potentials of bothinhibited systems slightly in the negative direction and inboth cases inhibited the anodic metal dissolution reactionas well as the cathodic hydrogen evolution reaction Sincethe 119864corr is not altered significantly the implication is thatthe corrosion inhibition process is under mixed control withpredominant cathodic effect In addition following observa-tions in Figure 5 both cathodic and anodic partial reactionsare affected as evident in decrease in the corrosion currentdensities This implies that EHEC functioned as a mixed-type inhibitor for both systems However marked cathodicpartial hydrogen evolution reaction is discerned Moresodocumented report [45] has it that when displacement in119864corr is gt85mV the inhibitor can be regarded as a cathodicor anodic type inhibitor and if the displacement in 119864corris lt85mV the inhibitor can be seen as mixed type In thepresent study the displacement in the corrosion potential(119864corr) in the presence of EHEC and EHEC + KI shifted952 and 2075mV respectively in the cathodic directioncompared to the blank which is a confirmation that theinhibitor acts as a mixed-type inhibitor with predominantcathodic effect
Journal of Materials 7
Table 4 Impedance and polarization parameters for mild steel in 05M H2SO4 in the presence and absence of EHEC and EHEC + KI
System Impedance data Polarization data119877ct 119899 IE 119862dl (uF cm
minus2) times 10minus3 119864corr (mV (SCE)) 119877119901(Ω cm2) IE
Inhibition efficiency was calculated from the polarizationdata as follows
119868 = [1 minus119877119901
119877119901
inh] times 100 (11)
where 119877119901and 119877
119901
inh are polarization resistance for uninhib-ited and inhibited systems respectivelyThe calculated valuesare given in Table 4 Observations from Table 4 show thatthe inhibition efficiencies obtained from both impedanceand polarization results are comparable The data confirmthe consistency of EHEC and EHEC + KI at the prevailingexperimental condition
The cooperative effect between EHEC and KI in hin-dering the corrosion of mild steel in 10MH
2SO4solution
is also evident in both the Nyquist and Tafel polarizationplots Addition of KI resulted in a significant increase in thediameter of the Nyquist semicircle and hence an increase in119877ct as well as 119868 and a decrease in the corrosion currentdensity of the Tafel polarization curves The presence ofiodide ions shifts 119864corr more in the cathodic direction andfurther decreases the anodic and cathodic reaction kineticsThe mechanism of this synergistic effect has been describedin detail in some reports [46] The iodide ions are stronglychemisorbed on the corrodingmild steel surface and facilitateEHEC adsorption by acting as intermediate bridges betweenthe positively charged metal surface and EHEC cations Thisstabilizes the adsorption of EHEC on the mild steel surfaceleading to higher surface coverage To account for the aboveobservations it is necessary to recognize that the process ofadsorption of an organic inhibitor on a corroding metal sur-face depends on factors such as the nature and surface chargeon the metal in the corrosive medium as well as the inhibitorstructure Consequently more iodide ions are adsorbed onmild steel which presents a more positive surface giving riseto increased synergistic interactions with protonated EHECspecies and hence higher inhibition efficiencies
E versus SCE (V)minus08 minus07 minus06 minus05 minus04 minus03 minus02
001
1E minus 3
1E minus 4
1E minus 5
1E minus 6
Blank25 gL EHEC25 gL EHEC + KI
i(A
cmminus2)
Figure 5 Polarization curves ofmild steel corrosion in 10MH2SO4
in the absence and presence of EHEC and EHEC + KI
37 Quantum Chemical Calculations The inhibition effec-tiveness of inhibitors has been reported to correlate with thequantum chemical parameters such as HOMO (the highestoccupied molecular orbital) LUMO (the lowest unoccupiedmolecular orbital) and the energy gap between the LUMOand HOMO (Δ119864 = 119864LUMO minus 119864HOMO) [47ndash49] A high119864HOMO (less negative) is associated with the capacity of amolecule to donate electrons to an appropriated acceptorwith empty molecular orbital that facilitated the adsorptionprocess and therefore indicated good performance of thecorrosion inhibitor [50] 119864LUMO corresponds to a tendencyfor electron acceptance Based on this the calculated dif-ference Δ119864 demonstrates inherent electron donating abilityand measures the interaction of the inhibitor molecule withthe metal surface
According to the frontier molecular orbital theory ofchemical reactivity transition of electrons is due to aninteraction between the frontier orbitals HOMOand LUMOof reacting species The energy of HOMO is directly relatedto the ionization potential and characterizes the susceptibilityof the molecule toward attack by electrophiles The energyof LUMO is directly related to the electron affinity andcharacterizes the susceptibility of the molecule toward attackby nucleophile The lower the values of 119864LUMO the strongerthe electron accepting ability of the molecule
8 Journal of Materials
(a) Optimized structure (b) Total electron density
(c) HOMO orbital (d) LUMO orbital
(e) Fukui function for nucleophilic attack (f) Fukui function for electrophilic attack
Figure 6 Electronic properties of ethyl hydroxyethyl cellulose (EHEC) [C grey H white O red]
The electronic structure of EHEC the distribution offrontier molecular orbital and Fukui indices have beenmod-eled in order to establish the active sites as well as local reac-tivity of the inhibitingmoleculesThis was achieved using theDFT electronic structure programs Forcite and DMol3 andusing a Mulliken population analysis Electronic parametersfor the simulation include restricted spin polarization usingtheDNDbasis set as the PerdewWang (PW) local correlationdensity functional The geometry optimized structures ofEHEC HOMO and LUMOorbitals Fukui functions and thetotal electron density are presented in Figure 6 In the EHEC
molecule theHOMOorbital is saturated around the aromaticnucleus which is the region of highest electron density andoften the site at which electrophiles attack and represents theactive centres with the utmost ability to bond to the metalsurface The LUMO orbital is saturated around the ethoxyfunction and represents the site at which nucleophilic attackoccurs
Local reactivity was analyzed by means of the Fukuiindices to assess the active regions in terms of nucleophilicand electrophilic behaviour Thus the site for nucleophilicattack will be the place where the value of 119891+ is maximum In
Journal of Materials 9
turn the site for electrophilic attack is controlled by the valueof 119891minus The values of 119864HOMO 119864LUMO Δ119864 and Fukui functionsare given inTable 5Higher values of119864HOMO indicate a greaterdisposition of a molecule to donate electrons to a metalsurface In the same way low values of the energy of the gapΔ119864 will afford good inhibition efficiency since the energyrequired to remove an electron from the last occupied orbitalwill be minimized [51] The above descriptors howeversuggest that EHEC possessed good inhibiting potential Thisis in agreement with the experimental findings
4 Conclusions
Ethyl hydroxyethyl cellulose was found to be an effectiveinhibitor of mild steel in 10MH
2SO4solution and its inhibi-
tion efficiency increased with increasing concentration Thecorrosion process is inhibited by adsorption of EHEC on themild steel surface following themodified Langmuir isothermThe inhibiting action is attributed to general adsorption ofboth protonated and molecular species of the additive on thecathodic and anodic sites on the corrodingmild steel surfaceIn addition corrosion inhibition is due to the formationof a chemisorbed film on the mild steel surface The EISmeasurement confirmed the adsorption of EHEC and EHEC+ KI on the mild steel surface Polarization studies showedthat EHEC and EHEC + KI were mixed-type inhibitorsystems with predominant cathodic effect The theoreticalstudy demonstrated that the inhibition efficiency is related tomolecular structure of inhibitor whereby increase in 119864HOMOand decrease in 119864LUMO favoured inhibition efficiency
Conflict of Interests
Theauthors hereby declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors are grateful to Udemmadu Tochukwu andOchiogu Valentine for assistance in carrying out some mea-surements
References
[1] E E Oguzie Y Li and F H Wang ldquoEffect of ascorbic acidon mild steel dissolution in sulphuric acid solution investigatedby electrochemical polarization and surface probe techniquesrdquoJournal of Applied Electrochemistry vol 37 no 10 pp 1183ndash11902007
[2] L G da Trindade and R S Goncalves ldquoEvidence of caffeineadsorption on a low-carbon steel surface in ethanolrdquo CorrosionScience vol 51 no 8 pp 1578ndash1583 2009
[3] F Bentiss M Outirite M Traisnel et al ldquoImprovementof corrosion resistance of carbon steel in hydrochloric acidmedium by 36-bis(3-pyridyl)pyridazinerdquo International Journalof Electrochemical Science vol 7 no 2 pp 1699ndash1723 2012
[4] S M A Shibli and V S Saji ldquoCo-inhibition characteristicsof sodium tungstate with potassium iodate on mild steelcorrosionrdquoCorrosion Science vol 47 no 9 pp 2213ndash2224 2005
[5] E E Oguzie C Unaegbu C N Ogukwe B N Okolue and AI Onuchukwu ldquoInhibition of mild steel corrosion in sulphuricacid using indigo dye and synergistic halide additivesrdquoMateri-als Chemistry and Physics vol 84 no 2-3 pp 363ndash368 2004
[6] V Kumpawat U Garg and R K Tak ldquoCorrosion inhibitionof aluminium in acid media by naturally occurring plantArtocarpus heterophyllus and Acacia senegalrdquo Journal of IndianCouncil of Chemists vol 26 no 1 pp 82ndash84 2009
[7] IA Akpan and N O Offiong ldquoEffect of ethanolamine andethylamine on the entropy content of the corrosion ofmild steelin tetraoxosulphate (VI) acid solutionrdquoChemistry andMaterialsResearch vol 2 no 7 pp 40ndash47 2012
[8] M Kissi M Bouklah B Hammouti and M BenkaddourldquoEstablishment of equivalent circuits from electrochemicalimpedance spectroscopy study of corrosion inhibition of steelby pyrazine in sulphuric acidic solutionrdquo Applied SurfaceScience vol 252 no 12 pp 4190ndash4197 2006
[9] S Rajendran S P Sridevi N Anthony A J Amalraj andM Sundaravadivelu ldquoCorrosion behaviour of carbon steel inpolyvinyl alcoholrdquo Anti-Corrosion Methods and Materials vol52 no 2 pp 102ndash107 2005
[10] B Qian J Wang M Zheng and B Hou ldquoSynergistic effect ofpolyaspartic acid and iodide ion on corrosion inhibition ofmildsteel in H
[11] D A Arthur A Jonathan P O Ameh and C Anya ldquoAreview on the assessment of polymeric materials used ascorrosion inhibitor of metals and alloysrdquo International Journalof Industrial Chemistry vol 4 article 2 pp 1ndash9 2013
[12] S A Umoren Y Li and F H Wang ldquoEffect of polyacrylicacid on the corrosion behaviour of aluminium in sulphuric acidsolutionrdquo Journal of Solid State Electrochemistry vol 14 no 12pp 2293ndash2305 2010
[13] S Banerjee A Mishra M M Singh B Maiti B Ray andP Maiti ldquoHighly efficient polyurethane ionomer corrosioninhibitor the effect of chain structurerdquo RSCAdvances vol 1 no2 pp 199ndash210 2011
[14] A K Dubey and G Singh ldquoCorrosion inhibition of mild steelin sulphuric acid solution by using polyethylene glycol methylether (PEGME)rdquo Portugaliae Electrochimica Acta vol 25 no 2pp 221ndash235 2007
[15] E E Oguzie S G Wang Y Li and F H Wang ldquoInfluenceof iron microstructure on corrosion inhibitor performance inacidic mediardquoThe Journal of Physical Chemistry C vol 113 no19 pp 8420ndash8429 2009
[16] S A Umoren E E Ebenso P C Okafor and O OgbobeldquoWater-soluble polymers as corrosion inhibitorsrdquo Pigment ampResin Technology vol 35 no 6 pp 346ndash352 2006
[17] S A Umoren and I B Obot ldquoPolyvinylpyrollidone andpolyacrylamide as corrosion inhibitors for mild steel in acidicmediumrdquo Surface Review and Letters vol 15 no 3 pp 277ndash2842008
[18] H Ashassi-Sorkhabi and N Ghalebsaz-Jeddi ldquoInhibition effectof polyethylene glycol on the corrosion of carbon steel insulphuric acidrdquoMaterials Chemistry and Physics vol 92 no 2-3pp 480ndash486 2005
[19] A Yurt V Butun and B Duran ldquoEffect of themolecular weightand structure of some novel water-soluble triblock copolymerson the electrochemical behaviour of mild steelrdquo MaterialsChemistry and Physics vol 105 no 1 pp 114ndash121 2007
10 Journal of Materials
[20] S A Umoren ldquoPolymers as corrosion inhibitors for metals indifferent mediamdasha reviewrdquo The Open Corrosion Journal vol 2pp 175ndash188 2009
[21] K F Khaled ldquoCorrosion control of copper in nitric acidsolutions using some amino acidsmdasha combined experimentaland theoretical studyrdquo Corrosion Science vol 52 no 10 pp3225ndash3234 2010
[22] E E Oguzie C O Akalezi C K Enenebeaku and J N AnekeldquoCorrosion inhibition and adsorption behavior of malachitegreen dye on aluminum corrosionrdquoChemical Engineering Com-munications vol 198 no 1 pp 46ndash60 2011
[23] J Cruz T Pandiyan and E Garcia-Ochoa ldquoA new inhibitor formild carbon steel electrochemical and DFT studiesrdquo Journal ofElectroanalytical Chemistry vol 583 no 1 pp 8ndash16 2005
[24] J Cruz R Martinez J Genesca and E Garcia-OchoaldquoExperimental and theoretical study of 1-(2-ethylamino)-2-methylimidazoline as an inhibitor of carbon steel corrosion inacid mediardquo Journal of Electroanalytical Chemistry vol 566 no1 pp 111ndash121 2004
[25] E E Oguzie Y Li S G Wang and F Wang ldquoUnderstandingcorrosion inhibition mechanismsmdashexperimental and theoreti-cal approachrdquo RSC Advances vol 1 no 5 pp 866ndash873 2011
[26] A Kumar A Sankara M Kumaravel and S RameshkumarldquoClitoria ternateamdashextracts as corrosion inhibitor for mild steelin acid mediumrdquo International Journal of Engineering Researchand Development vol 8 no 5 pp 64ndash67 2013
[27] E E Oguzie G N Onuoha and A I Onuchukwu ldquoInhibitorymechanism of mild steel corrosion in 2M sulphuric acidsolution by methylene blue dyerdquo Materials Chemistry andPhysics vol 89 no 2-3 pp 305ndash311 2005
[28] E E Oguzie C K Enenebeaku C O Akalezi S C Okoro AA Ayuk and E N Ejike ldquoAdsorption and corrosion-inhibitingeffect ofDacryodis edulis extract on low-carbon-steel corrosionin acidic mediardquo Journal of Colloid and Interface Science vol349 no 1 pp 283ndash292 2010
[29] E E Oguzie ldquoCorrosion inhibition of aluminium in acidicand alkaline media by Sansevieria trifasciata extractrdquo CorrosionScience vol 49 no 3 pp 1527ndash1539 2007
[30] S A Umoren I B Obot and E E Ebenso ldquoCorrosioninhibition of aluminium using exudate gum from Pachylobusedulis in the presence of halide ions in HClrdquo E-Journal ofChemistry vol 5 no 2 pp 355ndash364 2008
[31] P C Okafor E E Ebenso and U J Ekpe ldquoAzadirachta indicaextracts as corrosion inhibitor for mild steel in acid mediumrdquoInternational Journal of Electrochemical Science vol 5 no 7 pp978ndash993 2010
[32] M Lebrini F Robert A Lecente and C Roos ldquoCorrosioninhibition of C38 steel in 1M hydrochloric acid medium byalkaloids extract from Oxandra asbeckii plant rdquo CorrosionScience vol 53 no 2 pp 687ndash695 2011
[33] E E Oguzie ldquoInfluence of halide ions on the inhibitive effect ofcongo red dye on the corrosion of mild steel in sulphuric acidsolutionrdquoMaterials Chemistry and Physics vol 87 no 1 pp 212ndash217 2004
[34] E E Oguzie ldquoInhibition of acid corrosion of mild steel byTelfaria occidentalis extractrdquo Pigment amp Resin Technology vol34 no 6 pp 321ndash326 2005
[35] E E Oguzie V O Njoku C K Enenebeaku C O Akalezi andC Obi ldquoEffect of hexamethylpararosaniline chloride (crystalviolet) on mild steel corrosion in acidic mediardquo CorrosionScience vol 50 no 12 pp 3480ndash3486 2008
[36] M A Ameer E Khamis and G al-Senani ldquoEffect of temper-ature on stability of adsorbed inhibitors on steel in phosphoricacid solutionrdquo Journal of Applied Electrochemistry vol 32 no 2pp 149ndash156 2002
[37] P C Okafor E E Oguzie G E Iniama M E Ikpi and U JEkpe ldquoCorrosion inhibition properties of thiosemicarbazoneand semicarbazone derivatives in concentrated acid environ-mentrdquoGlobal Journal of Pure and Applied Sciences vol 14 no 1pp 89ndash96 2008
[38] I B Obot ldquoSynergistic effect of nizoral and iodide ions on thecorrosion inhibition of mild steel in sulphuric acid solutionrdquoPortugaliae ElectrochimicaActa vol 27 no 5 pp 539ndash553 2009
[39] N O Eddy S A Odoemelam and A O Odiongenyi ldquoEthanolextract of musa species peels as a green corrosion inhibitor formild steel kinetics adsorption and thermodynamic consider-ationsrdquo Electronic Journal of Environmental Agricultural andFood Chemistry vol 8 no 4 pp 243ndash255 2009
[40] M H Hussin and M J Kassim ldquoThe corrosion inhibition andadsorption behavior of Uncaria gambir extract on mild steel in1M HClrdquo Materials Chemistry and Physics vol 125 no 3 pp461ndash468 2010
[41] V K W Grips V E Selvi H C Barshilia and K S RajamldquoEffect of electroless nickel interlayer on the electrochemicalbehavior of single layer CrN TiN TiAlN coatings and nanolay-ered TiAlNCrN multilayer coatings prepared by reactive dcmagnetron sputteringrdquo Electrochimica Acta vol 51 no 17 pp3461ndash3468 2006
[42] E E Oguzie ldquoStudies on the inhibitive effect ofOccimum viridisextract on the acid corrosion of mild steelrdquoMaterials Chemistryand Physics vol 99 no 2-3 pp 441ndash446 2006
[43] B Wang M Du J Zhang and C J Gao ldquoElectrochemical andsurface analysis studies on corrosion inhibition of Q235 steelby imidazoline derivative against CO
2corrosionrdquo Corrosion
Science vol 53 no 1 pp 353ndash361 2011[44] G Mu and X Li ldquoInhibition of cold rolled steel corrosion
by Tween-20 in sulfuric acid weight loss electrochemical andAFM approaches rdquo Journal of Colloid and Interface Science vol289 no 1 pp 184ndash192 2005
[45] A K Satapathy G Gunasekaran S C Sahoo K Amit and PV Rodrigues ldquoCorrosion inhibition by Justicia gendarussa plantextract in hydrochloric acid solutionrdquoCorrosion Science vol 51no 12 pp 2848ndash2856 2009
[46] E E Oguzie Y Li and F H Wang ldquoCorrosion inhibition andadsorption behavior of methionine on mild steel in sulfuricacid and synergistic effect of iodide ionrdquo Journal of Colloid andInterface Science vol 310 no 1 pp 90ndash98 2007
[47] L M Rodrıguez-Valdez W Villamisar M Casales et alldquoComputational simulations of themolecular structure and cor-rosion properties of amidoethyl aminoethyl and hydroxyethylimidazolines inhibitorsrdquo Corrosion Science vol 48 no 12 pp4053ndash4064 2006
[48] H Ju Z P Kai and Y Li ldquoAminic nitrogen-bearing polydentateSchiff base compounds as corrosion inhibitors for iron in acidicmedia a quantum chemical calculationrdquo Corrosion Science vol50 no 3 pp 865ndash871 2008
[49] L M Rodrıguez-Valdez A Martınez-Villafane and DGlossman-Mitnik ldquoComputational simulation of themolecularstructure and properties of heterocyclic organic compoundswith possible corrosion inhibition propertiesrdquo Journal ofMolecular Structure THEOCHEM vol 713 no 1ndash3 pp 65ndash702005
Journal of Materials 11
[50] K F Khaled ldquoMolecular simulation quantum chemical calcu-lations and electrochemical studies for inhibition of mild steelby triazolesrdquo Electrochimica Acta vol 53 no 9 pp 3484ndash34922008
[51] R M Issa M K Awad and F M Atlam ldquoQuantum chemicalstudies on the inhibition of corrosion of copper surface bysubstituted uracilsrdquo Applied Surface Science vol 255 no 5 pp2433ndash2441 2008
Inhibition efficiency was calculated from the polarizationdata as follows
119868 = [1 minus119877119901
119877119901
inh] times 100 (11)
where 119877119901and 119877
119901
inh are polarization resistance for uninhib-ited and inhibited systems respectivelyThe calculated valuesare given in Table 4 Observations from Table 4 show thatthe inhibition efficiencies obtained from both impedanceand polarization results are comparable The data confirmthe consistency of EHEC and EHEC + KI at the prevailingexperimental condition
The cooperative effect between EHEC and KI in hin-dering the corrosion of mild steel in 10MH
2SO4solution
is also evident in both the Nyquist and Tafel polarizationplots Addition of KI resulted in a significant increase in thediameter of the Nyquist semicircle and hence an increase in119877ct as well as 119868 and a decrease in the corrosion currentdensity of the Tafel polarization curves The presence ofiodide ions shifts 119864corr more in the cathodic direction andfurther decreases the anodic and cathodic reaction kineticsThe mechanism of this synergistic effect has been describedin detail in some reports [46] The iodide ions are stronglychemisorbed on the corrodingmild steel surface and facilitateEHEC adsorption by acting as intermediate bridges betweenthe positively charged metal surface and EHEC cations Thisstabilizes the adsorption of EHEC on the mild steel surfaceleading to higher surface coverage To account for the aboveobservations it is necessary to recognize that the process ofadsorption of an organic inhibitor on a corroding metal sur-face depends on factors such as the nature and surface chargeon the metal in the corrosive medium as well as the inhibitorstructure Consequently more iodide ions are adsorbed onmild steel which presents a more positive surface giving riseto increased synergistic interactions with protonated EHECspecies and hence higher inhibition efficiencies
E versus SCE (V)minus08 minus07 minus06 minus05 minus04 minus03 minus02
001
1E minus 3
1E minus 4
1E minus 5
1E minus 6
Blank25 gL EHEC25 gL EHEC + KI
i(A
cmminus2)
Figure 5 Polarization curves ofmild steel corrosion in 10MH2SO4
in the absence and presence of EHEC and EHEC + KI
37 Quantum Chemical Calculations The inhibition effec-tiveness of inhibitors has been reported to correlate with thequantum chemical parameters such as HOMO (the highestoccupied molecular orbital) LUMO (the lowest unoccupiedmolecular orbital) and the energy gap between the LUMOand HOMO (Δ119864 = 119864LUMO minus 119864HOMO) [47ndash49] A high119864HOMO (less negative) is associated with the capacity of amolecule to donate electrons to an appropriated acceptorwith empty molecular orbital that facilitated the adsorptionprocess and therefore indicated good performance of thecorrosion inhibitor [50] 119864LUMO corresponds to a tendencyfor electron acceptance Based on this the calculated dif-ference Δ119864 demonstrates inherent electron donating abilityand measures the interaction of the inhibitor molecule withthe metal surface
According to the frontier molecular orbital theory ofchemical reactivity transition of electrons is due to aninteraction between the frontier orbitals HOMOand LUMOof reacting species The energy of HOMO is directly relatedto the ionization potential and characterizes the susceptibilityof the molecule toward attack by electrophiles The energyof LUMO is directly related to the electron affinity andcharacterizes the susceptibility of the molecule toward attackby nucleophile The lower the values of 119864LUMO the strongerthe electron accepting ability of the molecule
8 Journal of Materials
(a) Optimized structure (b) Total electron density
(c) HOMO orbital (d) LUMO orbital
(e) Fukui function for nucleophilic attack (f) Fukui function for electrophilic attack
Figure 6 Electronic properties of ethyl hydroxyethyl cellulose (EHEC) [C grey H white O red]
The electronic structure of EHEC the distribution offrontier molecular orbital and Fukui indices have beenmod-eled in order to establish the active sites as well as local reac-tivity of the inhibitingmoleculesThis was achieved using theDFT electronic structure programs Forcite and DMol3 andusing a Mulliken population analysis Electronic parametersfor the simulation include restricted spin polarization usingtheDNDbasis set as the PerdewWang (PW) local correlationdensity functional The geometry optimized structures ofEHEC HOMO and LUMOorbitals Fukui functions and thetotal electron density are presented in Figure 6 In the EHEC
molecule theHOMOorbital is saturated around the aromaticnucleus which is the region of highest electron density andoften the site at which electrophiles attack and represents theactive centres with the utmost ability to bond to the metalsurface The LUMO orbital is saturated around the ethoxyfunction and represents the site at which nucleophilic attackoccurs
Local reactivity was analyzed by means of the Fukuiindices to assess the active regions in terms of nucleophilicand electrophilic behaviour Thus the site for nucleophilicattack will be the place where the value of 119891+ is maximum In
Journal of Materials 9
turn the site for electrophilic attack is controlled by the valueof 119891minus The values of 119864HOMO 119864LUMO Δ119864 and Fukui functionsare given inTable 5Higher values of119864HOMO indicate a greaterdisposition of a molecule to donate electrons to a metalsurface In the same way low values of the energy of the gapΔ119864 will afford good inhibition efficiency since the energyrequired to remove an electron from the last occupied orbitalwill be minimized [51] The above descriptors howeversuggest that EHEC possessed good inhibiting potential Thisis in agreement with the experimental findings
4 Conclusions
Ethyl hydroxyethyl cellulose was found to be an effectiveinhibitor of mild steel in 10MH
2SO4solution and its inhibi-
tion efficiency increased with increasing concentration Thecorrosion process is inhibited by adsorption of EHEC on themild steel surface following themodified Langmuir isothermThe inhibiting action is attributed to general adsorption ofboth protonated and molecular species of the additive on thecathodic and anodic sites on the corrodingmild steel surfaceIn addition corrosion inhibition is due to the formationof a chemisorbed film on the mild steel surface The EISmeasurement confirmed the adsorption of EHEC and EHEC+ KI on the mild steel surface Polarization studies showedthat EHEC and EHEC + KI were mixed-type inhibitorsystems with predominant cathodic effect The theoreticalstudy demonstrated that the inhibition efficiency is related tomolecular structure of inhibitor whereby increase in 119864HOMOand decrease in 119864LUMO favoured inhibition efficiency
Conflict of Interests
Theauthors hereby declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors are grateful to Udemmadu Tochukwu andOchiogu Valentine for assistance in carrying out some mea-surements
References
[1] E E Oguzie Y Li and F H Wang ldquoEffect of ascorbic acidon mild steel dissolution in sulphuric acid solution investigatedby electrochemical polarization and surface probe techniquesrdquoJournal of Applied Electrochemistry vol 37 no 10 pp 1183ndash11902007
[2] L G da Trindade and R S Goncalves ldquoEvidence of caffeineadsorption on a low-carbon steel surface in ethanolrdquo CorrosionScience vol 51 no 8 pp 1578ndash1583 2009
[3] F Bentiss M Outirite M Traisnel et al ldquoImprovementof corrosion resistance of carbon steel in hydrochloric acidmedium by 36-bis(3-pyridyl)pyridazinerdquo International Journalof Electrochemical Science vol 7 no 2 pp 1699ndash1723 2012
[4] S M A Shibli and V S Saji ldquoCo-inhibition characteristicsof sodium tungstate with potassium iodate on mild steelcorrosionrdquoCorrosion Science vol 47 no 9 pp 2213ndash2224 2005
[5] E E Oguzie C Unaegbu C N Ogukwe B N Okolue and AI Onuchukwu ldquoInhibition of mild steel corrosion in sulphuricacid using indigo dye and synergistic halide additivesrdquoMateri-als Chemistry and Physics vol 84 no 2-3 pp 363ndash368 2004
[6] V Kumpawat U Garg and R K Tak ldquoCorrosion inhibitionof aluminium in acid media by naturally occurring plantArtocarpus heterophyllus and Acacia senegalrdquo Journal of IndianCouncil of Chemists vol 26 no 1 pp 82ndash84 2009
[7] IA Akpan and N O Offiong ldquoEffect of ethanolamine andethylamine on the entropy content of the corrosion ofmild steelin tetraoxosulphate (VI) acid solutionrdquoChemistry andMaterialsResearch vol 2 no 7 pp 40ndash47 2012
[8] M Kissi M Bouklah B Hammouti and M BenkaddourldquoEstablishment of equivalent circuits from electrochemicalimpedance spectroscopy study of corrosion inhibition of steelby pyrazine in sulphuric acidic solutionrdquo Applied SurfaceScience vol 252 no 12 pp 4190ndash4197 2006
[9] S Rajendran S P Sridevi N Anthony A J Amalraj andM Sundaravadivelu ldquoCorrosion behaviour of carbon steel inpolyvinyl alcoholrdquo Anti-Corrosion Methods and Materials vol52 no 2 pp 102ndash107 2005
[10] B Qian J Wang M Zheng and B Hou ldquoSynergistic effect ofpolyaspartic acid and iodide ion on corrosion inhibition ofmildsteel in H
[11] D A Arthur A Jonathan P O Ameh and C Anya ldquoAreview on the assessment of polymeric materials used ascorrosion inhibitor of metals and alloysrdquo International Journalof Industrial Chemistry vol 4 article 2 pp 1ndash9 2013
[12] S A Umoren Y Li and F H Wang ldquoEffect of polyacrylicacid on the corrosion behaviour of aluminium in sulphuric acidsolutionrdquo Journal of Solid State Electrochemistry vol 14 no 12pp 2293ndash2305 2010
[13] S Banerjee A Mishra M M Singh B Maiti B Ray andP Maiti ldquoHighly efficient polyurethane ionomer corrosioninhibitor the effect of chain structurerdquo RSCAdvances vol 1 no2 pp 199ndash210 2011
[14] A K Dubey and G Singh ldquoCorrosion inhibition of mild steelin sulphuric acid solution by using polyethylene glycol methylether (PEGME)rdquo Portugaliae Electrochimica Acta vol 25 no 2pp 221ndash235 2007
[15] E E Oguzie S G Wang Y Li and F H Wang ldquoInfluenceof iron microstructure on corrosion inhibitor performance inacidic mediardquoThe Journal of Physical Chemistry C vol 113 no19 pp 8420ndash8429 2009
[16] S A Umoren E E Ebenso P C Okafor and O OgbobeldquoWater-soluble polymers as corrosion inhibitorsrdquo Pigment ampResin Technology vol 35 no 6 pp 346ndash352 2006
[17] S A Umoren and I B Obot ldquoPolyvinylpyrollidone andpolyacrylamide as corrosion inhibitors for mild steel in acidicmediumrdquo Surface Review and Letters vol 15 no 3 pp 277ndash2842008
[18] H Ashassi-Sorkhabi and N Ghalebsaz-Jeddi ldquoInhibition effectof polyethylene glycol on the corrosion of carbon steel insulphuric acidrdquoMaterials Chemistry and Physics vol 92 no 2-3pp 480ndash486 2005
[19] A Yurt V Butun and B Duran ldquoEffect of themolecular weightand structure of some novel water-soluble triblock copolymerson the electrochemical behaviour of mild steelrdquo MaterialsChemistry and Physics vol 105 no 1 pp 114ndash121 2007
10 Journal of Materials
[20] S A Umoren ldquoPolymers as corrosion inhibitors for metals indifferent mediamdasha reviewrdquo The Open Corrosion Journal vol 2pp 175ndash188 2009
[21] K F Khaled ldquoCorrosion control of copper in nitric acidsolutions using some amino acidsmdasha combined experimentaland theoretical studyrdquo Corrosion Science vol 52 no 10 pp3225ndash3234 2010
[22] E E Oguzie C O Akalezi C K Enenebeaku and J N AnekeldquoCorrosion inhibition and adsorption behavior of malachitegreen dye on aluminum corrosionrdquoChemical Engineering Com-munications vol 198 no 1 pp 46ndash60 2011
[23] J Cruz T Pandiyan and E Garcia-Ochoa ldquoA new inhibitor formild carbon steel electrochemical and DFT studiesrdquo Journal ofElectroanalytical Chemistry vol 583 no 1 pp 8ndash16 2005
[24] J Cruz R Martinez J Genesca and E Garcia-OchoaldquoExperimental and theoretical study of 1-(2-ethylamino)-2-methylimidazoline as an inhibitor of carbon steel corrosion inacid mediardquo Journal of Electroanalytical Chemistry vol 566 no1 pp 111ndash121 2004
[25] E E Oguzie Y Li S G Wang and F Wang ldquoUnderstandingcorrosion inhibition mechanismsmdashexperimental and theoreti-cal approachrdquo RSC Advances vol 1 no 5 pp 866ndash873 2011
[26] A Kumar A Sankara M Kumaravel and S RameshkumarldquoClitoria ternateamdashextracts as corrosion inhibitor for mild steelin acid mediumrdquo International Journal of Engineering Researchand Development vol 8 no 5 pp 64ndash67 2013
[27] E E Oguzie G N Onuoha and A I Onuchukwu ldquoInhibitorymechanism of mild steel corrosion in 2M sulphuric acidsolution by methylene blue dyerdquo Materials Chemistry andPhysics vol 89 no 2-3 pp 305ndash311 2005
[28] E E Oguzie C K Enenebeaku C O Akalezi S C Okoro AA Ayuk and E N Ejike ldquoAdsorption and corrosion-inhibitingeffect ofDacryodis edulis extract on low-carbon-steel corrosionin acidic mediardquo Journal of Colloid and Interface Science vol349 no 1 pp 283ndash292 2010
[29] E E Oguzie ldquoCorrosion inhibition of aluminium in acidicand alkaline media by Sansevieria trifasciata extractrdquo CorrosionScience vol 49 no 3 pp 1527ndash1539 2007
[30] S A Umoren I B Obot and E E Ebenso ldquoCorrosioninhibition of aluminium using exudate gum from Pachylobusedulis in the presence of halide ions in HClrdquo E-Journal ofChemistry vol 5 no 2 pp 355ndash364 2008
[31] P C Okafor E E Ebenso and U J Ekpe ldquoAzadirachta indicaextracts as corrosion inhibitor for mild steel in acid mediumrdquoInternational Journal of Electrochemical Science vol 5 no 7 pp978ndash993 2010
[32] M Lebrini F Robert A Lecente and C Roos ldquoCorrosioninhibition of C38 steel in 1M hydrochloric acid medium byalkaloids extract from Oxandra asbeckii plant rdquo CorrosionScience vol 53 no 2 pp 687ndash695 2011
[33] E E Oguzie ldquoInfluence of halide ions on the inhibitive effect ofcongo red dye on the corrosion of mild steel in sulphuric acidsolutionrdquoMaterials Chemistry and Physics vol 87 no 1 pp 212ndash217 2004
[34] E E Oguzie ldquoInhibition of acid corrosion of mild steel byTelfaria occidentalis extractrdquo Pigment amp Resin Technology vol34 no 6 pp 321ndash326 2005
[35] E E Oguzie V O Njoku C K Enenebeaku C O Akalezi andC Obi ldquoEffect of hexamethylpararosaniline chloride (crystalviolet) on mild steel corrosion in acidic mediardquo CorrosionScience vol 50 no 12 pp 3480ndash3486 2008
[36] M A Ameer E Khamis and G al-Senani ldquoEffect of temper-ature on stability of adsorbed inhibitors on steel in phosphoricacid solutionrdquo Journal of Applied Electrochemistry vol 32 no 2pp 149ndash156 2002
[37] P C Okafor E E Oguzie G E Iniama M E Ikpi and U JEkpe ldquoCorrosion inhibition properties of thiosemicarbazoneand semicarbazone derivatives in concentrated acid environ-mentrdquoGlobal Journal of Pure and Applied Sciences vol 14 no 1pp 89ndash96 2008
[38] I B Obot ldquoSynergistic effect of nizoral and iodide ions on thecorrosion inhibition of mild steel in sulphuric acid solutionrdquoPortugaliae ElectrochimicaActa vol 27 no 5 pp 539ndash553 2009
[39] N O Eddy S A Odoemelam and A O Odiongenyi ldquoEthanolextract of musa species peels as a green corrosion inhibitor formild steel kinetics adsorption and thermodynamic consider-ationsrdquo Electronic Journal of Environmental Agricultural andFood Chemistry vol 8 no 4 pp 243ndash255 2009
[40] M H Hussin and M J Kassim ldquoThe corrosion inhibition andadsorption behavior of Uncaria gambir extract on mild steel in1M HClrdquo Materials Chemistry and Physics vol 125 no 3 pp461ndash468 2010
[41] V K W Grips V E Selvi H C Barshilia and K S RajamldquoEffect of electroless nickel interlayer on the electrochemicalbehavior of single layer CrN TiN TiAlN coatings and nanolay-ered TiAlNCrN multilayer coatings prepared by reactive dcmagnetron sputteringrdquo Electrochimica Acta vol 51 no 17 pp3461ndash3468 2006
[42] E E Oguzie ldquoStudies on the inhibitive effect ofOccimum viridisextract on the acid corrosion of mild steelrdquoMaterials Chemistryand Physics vol 99 no 2-3 pp 441ndash446 2006
[43] B Wang M Du J Zhang and C J Gao ldquoElectrochemical andsurface analysis studies on corrosion inhibition of Q235 steelby imidazoline derivative against CO
2corrosionrdquo Corrosion
Science vol 53 no 1 pp 353ndash361 2011[44] G Mu and X Li ldquoInhibition of cold rolled steel corrosion
by Tween-20 in sulfuric acid weight loss electrochemical andAFM approaches rdquo Journal of Colloid and Interface Science vol289 no 1 pp 184ndash192 2005
[45] A K Satapathy G Gunasekaran S C Sahoo K Amit and PV Rodrigues ldquoCorrosion inhibition by Justicia gendarussa plantextract in hydrochloric acid solutionrdquoCorrosion Science vol 51no 12 pp 2848ndash2856 2009
[46] E E Oguzie Y Li and F H Wang ldquoCorrosion inhibition andadsorption behavior of methionine on mild steel in sulfuricacid and synergistic effect of iodide ionrdquo Journal of Colloid andInterface Science vol 310 no 1 pp 90ndash98 2007
[47] L M Rodrıguez-Valdez W Villamisar M Casales et alldquoComputational simulations of themolecular structure and cor-rosion properties of amidoethyl aminoethyl and hydroxyethylimidazolines inhibitorsrdquo Corrosion Science vol 48 no 12 pp4053ndash4064 2006
[48] H Ju Z P Kai and Y Li ldquoAminic nitrogen-bearing polydentateSchiff base compounds as corrosion inhibitors for iron in acidicmedia a quantum chemical calculationrdquo Corrosion Science vol50 no 3 pp 865ndash871 2008
[49] L M Rodrıguez-Valdez A Martınez-Villafane and DGlossman-Mitnik ldquoComputational simulation of themolecularstructure and properties of heterocyclic organic compoundswith possible corrosion inhibition propertiesrdquo Journal ofMolecular Structure THEOCHEM vol 713 no 1ndash3 pp 65ndash702005
Journal of Materials 11
[50] K F Khaled ldquoMolecular simulation quantum chemical calcu-lations and electrochemical studies for inhibition of mild steelby triazolesrdquo Electrochimica Acta vol 53 no 9 pp 3484ndash34922008
[51] R M Issa M K Awad and F M Atlam ldquoQuantum chemicalstudies on the inhibition of corrosion of copper surface bysubstituted uracilsrdquo Applied Surface Science vol 255 no 5 pp2433ndash2441 2008
(a) Optimized structure (b) Total electron density
(c) HOMO orbital (d) LUMO orbital
(e) Fukui function for nucleophilic attack (f) Fukui function for electrophilic attack
Figure 6 Electronic properties of ethyl hydroxyethyl cellulose (EHEC) [C grey H white O red]
The electronic structure of EHEC the distribution offrontier molecular orbital and Fukui indices have beenmod-eled in order to establish the active sites as well as local reac-tivity of the inhibitingmoleculesThis was achieved using theDFT electronic structure programs Forcite and DMol3 andusing a Mulliken population analysis Electronic parametersfor the simulation include restricted spin polarization usingtheDNDbasis set as the PerdewWang (PW) local correlationdensity functional The geometry optimized structures ofEHEC HOMO and LUMOorbitals Fukui functions and thetotal electron density are presented in Figure 6 In the EHEC
molecule theHOMOorbital is saturated around the aromaticnucleus which is the region of highest electron density andoften the site at which electrophiles attack and represents theactive centres with the utmost ability to bond to the metalsurface The LUMO orbital is saturated around the ethoxyfunction and represents the site at which nucleophilic attackoccurs
Local reactivity was analyzed by means of the Fukuiindices to assess the active regions in terms of nucleophilicand electrophilic behaviour Thus the site for nucleophilicattack will be the place where the value of 119891+ is maximum In
Journal of Materials 9
turn the site for electrophilic attack is controlled by the valueof 119891minus The values of 119864HOMO 119864LUMO Δ119864 and Fukui functionsare given inTable 5Higher values of119864HOMO indicate a greaterdisposition of a molecule to donate electrons to a metalsurface In the same way low values of the energy of the gapΔ119864 will afford good inhibition efficiency since the energyrequired to remove an electron from the last occupied orbitalwill be minimized [51] The above descriptors howeversuggest that EHEC possessed good inhibiting potential Thisis in agreement with the experimental findings
4 Conclusions
Ethyl hydroxyethyl cellulose was found to be an effectiveinhibitor of mild steel in 10MH
2SO4solution and its inhibi-
tion efficiency increased with increasing concentration Thecorrosion process is inhibited by adsorption of EHEC on themild steel surface following themodified Langmuir isothermThe inhibiting action is attributed to general adsorption ofboth protonated and molecular species of the additive on thecathodic and anodic sites on the corrodingmild steel surfaceIn addition corrosion inhibition is due to the formationof a chemisorbed film on the mild steel surface The EISmeasurement confirmed the adsorption of EHEC and EHEC+ KI on the mild steel surface Polarization studies showedthat EHEC and EHEC + KI were mixed-type inhibitorsystems with predominant cathodic effect The theoreticalstudy demonstrated that the inhibition efficiency is related tomolecular structure of inhibitor whereby increase in 119864HOMOand decrease in 119864LUMO favoured inhibition efficiency
Conflict of Interests
Theauthors hereby declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors are grateful to Udemmadu Tochukwu andOchiogu Valentine for assistance in carrying out some mea-surements
References
[1] E E Oguzie Y Li and F H Wang ldquoEffect of ascorbic acidon mild steel dissolution in sulphuric acid solution investigatedby electrochemical polarization and surface probe techniquesrdquoJournal of Applied Electrochemistry vol 37 no 10 pp 1183ndash11902007
[2] L G da Trindade and R S Goncalves ldquoEvidence of caffeineadsorption on a low-carbon steel surface in ethanolrdquo CorrosionScience vol 51 no 8 pp 1578ndash1583 2009
[3] F Bentiss M Outirite M Traisnel et al ldquoImprovementof corrosion resistance of carbon steel in hydrochloric acidmedium by 36-bis(3-pyridyl)pyridazinerdquo International Journalof Electrochemical Science vol 7 no 2 pp 1699ndash1723 2012
[4] S M A Shibli and V S Saji ldquoCo-inhibition characteristicsof sodium tungstate with potassium iodate on mild steelcorrosionrdquoCorrosion Science vol 47 no 9 pp 2213ndash2224 2005
[5] E E Oguzie C Unaegbu C N Ogukwe B N Okolue and AI Onuchukwu ldquoInhibition of mild steel corrosion in sulphuricacid using indigo dye and synergistic halide additivesrdquoMateri-als Chemistry and Physics vol 84 no 2-3 pp 363ndash368 2004
[6] V Kumpawat U Garg and R K Tak ldquoCorrosion inhibitionof aluminium in acid media by naturally occurring plantArtocarpus heterophyllus and Acacia senegalrdquo Journal of IndianCouncil of Chemists vol 26 no 1 pp 82ndash84 2009
[7] IA Akpan and N O Offiong ldquoEffect of ethanolamine andethylamine on the entropy content of the corrosion ofmild steelin tetraoxosulphate (VI) acid solutionrdquoChemistry andMaterialsResearch vol 2 no 7 pp 40ndash47 2012
[8] M Kissi M Bouklah B Hammouti and M BenkaddourldquoEstablishment of equivalent circuits from electrochemicalimpedance spectroscopy study of corrosion inhibition of steelby pyrazine in sulphuric acidic solutionrdquo Applied SurfaceScience vol 252 no 12 pp 4190ndash4197 2006
[9] S Rajendran S P Sridevi N Anthony A J Amalraj andM Sundaravadivelu ldquoCorrosion behaviour of carbon steel inpolyvinyl alcoholrdquo Anti-Corrosion Methods and Materials vol52 no 2 pp 102ndash107 2005
[10] B Qian J Wang M Zheng and B Hou ldquoSynergistic effect ofpolyaspartic acid and iodide ion on corrosion inhibition ofmildsteel in H
[11] D A Arthur A Jonathan P O Ameh and C Anya ldquoAreview on the assessment of polymeric materials used ascorrosion inhibitor of metals and alloysrdquo International Journalof Industrial Chemistry vol 4 article 2 pp 1ndash9 2013
[12] S A Umoren Y Li and F H Wang ldquoEffect of polyacrylicacid on the corrosion behaviour of aluminium in sulphuric acidsolutionrdquo Journal of Solid State Electrochemistry vol 14 no 12pp 2293ndash2305 2010
[13] S Banerjee A Mishra M M Singh B Maiti B Ray andP Maiti ldquoHighly efficient polyurethane ionomer corrosioninhibitor the effect of chain structurerdquo RSCAdvances vol 1 no2 pp 199ndash210 2011
[14] A K Dubey and G Singh ldquoCorrosion inhibition of mild steelin sulphuric acid solution by using polyethylene glycol methylether (PEGME)rdquo Portugaliae Electrochimica Acta vol 25 no 2pp 221ndash235 2007
[15] E E Oguzie S G Wang Y Li and F H Wang ldquoInfluenceof iron microstructure on corrosion inhibitor performance inacidic mediardquoThe Journal of Physical Chemistry C vol 113 no19 pp 8420ndash8429 2009
[16] S A Umoren E E Ebenso P C Okafor and O OgbobeldquoWater-soluble polymers as corrosion inhibitorsrdquo Pigment ampResin Technology vol 35 no 6 pp 346ndash352 2006
[17] S A Umoren and I B Obot ldquoPolyvinylpyrollidone andpolyacrylamide as corrosion inhibitors for mild steel in acidicmediumrdquo Surface Review and Letters vol 15 no 3 pp 277ndash2842008
[18] H Ashassi-Sorkhabi and N Ghalebsaz-Jeddi ldquoInhibition effectof polyethylene glycol on the corrosion of carbon steel insulphuric acidrdquoMaterials Chemistry and Physics vol 92 no 2-3pp 480ndash486 2005
[19] A Yurt V Butun and B Duran ldquoEffect of themolecular weightand structure of some novel water-soluble triblock copolymerson the electrochemical behaviour of mild steelrdquo MaterialsChemistry and Physics vol 105 no 1 pp 114ndash121 2007
10 Journal of Materials
[20] S A Umoren ldquoPolymers as corrosion inhibitors for metals indifferent mediamdasha reviewrdquo The Open Corrosion Journal vol 2pp 175ndash188 2009
[21] K F Khaled ldquoCorrosion control of copper in nitric acidsolutions using some amino acidsmdasha combined experimentaland theoretical studyrdquo Corrosion Science vol 52 no 10 pp3225ndash3234 2010
[22] E E Oguzie C O Akalezi C K Enenebeaku and J N AnekeldquoCorrosion inhibition and adsorption behavior of malachitegreen dye on aluminum corrosionrdquoChemical Engineering Com-munications vol 198 no 1 pp 46ndash60 2011
[23] J Cruz T Pandiyan and E Garcia-Ochoa ldquoA new inhibitor formild carbon steel electrochemical and DFT studiesrdquo Journal ofElectroanalytical Chemistry vol 583 no 1 pp 8ndash16 2005
[24] J Cruz R Martinez J Genesca and E Garcia-OchoaldquoExperimental and theoretical study of 1-(2-ethylamino)-2-methylimidazoline as an inhibitor of carbon steel corrosion inacid mediardquo Journal of Electroanalytical Chemistry vol 566 no1 pp 111ndash121 2004
[25] E E Oguzie Y Li S G Wang and F Wang ldquoUnderstandingcorrosion inhibition mechanismsmdashexperimental and theoreti-cal approachrdquo RSC Advances vol 1 no 5 pp 866ndash873 2011
[26] A Kumar A Sankara M Kumaravel and S RameshkumarldquoClitoria ternateamdashextracts as corrosion inhibitor for mild steelin acid mediumrdquo International Journal of Engineering Researchand Development vol 8 no 5 pp 64ndash67 2013
[27] E E Oguzie G N Onuoha and A I Onuchukwu ldquoInhibitorymechanism of mild steel corrosion in 2M sulphuric acidsolution by methylene blue dyerdquo Materials Chemistry andPhysics vol 89 no 2-3 pp 305ndash311 2005
[28] E E Oguzie C K Enenebeaku C O Akalezi S C Okoro AA Ayuk and E N Ejike ldquoAdsorption and corrosion-inhibitingeffect ofDacryodis edulis extract on low-carbon-steel corrosionin acidic mediardquo Journal of Colloid and Interface Science vol349 no 1 pp 283ndash292 2010
[29] E E Oguzie ldquoCorrosion inhibition of aluminium in acidicand alkaline media by Sansevieria trifasciata extractrdquo CorrosionScience vol 49 no 3 pp 1527ndash1539 2007
[30] S A Umoren I B Obot and E E Ebenso ldquoCorrosioninhibition of aluminium using exudate gum from Pachylobusedulis in the presence of halide ions in HClrdquo E-Journal ofChemistry vol 5 no 2 pp 355ndash364 2008
[31] P C Okafor E E Ebenso and U J Ekpe ldquoAzadirachta indicaextracts as corrosion inhibitor for mild steel in acid mediumrdquoInternational Journal of Electrochemical Science vol 5 no 7 pp978ndash993 2010
[32] M Lebrini F Robert A Lecente and C Roos ldquoCorrosioninhibition of C38 steel in 1M hydrochloric acid medium byalkaloids extract from Oxandra asbeckii plant rdquo CorrosionScience vol 53 no 2 pp 687ndash695 2011
[33] E E Oguzie ldquoInfluence of halide ions on the inhibitive effect ofcongo red dye on the corrosion of mild steel in sulphuric acidsolutionrdquoMaterials Chemistry and Physics vol 87 no 1 pp 212ndash217 2004
[34] E E Oguzie ldquoInhibition of acid corrosion of mild steel byTelfaria occidentalis extractrdquo Pigment amp Resin Technology vol34 no 6 pp 321ndash326 2005
[35] E E Oguzie V O Njoku C K Enenebeaku C O Akalezi andC Obi ldquoEffect of hexamethylpararosaniline chloride (crystalviolet) on mild steel corrosion in acidic mediardquo CorrosionScience vol 50 no 12 pp 3480ndash3486 2008
[36] M A Ameer E Khamis and G al-Senani ldquoEffect of temper-ature on stability of adsorbed inhibitors on steel in phosphoricacid solutionrdquo Journal of Applied Electrochemistry vol 32 no 2pp 149ndash156 2002
[37] P C Okafor E E Oguzie G E Iniama M E Ikpi and U JEkpe ldquoCorrosion inhibition properties of thiosemicarbazoneand semicarbazone derivatives in concentrated acid environ-mentrdquoGlobal Journal of Pure and Applied Sciences vol 14 no 1pp 89ndash96 2008
[38] I B Obot ldquoSynergistic effect of nizoral and iodide ions on thecorrosion inhibition of mild steel in sulphuric acid solutionrdquoPortugaliae ElectrochimicaActa vol 27 no 5 pp 539ndash553 2009
[39] N O Eddy S A Odoemelam and A O Odiongenyi ldquoEthanolextract of musa species peels as a green corrosion inhibitor formild steel kinetics adsorption and thermodynamic consider-ationsrdquo Electronic Journal of Environmental Agricultural andFood Chemistry vol 8 no 4 pp 243ndash255 2009
[40] M H Hussin and M J Kassim ldquoThe corrosion inhibition andadsorption behavior of Uncaria gambir extract on mild steel in1M HClrdquo Materials Chemistry and Physics vol 125 no 3 pp461ndash468 2010
[41] V K W Grips V E Selvi H C Barshilia and K S RajamldquoEffect of electroless nickel interlayer on the electrochemicalbehavior of single layer CrN TiN TiAlN coatings and nanolay-ered TiAlNCrN multilayer coatings prepared by reactive dcmagnetron sputteringrdquo Electrochimica Acta vol 51 no 17 pp3461ndash3468 2006
[42] E E Oguzie ldquoStudies on the inhibitive effect ofOccimum viridisextract on the acid corrosion of mild steelrdquoMaterials Chemistryand Physics vol 99 no 2-3 pp 441ndash446 2006
[43] B Wang M Du J Zhang and C J Gao ldquoElectrochemical andsurface analysis studies on corrosion inhibition of Q235 steelby imidazoline derivative against CO
2corrosionrdquo Corrosion
Science vol 53 no 1 pp 353ndash361 2011[44] G Mu and X Li ldquoInhibition of cold rolled steel corrosion
by Tween-20 in sulfuric acid weight loss electrochemical andAFM approaches rdquo Journal of Colloid and Interface Science vol289 no 1 pp 184ndash192 2005
[45] A K Satapathy G Gunasekaran S C Sahoo K Amit and PV Rodrigues ldquoCorrosion inhibition by Justicia gendarussa plantextract in hydrochloric acid solutionrdquoCorrosion Science vol 51no 12 pp 2848ndash2856 2009
[46] E E Oguzie Y Li and F H Wang ldquoCorrosion inhibition andadsorption behavior of methionine on mild steel in sulfuricacid and synergistic effect of iodide ionrdquo Journal of Colloid andInterface Science vol 310 no 1 pp 90ndash98 2007
[47] L M Rodrıguez-Valdez W Villamisar M Casales et alldquoComputational simulations of themolecular structure and cor-rosion properties of amidoethyl aminoethyl and hydroxyethylimidazolines inhibitorsrdquo Corrosion Science vol 48 no 12 pp4053ndash4064 2006
[48] H Ju Z P Kai and Y Li ldquoAminic nitrogen-bearing polydentateSchiff base compounds as corrosion inhibitors for iron in acidicmedia a quantum chemical calculationrdquo Corrosion Science vol50 no 3 pp 865ndash871 2008
[49] L M Rodrıguez-Valdez A Martınez-Villafane and DGlossman-Mitnik ldquoComputational simulation of themolecularstructure and properties of heterocyclic organic compoundswith possible corrosion inhibition propertiesrdquo Journal ofMolecular Structure THEOCHEM vol 713 no 1ndash3 pp 65ndash702005
Journal of Materials 11
[50] K F Khaled ldquoMolecular simulation quantum chemical calcu-lations and electrochemical studies for inhibition of mild steelby triazolesrdquo Electrochimica Acta vol 53 no 9 pp 3484ndash34922008
[51] R M Issa M K Awad and F M Atlam ldquoQuantum chemicalstudies on the inhibition of corrosion of copper surface bysubstituted uracilsrdquo Applied Surface Science vol 255 no 5 pp2433ndash2441 2008
turn the site for electrophilic attack is controlled by the valueof 119891minus The values of 119864HOMO 119864LUMO Δ119864 and Fukui functionsare given inTable 5Higher values of119864HOMO indicate a greaterdisposition of a molecule to donate electrons to a metalsurface In the same way low values of the energy of the gapΔ119864 will afford good inhibition efficiency since the energyrequired to remove an electron from the last occupied orbitalwill be minimized [51] The above descriptors howeversuggest that EHEC possessed good inhibiting potential Thisis in agreement with the experimental findings
4 Conclusions
Ethyl hydroxyethyl cellulose was found to be an effectiveinhibitor of mild steel in 10MH
2SO4solution and its inhibi-
tion efficiency increased with increasing concentration Thecorrosion process is inhibited by adsorption of EHEC on themild steel surface following themodified Langmuir isothermThe inhibiting action is attributed to general adsorption ofboth protonated and molecular species of the additive on thecathodic and anodic sites on the corrodingmild steel surfaceIn addition corrosion inhibition is due to the formationof a chemisorbed film on the mild steel surface The EISmeasurement confirmed the adsorption of EHEC and EHEC+ KI on the mild steel surface Polarization studies showedthat EHEC and EHEC + KI were mixed-type inhibitorsystems with predominant cathodic effect The theoreticalstudy demonstrated that the inhibition efficiency is related tomolecular structure of inhibitor whereby increase in 119864HOMOand decrease in 119864LUMO favoured inhibition efficiency
Conflict of Interests
Theauthors hereby declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors are grateful to Udemmadu Tochukwu andOchiogu Valentine for assistance in carrying out some mea-surements
References
[1] E E Oguzie Y Li and F H Wang ldquoEffect of ascorbic acidon mild steel dissolution in sulphuric acid solution investigatedby electrochemical polarization and surface probe techniquesrdquoJournal of Applied Electrochemistry vol 37 no 10 pp 1183ndash11902007
[2] L G da Trindade and R S Goncalves ldquoEvidence of caffeineadsorption on a low-carbon steel surface in ethanolrdquo CorrosionScience vol 51 no 8 pp 1578ndash1583 2009
[3] F Bentiss M Outirite M Traisnel et al ldquoImprovementof corrosion resistance of carbon steel in hydrochloric acidmedium by 36-bis(3-pyridyl)pyridazinerdquo International Journalof Electrochemical Science vol 7 no 2 pp 1699ndash1723 2012
[4] S M A Shibli and V S Saji ldquoCo-inhibition characteristicsof sodium tungstate with potassium iodate on mild steelcorrosionrdquoCorrosion Science vol 47 no 9 pp 2213ndash2224 2005
[5] E E Oguzie C Unaegbu C N Ogukwe B N Okolue and AI Onuchukwu ldquoInhibition of mild steel corrosion in sulphuricacid using indigo dye and synergistic halide additivesrdquoMateri-als Chemistry and Physics vol 84 no 2-3 pp 363ndash368 2004
[6] V Kumpawat U Garg and R K Tak ldquoCorrosion inhibitionof aluminium in acid media by naturally occurring plantArtocarpus heterophyllus and Acacia senegalrdquo Journal of IndianCouncil of Chemists vol 26 no 1 pp 82ndash84 2009
[7] IA Akpan and N O Offiong ldquoEffect of ethanolamine andethylamine on the entropy content of the corrosion ofmild steelin tetraoxosulphate (VI) acid solutionrdquoChemistry andMaterialsResearch vol 2 no 7 pp 40ndash47 2012
[8] M Kissi M Bouklah B Hammouti and M BenkaddourldquoEstablishment of equivalent circuits from electrochemicalimpedance spectroscopy study of corrosion inhibition of steelby pyrazine in sulphuric acidic solutionrdquo Applied SurfaceScience vol 252 no 12 pp 4190ndash4197 2006
[9] S Rajendran S P Sridevi N Anthony A J Amalraj andM Sundaravadivelu ldquoCorrosion behaviour of carbon steel inpolyvinyl alcoholrdquo Anti-Corrosion Methods and Materials vol52 no 2 pp 102ndash107 2005
[10] B Qian J Wang M Zheng and B Hou ldquoSynergistic effect ofpolyaspartic acid and iodide ion on corrosion inhibition ofmildsteel in H
[11] D A Arthur A Jonathan P O Ameh and C Anya ldquoAreview on the assessment of polymeric materials used ascorrosion inhibitor of metals and alloysrdquo International Journalof Industrial Chemistry vol 4 article 2 pp 1ndash9 2013
[12] S A Umoren Y Li and F H Wang ldquoEffect of polyacrylicacid on the corrosion behaviour of aluminium in sulphuric acidsolutionrdquo Journal of Solid State Electrochemistry vol 14 no 12pp 2293ndash2305 2010
[13] S Banerjee A Mishra M M Singh B Maiti B Ray andP Maiti ldquoHighly efficient polyurethane ionomer corrosioninhibitor the effect of chain structurerdquo RSCAdvances vol 1 no2 pp 199ndash210 2011
[14] A K Dubey and G Singh ldquoCorrosion inhibition of mild steelin sulphuric acid solution by using polyethylene glycol methylether (PEGME)rdquo Portugaliae Electrochimica Acta vol 25 no 2pp 221ndash235 2007
[15] E E Oguzie S G Wang Y Li and F H Wang ldquoInfluenceof iron microstructure on corrosion inhibitor performance inacidic mediardquoThe Journal of Physical Chemistry C vol 113 no19 pp 8420ndash8429 2009
[16] S A Umoren E E Ebenso P C Okafor and O OgbobeldquoWater-soluble polymers as corrosion inhibitorsrdquo Pigment ampResin Technology vol 35 no 6 pp 346ndash352 2006
[17] S A Umoren and I B Obot ldquoPolyvinylpyrollidone andpolyacrylamide as corrosion inhibitors for mild steel in acidicmediumrdquo Surface Review and Letters vol 15 no 3 pp 277ndash2842008
[18] H Ashassi-Sorkhabi and N Ghalebsaz-Jeddi ldquoInhibition effectof polyethylene glycol on the corrosion of carbon steel insulphuric acidrdquoMaterials Chemistry and Physics vol 92 no 2-3pp 480ndash486 2005
[19] A Yurt V Butun and B Duran ldquoEffect of themolecular weightand structure of some novel water-soluble triblock copolymerson the electrochemical behaviour of mild steelrdquo MaterialsChemistry and Physics vol 105 no 1 pp 114ndash121 2007
10 Journal of Materials
[20] S A Umoren ldquoPolymers as corrosion inhibitors for metals indifferent mediamdasha reviewrdquo The Open Corrosion Journal vol 2pp 175ndash188 2009
[21] K F Khaled ldquoCorrosion control of copper in nitric acidsolutions using some amino acidsmdasha combined experimentaland theoretical studyrdquo Corrosion Science vol 52 no 10 pp3225ndash3234 2010
[22] E E Oguzie C O Akalezi C K Enenebeaku and J N AnekeldquoCorrosion inhibition and adsorption behavior of malachitegreen dye on aluminum corrosionrdquoChemical Engineering Com-munications vol 198 no 1 pp 46ndash60 2011
[23] J Cruz T Pandiyan and E Garcia-Ochoa ldquoA new inhibitor formild carbon steel electrochemical and DFT studiesrdquo Journal ofElectroanalytical Chemistry vol 583 no 1 pp 8ndash16 2005
[24] J Cruz R Martinez J Genesca and E Garcia-OchoaldquoExperimental and theoretical study of 1-(2-ethylamino)-2-methylimidazoline as an inhibitor of carbon steel corrosion inacid mediardquo Journal of Electroanalytical Chemistry vol 566 no1 pp 111ndash121 2004
[25] E E Oguzie Y Li S G Wang and F Wang ldquoUnderstandingcorrosion inhibition mechanismsmdashexperimental and theoreti-cal approachrdquo RSC Advances vol 1 no 5 pp 866ndash873 2011
[26] A Kumar A Sankara M Kumaravel and S RameshkumarldquoClitoria ternateamdashextracts as corrosion inhibitor for mild steelin acid mediumrdquo International Journal of Engineering Researchand Development vol 8 no 5 pp 64ndash67 2013
[27] E E Oguzie G N Onuoha and A I Onuchukwu ldquoInhibitorymechanism of mild steel corrosion in 2M sulphuric acidsolution by methylene blue dyerdquo Materials Chemistry andPhysics vol 89 no 2-3 pp 305ndash311 2005
[28] E E Oguzie C K Enenebeaku C O Akalezi S C Okoro AA Ayuk and E N Ejike ldquoAdsorption and corrosion-inhibitingeffect ofDacryodis edulis extract on low-carbon-steel corrosionin acidic mediardquo Journal of Colloid and Interface Science vol349 no 1 pp 283ndash292 2010
[29] E E Oguzie ldquoCorrosion inhibition of aluminium in acidicand alkaline media by Sansevieria trifasciata extractrdquo CorrosionScience vol 49 no 3 pp 1527ndash1539 2007
[30] S A Umoren I B Obot and E E Ebenso ldquoCorrosioninhibition of aluminium using exudate gum from Pachylobusedulis in the presence of halide ions in HClrdquo E-Journal ofChemistry vol 5 no 2 pp 355ndash364 2008
[31] P C Okafor E E Ebenso and U J Ekpe ldquoAzadirachta indicaextracts as corrosion inhibitor for mild steel in acid mediumrdquoInternational Journal of Electrochemical Science vol 5 no 7 pp978ndash993 2010
[32] M Lebrini F Robert A Lecente and C Roos ldquoCorrosioninhibition of C38 steel in 1M hydrochloric acid medium byalkaloids extract from Oxandra asbeckii plant rdquo CorrosionScience vol 53 no 2 pp 687ndash695 2011
[33] E E Oguzie ldquoInfluence of halide ions on the inhibitive effect ofcongo red dye on the corrosion of mild steel in sulphuric acidsolutionrdquoMaterials Chemistry and Physics vol 87 no 1 pp 212ndash217 2004
[34] E E Oguzie ldquoInhibition of acid corrosion of mild steel byTelfaria occidentalis extractrdquo Pigment amp Resin Technology vol34 no 6 pp 321ndash326 2005
[35] E E Oguzie V O Njoku C K Enenebeaku C O Akalezi andC Obi ldquoEffect of hexamethylpararosaniline chloride (crystalviolet) on mild steel corrosion in acidic mediardquo CorrosionScience vol 50 no 12 pp 3480ndash3486 2008
[36] M A Ameer E Khamis and G al-Senani ldquoEffect of temper-ature on stability of adsorbed inhibitors on steel in phosphoricacid solutionrdquo Journal of Applied Electrochemistry vol 32 no 2pp 149ndash156 2002
[37] P C Okafor E E Oguzie G E Iniama M E Ikpi and U JEkpe ldquoCorrosion inhibition properties of thiosemicarbazoneand semicarbazone derivatives in concentrated acid environ-mentrdquoGlobal Journal of Pure and Applied Sciences vol 14 no 1pp 89ndash96 2008
[38] I B Obot ldquoSynergistic effect of nizoral and iodide ions on thecorrosion inhibition of mild steel in sulphuric acid solutionrdquoPortugaliae ElectrochimicaActa vol 27 no 5 pp 539ndash553 2009
[39] N O Eddy S A Odoemelam and A O Odiongenyi ldquoEthanolextract of musa species peels as a green corrosion inhibitor formild steel kinetics adsorption and thermodynamic consider-ationsrdquo Electronic Journal of Environmental Agricultural andFood Chemistry vol 8 no 4 pp 243ndash255 2009
[40] M H Hussin and M J Kassim ldquoThe corrosion inhibition andadsorption behavior of Uncaria gambir extract on mild steel in1M HClrdquo Materials Chemistry and Physics vol 125 no 3 pp461ndash468 2010
[41] V K W Grips V E Selvi H C Barshilia and K S RajamldquoEffect of electroless nickel interlayer on the electrochemicalbehavior of single layer CrN TiN TiAlN coatings and nanolay-ered TiAlNCrN multilayer coatings prepared by reactive dcmagnetron sputteringrdquo Electrochimica Acta vol 51 no 17 pp3461ndash3468 2006
[42] E E Oguzie ldquoStudies on the inhibitive effect ofOccimum viridisextract on the acid corrosion of mild steelrdquoMaterials Chemistryand Physics vol 99 no 2-3 pp 441ndash446 2006
[43] B Wang M Du J Zhang and C J Gao ldquoElectrochemical andsurface analysis studies on corrosion inhibition of Q235 steelby imidazoline derivative against CO
2corrosionrdquo Corrosion
Science vol 53 no 1 pp 353ndash361 2011[44] G Mu and X Li ldquoInhibition of cold rolled steel corrosion
by Tween-20 in sulfuric acid weight loss electrochemical andAFM approaches rdquo Journal of Colloid and Interface Science vol289 no 1 pp 184ndash192 2005
[45] A K Satapathy G Gunasekaran S C Sahoo K Amit and PV Rodrigues ldquoCorrosion inhibition by Justicia gendarussa plantextract in hydrochloric acid solutionrdquoCorrosion Science vol 51no 12 pp 2848ndash2856 2009
[46] E E Oguzie Y Li and F H Wang ldquoCorrosion inhibition andadsorption behavior of methionine on mild steel in sulfuricacid and synergistic effect of iodide ionrdquo Journal of Colloid andInterface Science vol 310 no 1 pp 90ndash98 2007
[47] L M Rodrıguez-Valdez W Villamisar M Casales et alldquoComputational simulations of themolecular structure and cor-rosion properties of amidoethyl aminoethyl and hydroxyethylimidazolines inhibitorsrdquo Corrosion Science vol 48 no 12 pp4053ndash4064 2006
[48] H Ju Z P Kai and Y Li ldquoAminic nitrogen-bearing polydentateSchiff base compounds as corrosion inhibitors for iron in acidicmedia a quantum chemical calculationrdquo Corrosion Science vol50 no 3 pp 865ndash871 2008
[49] L M Rodrıguez-Valdez A Martınez-Villafane and DGlossman-Mitnik ldquoComputational simulation of themolecularstructure and properties of heterocyclic organic compoundswith possible corrosion inhibition propertiesrdquo Journal ofMolecular Structure THEOCHEM vol 713 no 1ndash3 pp 65ndash702005
Journal of Materials 11
[50] K F Khaled ldquoMolecular simulation quantum chemical calcu-lations and electrochemical studies for inhibition of mild steelby triazolesrdquo Electrochimica Acta vol 53 no 9 pp 3484ndash34922008
[51] R M Issa M K Awad and F M Atlam ldquoQuantum chemicalstudies on the inhibition of corrosion of copper surface bysubstituted uracilsrdquo Applied Surface Science vol 255 no 5 pp2433ndash2441 2008
[20] S A Umoren ldquoPolymers as corrosion inhibitors for metals indifferent mediamdasha reviewrdquo The Open Corrosion Journal vol 2pp 175ndash188 2009
[21] K F Khaled ldquoCorrosion control of copper in nitric acidsolutions using some amino acidsmdasha combined experimentaland theoretical studyrdquo Corrosion Science vol 52 no 10 pp3225ndash3234 2010
[22] E E Oguzie C O Akalezi C K Enenebeaku and J N AnekeldquoCorrosion inhibition and adsorption behavior of malachitegreen dye on aluminum corrosionrdquoChemical Engineering Com-munications vol 198 no 1 pp 46ndash60 2011
[23] J Cruz T Pandiyan and E Garcia-Ochoa ldquoA new inhibitor formild carbon steel electrochemical and DFT studiesrdquo Journal ofElectroanalytical Chemistry vol 583 no 1 pp 8ndash16 2005
[24] J Cruz R Martinez J Genesca and E Garcia-OchoaldquoExperimental and theoretical study of 1-(2-ethylamino)-2-methylimidazoline as an inhibitor of carbon steel corrosion inacid mediardquo Journal of Electroanalytical Chemistry vol 566 no1 pp 111ndash121 2004
[25] E E Oguzie Y Li S G Wang and F Wang ldquoUnderstandingcorrosion inhibition mechanismsmdashexperimental and theoreti-cal approachrdquo RSC Advances vol 1 no 5 pp 866ndash873 2011
[26] A Kumar A Sankara M Kumaravel and S RameshkumarldquoClitoria ternateamdashextracts as corrosion inhibitor for mild steelin acid mediumrdquo International Journal of Engineering Researchand Development vol 8 no 5 pp 64ndash67 2013
[27] E E Oguzie G N Onuoha and A I Onuchukwu ldquoInhibitorymechanism of mild steel corrosion in 2M sulphuric acidsolution by methylene blue dyerdquo Materials Chemistry andPhysics vol 89 no 2-3 pp 305ndash311 2005
[28] E E Oguzie C K Enenebeaku C O Akalezi S C Okoro AA Ayuk and E N Ejike ldquoAdsorption and corrosion-inhibitingeffect ofDacryodis edulis extract on low-carbon-steel corrosionin acidic mediardquo Journal of Colloid and Interface Science vol349 no 1 pp 283ndash292 2010
[29] E E Oguzie ldquoCorrosion inhibition of aluminium in acidicand alkaline media by Sansevieria trifasciata extractrdquo CorrosionScience vol 49 no 3 pp 1527ndash1539 2007
[30] S A Umoren I B Obot and E E Ebenso ldquoCorrosioninhibition of aluminium using exudate gum from Pachylobusedulis in the presence of halide ions in HClrdquo E-Journal ofChemistry vol 5 no 2 pp 355ndash364 2008
[31] P C Okafor E E Ebenso and U J Ekpe ldquoAzadirachta indicaextracts as corrosion inhibitor for mild steel in acid mediumrdquoInternational Journal of Electrochemical Science vol 5 no 7 pp978ndash993 2010
[32] M Lebrini F Robert A Lecente and C Roos ldquoCorrosioninhibition of C38 steel in 1M hydrochloric acid medium byalkaloids extract from Oxandra asbeckii plant rdquo CorrosionScience vol 53 no 2 pp 687ndash695 2011
[33] E E Oguzie ldquoInfluence of halide ions on the inhibitive effect ofcongo red dye on the corrosion of mild steel in sulphuric acidsolutionrdquoMaterials Chemistry and Physics vol 87 no 1 pp 212ndash217 2004
[34] E E Oguzie ldquoInhibition of acid corrosion of mild steel byTelfaria occidentalis extractrdquo Pigment amp Resin Technology vol34 no 6 pp 321ndash326 2005
[35] E E Oguzie V O Njoku C K Enenebeaku C O Akalezi andC Obi ldquoEffect of hexamethylpararosaniline chloride (crystalviolet) on mild steel corrosion in acidic mediardquo CorrosionScience vol 50 no 12 pp 3480ndash3486 2008
[36] M A Ameer E Khamis and G al-Senani ldquoEffect of temper-ature on stability of adsorbed inhibitors on steel in phosphoricacid solutionrdquo Journal of Applied Electrochemistry vol 32 no 2pp 149ndash156 2002
[37] P C Okafor E E Oguzie G E Iniama M E Ikpi and U JEkpe ldquoCorrosion inhibition properties of thiosemicarbazoneand semicarbazone derivatives in concentrated acid environ-mentrdquoGlobal Journal of Pure and Applied Sciences vol 14 no 1pp 89ndash96 2008
[38] I B Obot ldquoSynergistic effect of nizoral and iodide ions on thecorrosion inhibition of mild steel in sulphuric acid solutionrdquoPortugaliae ElectrochimicaActa vol 27 no 5 pp 539ndash553 2009
[39] N O Eddy S A Odoemelam and A O Odiongenyi ldquoEthanolextract of musa species peels as a green corrosion inhibitor formild steel kinetics adsorption and thermodynamic consider-ationsrdquo Electronic Journal of Environmental Agricultural andFood Chemistry vol 8 no 4 pp 243ndash255 2009
[40] M H Hussin and M J Kassim ldquoThe corrosion inhibition andadsorption behavior of Uncaria gambir extract on mild steel in1M HClrdquo Materials Chemistry and Physics vol 125 no 3 pp461ndash468 2010
[41] V K W Grips V E Selvi H C Barshilia and K S RajamldquoEffect of electroless nickel interlayer on the electrochemicalbehavior of single layer CrN TiN TiAlN coatings and nanolay-ered TiAlNCrN multilayer coatings prepared by reactive dcmagnetron sputteringrdquo Electrochimica Acta vol 51 no 17 pp3461ndash3468 2006
[42] E E Oguzie ldquoStudies on the inhibitive effect ofOccimum viridisextract on the acid corrosion of mild steelrdquoMaterials Chemistryand Physics vol 99 no 2-3 pp 441ndash446 2006
[43] B Wang M Du J Zhang and C J Gao ldquoElectrochemical andsurface analysis studies on corrosion inhibition of Q235 steelby imidazoline derivative against CO
2corrosionrdquo Corrosion
Science vol 53 no 1 pp 353ndash361 2011[44] G Mu and X Li ldquoInhibition of cold rolled steel corrosion
by Tween-20 in sulfuric acid weight loss electrochemical andAFM approaches rdquo Journal of Colloid and Interface Science vol289 no 1 pp 184ndash192 2005
[45] A K Satapathy G Gunasekaran S C Sahoo K Amit and PV Rodrigues ldquoCorrosion inhibition by Justicia gendarussa plantextract in hydrochloric acid solutionrdquoCorrosion Science vol 51no 12 pp 2848ndash2856 2009
[46] E E Oguzie Y Li and F H Wang ldquoCorrosion inhibition andadsorption behavior of methionine on mild steel in sulfuricacid and synergistic effect of iodide ionrdquo Journal of Colloid andInterface Science vol 310 no 1 pp 90ndash98 2007
[47] L M Rodrıguez-Valdez W Villamisar M Casales et alldquoComputational simulations of themolecular structure and cor-rosion properties of amidoethyl aminoethyl and hydroxyethylimidazolines inhibitorsrdquo Corrosion Science vol 48 no 12 pp4053ndash4064 2006
[48] H Ju Z P Kai and Y Li ldquoAminic nitrogen-bearing polydentateSchiff base compounds as corrosion inhibitors for iron in acidicmedia a quantum chemical calculationrdquo Corrosion Science vol50 no 3 pp 865ndash871 2008
[49] L M Rodrıguez-Valdez A Martınez-Villafane and DGlossman-Mitnik ldquoComputational simulation of themolecularstructure and properties of heterocyclic organic compoundswith possible corrosion inhibition propertiesrdquo Journal ofMolecular Structure THEOCHEM vol 713 no 1ndash3 pp 65ndash702005
Journal of Materials 11
[50] K F Khaled ldquoMolecular simulation quantum chemical calcu-lations and electrochemical studies for inhibition of mild steelby triazolesrdquo Electrochimica Acta vol 53 no 9 pp 3484ndash34922008
[51] R M Issa M K Awad and F M Atlam ldquoQuantum chemicalstudies on the inhibition of corrosion of copper surface bysubstituted uracilsrdquo Applied Surface Science vol 255 no 5 pp2433ndash2441 2008
[50] K F Khaled ldquoMolecular simulation quantum chemical calcu-lations and electrochemical studies for inhibition of mild steelby triazolesrdquo Electrochimica Acta vol 53 no 9 pp 3484ndash34922008
[51] R M Issa M K Awad and F M Atlam ldquoQuantum chemicalstudies on the inhibition of corrosion of copper surface bysubstituted uracilsrdquo Applied Surface Science vol 255 no 5 pp2433ndash2441 2008
