Corrosion inhibition and Biocidal effect of some cationic surfactants based on Schiff base Samy M. Shaban *, Atef Saied, Salah M. Tawfik, A. Abd-Elaal, Ismail Aiad Egyptian Petroleum Research Institute, EPRI, Cairo, Egypt 1. Introduction The study of the mild steel corrosion phenomena has become important particularly in acidic media due to increasing the industrial applications in acid solutions. As an example, the refining of crude oil results in a variety of corrosive conditions. Refinery corrosion is generally caused by a strong acid attacking the equipment surface [1]. The other important fields of application are acid pickling, industrial cleaning, acid descaling, oil well acid in oil recovery and the petrochemical processes [2]. Among the acid solutions, hydrochloric acid is one of the most widely used one. Due to the exposure of mild steel to corrosive environments, they are susceptible to different types of corrosion mechanisms; therefore, the use of corrosion inhibitors to prevent metal dissolution will be inevitable. Corrosion inhibition efficiency of organic compounds is related to their adsorption properties [3]. Corrosion protection of steel in acidic media is of great important both for industrial facilities and theoretical aspects [4]. The adsorption of these molecules depends mainly on certain physicochemical properties of the inhibitor molecule such as the presence of heteroatoms including: oxygen, sulfur, nitrogen and phosphorus atoms and multiple bonds in the molecule through which they are adsorbed on the metal surface [5–9]. The selection of a suitable inhibitor for a particular system is a difficult task because of the selectivity of the inhibitors and wide variety of corrosive environment. As a result, several types of corrosion inhibitors were developed to fit the different types of corrosion processes and also the medium where the corrosion takes place. Schiff bases are one of the important classes of organic compounds which have many interesting properties and extensive applications in medicinal, agricultural, pharmaceutical fields and material science [10,11]. The antimicrobial action of cationic surfactants is based on their ability to disrupt and disorganize the integral bacterial membrane by combined hydrophobic and electrostatic adsorption phenomena at the membrane–water interface [12,13]. Schiff bases are considered good bases for synthesis of several antibacterial compounds due to their easily preparing procedures and their ability to attach to several functional groups on their chemical skeleton [14]. Heterocyclic inhibitors showed excellent efficiency as corrosion inhibitors for carbon steel and aluminum alloys in acidic media [15–20]. The strategies to mitigate or control the effects of microbiolog- ically influenced corrosion (MIC) in Oil Field Companies include the following. Reduce the numbers and types of the sulfate reducing bacteria (SRB) in the system using biocides to the bulk water to kill the organisms which entering the system, or reduce the growth rate of microorganisms within the biofilm, mechanical removal of biofilm Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx A R T I C L E I N F O Article history: Received 1 February 2013 Accepted 12 March 2013 Available online xxx Keywords: Cationic surfactants Corrosion inhibition Sulfate reducing bacteria A B S T R A C T The three cationic surfactants based on Schiff base were laboratory prepared, (E)-decyl-4-[(2- hydroxyethylamino) methyl]-N,N-dimethyl benzenaminium bromide (I), (E)-dodecyl-4-[(2-hydro- xyethylamino)methyl]-N,N-dimethyl benzenaminium bromide (II) and (E)-hexadecyl-4-[(2-hydro- xyethylamino)methyl]-N,N-dimethyl benzenaminium bromide (III) were evaluated as corrosion inhibitors for carbon steel in acid medium and antimicrobial agents against sulfate reducing bacteria, SRB. Three techniques were used for the corrosion inhibition evaluation, namely; weight loss, polarization and electrochemical impedance. The serial dilution method was used to evaluate the inhibiting effect of these compounds on the sulfate reducing bacteria growth. The results showed that the prepared compounds have good antimicrobial activities against the SRB as well as they have high efficiency as corrosion inhibitors for carbon steel in 1 M HCl. ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +20 1276792188. E-mail address: [email protected](S.M. Shaban). G Model JIEC-1278; No. of Pages 6 Please cite this article in press as: S.M. Shaban, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.03.013 Contents lists available at SciVerse ScienceDirect Journal of Industrial and Engineering Chemistry jou r n al h o mep ag e: w ww .elsevier .co m /loc ate/jiec 1226-086X/$ – see front matter ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2013.03.013
Transcript
Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
G Model
JIEC-1278; No. of Pages 6
Corrosion inhibition and Biocidal effect of some cationic surfactantsbased on Schiff base
Samy M. Shaban *, Atef Saied, Salah M. Tawfik, A. Abd-Elaal, Ismail Aiad
Egyptian Petroleum Research Institute, EPRI, Cairo, Egypt
A R T I C L E I N F O
Article history:
Received 1 February 2013
Accepted 12 March 2013
Available online xxx
Keywords:
Cationic surfactants
Corrosion inhibition
Sulfate reducing bacteria
A B S T R A C T
The three cationic surfactants based on Schiff base were laboratory prepared, (E)-decyl-4-[(2-
xyethylamino)methyl]-N,N-dimethyl benzenaminium bromide (II) and (E)-hexadecyl-4-[(2-hydro-
xyethylamino)methyl]-N,N-dimethyl benzenaminium bromide (III) were evaluated as corrosion
inhibitors for carbon steel in acid medium and antimicrobial agents against sulfate reducing bacteria,
SRB. Three techniques were used for the corrosion inhibition evaluation, namely; weight loss,
polarization and electrochemical impedance. The serial dilution method was used to evaluate the
inhibiting effect of these compounds on the sulfate reducing bacteria growth. The results showed that
the prepared compounds have good antimicrobial activities against the SRB as well as they have high
efficiency as corrosion inhibitors for carbon steel in 1 M HCl.
� 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights
reserved.
Contents lists available at SciVerse ScienceDirect
Journal of Industrial and Engineering Chemistry
jou r n al h o mep ag e: w ww .e lsev ier . co m / loc ate / j iec
1. Introduction
The study of the mild steel corrosion phenomena has becomeimportant particularly in acidic media due to increasing theindustrial applications in acid solutions. As an example, therefining of crude oil results in a variety of corrosive conditions.Refinery corrosion is generally caused by a strong acid attackingthe equipment surface [1]. The other important fields ofapplication are acid pickling, industrial cleaning, acid descaling,oil well acid in oil recovery and the petrochemical processes [2].Among the acid solutions, hydrochloric acid is one of the mostwidely used one. Due to the exposure of mild steel to corrosiveenvironments, they are susceptible to different types of corrosionmechanisms; therefore, the use of corrosion inhibitors to preventmetal dissolution will be inevitable. Corrosion inhibition efficiencyof organic compounds is related to their adsorption properties[3]. Corrosion protection of steel in acidic media is of greatimportant both for industrial facilities and theoretical aspects [4].The adsorption of these molecules depends mainly on certainphysicochemical properties of the inhibitor molecule such as thepresence of heteroatoms including: oxygen, sulfur, nitrogen andphosphorus atoms and multiple bonds in the molecule throughwhich they are adsorbed on the metal surface [5–9]. The selection
Please cite this article in press as: S.M. Shaban, et al., J. Ind. Eng. Ch
1226-086X/$ – see front matter � 2013 The Korean Society of Industrial and Engineer
http://dx.doi.org/10.1016/j.jiec.2013.03.013
of a suitable inhibitor for a particular system is a difficult taskbecause of the selectivity of the inhibitors and wide variety ofcorrosive environment. As a result, several types of corrosioninhibitors were developed to fit the different types of corrosionprocesses and also the medium where the corrosion takes place.
Schiff bases are one of the important classes of organiccompounds which have many interesting properties and extensiveapplications in medicinal, agricultural, pharmaceutical fields andmaterial science [10,11].
The antimicrobial action of cationic surfactants is based on theirability to disrupt and disorganize the integral bacterial membraneby combined hydrophobic and electrostatic adsorption phenomenaat the membrane–water interface [12,13].
Schiff bases are considered good bases for synthesis of severalantibacterial compounds due to their easily preparing proceduresand their ability to attach to several functional groups on theirchemical skeleton [14].
Heterocyclic inhibitors showed excellent efficiency as corrosioninhibitors for carbon steel and aluminum alloys in acidic media[15–20].
The strategies to mitigate or control the effects of microbiolog-ically influenced corrosion (MIC) in Oil Field Companies include thefollowing.
Reduce the numbers and types of the sulfate reducing bacteria(SRB) in the system using biocides to the bulk water to kill theorganisms which entering the system, or reduce the growth rate ofmicroorganisms within the biofilm, mechanical removal of biofilm
S.M. Shaban et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx2
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from the substratum (sponge balls, brushes), and water treatmentsto decrease the numbers and types of organisms (aeration anddeaeration).
2. Materials and methods
2.1. Synthesis
2.1.1. Synthesis of Schiff base compound
Schiff-base was synthesized throughout condensation reactionof monoethanolamine with 4-dimethylaminobenzaldehyde. Equi-molar amount was refluxed in ethanol for 6 h. The reaction mixturewas left to cool to ambient temperature and filtered. The productswere recrystallized twice from ethanol, washed with water anddried in vacuum oven at 40 8C.
2.1.2. Synthesis of cationic Schiff base compounds
0.1 mol of Schiff base in absolute ethanol was refluxed with0.1 mol alkyl bromide for 45 h. The solution was evaporated underreduced pressure. The products were crystallized from acetonethree times to obtain the purified cationic surfactants the synthesisand chemical structure were discussed and elucidated in anotherpaper under press now. The chemical structures of the synthesizedcompounds are shown in Scheme 1.
2.2. Measurements
2.2.1. Corrosion measurements
2.2.1.1. Weight loss measurements. The weight loss experimentswere performed with carbon steel specimens having a compositionof (wt%): 0.21 C, 0.035 Si, 0.025 Mn, 0.082 P and the remainder is Fe.The carbon steel sheets dimensions are 6 cm � 3.0 cm � 0.6 cm.The test was done according to ASTM G1-72 (reapproved 2004). Thesteel coupons were immersed in 1 M HCl with and without thetested inhibitors I, II and III at different concentrations ranging from1 � 10�2 to 1 � 10�5 mol/L for 24 h at different temperatures 25, 50and 70 8C. The tested coupons were taken out from the solutions,washed, dried and weighed accurately [21]. The test was repeatedthree times and the weight loss was the average of them. Thecoupons were polished by hard plastic brush, hot water then byethanol to remove the corrosion products. The corrosion rate (R) andthe inhibition efficiency (h%) were calculated using Eqs. (1) and (2)
R ¼W
At(1)
h% ¼ R0 � R
R0
� �� 100 (2)
where W is the average weight loss of three parallel carbon steelsheets, A is the total surface area of the specimen, t is immersion
Scheme 1. The chemical structures of the synthesized compounds.
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time, R0 and R are the values of the corrosion rate without and withaddition of the inhibitor, respectively [22,23].
2.2.1.2. Polarization measurements. The polarization measure-ments were carried out using a laboratory potentiostat (Voltalab 40 PGZ 301 in a conventional three electrodes cell system,France). The working electrode was immersed in the test solutionfor 30 min until the open circuit potential reached. After that theworking electrode was polarized in both cathodic and anodicdirections. The values of corrosion current density (Icorr) werecalculated from the extrapolation of Tafel lines to pre-determineopen circuit potential [24]. Standard ASTM glass electrochemicalcell was used and platinum electrode was used as an auxiliaryelectrode. All potentials were measured against saturated calomelelectrode (SCE) as a reference electrode. The potential increasedwith a speed of 30 mV/min started from �900 mV to �250 mV. Theinhibition efficiency (h%) was defined as:
h% ¼ I0 � I
I0
� �� 100 (3)
where the I0 and I are the current density values without and withinhibitors, respectively.
2.2.1.3. Electrochemical impedance techniques. The electrochemicalimpedance spectroscopy (EIS) measurements were carried outusing alternating current (AC) signals of amplitude 10 mV peak topeak at the open circuit potential (OCP) in the frequency range of100 kHz–30 mHz,with the same potentiostat used in polarizationtechnique.
2.2.2. Biocidal measurements
The inhibition activity of the prepared compounds on thesulfate reducing bacteria growth was measured using the serialdilution method.
SRB-contaminated water was supplied from Qarun PetroleumCo. (West Desert, Egypt). This water was used for microbialinhibition test. The test has been conducted according to ASTMD4412-84 [25]. The tested water was subjected to growth of about1,000,000 bacteria cell/mL. The prepared compounds were testedas biocide for the SRB by dose of (20, 30, 40, 50, 100, 125, 200 and400 ppm). The system was incubated to contact time of 3.0 h; eachsystem was cultured in SRB specific media for 21 days at 37–40 8C.
2.2.3. Surface measurements
Surface tension of the prepared compounds solutions wasmeasured using Du-Nouy tensiometer (Kruss type 845, Hamburg,Germany). Freshly prepared aqueous cationic surfactants solutionswith a concentration range of 1 � 10�2–1 � 10�5 mol/L were pouredinto a clean 25 mL Teflon holder and allowed to equilibrate for 30–45 min. Then, the platinum ring was adjusted at the air–waterinterface of the surfactant solution. The reading was recorded whenthe ring detached itself from the solution surface. The platinum ringwas removed after each reading, washed with diluted HCl followedby distilled water. Apparent surface tension values were taken as theaverage of three replicates at temperatures of 25 8C.
3. Results and discussion
3.1. Corrosion inhibition efficiency
3.1.1. Weight loss technique
3.1.1.1. Effect of inhibitor concentration. The inhibiting efficiencies(h%) of the studied prepared inhibitors toward the corrosionof carbon steel in 1.0 M HCl were measured at different tempera-tures. Different inhibitor concentrations ranging from 1 � 10�2 to
Fig. 1. Variation of h% against temperatures for inhibitor I at 25 8C.
30
40
50
60
70
80
90
100
110
20 30 40 50 60 70 80
η(%
)
Temperature (oC)
0.01
0.005
0.001
0.0005
0.0001
0.00005
0.00001
Fig. 3. Variation of h% against temperatures for inhibitor III at 25 8C.
0
Blank0.000010.000050.0001
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1 � 10�5 mol/L were used. The influence of I, II and III doses on thecorrosion rates and inhibition efficiencies of the carbon steel in1.0 M HCl solution at 25–70 8C is shown in Figs. 1–3. It was foundthat the prepared cationic surfactant have high efficiencycompared to some other data [26,27] and the inhibition efficienciesare depending on its concentration in the tested solution. Also, it isclear that the gradual increasing the dose from 1 � 10�5 to1 � 10�2 mol/L decreases the steel corrosion rate.
The increase in h with increasing in concentration of inhibitor isattributed to the adsorption of the inhibitor molecules on the steelsurface and thus increases the metal surface coverage [28].
It is well known that the surfactant molecules consists ofhydrophilic and hydrophobic part, the hydrophobic part (tail)carries the molecule to the air/water interface and it oriented in theair meanwhile the hydrophile (head) oriented in the water so thesurfactant molecule isolate the metal surface from corrosivemedium.
3.1.1.2. Effect of solution temperature. To examine the action ofinhibitors at elevated temperatures, mass loss experiments werecarried out at different temperatures. The variation of h withtemperature are shown in Figs. 1–3 which indicated that h showsdifferent trends for tested compounds. Where at lower concentra-tions all inhibitors show a decrease in efficiency with an increasingin temperatures. Meanwhile at higher concentration from 5 � 10�4
to 1 � 10�2 M solutions, efficiency increase with increasing thetemperature from 25 to 50 8C and decreased after 50 8C, but it isstill in all cases higher than 25 8C [29]. At any temperature, theorder of inhibition efficiency was found to be III > II > I.
As known the decreases in efficiency with the increases oftemperatures is attributed to the physical adsorption. The time gap
30
40
50
60
70
80
90
100
20 30 40 50 60 70
η(%
)
Temperature (oC)
0.01
0.005
0.001
0.0005
0.0001
0.00005
0.00001
Fig. 2. Variation of h% against temperatures for inhibitor II at 25 8C.
Please cite this article in press as: S.M. Shaban, et al., J. Ind. Eng. Ch
between the process of adsorption and desorption of inhibitormolecules over the metal surface is becoming shorter withincrease in the temperature. Hence, the metal surface remainsexposed to the acid environment for longer period, therefore theinhibition efficiency falls at elevated temperature [29]. A slightincrease or constancy in h with the increase of temperature athigher concentration may be due to the chemical adsorption aloneor due to the combination of physical and chemical adsorption[30]. Mass loss experiment showed rapid increase in weight loss atelevated temperature in the absence of inhibitor. This shows thattested inhibitor molecules are good corrosion inhibitors for steel in1.0 M HCl in the range of temperature studied.
3.1.2. Potentiodynamic polarization
The polarization curves for carbon steel in 1.0 M HCl with thestudied inhibitors, I, II and III at different concentrations at 25 8Cwere shown in Figs. 4–6. The electrochemical corrosion kineticparameters, i.e., anodic and cathodic Tafel slopes (ba, bc), corrosioncurrent density (Icorr) and inhibition efficiency (hp%) are listed inTable 1. The surface coverage area u was calculated from thefollowing equation:
u ¼ 1 � Iinh
Icorr
� �
-1.2
-1
-0.8
-0.6
-0.4
-0.2
-8 -6 -4 -2 0
Pote
n�al
[ V]
log (A/cm²)
0.00050.0010.0050.01
Fig. 4. Anodic and cathodic polarization curves obtained at 25 8C in 1 M HCl in
Fig. 5. Anodic and cathodic polarization curves obtained at 25 8C in 1 M HCl in
different concentrations of inhibitor II.
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
-8 -6 -4 -2 0
Pote
n�al
[ V]
log (A/cm²)
Blank
0.00001
0.00005
0.0001
0.0005
0.001
0.005
0.01
Fig. 6. Anodic and cathodic polarization curves obtained at 25 8C in 1 M HCl in
different concentrations of inhibitor III.
S.M. Shaban et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx4
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where Icorr and Iinh are the uninhibited and inhibited corrosioncurrent densities, respectively.
The inhibition efficiency (hp%) of this inhibitor was obtainedfrom the following equation:
hp% ¼ u � 100
It is clear from the polarization curves that the increase of theinhibitor concentration of I, II and III decreases the corrosioncurrent density (Icorr) which consequently increases the surfacecoverage values Table 1. Also, (Icorr) of carbon steel corrosionreaction is decreased by increasing length of carbon chain in theprepared inhibitors.
These inhibitors cause change in the anodic and cathodic Tafelslopes and no definite trend was observed in the shift of Ecorr valuesin the presence of different concentrations of the synthesizedinhibitors, suggesting that these compounds behave as mixed-typeinhibitors.
The results show that most effective compound is III which havethe longest hydrocarbon chain length. The maximum inhibition
Table 1Potentiodynamic polarization parameters for corrosion of carbon steel in 1 M HCl in abse
Molecule Concentration of inhibitor (M) Ecorr (mV) (SCE) Icorr (mA cm�
1 M HCl 0.00 �529.7 0.2250
I 1 � 10�5 �518 0.0787
5 � 10�5 �533 0.0664
1 � 10�4 �545.4 0.0455
5 � 10�4 �529.6 0.0411
1 � 10�3 �534.1 0.0404
5 � 10�3 �539.8 0.027
1 � 102 �534.2 0.0219
II 1 � 10�5 �547.2 0.0703
5 � 10�5 �515.9 0.0591
1 � 10�4 �555.6 0.0476
5 � 10�4 �522.6 0.0363
1 � 10�3 �537.2 0.0300
5 � 10�3 �546 0.0238
1 � 102 �530.5 0.0203
III 1 � 10�5 �567.1 0.0544
5 � 10�5 �511.5 0.0370
1 � 10�4 �527.7 0.025
5 � 10�4 �497.7 0.0246
1 � 10�3 �536.8 0.0231
5 � 10�3 �537.2 0.0212
1 � 102 �526 0.0155
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efficiencies were 90, 91 and 93%, for compounds I, II and III,respectively [31–34].
Results obtained from EIS can be interpreted in terms of theequivalent circuit of the electrical double layer shown in Fig. 7[35].
Figs. 8 and 9 show the Nyquist plots for carbon steel in 1 M HClsolution with and without different concentrations of theprepared cationic surfactants (I, II, and III) at 25 8C. The Nyquistplots were regarded as one part of a semicircle. The charge transferresistance values (Rct) were calculated from the difference inimpedance at lower and higher frequencies [36]. The double layercapacitance (Cdl), values were calculated from the followingequation [37].
f ð�ZmaxÞ ¼ ð2pCdlRctÞ�1
where ƒ(�Zmax) is the frequency at maximum imaginarycomponent of the impedance. The inhibition efficiency was
nce and presence of different concentrations of three prepared compounds at 25 8C.
Fig. 7. The suggested equivalent circuit model for the studied system.
0
50
100
150
200
250
300
350
400
450
500
0 200 400 600 800 1000 1200
Zr [
ohm
.cm
²]
Zi [ ohm.c m²]
1M HCl
0.00001
0.00005
0.0001
0.0005
0.001
0.005
0.01
Fig. 8. Nyquist plots for carbon steel in 1 M HCl in absence and presence of different
concentrations of inhibitor I.
0
50
100
150
200
250
300
350
400
450
500
0 200 400 600 800 1000 1200 1400
Zr [
ohm
.cm
²]
Zi [ ohm.c m²
1M HCl
0.00001
0.00005
0.0001
0.0005
0.001
0.005
0.01
Fig. 9. Nyquist plots for carbon steel in 1 M HCl in absence and presence of different
concentrations of inhibitor II.
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calculated using charge transfer resistance using the followingequation:
h% ¼ Rct � R0ct
Rct
� �� 100
where Rct and R0ct are the charge transfer resistance values with and
without inhibitor for carbon steel in 1 M HCl, respectively. Theelectrochemical impedance parameters derived from the Nyquistplots and the inhibition efficiency are listed in Table 2. It was clearthat, Rct values in the presence of the inhibitor were always greaterthan their values in the absence of the inhibitor and also increase
Table 2EIS parameters for corrosion of carbon steel in 1 M HCl in the absence and presence of
Molecule Concentration of inhibitor (M) Rs (V cm2)
1 M HCl 0.00 2.429
I 1 � 10�5 5.69
5 � 10�5 25.45
1 � 10�4 9.547
5 � 10�4 17.81
1 � 10�3 6.027
5 � 10�3 11.52
1 � 102 11.86
II 1 � 10�5 10.56
5 � 10�5 21.33
1 � 10�4 2.019
5 � 10�4 18.51
1 � 10�3 22.01
5 � 10�3 12.11
1 � 102 14
III 1 � 10�5 2.96
5 � 10�5 5.772
1 � 10�4 11.15
5 � 10�4 1.989
1 � 10�3 9.445
5 � 10�3 5.19
1 � 102 47.28
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with increasing inhibitor concentration, which indicates a reduc-tion in the steel corrosion rate. The capacitance, Cdl, values weredecreased due to a decrease in local dielectric constant and/or anincrease in the thickness of the electrical double layer, suggestingthat the inhibitor molecules acted by adsorption at the metal/solution interface [38].
The inhibiting efficiency was in the following order: III > II > I.
3.2. Antimicrobial activity of the studied cationic surfactants
against sulfate reducing bacteria (SRB)
Sulfate reducing bacteria (SRB) produces H2S which increasesthe corrosiveness of brine and causing metals to crack and blister.In addition, bacterially (biogenic) produced H2S reacts with ironthat is solubilized at the anode, thereby removing anothercorrosion byproduct to accelerate the corrosion process.
The sessile bacteria accelerate the corrosion processes inseveral ways. They accelerate pitting corrosion by removing acorrosion by-product (atomic hydrogen) from the cathode. Inremoving hydrogen, bacteria depolarize the surface and allowcorrosion reactions to continue.
The antimicrobial activity of the three studied biocides (I, II andIII) against SRB growth was determined by serial dilution methodat dose of 100, 200, 400 and 600 ppm and the results are listed in
different concentrations of three prepared compounds 25 8C.
Table 3Biocidel effect of the prepared compounds against sulfate reducing bacteria, SRB.
Type Dose (ppm)
20 30 40 50 100 125 200 300
I >103 >103 103 102 Nil Nil Nil Nil
II >103 >103 >103 >103 10 Nil Nil Nil
III >103 >103 >103 >103 >103 103 102 Nil
Table 4Critical micelle concentration and effectiveness of prepared cationic surfactants.
Compound CMC (mol/L) pCMC (mN m�1)
I 0.005412 39.16
II 0.003043 41.5
III 0.001413 43.16
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Table 3. The three studied cationic surfactants showed imperativeresults due to their relatively high efficiency against this type ofbacteria [39]. The results indicate that the studied cationicsurfactants have antimicrobial activity against the tested organ-isms (SRB). The ammonium salt with a decyl, dodecyl andhexadecyl group (I, II, and III), was inactive at the lowestconcentration (20–40 ppm). In the relative high doses, the threecompounds have relative activity; the activity of the preparedcompounds is depending on the alkyl chain length which isdetermined the compound solubility in the water, so as the alkylchain length increases, the solubility of the compounds decreases,so its activity decreases. As shown in Table 3, the more effectivecompound is compound (I) which has alkyl chain length of C10.This activity is slightly decreases for the compound (II) which havealkyl chain length of C12. In all cases, the three compounds haveBiocidal effect on the dose of 300 ppm.
As we know the bacterial cell membrane is composed of athick wall containing many layers of peptidoglycan and teichoi-cacids, which are glycerol–ribitol (polyhydric alcohol) through aphosphorus bond surrounded by lipids of lipopolysaccharides andproteins [40–42]. It is believed from the recent studies on cationicsurfactants that they have excellent bactericidal activity [43]. Thisactivity depends on the hydrophobic chain length, surface activitiesand the dosage of these cationics, where due to amphiphilic natureof surfactants, they adsorb on the outer cell membrane In addition,the similarity between the hydrophobic chains and the lipid layersand the building units of the cell membranes and the monosaccha-ride in these compounds facilitates that adsorption At the completecoverage, the molecules penetrate through it. Furthermore, thepositive charges in the cationic molecules neutralize the negativecharges on the bacterial cell membranes. Accordingly, the selectivepermeability which characterizes the outer cellular membrane iscompletely deactivated hence; the vital transportation of essentialcomponents for cell bio reactions and activities is disturbed, causingdeath for these microorganisms.
3.3. Critical micelle concentration
The tested compounds have good surface properties, the CMC ofthem depend on their chemical structure as we see in Table 4 andall other surface parameters were discussed in details in anotherpaper under press.
4. Conclusion
From the above results we can conclude the following:
1 Electrochemical studies and weight loss measurements givesimilar results.
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2 The synthesized cationic surfactants can be used as corrosioninhibitors for carbon steel in 1 M HCl. Their inhibiting propertiesincrease with increasing the concentration of the inhibitorsaccording to order: III > II > I.
3 Polarization measurements showed that the cationic surfactantsare mixed-type inhibitors, inhibiting the corrosion of carbonsteel by blocking the active sites of the metal surface.
4 Double-layer capacitances decrease with respect to the blanksolution when these inhibitors are added. This fact may beexplained on the basis of adsorption of these inhibitors on thesteel surface.
5 The prepared compound have high tendency to prevent thesulfate reducing bacteria growth.
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