�������� ����� ��

Morphological and Electrochemical Characterization of ElectrodepositedZn-Ag nanoparticle composite coatings

M.K. Punith Kumar, Chandan Srivastava

PII: S1044-5803(13)00253-2DOI: doi: 10.1016/j.matchar.2013.08.017Reference: MTL 7411

To appear in: Materials Characterization

Received date: 23 May 2013Revised date: 20 August 2013Accepted date: 29 August 2013

Please cite this article as: Punith Kumar MK, Srivastava Chandan, Morphologicaland Electrochemical Characterization of Electrodeposited Zn-Ag nanoparticle compositecoatings, Materials Characterization (2013), doi: 10.1016/j.matchar.2013.08.017

This is a PDF file of an unedited manuscript that has been accepted for publication.As a service to our customers we are providing this early version of the manuscript.The manuscript will undergo copyediting, typesetting, and review of the resulting proofbefore it is published in its final form. Please note that during the production processerrors may be discovered which could affect the content, and all legal disclaimers thatapply to the journal pertain.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

1

Morphological and Electrochemical Characterization of Electrodeposited

Zn-Ag nanoparticle composite coatings

Punith Kumar M. K. and Chandan Srivastava

Dept. of Materials Engineering, Indian Institute of Science (IISc), Bangalore- 560012

Abstract:

Silver nanoparticles with an average size of 23 nm were chemically synthesized and used

to fabricate Zn-Ag composite coatings. The Zn-Ag composite coatings were generated by

electrodeposition method using simple sulphate plating bath dispersed with 0.5, 1 and 1.5 g/l of

Ag nanoparticles. Scanning Electron Microscopy, X-Ray diffraction and Texture co-efficient

calculations revealed that Ag nanoparticles appreciably influenced the morphology, micro-

structure and texture of the deposit. It was also noticed that agglomerates of Ag nanoparticles, in

the case of high bath load conditions, produced defects and dislocations on the deposit surface.

Ag nanoparticles altered the corrosion resistance property of Zn-Ag composite coatings as

observed from Tafel polarization, Electrochemical Impedance analysis and immersion test.

Reduction in corrosion rate with increased charge transfer resistance was observed for Zn-Ag

composite coatings when compared to pure Zn coating. However, the particle concentration in

plating bath and their agglomeration state directly influenced the surface morphology and the

subsequent corrosion behavior of the deposits.

Key words: Ag nanoparticles, Zn-Ag composite coating, Chemical heterogeneities, Corrosion.

*Corresponding author. Tel: +91-80-22932834

E-mail: csrivastava@materials.iisc.ernet.in (Chandan Srivastava)

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

2

1. Introduction:

Iron and its alloys like mild steel find large number of engineering applications due to

their low cost and favorable mechanical properties. Iron based materials, however, are

vulnerable to the damaging effects of corrosion and requires protection from corrosive

environments in order to maximize the reliability of the structures constructed from using iron

based materials [1]. Among the various corrosion control methodologies, sacrificial nature of

zinc coating has shown to provide corrosion protection to ferrous substrates. However, under

aggressive environments, life span of zinc coating is reduced as zinc itself undergoes corrosion

by forming white rust like products [2]. Hence, in order to protect the underlying substrate for

longer times, microstructural modifications of zinc coating is required for improving its

chemical, electrochemical and mechanical properties [3-5].

Inclusion of inert nanoparticles into growing Zn deposit has shown to increase the

resistance of the zinc deposit towards aggressive environments [1, 6-8]. Co-deposition of inert

particles with zinc matrix is environmental friendly compared to surface modifications using

organic chelating agents and hazardous post plating treatment like chrome passivation [9, 10].

To obtain metal matrix-particles composite coatings, electrodeposition is a desirable process due

to the fact that this process is cost effective, non-equipment intensive, suitable for large scale

production less polluting in nature etc [6, 11]. Literature contains reports on the co-deposition of

different types of nanoparticles such as oxides [3, 11], sulphides [12] and carbides [13] of

different metals into the zinc matrix in order to improve its performance. Adriana Vlasa et al

[14] successfully fabricated Zn-TiO2 nanoparticle composite coatings on mild steel using the

electrodeposition process and found that the inclusion of TiO2 nanoparticles into zinc matrix

leads to change in deposit morphology and increase in corrosion resistance of the deposit. They

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

3

[14] have investigated the corrosion resistance of the deposits up to 48 hrs and observed superior

properties in Zn-TiO2 composite coatings when compared to pure Zn coating. Praveen Kumar et

al [13] studied the effect of B4C nanoparticles and surfactants on the corrosion resistance of

electrolytically obtained zinc deposits. In this [13] study, it was observed that the surfactants

have an effect on altering the surface morphology of the Zn-B4C composite coatings which

showed higher corrosion resistance as compared to pure Zn coating. Panagopoulos et al [8]

investigated morphology, mechanical and electrochemical behavior of Zn-Fly ash coatings on

mild steel. They [8] found that incorporation of fly ash particles improved hardness, adhesion

strength, friction and corrosion resistance of the zinc coating.

Although a variety of nanoparticles have been used with zinc matrix to provide improved

corrosion protection till date, there are no reports in the literature on the electrochemical

investigation of zinc- silver nanoparticles composite coatings. Incorporation of Ag nanoparticles

can be beneficial due to its excellent antimicrobial and antibacterial properties [15-20].

Furthermore, it has been shown in the literature that Ag nanoparticle incorporation into Ni film

leads to better micro hardness, wear resistance and lubrication properties for the composite film

when compared to pure Ni film [21-23]. A similar enhancement in properties can be expected for

Zn-Ag nanoparticle composite coatings also. In the present work, chemically synthesized Ag

nanoparticles were used to fabricate Zn-Ag composite coatings electrolytically. The surface

morphology and microstructure of the coatings were investigated. Corrosion resistance

properties of the coatings were measured in 3.5% NaCl solution using Tafel polarization,

Electrochemical Impedance Spectroscopic (EIS) analysis and immersion test. The properties of

composite coatings were compared with respect to pure Zn coating.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

4

2. Experiment

2.1. Synthesis of Ag nanoparticles:

To synthesize Ag nanoparticles, 1mmole of AgNO3 and 10 mmoles of Poly vinyl

pyrrolidone (PVP) were added into 25mL of water in three necked round bottom flask fitted with

a magnetic stirrer and a reflux condenser. The reaction mixture was heated up to 100ºC under

Argon atmosphere. At 1000C, 2 mmoles of NaBH4 dissolved in NaOH solution was slowly

added into the AgNO3+PVP mixture. After the addition of the reducing agent, the reaction

mixture was refluxed for 30 minutes. After 30 minutes, the reaction mixture containing

nanoparticles was left cool to the room temperature after which the as synthesized nanoparticles

were thoroughly washed with ethyl alcohol.

2.2. Fabrication of Zn-Ag composite coatings:

Mild steel plate and zinc foil were used as cathode and anode respectively for the

deposition process. The mild steel surface was degreased and cleaned by dipping in 10% HCl

and 10% NaOH solution and was mechanically polished using different grit emery papers

followed by water rinsing. The anode was activated by dipping in 10% HCl for 10 sec. followed

by water wash prior. Zinc electrodeposition was carried using the plating bath and operating

parameters provided in the Table 1. Zn-Ag composite coatings were generated from zinc plating

bath containing 0.5, 1.0 and 1.5 g/l of Ag nanoparticles. The plating solutions containing Ag

nanoparticles were stirred for 12 hr by magnetic stirrer and sonicated for 15 min to ensure

uniform dispersion of Ag nanoparticles in the plating bath. The deposits were obtained by

applying the operating conditions details provided in Table 1 and were identified with different

deposit code as provided in the same table.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

5

2.3. Characterization:

Zeta potential (surface charge) of Ag nanoparticles in aqueous solution was determined

using a Malveron zeta potential analyzer. The dynamic laser light scattering was used to

measure particle size distribution (PSD) of Ag nanoparticles in the plating bath. Surface

morphology of the coating was investigated using scanning electron microscope (SEM)

operating at 20 KV. Ag nanoparticle content within the coated film was determined using the

energy dispersive spectroscopy (EDS) analysis technique. X-ray diffraction (XRD) profile from

the electrodeposits was obtained using X-pert pro X-ray diffractometer employing a Cu Kα

radiation (λ = 0.1540 nm) source. The average size and size distribution histogram of the as-

synthesized Ag nanoparticles was determined from the analysis of transmission electron

microscopy (TEM) bright field images of as-synthesized nanoparticles acquired on JEOL 2000

FX-II TEM. The electrochemical corrosion studies were carried in a conventional three electrode

glass cell. A saturated calomel electrode (SCE) and a platinum foil served as the reference and

counter electrodes respectively. Pure Zn and Zn-Ag coated specimens with 1 cm2 exposed area

were used as working electrode. Before each measurement, the working electrode was immersed

in 3.5% NaCl for 15 min to attain the steady state potential or open circuit potential (OCP). The

polarization curves were measured at the potential ±200mV against OCP of the respective

working electrode using CHI 640 electrochemical workstation. The electrochemical impedance

spectroscopic (EIS) behavior of coatings is analyzed using Solartron equipment. The EIS

response of the coatings was measured at their OCP and the sinusoidal signal amplitude of 5 mV

was employed with an AC frequency range from 100 KHz to 10 mHz at 10 points per decade.

The measured EIS data were curve fitted and analyzed by using ZSimpWin 3.21 software. The

immersion test or weight loss measurements were performed by immersing the Zn and Zn-Ag

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

6

composite coating specimens of 2 X 3.5 cm2 area in glass beakers containing 100 ml of 3.5 %

NaCl solution at room temperature. After every 12 hour the immersed specimens were taken out

and washed with distilled water. The specimens were then dried and weighed accurately using

digital balance to determine the corrosion rate. All the experiments were repeated to confirm the

reproducibility of results.

3. Results and Discussion

3.1. Characterization

XRD profile for the as-synthesized silver nanoparticles is shown in Fig. 1(a). The

diffraction peaks at 2θ values of 38.12º, 44.31º, 64.60º and 77.41º corresponds respectively to (1

1 1), (2 0 0), (2 2 0) and (3 1 1) planes of face centered cubic structure of silver (JDPDS card

number 03-0921). Average particle size for the Ag nanoparticles obtained from the XRD profile

and the Scherrer formula [24] was 23 nm. Size distribution histogram for as-synthesized Ag

nanoparticles is shown in Fig. 1(b). Insert in Fig. 1(b) is a representative TEM bright field image

of the as-synthesized Ag nanoparticles. It can be observed from Figure 1(b) there exists a large

distribution in particles sizes in the as-synthesized nanoparticle dispersion. Sizes of the majority

of particles, however, are in agreement with the average size obtained from the Scherrer analysis.

A non agreement in case of particles in the large size range indicates a polycrystalline nature for

the large sized particles.

Zeta potential and PSD measurements are important parameters used to characterize the

behaviour of suspended particles in the plating electrolyte [12, 25]. In this work, Zeta potential

and PSD measurements were carried for all composite coating electrolyte baths i.e., B1, B2 and

B3 (Table 1) and also for as-synthesized silver nanoparticles in aqueous media. Silver

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

7

nanoparticles dispersed in aqueous media showed surface charge of -0.176 mV, but the particles

dispersed in zinc plating bath acquired positive surface charge i.e.,+0.428mV, +1.7mV and

+1.78mV for Ag particles in B1, B2 and B3 plating baths respectively . The inversion in surface

charge of the Ag nanoparticles may due to the adsorption of Zn2+

ions and cationic surfactant

CTAB on the surface of the Ag nanoparticles. The zeta potential of the dispersed silver particles

increased with increase in particle concentration in the plating bath. The positive surface charge

on Ag particles would mean that the dispersed Ag nanoparticles possessed normal tendency to

move towards cathode and embed within the growing zinc film. The PSD analyses provided

important information regarding the extent of agglomeration of the nanoparticles in the plating

bath. In the plating bath B1 the maximum size of Ag nanoparticles agglomerate was around

320.4 nm and it slightly increased to 364.5 nm in B2 and still larger clusters of around 408.3 nm

were noticed in B3 plating solution. It can be seen that, an increase in the Ag nanoparticles

concentration in the plating electrolyte increased the particle agglomeration tendency. Increase in

the affinity to form agglomerates can be due to high surface energy and increased interactions

between the nanoparticles.

Ag content in the composite coatings was determined by SEM-EDS analysis. Volume

percent of Ag nanoparticles in the deposit is given in Table 2. It can be observed from Table 2

that the amount of Ag nanoparticles embedded into zinc matrix increased with increase in the

concentration of Ag nanoparticles in the electrolyte. This is due to the increase in particle

concentration and zeta potential of the particles. However it was noticed that, the deposit ZAg3

has same amount of Ag content as was observed in ZAg2 deposit, this may due to the fact that

the dispersed Ag particles in bath B2 and B3 exhibited similar zeta potential values.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

8

SEM micrographs corresponding to Zn and Zn-Ag composite coatings are given in Fig.

2. The SEM images show randomly oriented hexagonal zinc platelets. It can be seen from Fig.

2 that a large number of pores are present in the pure Zn deposit as compared to the composite

coatings which exhibit relatively compact and uniform morphology. This implies that, during the

electrodeposition process the nanoparticles dispersed in the plating bath inhibit the formation of

pores in the growing metal matrix. It can also be observed in Fig. 2 that in the case of deposit

ZAg3 large cavities are present which it is due to the relatively higher agglomeration of Ag

nanoparticles in the B3 plating bath as revealed from the PSD analysis. During the

electrodeposition process the electrolyte bath was vigorously stirred which may have caused the

bigger nanoparticle agglomerates formed in the B3 bath to hit the coating surface and create

surface heterogeneities.

To discover the effect of Ag nanoparticles on the average crystallite size and orientation

of zinc crystals, XRD patterns were obtained for pure Zn and Zn-Ag composite coatings and are

provided in Fig. 3. The observed diffraction peaks corresponded to the zinc hexagonal crystal

structure (JCPDS card number. 04-0831). The average crystallite size (S) of the coatings

calculated using the Scherrer equation [24] are given in Table 2. From the Table 2 it can be seen

that the inclusion of silver nanoparticles does not have any appreciable effect on the grain size of

the deposit. Texture co-efficient calculations were made using the Eq (1) [26] for all the XRD

profiles presented in Fig. 3. The determined texture co-efficient values are plotted in Fig. 4.

------------------------------- (1)

Where, Tc(hkl) is the Texture coefficient; I(hkl) is Peak intensity of the zinc electrodeposits

(hkl)I

(hkl)I

I(hkl)

I(hkl)(hkl)T

o

o

c

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

9

∑I(hkl) - Sum of intensities of the independent peaks and the index ‘o’ refers the intensities for

the standard zinc sample.

The plot in Fig. 4 reveals that in pure Zn deposit orientation of the zinc crystals is

dominated in (1 1 0) plane, however it is changed to (1 0 0) plane after the inclusion of Ag

nanoparticles into the zinc matrix. This result confirms that the silver nanoparticles influence the

morphology and microstructure of the deposit. The literature also contains reports on the

alteration in preferred orientation of the deposit due to inclusion of nanoparticles into the

growing metal matrix [5, 14]

3.2. Electrochemical corrosion studies:

The electrochemical corrosion analysis was carried out in order to correlate the quality of

Zn-Ag composite coatings with respect to pure Zn coating.

3.2.1. Tafel polarization:

To investigate the influence of Ag nanoparticles on the corrosion behavior of zinc

deposit, polarization measurements were carried out in a potential range of ±200mV from OCP

using 3.5% NaCl as corrosion media. The Tafel plots of pure Zn and Zn-Ag composite coatings

are given in Fig. 5. The electrochemical corrosion characteristics such as Corrosion potential

(Ecorr), Corrosion current (Icorr), Corrosion Rate (CR), anodic and cathodic slopes (βa and βc)

obtained from the potentiodynamic polarization curves are tabulated in Table 3. The results

reveal that except ZAg3 deposit, the corrosion potential of Zn-Ag composite coatings is more

positive and corrosion current and corrosion rate also lower than that of pure Zn coating. In

particular the deposit ZAg2 had shown better corrosion resistance by exhibiting least Icorr and

corrosion rate compared to other deposits. The anodic and cathodic Tafel co-efficient values

obtained for composite coatings were different from that of pure Zn coating, this indicates that

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

10

the presence of Ag nanoparticles in zinc matrix influence the kinetics of both anodic and

cathodic electrochemical reactions. The better corrosion resistance of Zn–Ag composite coatings

can be due to the fact that the presence of Ag nanoparticles minimizes the defects in the

composite coating. These defects, if present, act as active sites for corrosion. Also, the uniformly

distributed silver nanoparticles in the deposit behave as passive layer between corrosive media

and the deposit surface. The deposit ZAg3 (deposit obtained by the bath loaded with highest

amount Ag nanoparticles) however showed meager protection towards aggressive media as

compared to ZAg1 and ZAg2 composite coatings. The acceleration of the corrosion process for

ZAg3 can be because of the chemical heterogeneities created in the metal matrix due to non

uniform distribution of agglomerates of silver nanoparticles, as observed in the SEM image of

ZAg3 deposit.

3.2.2. EIS:

In this work electrochemical impedance measurements were carried out for all coatings at

their OCP in the frequency range of 100kHz to 10mHz with sinusoidal signal amplitude of 5mV.

The measured impedance spectra for pure Zn and Zn-Ag composite coatings are depicted as

Nyquist plot in Fig. 6(a) and as bode plots in Fig. 6(b).

The Nyquist plots show that the width of the capacitive loop corresponding to composite

coatings (except for ZAg3) are larger than that of pure Zn coating, implying that the composite

coatings exhibit better resistance to corrosion process. Also it can be seen that the measured

curves consists of three capacitive loops, which means that during corrosion process three

relaxation steps were taking place and these are well resolved in the Bode plot. To get the

electrochemical impedance parameters, the Nyquist plots were curve fitted with suitable

electrical equivalent circuit (EEC) which is given in Fig. 7 and the parameters are tabulated in

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

11

Table 4. To obtain more accurate fitting results the middle and low frequency capacitance

element C was replaced with the constant phase element (CPE). The impedance of CPE is

defined as

Z(jω) = (Q)-1

(jω)-n

Where Q is the CPE constant, j is the imaginary unit, ω is the angular frequency (ω=2πf, f

is the frequency) and n is the CPE exponent (where ‘Q’ and ‘n’ are frequency independent

parameters). The value of ‘n’ leys between -1 and 1 (i.e., -1≤n≤1), for ideal capacitor n = 1, for

ideal inductor n = -1, if n = 0 the CPE is ideal resistor [27, 28].

The contribution of each element in the used EEC is as follows [14, 29].

Re: is the electrolyte resistance appeared between the reference electrode and the surface of the

coated specimen. i.e., working electrode.

The high frequency contribution (Cd – Rd) is ascribed to the dielectric character of the

thin surface layer formed from the corrosion products (Cd) and its electrical leakage from ionic

conduction through its pores (Rd).

The medium frequency contribution is attributed to the double layer capacitance (Qdl) at

the electrolyte / coated surface (Zn and Zn-Ag) interface at the bottom of the pores coupled with

the charge transfer resistance (Rct). This charge transfer resistance is closely related to corrosion

rate.

The low frequency couples (QF - RF) may be related to a redox process taking place at the

surface likely involving the thin layer of corrosion products accumulated at the electrolyte /

working electrode interface.

The simulated statistics revealed better coincidence with the experimental data in spite of

the approximation made as shown in Nyquist plots. The tabulated data reveal that, the

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

12

contribution of high and low frequency couple Rd-Cd and RF-QF is minimum, meaning that there

is no much corrosion products formed on the working electrode during immersion and

measurement time. Therefore the charge transfer resistance is the factor that is closely related to

the corrosion rate. The coating ZAg1 and ZAg2 showed higher charge transfer resistance with

minimum double layer capacitance showing that the incorporated Ag nanoparticles decreased the

electroactive surface area by inducing compactness to deposit and forming passive layer on the

surface by uniform distribution. The total polarization resistance value was calculated by adding

Rd, Rct and RF values. The composite coating ZAg2 showed higher Rp value than other coatings.

The three capacitive loops which were observed in Nyquist plot are well resolved in Bode

plots. The impedance modulus Vs frequency plot shows that impedance modulus value of

the coatings ZAg1 and ZAg2 are greater than that of Z and ZAg3 coatings value, and it

obeyed the trend obtained from polarization and Nyquist plot analysis.

3.2.3. Weight loss measurements:

Fig. 8 shows the corrosion rate of Zn and Zn-Ag composite coating samples immersed in

3.5% NaCl solution for 48 hours. The corrosion rate or corrosion velocity of the coatings was

calculated by using Eq (2). Increase in corrosion rate was observed for all coating, but the extent

of increase was minimum for ZAg1 and ZAg2 coatings compared to Z and ZAg3 coatings. As

noticed in electrochemical corrosion analysis, weight loss measurement data also confirms that

the ZAg1 and ZAg2 composite coatings exhibit significant resistance towards corrosive media as

compare to pure Zn and ZAg3 composite coating.

------------------------------- (2)

Where Δm is the weight loss in mg, S is the area in cm2 and ‘t’ is the immersion period in hour.

St

mW

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

13

The result shows that the change in morphology and microstructure of zinc deposit due to

the incorporation of Ag nanoparticles improved the corrosion resistance of zinc coating for ZAg1

and ZAg2 cases. Whereas, the chemical and morphological heterogeneities in the deposit Z and

in composite coating ZAg3 accelerated the corrosion process. The SEM images given in Fig. 9

show the surface morphology of pure Zn and Zn-Ag composite coatings after 48hr immersion in

3.5 % NaCl solution. The deposit Z and ZAg3 shows highly deteriorated surface compared to

ZAg1 and ZAg2. After the corrosion process large numbers of cavities are observed on the

coatings except ZAg2. These pits will expose the substrate to the electroactive media and

accelerate the dissolution of zinc layer by making the mild steel substrate a cathode. Uniform

corrosion was, however, observed on ZAg2 composite coating; it may due to the defect free

nature of the deposit. This confirms that an optimum concentration of Ag nanoparticles in zinc

plating bath will lead to improved surface morphology and microstructure of the zinc deposit

along with desired electrochemical properties. The present work clearly illustrates that the

corrosion resistance of composite coatings is primarily due to the fact that the Ag nanoparticles

in the film minimizes the film defects which are active sites for corrosion. Furthermore, it is also

speculated that silver nanoparticles which may be present on the matrix surface behave as

passive sites inhibiting electrochemical interaction between the corrosive media and the

composite deposit.

Conclusion:

In the present work, the Zn-Ag composite coatings were fabricated by using chemically

synthesized Ag nanoparticles with an average size of 23 nm. A more compact nature and change

in preferred orientation [from (1 1 0) to (1 0 0) plane] was observed for composite coatings as

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

14

compared to pure Zn coating. Meanwhile, the chemical heterogeneities were observed on the

surface of ZAg3composite coating, it may due to the non uniform distribution of agglomerated

Ag nanoparticles in the metal matrix. The change in morphology and microstructure of the zinc

deposits influenced the corrosion behavior of the coatings as confirmed by weight loss

measurement, Tafel polarization and Electrochemical Impedance analysis. The composite

coatings ZAg1 and ZAg2 showed better resistance towards aggressive media. In particular,

doubled polarization resistance (Rp) with half reduced double layer capacitance (Cdl) and

corrosion rate values were observed for the deposit ZAg2 when compare to pure Zn coating. On

the other hand, defects on the surface of ZAg3 composite coating may have lead to accelerated

corrosion process which is confirmed by electrochemical and SEM analysis. This work, using a

specific example of Zn-Ag composite coating, revealed that during the composite coating

process an optimum particles concentration in the electrolyte is necessary for fabrication of

composite coatings with improved electrochemical properties.

Acknowledgements:

Authors thank to Dept. of Materials Engineering, Indian Institute of Science (IISc.) for

providing the laboratory facilities to bring about this work. Research funding from Joint

Advanced Technology Program (JATP), Indian Institute of Science, Bangalore, India is deeply

acknowledged. The authors deeply acknowledge the facilities available in Professor N.

Munichandraiah laboratory, IPC, Indian Institute of Science, Bangalore and Professor Praveen C

Ramamurthy Laboratory, Materials Engineering, Indian Institute of Science, Bangalore.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

15

Reference:

[1] Shengqiang Ma, Jiandong Xing, Dawei Yi, Hanguang Fu, Guofeng Liu, Shengchao Ma.

Microstructure and corrosion behavior of cast Fe–B alloys dipped into liquid zinc bath.

Mater Charact 2010;61:86-72

[2] Rajappa SK, Venkatesha TV, Praveen BM. Chemical treatment of zinc surface

and its corrosion inhibition studies. Bull Mater Sci 2008;31:37-41.

[3] Tolumoye J. Tuaweri, Wilcox GD. Behavior of Zn-SiO2 electrodeposition in the presence

of N,N-dimethyldodecylaine. Surf Coat Technol 2006;200:5921-30.

[4] Gomes A, da Silva Pereira MI. Zn electrodeposition in the presence of Surfactants Part I.

Voltammetric and structural studies. Electrochim Acta 2006;52:863-71.

[5] Nayana KO, Venkatesha TV, Praveen BM, Vathsala K. Synergistic effect of

additives on bright nanocrystalline zinc electrodeposition. J Appl Electrochem 2011;41:

39-49.

[6] Fustes J, Gomes A, da Silva Periera MI. Electrodeposition of Zn-TiO2 nanocomposite

films-effect of bath composition. J Solid State Electrochem 2008;12:1435-43.

[7] Tabrisur Rahman Khan, Andreas Erbe, Michael Auinger, Frank Marlow and Michael

Rohwerder. Electrodeposition of zinc-silica composite coatings: challenges in

Incorporation functionalized silica particles into a zinc matrix. Sci Technol Adv Mat.

2011;12:1-9.

[8] Panagopoulos CN, Georgiou EP, Gavras AG. Composite zinc-fly ash coating on mild

steel. Surf Coat Technol 2009;204:37-41.

[9] Praveen BM, Venkatesha TV, Arthoba Naik Y, Prashantha K. Corrosion studies of

carbon nanotubes–Zn composite coating. Surf Coat Technol 2007;201:5836–42.

[10] Giovanni Bolelli, Roberto Giovanardi, Luca Lusvarghi, Tiziano Manfredini. Corrosion

resistance of HVOF-sprayed coatings for hard chrome replacement. Corros Sci 2006;48:

3375–97.

[11] Frade T, Bouzon V, Gomes A, da Silva Pereira MI. Pulsed-reverse current

electrodeposition of Zn and Zn-TiO2 nanocomposite films. Surf Coat Technol 2010;204:

3592-8.

[12] Vathsala Kanagalasara, Thimmappa Venkatarangaiah Venkatesha. Studies on

electrodeposition of Zn–MoS2 nanocomposite coatings on mild steel and its properties.

J. Solid State Electrochem. 2012;16:993-01.

[13] Praveen Kumar CM, Venkatesha TV, Chandrappa KG. Effect of surfactants on co-

deposition of B4C nanoparticles in Zn matrix by electrodeposition and its corrosion

behavior. Surf Coa. Technol 2012;206:2249-57.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

16

[14] Adriana Vlasa, Simona Varvara, Aurel Pop, Caius Bulea, Liana Maria Muresan.

Electrodeposited Zn-TiO2 nanocomposite coatings and their corrosion behavior. J

Appl Electrochem 2010;40:1519-27.

[15] Virender K. Sharma, Ria A. Yngard, Yekaterina Lin. Silver nanoparticles: Green synthesis

and their antimicrobial activities. Adv Colloid Interfac 2009;145: 83–96.

[16] Valentina A. Litvin, Boris F. Minaev. Spectroscopy study of silver nanoparticles

fabrication using synthetic humic substances and their antimicrobial activity.

Spectrochi Acta Part A: Molecular and Biomolecular Spectroscopy 2013;108:115-22.

[17] Ghosh S, Kaushik R, Nagalakshmi K, Hoti SL, Menezes GA, Harish BN,

Vasan HN. Antimicrobial activity of highly stable silver nanoparticles embedded in agar–

agar matrix as a thin film. Carbohyd Res 2010;345:2220-7.

[18] Maribel Guzman, Jean Dille, Stéphane Godet. Synthesis and antibacterial activity of silver

nanoparticles against gram-positive and gram-negative bacteria. Nanomed-Nanotechnol

2012;8:37-45.

[19] Dongwei Wei, Wuyong Sun, Weiping Qian, Yongzhong Ye, Xiaoyuan Ma. The synthesis

of chitosan-based silver nanoparticles and their antibacterial activity. Carbohyd Res

2009;344:2375-82.

[20] Antariksh Saxena, Tripathi RM, Fahmina Zafar, Priti Singh. Green synthesis of silver

nanoparticles using aqueous solution of Ficus benghalensis leaf extract and

characterization of their antibacterial activity. Mater Lett 2012;67:91-4.

[21] Hongfang Maa, Fang Tian , Dan Li, Qiang Guo. Study on the nano-composite electroless

coating of Ni–P/Ag. J Alloy Compd 2009;474:264–67.

[22] Alirezaei S, Monir Vaghefi SM, Urgen M, Saatchi A, Kazmanli K. Novel investigation

on nanostructure Ni–P–Ag composite coatings. Appl Surf Sci 2012;261:155-58.

[23] Alirezaei S, Monirvaghefi SM, Saatchi A, Urgen M, Kazmanl K. Novel investigation on

tribological properties of Ni–P–Ag–Al2O3hybrid nanocomposite coatings. Tribol Lett

2013;62:110-16.

[24] Patterson AL. The Scherrer Formula for I-Ray Particle Size Determination. Physical

Review 1939;56:978-82.

[25] Azizi M, Schneider W, Plieth W. Electrolytic co-deposition of silicate and mica

particles with zinc. J Solid State Electrochem 2005;9:429–37.

[26] Mouanga M, Ricq L, Douglade J, Berçot P. Corrosion behaviour of zinc deposits

obtained under pulse current electrodeposition: Effects of coumarin as additive.

Corros Sci 2009;51:690–8.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

17

[27] Jan Macak, Petr Sajdl, Pavel Kucera, Radek Novotny, Jan Vosta. In situ electrochemical

impedance and noise measurements of corroding stainless steel in high temperature

water. Electrochim Acta 2006;51:3566-77.

[28] Mishra AK, Balasubramaniam R, Tiwari S. Corrosion inhibition of 6061-SiC by rare

earth chlorides. Anti-Corros Method M 2007;54/1:37-46.

[29] Kinlen PJ, Silverman DC, Jeffreys CR. Corrosion Protection Using Polyaniline Coating

Formulations. Synth Met 1997:85:1327-32.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

18

Fig. 1(a) - XRD pattern of chemically synthesized silver nanoparticles.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

19

Figure 1(b): Size distribution histogram for as-synthesized Ag nanoparticles. Insert is a

representative bright field TEM image of as-synthesized nanoparticles.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

20

Fig. 2 - SEM micrographs of as prepared zinc and Zn-Ag composite coatings surface. The

white arrow points out a representative heterogeneity in the ZAg3 composite coating.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

21

Fig. 3 - XRD patterns of zinc and Zn-Ag composite coatings.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

22

Fig. 4 - Preferred orientation of zinc crystallites in zinc and Zn-Ag composite coatings.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

23

Fig. 5 - Tafel polarization curves v/s SCE for zinc and Zn-Ag composite coatings recorded

in 3.5% NaCl solution with respect to SCE.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

24

Fig. 6 - Electrochemical Impedance (a) Nyquist & (b) Bode plots v/s SCE corresponds to

pure Zn and Zn-Ag composite coatings recorded in 3.5% NaCl solution with

respect to SCE. (Inset in Fig. 6(a) shows the capacitive loop at higher frequency

range)

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

25

Fig. 7 - Electrical Equivalent Circuit (EEC) used to fit EIS data.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

26

Fig. 8 - Variation of the corrosion rate with immersion time for Zn and Zn- Ag coated

samples in 3.5% NaCl solution.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

27

Fig. 9 - SEM micrographs of zinc and Zn-Ag composite coatings surface after 48 hour

immersion in 3.5% NaCl corrosive media.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

28

Table 1 - Plating bath composition and operating parameters.

Bath Constituents Concentration in g/l Deposit code Operating parameters

Basic ZnSO4 220 Z Anode: Zinc plate

bath Na2SO4 11 Cathode: Mild steel plate

(BB) H3BO3 9 Current density: 0.04 A cm-2

CTAB 0.05 Plating time: 10 min

B1 Ag nanoparticles +BB 0.5 ZAg1 pH:3

B2 Ag nanoparticles +BB 1.0 ZAg2 Temperature: 27 ± 2 C

B3 Ag nanoparticles +BB 1.5 ZAg3

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

29

Table 2 - ‘Ag’ volume percent in composite coatings and average crystallite size (S) of the

deposits.

Sample Vol% S

Z 56.45

ZAg1 1.95 65.74

ZAg2 2.24 56.57

ZAg3 2.24 57.08

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

30

Table 3 - Corrosion parameters derived from potentiodynamic polarization curves.

Sample Ecorr

V Icorr

µA/cm2

βa

V-1

βc V

-1

CR µg/hr

Z -1.077 13.16 18.83 5.61 16.06

ZAg1 -1.059 8.057 22.13 5.17 9.828

ZAg2 -1.054 6.804 31.14 6.66 8.299

ZAg3 -1.098 11.51 19.45 7.57 14.04

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

31

Table 4 - Electrochemical parameters drawn from EEC simulated EIS plots.

*Rp = (Rd + Rct + RF)

Sample Cd in

μF cm-2

Rd in

Ω cm2

Qdl in10-6

(Ω-1

cm-2

S-n

) ndl Rct in

Ω cm2

QF in 10-3

(Ω-1

cm-2

S-n

) nF RF in

Ω cm2

*Rp in Ω cm

2

Z 0.240 7.059 48.18 0.885 447.3 2.649 0.842 105.5 559.8

ZAg1 0.197 8.428 32.65 0.872 595.1 6.510 0.969 130.4 733.9

ZAg2 0.304 3.747 19.37 0.931 794.1 0.865 0.892 395.4 1193.2

ZAg3 0.267 6.335 34.98 0.864 389.5 2.827 0.826 78.48 474.3

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

32

Highlights:

Synthesis of Ag nanoparticles with an average size of 23nm.

Fabrication of Zn/nano Ag composite coating on mild steel.

Composite coatings showed better corrosion resistance.

Optimization of particles concentration is necessary.