Surfactants Effect on ZnâSi3N4 Coating, Electrochemical Properties

Article pubs.acs.org/IECR

Surfactants Effect on Zn−Si3N4 Coating, Electrochemical Properties, and Their Corrosion Behaviors Praveenkumar C. Mohankumar and Venkatarangaiah T. Venkatesha* Department of P.G. Studies and Research in Chemistry, School of Chemical Sciences, Kuvempu University, Shankaraghatta-577451, Karnataka, India ABSTRACT: The effect of sodium dodecyl sulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB) on electrodeposited Zn-Si3N4 composite coating, on a mild steel substrate, was examined. The cathodic polarization and cyclic voltammetric techniques were adopted to understand the role of surfactants. The structure and morphology of the coatings were studied by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray analysis. The influence of Si3N4 and surfactants on the preferred orientation of Zn was examined on X-ray diffraction data. The nucleation mechanism of Zn and the Zn+Si3N4 composite in the presence of SDS and CTAB was examined. The corrosion resistance properties of Zn and Zn−Si3N4 coatings were measured.

1. INTRODUCTION The zinc coated ferrous materials are extensively used in industries because of their higher corrosion resistance.1 However, their application is limited due to the formation of corrosion products known as white rust in aggressive environments like those with high temperature, pH, and humidity.2 In order to enhance the corrosion resistance of zinc coatings, Zn-based alloy coatings containing metals such as Ni, Co, and Fe have been developed.3 Another option is to plate Zn-based composite coatings on steel. The Zn coatings containing nanosized metal oxides, carbides, nitrides, and sulfide particles show improved corrosion resistance, wear resistance, self-lubrication, high-temperature stability, and unique magnetic, mechanical, and optical properties.4 Among the various methods of producing metallic nanocomposite coatings, electrodeposition is regarded as one of the most convenient techniques. In this method, the coating characteristics are influenced by the deposition parameters, namely current density, type of applied current (pulsed or direct), bath composition, pH, particle concentration, type of particle, surfactants, and temperature.5,6 Out of these process parameters, the type of particle to be codeposited and the nature and concentration of surfactants play a major role in the nanocomposite electrodeposition. Normally surfactants are used in order to change surface charge of the particles and to decrease their tendency of agglomeration in the electrolyte. Anionic surfactants generally inhibit the formation of pin holes in the metal matrix and may combine with metal ions to form its complexes. On the other hand, a cationic surfactant can promote codeposition of hydrophobic particles such as PTFE, SiC, MoS2, and carbon nanotubes and increase the uniform distribution of particles in the composite coating.7,8 Several authors have studied the effect of surfactants in the codeposition of nanosized particles in different matrices (Ni, Ni−P, Zn, etc.). Ewa et al. evaluated the effect of CTAB on the electrodeposition of nickel/SiC composites and concluded that CTAB inhibits the cathodic process, but the polarization was slightly affected by its concentration. This results in a fine grained nickel matrix of the composite deposits characterized with high microhardness.9 Malfatti et al. studied the effect of © 2013 American Chemical Society

cationic and anionic surfactants in NiP−SiC composite coatings. The effect of surfactant on grain size and texture of electrodeposited coatings was also investigated.10 Shirani et al. studied the surfactant effect on the electrochemical behavior of CoTiO2 nanocomposite coatings and determined that coatings from SDS containing solution has high corrosion resistance with lesser grain size compared to the composite coatings obtained from CTAB.11 Pignolet et al. electrodeposited the latex particles in the presence of surfactant and investigated the deposit morphology and concluded that the formation of the aggregates was reversible, and their morphologies were strongly dependent on the kind of counterion. Aggregates formed in CTAB solution were dense, while more open structures were observed with CTAC (cetyl trimethyle ammonium chloride).12 Rajan et al. investigated the influence of surfactant sodium dodecyl sulfate (SDS) in the codeposition of nano sized CeO2 to nickel matrix and have found that the concentration of surfactant up to 0.1 g L−1 increased the inclusion of CeO2 particles in the nickel matrix and imparted higher micro hardness.13 Tabrisur et al. studied the challenges in the incorporation of functionalized silica particles into a Zn matrix by electrodesition techniques and reported that the best incorporation was achieved for particles with modified SiO2−SH, dithioxamide, or cysteamide compared to the other modifications (SiO2−NH3+, SiO2−Cl, and N,Ndimethyl dodecylamine).14 Wang and others investigated the microstructure and fracture characteristics of Mg−Al−Zn− Si3N4 composites and inferred that when the volume fraction of reinforcement is not in excess of 6 wt %, the composite had an improved fracture toughness.15 Silicon nitride has good material properties such as low density, high hardness, high fracture toughness, and excellent strength over a wide range of temperatures, good thermal shock, and chemical resistance. In addition Received: Revised: Accepted: Published: 12827

September 17, 2012 June 25, 2013 July 25, 2013 July 25, 2013 dx.doi.org/10.1021/ie302525r | Ind. Eng. Chem. Res. 2013, 52, 12827−12837

Industrial & Engineering Chemistry Research

Article

with distilled water. The anode was activated by dipping it in 10 wt % dilute HCl solution for a few seconds, washed with water, and then placed in a bath solution. The deposits obtained from the respective bath solution of Table 1 were designated as C0, Cs, Cc, Csp, and Ccp. After the electrodeposition, the coatings were washed, dried, and then used for further studies. The cathodic polarization and cyclic voltammetric measurements were undertaken using a disc of mild steel with an area of 0.077 cm2 as the working electrode. The measurements were made for plating bath solutions with and without Si3N4 particles. The reference and counter electrodes used in the present study were calomel and platinum, respectively. The surface morphologies of samples were observed using a scanning electron microscope (SEM; JEOL-JEM-1200-EX II) equipped with an attachment for energy dispersive X-ray spectrometry (EDAX) analysis. X-ray diffraction (XRD) patterns were obtained using an X-ray diffractometer (PANalytical X′ pert propowder diffractometer) with Cu Kα radiation (λCu = 1.5418 Å), works at 30 mA and 40 KV. The hardness of the coatings was measured in the “Clemex Microhardnes Tester,” an instrument made in Japan, using a Vickers diamond as the indenter at a load of 50 and 100 g for a loading time of 5 s. The average value of five indentations was recorded. The chronoamperometry test was performed at deposition potentials of −1.3900, −1.4630, −1.4300, −1.3420, and −1.4190 V for the bath solutions C0, Cs, Cc, Csp, and Ccp, respectively. The corrosive media used for the weight loss measurement of Zn and Zn composite coatings were 3.5 wt % NaCl solutions. These solutions were prepared with analytical grade chemicals and distilled water. For the weight loss measurements, the Zn and Zn−Si3N4 composite coated specimens (coated on both sides of the specimens) obtained in the presence of SDS and CTAB were immersed in a beaker containing 100 mL of 3.5 wt % NaCl solution separately. The test was performed under unstirred conditions at room temperature for a period of 960 h. The mass loss of the specimens was measured at different intervals of time. The mass of the specimens before and after immersion was determined using an analytical balance (Anamed Instruments (p) Ltd.), and the corrosion rate (r) was calculated from the following equation:

to this, it also possesses excellent wear resistance and antifriction properties.16,17 From a study of earlier literature, it came to be known that no work has been carried out on the effect of surfactants (anionic or cationic) on Zn−Si3N4 composite electrodeposition. The aim of this work is to study the effect of surfactant on the Zn− Si3N4 electrodeposition process, nucleation mechanism, and characterization and their corrosion behavior. Hardness of the deposit was also measured.

2. EXPERIMENTAL DETAILS Analytical grade chemicals [from Himedia AR, Mumbai] and Millipore water [Elix Pvt. Ltd., USA] were used in all experiments. The Si3N4 nanoparticles were purchased from Sigma Aldrich and used as is. The compositions of the bath solutions are given in Table 1 and were used for the electrodeposition Table 1. Constituents of Bath Solutions C0 (g L−1)

Cs

Cc

Csp

Ccp

C0 + CTAB C0 + SDS + C0 + CTAB + ZnSO4-200 C0 + SDS (0.05 g L−1) (0.05 g L−1) Si3N4 (1 g L−1) Si3N4 (1 g L−1) Na2SO4-40 H3BO3-8

experiments. The concentration of surfactants and the Si3N4 particles were selected from the Hull Cell studies.2 Figure 1 shows the XRD and SEM pattern of Si3N4 powder used in the study. The mean crystallite size calculated from the XRD data using the Schrrer equation was 40 nm. And the hkl values match the JCPDS file of Si3N4 particles (JCPDS card no 41-0360). In SEM images, agglomerated particles are shown. The Zn and Zn−Si3N4 composite coatings were generated on mild steel plates from the bath solutions of Table 1. The pH of bath solutions was adjusted to 3 with dilute sulfuric acid or sodium bicarbonate solution. Deposition was carried out at a current density of 4 A dm−2 for about 20 min with a 300 rpm stirring speed, and the temperature of bath solution was 28 ± 2 °C. Prior to composite coating, the bath solution was stirred using a magnetic stirrer at 600 rpm for about 24 h and subsequently via ultrasonic agitation for 30 min. Zn metal plate of 99.99 wt % (anode) and steel plates of 4 × 5 × 0.1 cm (cathode) were employed. Prior to deposition, mild steel plates were mechanically polished with different grades of emery paper, degreased in vapors of trichloroethylene and washed

r=

⎛ m1 − m2 ⎞ ⎜ ⎟ ⎝ s×t ⎠

(1)

Figure 1. (a) XRD pattern and (b) SEM image of Si3N4 particle. 12828

dx.doi.org/10.1021/ie302525r | Ind. Eng. Chem. Res. 2013, 52, 12827−12837


Article

where m1 is the mass of the specimen before corrosion, m2 is the mass of the specimen after corrosion, S is the total area of the specimen, t is the corrosion time, and r is the corrosion rate. The potentiodynamic polarization and electrochemical impedance measurements were performed using a conventional three electrode cell, wherein calomel and platinum wire were reference and counter electrodes, respectively. The working electrodes were pure Zn and Zn composite coated samples with an exposed surface area of 1 cm2. The working electrodes were immersed in 3.5 wt % NaCl corrosive media while carrying the electrochemical measurement.

corresponds to the bath solution Cs, which contains C0 and SDS, and in this, Zn deposition occurs at −1.1021 V, which is more negative than C0 (−1.0833 V). This infers that the presence of SDS in the bath solution slightly influenced the Zn (Zn2+ → Zn) deposition potential . Curve c for Cc (C0+CTAB) has a deposition potential of −1.1772 V, which is greater than those of C0 and Cs. This suggests that CTAB influences greatly the Zn deposition relative to SDS. Curves d and e represent the polarization behavior of Csp and Ccp, respectively. These bath solutions contain both the Si3N4 and surfactants, which shows the Zn deposition potentials −1.1541 and −1.2355 V. Among all the Zn deposition potential, s Ccp shows the higher deposition potential compared to C0, Cs, Cc, and Csp (−1.0883, −1.1021, −1.1772, −1.1541 V).18 The zeta potential of the Si3N4 particles in aqueous solution at a pH between 0 and 4 is 30 to 35 mV in the presence of the anionic surfactant SDS. The Si3N4 particles exhibit a negative charge on it, and they will be repelled from the deposition on cathode material, which leads to lesser particle incorporation into the deposit. But in the case of CTAB, the positive charge on the surfactant chain will induce its charge on the particle, because of the presence of opposite charges present on the particle, and in the vicinity of the cathode, the Si3N4 particles will incorporate into the Zn deposition. Hence we can observe a higher shift in the cathodic polarization of the Ccp. From the above observations in the deposition potential of bath solutions, it came to be known that C0 has less −ve potential for the deposition of Zn but is greater for Cs and Cc and is more negative for Csp and Ccp. This shows that the presence of particles along with the surfactants will greatly influence the deposition mechanism.19 3.1.2. Voltammetric Analysis. Cyclic voltammograms were recorded for the bath solutions C0, Cs, Cc, Csp, and Ccp to know the effect of surfactants (anionic and cationic) and Si3N4 particles on the deposition mechanism. The voltammograms are shown in Figure 3. The voltammograms were recorded in the potential range between −0.2 and −1.8 V, which consists of two regions, that is, anodic and cathodic regions. The anodic part will lie between −0.5 and −1.1 V, and the cathodic region i sfrom −1.2 to −1.7 V. The peak currents and peak potentials of the both anodic and cathodic curves are given in Table 2. The anodic part of the voltammograms of Cs

3. RESULTS AND DISCUSSION 3.1.1. Influences of Surfactants on Cathodic Polarization. To study the effect of Si3N4 particles and surfactants on the reduction process during the electrodeposition, cathodic polarization profiles were recorded for the bath solutions C0, Cs, Cc, Csp, and Ccp and are shown in Figure 2. The potential

Figure 2. Cathodic polarization for the deposition of Zn from different bath solutions.

range selected for the study was −0.4 to −1.6 V. Curve a represents the polarization behavior of Zn deposition from bath solution C0. The deposition of Zn metal begins at −1.0883 V, and after this a sharp decrease in current was noticed. Curve b

Figure 3. Cyclic voltammetric responses for the codeposition of Si3N4 with Zn in the presence of surfactants. 12829



Article

from the bath solution C0, Cs, Cc, Csp, and Ccp following the operating conditions as given in the Experimental Details. The SEM images were recorded for each deposit and are shown in Figure 4. For C0, the SEM image shows hexagonal shaped platelets with random distribution. The deposit Cs displayed a smaller grain size compared to C0. The deposit Cc exhibits a smaller and uniform grain size than C0 and Cs. The coating Cc shows a more porous nature than C0.18 The composite coating obtained from bath solutions Csp and Ccp shows a compact thin zinc film. The coating obtained from Csp was semi-smooth and uniform. Ccp shows a non-uniform distribution of Zn crystals all over the substrate with the lowest grain size compared to C0, Cs, Cc, and Csp coatings. Cross sectional SEM images and the EDAX pattern of composite electrodeposits of Csp and Ccp are shown in Figures 5 and 6, respectively. EDAX analysis was carried out at the cross sections of Csp and Ccp.21 It suggests that Si3N4 particles were successfully incorporated into the Zn matrix. The elemental composition derived from the EDAX spectra (given in Table 3) reveals a higher percentage composition of Si3N4 particles in Ccp than in the Csp deposit. XRD was used to examine the crystal structure and purity of the deposits. Typical XRD patterns of the deposits C0, Cs, Cc, Csp, and Ccp are shown in Figure 7. The diffraction peaks in the diffratogram will identify the peaks as hexagonal structures of the Zn. The peaks in the diffratogram were indexed using

Table 2. Parameters Derived from Cyclic Voltammetric Studies anodic region

cathodic region

solutions

peak current (A)

peak potential (V)

peak current (A) × 10−3

peak potential (V)

C0 Cs Cc Csp Ccp

0.0123 0.0113 0.0129 0.0091 0.0082

−0.6360 −0.6210 −0.6610 −0.7050 −0.7100

−5.90 −6.30 −5.04 −9.12 −8.16

−1.3900 −1.4630 −1.4300 −1.3420 −1.4190

and Csp shows the higher anodic peak current for Csp than Cs. Obviously it indicates a higher dissolution rate of zinc in the Csp composite, inferring its lower corrosion resistance property. In Cc and Ccp, the Ccp (C0+CTAB) has the lowest anodic peak current compared to Cc and to that of C0, Cs, and Csp, indicating that the lower amount of zinc dissolution inferred a better corrosion resistance property of Ccp. In the cathodic region of the cyclic voltammograms, the cathodic potential of Ccp is shifted to a more negative −ve potential (−1.4650) compared to other curves. This negative shift in peak potentials is due to the adsorption of Si3N4 particles on the active sites of the cathode surface.19,20 3.2. Surfactants’ Influence on Composite Coating Morphology. Zinc electrodeposition on mild steel is obtained

Figure 4. Surface morphology of deposits C0, Cs, Cc, Csp, and Ccp.

Figure 5. SEM cross-section image of deposits Csp and Ccp. 12830



Article

Figure 6. EDAX pattern of deposits Csp and Ccp.

⎛ Kλ ⎞ L=⎜ ⎟ ⎝ β cos θ ⎠

Table 3. Showing the Presence of wt % of Different Elements of Deposits Csp and Ccp deposits Csp

Ccp

elements

wt %

Si N Zn Si N Zn

0.22 0.53 99.25 20.75 3.51 75.74

(2)

standard deviation

where L is the average crystallite size, K is the Scherrer constant, λ is the wavelength, β is the full width at half maximum, and θ is the diffraction angle. Average crystallite sizes of the deposits are given in Table 4. These observations inferred that the Zn+Si3N4 composite with the surfactant CTAB has a lesser crystallite size compared to the Zn composite obtained from the bath solution containing SDS +Si3N4. The texture coefficient of the electrodeposits C0, Cs, Cc, Csp, and Ccp were calculated from the XRD data, using eq 3. And the preferred orientations of the deposits were determined using the Muresons method.23,24

0.29

1.02

JCPDS card no. 87-0713. The diffraction lines of the deposit Ccp show low intensity and a broader peak width compared to the peaks of C0, Cs, Cc, and Csp, which identify the lesser crystallite size of the Ccp.22 This was also supported by the crystallite size calculation using the Scherrer equation given in eq 2. 12831



Article

⟨101⟩, respectively. The Csp (B0+SDS+Si3N4) deposit shows preferred orientations in ⟨101⟩ and ⟨102⟩, and Ccp shows ⟨101⟩ and ⟨112⟩. All of these preferred orientations will have the maximum Tc value, indicating the maximum number of crystallographic orientations of the zinc deposit in that plane. It is evident from the above observations that the presence of Si3N4 particles in the bath solution and in the matrix will largely influence the deposit morphology and preferred orientation of the deposit. A similar observation was made by Shirani et al. for Co−TiO2 electrodeposited composite coatings, where they observed lower RTC (Texture Coefficient) values in the (100) and (110) planes, and coatings from CTAB containing electrolytes have a higher RTC for other planes.11 Vickers microhardnesses of the electrodeposits C0, Cs, Cc, Csp, and Ccp are presented in Figure 9. It is observed from the Figure 7. XRD pattern of the deposits C0, Cs, Cc, Csp, and Ccp.

Table 4. Crystallite Size of the Deposits deposits of bath solutions

crystallite size in nm

standard error deviation

C0 Cs Cc Csp Ccp

72.00 25.08 23.08 20.60 19.20

0.8550 0.4410 0.2010 0.2120 0.5330

Tc(hkl) =

I(hkl) ∑ I(hkl)

×

∑ Io(hkl) Io(hkl)

× 100 (3)

where I(hkl) is the peak intensity of Zn electrodeposits and ∑ I(hkl) is the sum of the intensities of all the diffraction peaks. The index 0 refers to the intensities of the peaks of the standard Zn powder sample, taken from JCPDS file card number 87-0713. The deposit with the maximum Tc value is the preferred orientation of the deposit. A bar graph of texture coefficients of the electrodeposits C0, Cs, Cc, Csp, and Ccp is given in Figure 8.

Figure 9. Vickers microhardness measurements for the deposits C0, Cs, Cc, Csp, and Ccp.

figure that the zinc deposit obtained in the presence of CTAB has a higher hardness compared to the Zn deposit in the presence of SDS and bare Zn deposit. Furthermore, the Zn composite that is Ccp shows a greater hardness compared to the Bsp and other Zn coatings. Whereas the hardness of Bsp is decreased relative to the deposit, Bs because of the Si3N4 particles finds it difficult to incorporate into the Zn matrix because of the similar charges present on the cathodic surface and the surface of the particles. Also the chance of particles embedding into the Cs matrix is less due to the compact arrangement of Zn layers. Chronoamperometry is a very powerful method for the quantitative analysis of a nucleation process. This useful technique leads to obtaining the initial information about nucleation and the growth mechanism of the coating. The effect of SDS and CTAB on the nucleation mechanism of Zn deposition in the presence and absence of Si3N4 nanoparticles was evaluated by chronoamperometry. The chronoamperometric diagrams for the electrolytes C0, Cs, Cc, Csp, and Ccp are plotted in Figure 10. From the figure, it is observed that all of the chronoamperometric curves (C0, Cs, Cc, Csp, and Ccp) nearly at 0 time showed a sharp rise in curves corresponding to the birth and growth of nuclei; later the diffusion of the zones of adjacent nuclei overlap and reach a maximum value (imax). The decay in current density after imax of each transient decreases and converges at most to a limiting value, which infers linear diffusion of zinc ions to the electrode surface. Also,

Figure 8. Preferential orientation for Zn deposits C0, Cs, Cc, Csp, and Ccp.

The deposit C0 shows a preferred orientation of ⟨103⟩. Deposits Cs and Cc have preferred orientations at ⟨112⟩ and 12832



Article

Figure 10. Chronoamperometry diagrams carried at the depositon potentials of −1.3900, −1.4630, −1.4300, −1.3420, and −1.4190 V for bath solutions C0, Cs, Cc, Csp, and Ccp, respectively.

Table 5. Electrochemical Parameters of the Coatings Derived from Tafel Plots medium 3.5% NaCl solution

specimen C0 Cs Cc Csp Ccp

Icorr (A cm−2) 6.3160 1.8430 4.9700 1.3140 1.3070

× × × × ×

−5

10 10−5 10−5 10−5 10−5

Ecorr (V)

βc (V−1)

βa (V−1)

corrosion rate (g h−1) × 10−5

−1.1050 −1.0300 −1.0460 −1.0370 −1.0210

3.796 2.415 4.243 1.738 1.700

17.640 18.290 20.135 17.616 24.540

7.705 2.245 6.063 1.603 1.595

corrosive media using chemical (weightloss) and electrochemical methods. The Tafel extrapolation, anodic polarization, and impedance spectroscopy were adopted to measure the corrosion resistance. Figure 12 shows the weight loss measurement corrosion rate profiles of C0, Csp, and Ccp in 3.5 wt % NaCl solution. It is clear from the figure that deposit Ccp has the lower corrosion rate compared to deposits C0 and Csp, indicating that Ccp has the highest corrosion resistance compared to C0 and Csp. This reveals that the deposit obtained by the combination of C0+CTAB+Si3N4 alters the deposition mechanism and favors good coating with higher corrosion resistance. The anodic and cathodic potentiodynamic polarization curves of Zn deposits (obtained from bath solutions of Table 1) were recorded in 3.5 wt % NaCl corrosive media with a scan rate of 10 mV s−1, in the potential range of ±200 mV from their open circuit potential. Tafel curves of the deposits C0, Cs, Cc, Csp, and Ccp are shown in Figure 13. From the figure, it is observed that the Ecorr (−1.030 V) value of Cs is shifted to a more +ve direction and its icorr value (1.8430 × 10−5 A cm−2) is decreased compared to that of the deposit C0. But the deposit Cc shows a small shift in the +ve direction of its Ecorr value (−1.0460 V) and a little decrease in the icorr value (4.9700 × 10−5 A cm−2) than the basic coating C0, which reveals that the Zn deposits obtained from the bath solution C0+CTAB have lesser corrosion resistance compared to the coating from the bath solution C0+SDS. This behavior of the deposit Cs may be due to the fact that the presence of SDS makes a compact arrangement of Zn crystals without allowing a small crack or gaps in the deposit. But CTAB causes the blocking effect, which enlarges nuclei renewal rates, leading to an increase of nuclei number and needle shaped growth of Zn crystals [20] having a highly porous natured coating. This becomes responsible for the less corrosion resistant property of the Cc. Kinetic data obtained from the Tafel curves are given in Table 5.

it is noted that the maximum current densities of electrolytes C0, Cs, and Cc are 0.695 s, 0.805 s, 1.335 s, and for Csp it is 1.153 s. For Ccp, it is 0.622 s, which is less than the value of the SDS containing composite solution.11 The nucleation mechanism was identified by drawing dimensionless curves and compared with those obtained using the model of Schariker and Hills for 3D instantaneous and progressive nucleation processes. The model uses the following equations for identifying 3D instantaneous and progressive nucleation process.25 Instantaneous Nucleation: ⎛ i ⎞2 ⎜ ⎟ = 1.9542{1 − exp[−1.2564(t /tm)]}2 (t /tm)−1 ⎝ im ⎠

(4)

Progressive Nucleation: ⎛ i ⎞2 ⎜ ⎟ = 1.2254{1 − exp[ − 2.3367(t /tm)2 ]}2 (t /tm)−1 ⎝ im ⎠ (5)

where i represents the current density at any instant of time t and im is the maximum current density with corresponding time tm. Figure 11 shows the dimensionless experimental curves with their theoretical curves for instantaneous and progressive nucleation processes for electrolytes C0, Cs, Cc, Csp, and Ccp. The theoretical progressive and instantaneous curves were plotted using eqs 4 and 5.The electrolytes of C0, Cs, Cc, Csp, and Ccp will obey the instantaneous nucleation growth, which corresponds to the slow growth of nuclei on a small number of active sites, and all are activated at the same time, which also infers that the presence of surfactants (SDS and CTAB) alone or in combination with Si3N4 particles did not affect the nucleation and growth process of zinc ions. 3.3. Corrosion Resistance Properties. Corrosion resistance properties of coatings were evaluated in 3.5 wt % NaCl 12833



Article

Figure 11. Selection of dimensionless experimental curves with their theoretical curves for instantaneous and progressive nucleation processes of bath solutions C0, Cs, Cc, Csp, and Ccp.

Tafel curves of the composite electrodeposits Csp and Ccp suggest that the Ecorr value of Ccp (−1.0210 V) is shifted to a more +ve direction, and its icorr value is significantly reduced compared to the Csp coating. All of these results impart that the presence of SDS makes a compact hexagonal arrangement of Zn crystals on the steel substrates, hence fewer chances for

the Si3N4 particles to entrap in the Zn coating. However, CTAB promotes the codeposition of Si3N4 particles in the Zn matrix due to the fact that the CTAB induces the positive charge on the Si3N4 particles, and also the porous nature of the Zn matrix with the existence of CTAB allows a larger number of particles to incorporate into the coating. 12834



Article

potential range of −2.0 to 0.0 V and are shown Figure 14. It is evident from the figure that the corrosion potential of the deposit Ccp is shifted in a more positive direction at all current density regions in relation to the deposits C0 and Csp. This shift of potential toward the positive direction indicated the noble character of the Ccp composite coating compared to the C0 and Csp deposits. This shift further indicates that there is a requirement of higher potential for the dissolution Zn coating deposited from the bath solution of C0+CTAB+Si3N4. Usually, during the electrodeposition of Zn on steel substrate cracks, micrometer sized holes are formed, and these will act as the active sites for corrosion to occur, but during the composite electrodeposition, these micrometer sized holes are filled by nanosized particles and prevent the corrosion from occurring. This corrosion resistance behavior of the composite coating is greater with the presence of CTAB because the cationic surfactant has a strong enough attraction of the particles to the cathode surface; surfactant CTAB keeps the particle at the cathode surface for a time sufficient for their incorporation into the growing metal matrix. But anionic surfactant SDS creates a negative charge on the particles, which is repelled by the cathodic surface; hence there is lesser incorporation into the matrix. Hence, Ccp shows a higher resistance to corrosion compared to Csp and the basic bath coating C0. Impedance measurement is one of the most useful and important nondestructive methods to measure the corrosion resistance of the metal coatings. Figure 15 shows the Nyquist plot of electrochemical impedance spectroscopy for the C0, Csp, and Ccp coatings in a 3.5 wt % NaCl solution, where Z′ and Z″ are the real and imaginary parts of measured impedance. The experiment was carried out separately at the open circuit potential of each deposit; the applied frequency range was from 1 Hz to 100 kHz. The experimental impedance data were modeled with the electrical equivalent circuit given in Figure 16, where each element is as follows: Rs, solution resistance; Rc, coating resistance; Cc, coating capacitance; Rct, charge transfer resistance of the double layer capacitance; and Cdl, capacitence of the double layer. The fitted model was the two time constant model, i.e., consisting of two RC circuits, because of the presence of both passive and corroding regions on the coating surfaces, where Rs electrolyte resistance arises from the 3.5 wt % corrosive media. Rct and Cdl describe the electrode Faraday process, i.e., dissolution of the Zn coating, and it corresponds to

Figure 12. Corrosion rate with immersion time for electrodeposits C0, Csp, and Ccp.

Figure 13. Tafel curves of Zn deposits C0, Cs, Cc, Csp, and Ccp.

This becomes responsible for the higher corrosion resistance of Ccp compared to Csp.26 The anodic polarization method is one of the useful and fastest methods to determine the corrosion resistance of the coatings. The anodic polarization profiles of the deposits C0, Csp, and Ccp were examined in 3.5 wt % NaCl solution in the

Figure 14. Anodic polarization profiles of deposits C0, Csp, and Ccp. 12835



Article

Table 6. Electrochemical Parameters of Impedance Data of Zn−Si3N4 Films in 3.5% NaCl Solution medium

specimens

Rs (Ω)

Rc (Ω cm2)

Cc (F) × 10−6

Rct (Ω cm2)

Cdl (F) × 10−6

Rp = Rc + Rct (Ω cm2)

3.5% NaCl

C0 Csp Ccp

6.659 6.597 8.191

131.8 174.6 155.5

2.330 4.400 1.788

262.8 433.5 1349.0

4.875 6.941 4.965

394.6 608.1 150.5

■

AUTHOR INFORMATION

Corresponding Author

*Tel.: +91-9448855079. Fax: +91-08282-256255. E-mail address:[email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors gratefully acknowledge the department of Chemistry, Kuvempu University for providing the laboratory facility and the DST (Department of Science and Technology) government of India, New Delhi for providing the CHI 660C electrochemical workstation.

■

Figure 15. Nyquist plots for deposits C0, Csp, and Ccp at their respective open circuit potential where symbols represent fitted curves.

REFERENCES

(1) Adriana, V.; Simona, V.; Aurel, P.; Caius, B.; Liana, M. M. Electrodeposited Zn-TiO2 nanocomposite coatings and their corrosion behavior. J. Appl. Electrochem. 2010, 40, 1527−1519. (2) Praveenkumar, C M.; Venkatesha, T .V. Characterization and corrosion behavior of Electrodeposited Zn and Zn-BN coatings. Synth. React. Inorg. Met.-Org. Chem. 2012, 42, 351−359. (3) Panagopoulos, C. N.; Georgiu, E. P.; Gavras, A. G. Composite Zn-Fly ash coatings on mild steel. Surf. Coat. Technol. 2009, 204, 37− 41. (4) Toulemye, J. T.; Wilcox, G. D. Behavior of Zn-SiO2 electrodeposition in the presence of N,N-dimethyldodecylamine. Surf. Coat. Technol. 2006, 200, 5921−5930. (5) Li, C.; Liping, W.; Zhixiang, Z.; Junyan, Z. Effect of surfactant on the electrodeposition and wear resistance of Ni-Al2O3 composite coatings. Mater. Sci. Eng., A 2006, 434, 319−325. (6) Gomes, A.; da Silva Pereira, M. I.; Mendonca, M. H.; Costa, F. M. Zn- TiO2 composite films prepared by pulsed electrodeposition. J. Solid State Electrochem. 2005, 9, 190−196. (7) Chao, G.; Yu, Z.; Xuhui, Z.; Jingmao, Z.; Jinping, X. Effect of surfactant on electrodeposition of nickel- carbon nanotubes composite coatings. Surf. Coat. Technol. 2008, 202, 3385−3390. (8) Gomez, E.; Pane, S.; Alcobe, X.; Valles, E. Influence of a cationic surfactant in the properties of cobalt-nickel electrodeposits. Electrochim. Acta 2006, 51, 5703−5709. (9) Ewa, R.; Lidia, B.; Lukasz, D.; Maceij, M. Electrodeposition of nickel/Sic composites in the presence of cetyltrimethyl ammonium bromide. Appl. Surf. Sci. 2010, 256, 7414−7420. (10) Malfatti, C. F.; Veit, H. M.; Menezes, T. L.; Zoppas, F. J.; Rodrigues, J. S.; Bnino, J. P. The surfactant addition effect in the elaboration of electrodeposited Nip-SIC composite coatings. Surf. Coat. Technol. 2007, 201, 6318−6320. (11) Shirani, A.; Momenzadeh, M.; Sanjabi, S. Surfactant effect on electrochemical behavior of Co-TiO2 nanocomposite coatings. Surf. Coat. Technol. 2012, 206, 2870−2876. (12) Pignolet, C.; Euvard, M.; Foissy, A.; Filiatre, C. Electrodeppsition of latex particles in the presence of surfactant; Investigation of the deposit morphology. J. Colloid Interface Sci. 2010, 349, 41−48. (13) Rajan, S.; Sumit, B.; Siddharta, D.; Karabi, D. Effect of Surfactant on the co-deposition of the nano-sized ceria particles in the nickel matrix. J. Alloys Compd. 2010, 489, 650−658. (14) Tabrisur, R. K.; Andreas, E.; Michael, A.; Frank, M.; Michael, R. Electrodeposition of zinc-silica composite coatings: challenges in incorporating functionalized silica particles into a zinc matrix. Sci. Technol. Adv. Mater 2011, 12, 055005.

Figure 16. Equivalent circuit for the Zn−Si3N4 composite electrodeposit.

the low frequency impedance, while the Rc and Cc elements of the circuit show coating resistance due to the blocking of the active sites of corrosion by the incorporation of Si3N4 particles, which corresponds to the high frequency region of the impedance.27 The values of the equivalent circuits were given in Table 6. From the figure, it is observed that the impedance curve of the deposit Ccp has a larger diameter compared to the deposits C0 and Csp, which evidence the higher corrosion resistance of Ccp compared to the others. This is also supported by the maximum Rp value of the deposit Ccp.

4. CONCLUSION Zn−Si3N4 composite electrodeposition was successfully generated with the electrolytic method in the presence of surfactants SDS and CTAB. The cathodic polarization and the voltammetric studies reveal that CTAB influenced the incorporation of Si3N4 particles into the Zn matrix more than SDS. The cross sectional SEM images and EDAX spectra showed the presence of Si3N4 particles with Zn. The Zn−Si3N4 composite obtained in the presence of CTAB shows smaller crystallite size and increased mechanical strength. Both SDS and CTAB influenced the preferred orientation of the Zn composite. The SEM image of the Zn−Si3N4 composite in the presence of CTAB showed a smaller grain size. The Zn nucleation with and without Si3N4 particles proceeds as a 3D instantaneous nucleation in the presence of SDS and CTAB. Zn composite fabricated in the presence of CTAB shows the highest corrosion resistance. 12836



Article

(15) Wang, S. R.; Geng, H. R.; Wang, Y. Z.; Zhang, J. C. Microstructure and fracture characteristic of Mg-Al-Zn-Si 3 N 4 composites. Theor. Appl. Fract. Mech. 2006, 46, 57−69. (16) Ramesh, C. S.; Keshavamurthy, R.; Channabasappa, B. H.; Pramod, S. Friction and Wear Behavior of Ni−P Coated Si3N4 Reinforced Al6061 Composites. Tribol. Int. 2010, 43, 623−634. (17) Balaraju, J. N.; Rajam, K. S. Electroless deposition and characterization of high phosphorus Ni-P- Si3N4 composite coatings. Int. J. Electrochem. Sci. 2007, 2, 747−761. (18) Gomes, A.; da Silva Pereira, M. I. Pulsed electrodeposition of Zn in the presence of Surfactant. Electrochim. Acta 2006, 51, 1342−1350. (19) Praveen, B. M.; Venkatesha, T. V. Electrodeposition and properties of Zn-Ni-CNT composite coatings. J. Alloys Compd. 2009, 482, 53−57. (20) Praveen Kumar, C. M.; Venkatesha, T. V.; Chandrappa, K. G. Effect of surfactants on co-deposition of B4C nanoparticles in Zn matrix by electrodeposition and its corrosion behavior. Surf. Coat. Technol. 2012, 206, 2249−2257. (21) Ramalingam, S.; Murulidharan, V. S.; Subramania, A. Electrodepsoition and characterization of Cu-TiO2 nanocomposite coatings. J. Solid State Electrochem. 2009, 13, 1777−1783. (22) Shi, L.; Sun, D .F.; Gao, P.; Zhou, F.; Liu, W. M. Electrodepsoition and characterization of Ni-Co-Carbon nanotubes composite coatings. Surf. Coat. Technol. 2006, 200, 4870−4875. (23) Fustes, J.; Gomes, A.; da Silva Pereira, M. I. J. Solid State Electrochem. 2008, 12, 1435−1443. (24) Mounga, M.; Ricq, L.; Douglade, J.; Bercot, P. J. Appl. Electrochem. 2007, 37, 283−289. (25) Nayana, K. O.; Venkatesha, T. V.; Praveen, B .M.; Vathsala, K. Synergistic effect of additives on bright nanocrystalline zinc electrodeposition. J. Appl. Electrochem. 2011, 41, 39−49. (26) Shang, W.; Baizhen, C.; Xichang, S.; Chen, Y.; Xiang, X. Electrochemical corrosion behavior of composite MAO/Sol-gel coatings on magnesium Alloy AZ91D using combined micro-arc oxidation and Sol-gel technique. J. Alloys Compd. 2009, 474, 541−545. (27) Bogdan, S.; Malgorzata, K. Composite Ni/Al2O3 coatings and their corrosion resistance. Electrochim. Acta 2005, 50, 4188−4195.

12837


Surfactants Effect on ZnâSi3N4 Coating, Electrochemical Properties

Recommend Documents

Surfactants Effect on ZnâSi3N4 Coating, Electrochemical Properties