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Item Layered coating of Zn-Co alloys on mild steel using triangular current pulses for better corrosion protection(2013) Bhat, S.R.; Bhat, K.; Hegde, A.C.Cyclic multilayer alloy (CMA) coatings of Zn-Co were electrodeposited on to mild steel (MS) from acid sulphate bath having thiamine hydrochloride and citric acid as additives. Depositions were carried out galvanostatically from a single bath containing Zn+2 and Co+2 ions. The triangular current pulses cycling between two cathode current densities were used for gradual change in composition in each layer. CMA coatings were developed under different sets of cathode current densities and number of layers, their corrosion resistances were evaluated by potentiodynamic polarization and Electrochemical Impedance Spectroscopy method, results were compared with that of monolayer Zn-Co alloy coatings. At optimal configuration, CMA coating represented as (Zn-Co)3.0/5.0/300 was found to exhibit ∼11 times better corrosion resistance compared to monolayer, (Zn-Co)4.0, deposited for same length of time from same bath. The formation of layered and corrosion mechanism was analyzed using Scanning Electron Microscopy. The corrosion protection of layered coatings of Zn-Co alloy was attributed to the different phase structure of the alloys in alternate layers, evidenced by XRD analysis. © 2013 Indian Institute of Metals.Item Effect of bath composition and operating parameters on deposit character and corrosion behaviour of Zn-Ni alloy(2008) Venkatakrishna, K.; Tangaraj, V.; Hegde, A.Electrodcpositcd Zn-Ni alloys arc extensively used as protective coatings for steel substrates and hence:lhe studies, on the factors which enhance corrosion resistance are of considerable significance. The present work details the optimization of acid chloride bath for bright Zn-Ni alloy over mild steel and study of the parameters which influence Ni content in the deposit. Use of sulphanilic acid and gelatin was found to show significant effect on brightness of the deposit. The effect of molar ratio of Ni+2/Zn+2 in the bath on limiting current density of nickel deposition was emphasized. Under no conditions of bath compositions and operating parameters studied, the change in codeposition behaviour from anomalous to normal type was observed. The wt. %Ni in the deposit was found to be the independent factor of its corrosion resistance. The photomicrograph of electroplates confirmed that superior corrosion resistance is due to good surface morphology. Tjhe effect of bath composition, current density (c.d.), pH and temperature on appearance, hardness and corrosion resistance oi.deposits were studied and discussed. Corrosion behaviour of electroplates has been studied by Tafel's extrapolation method. Electrochemical impedance spectroscopy analysis revealed that superior corrosion resistance of Zn-Ni alloys coatings at optimized current density is due to' barrier resistance at the interface of deposit and medium. Formation Of n-typc semiconductor film at the interface was confirmed by Mott-Schottky plot. Addition of small amount of cadmjutrrchloride did not increase corrosion resistance.Item Inhibition of corrosion of mild steel in acid media by N'-benzylidene-3- (quinolin-4-ylthio)propanohydrazide(2008) Ramesh Saliyan, V.; Vasudeva Adhikari, A.V.In the present investigation a new corrosion inhibitor, N'-(3,4-dihydroxybenzylidene)-3-{[8-(trifluoromethyl)quinolin-4-yl]thio} propanohydrazide(DHBTPH) was synthesized, characterized and tested as a corrosion inhibitor for mild steel in HCl (1 M, 2 M) and H2SO 4 (0.5 M, 1 M) solutions using weight-loss method, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization methods. The corrosion inhibition efficiency measured by all the above three techniques were in good agreement with each other. The results showed that DHBTPH is a very good inhibitor for mild steel in acidic media. The inhibition efficiency in different acid media was found to be in the decreasing order 0.5 M H 2SO4 > 1 M HCl > 1M H2SO4 > 2 M HCL The inhibition efficiency increases with increasing inhibitor concentration and with increasing temperature. It acts as an anodic inhibitor. Thermodynamic and activation parameters are discussed. Adsorption of DHBTPH was found to follow the Langmuir's adsorption isotherm. Chemisorption mechanism is proposed. The mild steel samples were also analysed by scanning electron microscopy (SEM). © Indian Academy of Sciences.Item Corrosion behavior of composition modulated multilayer Zn-Co electrodeposits produced using a single-bath technique(2009) Thangaraj, V.; Eliaz, N.; Hegde, A.Composition modulated alloy (CMA) electrodeposits of Zn-Co were produced from acid chloride baths by the single-bath technique. Their corrosion behavior was evaluated as a function of the switched cathode current densities and the number of layers. The process was optimized with respect to the highest corrosion resistance. Enhanced corrosion resistance was obtained when the outer layer was slightly richer with cobalt. At the optimum switched current densities 40/55 mA cm-2, a coating with 600 layers showed ~6 times higher corrosion resistance than monolithic Zn-Co electrodeposit having the same thickness. The CMA coating exhibited red rust only after 1,130 h in a salt-spray test. The increased corrosion resistance of the multilayer alloys was related to their inherent barrier properties, as revealed by Electrochemical Impedance Spectroscopy. The corrosion resistance was explained in terms of n-type semiconductor films at the interface as supported by Mott-Schottky plots. © 2008 Springer Science+Business Media B.V.Item Electrodeposition and characterization Zn-Co alloy(2009) Hegde, A.; Thangaraj, V.The present work details optimization of a stable acid chloride bath for electroplating of bright Zn-Co alloy on mild steel using gelatin and glycine as additives. It was found that the addition of gelatin along with glycine changed the deposition pattern markedly. A suitable bath has been formulated using conventional Hull cell experiments. The bath under plating conditions were found to exhibit anomalous codeposition with preferential deposition of less noble (zinc) over more noble (cobalt) as characterized by Zn-Fe group metal alloys. Investigation revealed that the current density (c.d.), temperature, and pH of the bath have strong effect on the composition of the deposit. Influence of bath constituents and operating parameters on appearance and composition of deposits were studied as measure of their performance against corrosion. A variety of deposits were obtained and their corrosion resistances were measured by Tafel method with/without chrome passivation. Experimental results demonstrated the fact that the corrosion resistances of Zn-Co alloys increased with percent of Co in the deposit except at very high c.d. This is due to the fact at very high c.d. the deposit becomes very porous and thick as evidenced by SEM image. The formation of Zn-Co alloy is confirmed by EDAX analysis. A stable chloride bath for Zn-Co alloy deposition has been proposed and discussed. The formation of passive film on chromatization is indicated by almost same E corr value of all Zn-Co electroplates irrespective of the current densities at which they have been deposited. © 2009 Pleiades Publishing, Ltd.Item Electrolytic preparation of cyclic multilayer Zn-Ni alloy coating using switching cathode current densities(2010) Venkatakrishna, K.; Hegde, A.C.Cyclic multilayer alloy (CMA) coating of Zn-Ni was developed on mild steel using single bath technique, by proper manipulation of cathode current densities. The thickness and composition of the individual layers were altered precisely and conveniently by cyclic modulation of cathode current densities. Multilayer coatings, having sharp change in compositions were developed using square current pulses. Gelatin and sulphanilic acid (SA) acid were used as additives. Laminar deposits with different configurations were produced, and their corrosion behaviors were studied, in 5% NaCl solution by electrochemical methods. It was observed that the corrosion resistance of CMA coating increased progressively with number of layers (up to certain optimal numbers) and then decreased. Cyclic voltammetry study demonstrated the role of gelatin and SA in multilayer coating. The coating configuration has been optimized for the peak performance against corrosion. The substantial decrease of corrosion rate, in the case of multilayer coatings was attributed to the changed intrinsic electric properties, evidenced by Electrochemical Impedance Spectroscopy (EIS) study. The surface morphology and its roughness were examined by Atomic Force Microscopy (AFM). The surface and cross-sectional view of coatings were examined, using Scanning Electron Microscopy (SEM). X-ray photoelectron spectrum (XPS) study was carried out for surface analysis. The relative performance of pure Zn, monolithic and CMA coatings were compared and discussed. © 2010 Springer Science+Business Media B.V.Item Electrodeposition of high performance multilayer coatings of Zn-Co using triangular current pulses(2010) Yogesha, S.; Hegde, A.C.Compositionally modulated alloy (CMA) coatings of Zn-Co were electrodeposited on to mild steel from an acid chloride bath containing thiamine hydrochloride, as an additive. Electroplating was carried out galvanostatically from a single bath containing Zn2+ and Co2+ ions. Gradual change in composition in each layer was effected by triangular current pulses, cycling between two cathode current densities. Compositionally modulated alloy coatings were developed under different conditions of cyclic cathode current density and number of layers, and their corrosion resistances were evaluated by potentiodynamic polarisation and electrochemical impedance spectroscopy. The formation of multilayer and corrosion mechanism was analysed using scanning electron microscopy. The corrosion resistances of CMA and monolithic alloy coatings were compared with that of the base metal. Compositionally modulated alloy coating at optimal configuration, represented as (Zn-Co) 2•0/4•0/300, was found to exhibit ?80 times better corrosion resistance compared with monolithic (Zn-Co)3•0 alloy, deposited for the same length of time from the same bath. Improved corrosion resistance was attributed to the formation of n-type semiconductor film at the interface, supported by Mott-Schottky plots. Decrease in corrosion resistance at high degree of layering was found, and is due to lower relaxation time for redistribution of solutes in the diffusion double layer, during plating. © 2010 Maney Publishing.Item Optimization of bright zinc-nickel alloy bath for better corrosion resistance(2010) Yogesha, S.; Hegde, A.C.Optimization of an acid chloride bath for electrodeposition of smooth Zn-Ni alloy on to mild steel was studied using thiamine hydrochloride (THC) as brightener. The influence of deposition current density, temperature, composition, and corrosion properties of Zn-Ni alloy coatings was investigated. The effect of bath composition and operating parameters on deposits characters like composition, micro-hardness, thickness and adhesions were tested. Under no conditions of current density employed in the present study, the anomalous type of co-deposition has changed to normal type. Electrolytically deposited Zn-Ni alloys were characterized by electrochemical AC and DC techniques. The experimental results revealed that coatings having ? 3.16 wt. % Ni at 3.0 A/dm2 was the most corrosion resistant. The better corrosion resistance at optimal current density was attributed to the formation of n-type semiconductor film at the interface using Mott-Schottky (M-S) analysis. The effect of THC on plating process was investigated through cyclic voltammetry techniques. X-ray diffraction (XRD) studies of the coatings showed the presence of ?-Phase with composition of Ni5Zn21, responsible for it extended orrosion resistance. The change in the surface morphology of the coatings, with current density was analyzed using scanning electron microscopy (SEM). © 2010 Indian Institute of Metals.Item Electroplating and characterization of Zn-Ni, Zn-Co and Zn-Ni-Co alloys(2010) Eliaz, N.; Venkatakrishna, K.; Hegde, A.C.Zn-Ni, Zn-Co and Zn-Ni-Co coatings were electrodeposited on mild steel from an acidic chloride bath containing p-aminobenzenesulphonic acid (SA) and gelatin. These additives changed the phase content in the coatings, most likely as a result of their adsorption at the surface of the cathode. The effect of gelatin was more pronounced than that of SA. The Faradaic efficiency was higher than 90%. As the current density was increased or the bath temperature was decreased, the concentration of the nobler metal in the coating increased. Both concentrations of Ni and Co in the ternary alloy increased as the applied current density was increased. Nickel and cobalt were found to have a synergistic catalytic effect. The thickness of all coatings increased as the applied current density was increased. The hardness increased with current density to a peak value, and then decreased. The rate of Zn deposition was heavily influenced by mass-transport limitation at high applied current densities, while the rates of Ni and Co deposition were not. The anomalous codeposition was explained by the great difference between the exchange current densities of Zn and the iron-group metal. Potentiodynamic polarization scans and electrochemical impedance spectroscopy showed that the corrosion resistance of the ternary Zn-Ni-Co alloy coatings was approximately 10 times higher than that of Zn-Ni and 7 times higher than that of Zn-Co. The improved corrosion resistance of the ternary alloy was attributed to its surface chemistry, phase content, texture, and surface morphology. The ternary Zn-Ni-Co coating may thus replace the conventional Zn-Ni and Zn-Co coatings in a variety of applications. © 2010 Elsevier B.V.Item Electrodeposition of Zn-Ni, Zn-Fe and Zn-Ni-Fe alloys(2010) Hegde, A.C.; Venkatakrishna, K.; Eliaz, N.Zn-Fe, Zn-Ni and Zn-Ni-Fe coatings were electrodeposited galvanostatically on mild steel from acidic baths (pH 3.5) consisted of ZnCl2, NiCl2, FeCl2, gelatin, sulfanilic (p-aminobenzenesulfonic) acid and ascorbic acid. Cyclic voltammetry showed that the effect of gelatin was more pronounced than that of sulfanilic acid, and that the deposition of the ternary alloy behaved differently from the deposition of the binary alloys. In all three systems, the Faradaic efficiency was higher than 88%, the rate of Zn deposition was heavily influenced by mass-transport limitation at high applied current densities, and the deposition was of anomalous type. For each applied current density, the concentrations of Ni and Fe in the ternary alloy were higher than the corresponding concentrations in the binary alloys. The hardness of Zn-Ni coatings was the highest, while that of Zn-Fe coatings was the lowest. The Zn-Ni-Fe coatings were the smoothest, had distinguished surface morphology, and contained ZnO in the bulk, not just on the surface. The lowest corrosion rate in each alloy system (214, 325 and 26?m year-1 for Zn-Ni, Zn-Fe and Zn-Ni-Fe, respectively) was characteristic of coatings deposited at 30, 30 and 40mAcm-2, respectively. The higher corrosion resistance of the ternary alloy was also reflected by a higher corrosion potential, a higher impedance and a higher slope of the Mott-Schottky line. The enhanced corrosion behavior of the ternary alloy was thus attributed to its chemical composition, phase content, roughness and the synergistic effect of Ni and Fe on the n-type semiconductor surface film. © 2010 Elsevier B.V.