Faculty Publications
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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 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 Electrodeposition of Zn–Co Coating and its Electrochemical Performance(Pleiades journals, 2022) Bhat, R.S.; Manjunatha, K.B.; Venkatakrishna, K.; Hegde, A.C.Abstract: We report the acid chloride bath based electroplating of Zn–Co alloy on low carbon steel (LCS). As additives, the sulphanilic acid (SA) and gelatin were used for electroplating. The bath exhibited an anomalous co-deposition with a higher deposition of Zn over nobler Co. The role of bath composition, current density, partial current density, pH, and temperature on thickness, hardness, and corrosion resistance of deposit was studied. The corrosion behavior in 3.5 wt % sodium chloride solution and electrochemical behavior in acid chloride solutions of Zn–Co alloy coatings were studied using the potentiodynamic polarization method and cyclic voltammetry technique respectively. Mott–Schottky plot with positive slope confirms the development of n-type semiconductor layer at the interface of substrate and coating, which results in superior corrosion resistance of coatings. The colorimetric method has been used to estimate the composition of the deposit and further verified by energy dispersive X-ray spectroscopy (EDX) technique. The surface features and the topographical structure of the alloy film were obtained by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The results indicate that the Zn–Co alloy films exhibited superior corrosion resistance with the lowest corrosion rate (138 µm y–1). Hence this alloy coating will find suitable applications in automobile and aerospace industries. © 2022, Pleiades Publishing, Ltd.Item Electrochemical Studies of Zn-Ni-Fe Alloy Coatings for Better Corrosion Resistance Applications(Springer, 2022) Bhat, R.S.; Munjunatha, K.B.; Bhat, S.I.; Venkatakrishna, K.; Hegde, A.C.Anti-corrosive alloy coatings are a valuable solution to the protection of low carbon steel structures/equipment against corrosion. The Zn-Ni-Fe coatings have been deposited galvanostatically on low carbon steel from an acid chloride bath. Sulfanilic acid and gelatin were used as additives for the homogeneity of the deposit. The Hull cell method has been used to optimize both bath constituents and plating conditions. The corrosion behavior of the coating films was examined with potentiodynamic polarization and the electrochemical impedance spectroscopy methods. The effects of current density, pH, and temperature on deposit properties like hardness, thickness, and corrosion rates were examined. The electrochemical characteristics of the Zn-Ni-Fe have been studied by the cyclic voltammetry technique. The morphology of the deposit was investigated with scanning electron microscopy and the surface roughness of the coating film was analyzed by atomic force microscopy. The Ni and Fe contents in the deposit were analyzed by colorimetric technique and cross-checked with energy-dispersive x-ray analysis. The capacitive reactance at the interface is attributed to the excellent corrosion resistance at optimal current density (40 mA cm−2) as indicated by the Nyquist plot with large polarization resistance. Furthermore, the positive slope of Mott-Schottky revealed that the semiconductor film at the interface is n-type. The results show that a new Zn-Ni-Fe alloy coating film exhibits better corrosion resistance properties and can be executed in industrial applications such as machine tools, bolts, and nuts in the automobile for corrosion protection, etc. © 2022, ASM International.