Faculty Publications
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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 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.Item Development of anti-corrosive multi-layered coatings of zinc-nickel alloy(2011) Subbaiah, Y.; Kaje, V.; Hegde, A.C.Purpose: The purpose of this paper is to develop and optimize anti-corrosive multi-layered coatings of zinc-nickel alloy on carbon steel. Design/methodology/approach: A variety of composition-modulated multi-layer alloy (CMMA) coatings of zinc-nickel were developed on a carbon steel substrate by cyclic changes in cathode current during electrodeposition, coupled with variation of the thicknesses of the individual layers. The corrosion behavior of the coatings was studied in 5 percent NaCl solution by electrochemical methods. Cyclic cathode current densities (CCCDs) and the number of alloy layers were optimized for highest performance of the coatings against corrosion. The factors responsible for improved corrosion resistance were analyzed in terms of change in the intrinsic electrical properties of the capacitance value at the electrical double layer that was associated with micro/nanometric layering. The formation of the semi-conductive surface film, which was responsible for the improved corrosion resistance, was supported by a Mott-Schottky plot and the cyclic polarization study. The formation of multi-layered deposit and the mechanism of corrosion degradation of the coating were analyzed using scanning electron microscopy. Findings: CMMA coatings with an optimal configuration of (Zn-Ni)2.0/4.0/300 showed ~35 times better corrosion resistance compared to a monolithic (Zn-Ni)3.0 alloy coating of the same thickness. The peak performance was attributed to the change in intrinsic electrical properties of the coating and this conclusion was supported by dielectric spectroscopy. Originality/value: The paper describes the optimization of CCCD and the number of deposited layers by development of electrolytic deposition of anti-corrosive multi-layered zinc-nickel coatings from a single plating technique. © Emerald Group Publishing Limited.Item Development of nano-structured cyclic multilayer Zn-Ni alloy coatings using triangular current pulses(2011) Bhat, R.S.; Hegde, A.C.Cyclic multilayer alloy (CMA) deposits of Zn-Ni were developed on mild steel from sulphate bath having thiamine hydrochloride (THC) and citric acid (CA) as additives. CMA coatings were developed galvanostatically using triangular current pulses, under different conditions of cyclic cathode current density (CCCD's) and number of layers. The corrosion behaviors of the coatings were evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy methods, and were compared with that of monolayer Zn-Ni alloy of same thickness. At optimal configuration, CMA coating represented as, (Zn-Ni)2.0/5.0/300 was found to exhibit ?40 times better corrosion resistance compared to monolayer alloy, (Zn-Ni)3.0. Cyclic voltammetry study demonstrated that THC and CA have improved the appearance of the deposit by complexation with metal ions. The corrosion protection efficacy of CMA coatings was attributed to the difference in phase structure of the alloy in successive layers, evidenced by XRD analysis. The formation of multilayer and corrosion mechanism was analyzed by Scanning Electron Microscopy (SEM) study. © 2011 Allerton Press, Inc.Item Development of nanostructure multilayer Co-Ni alloy coatings for enhanced corrosion protection(2013) Pavithra, G.P.; Hegde, A.C.Nanostructure multilayer alloy coatings (NMAC) of Co-Ni were developed on copper in layered manner using different current pulses. NMAC of Co-Ni was deposited galvaostatically from acid sulphate bath under different combination of cyclic cathode current densities (CCCD's) and number of layers. Corrosion behaviors of coatings were evaluated in 1 M hydrochloric acid, as representative corrosion medium. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) study revealed that NMAC (Co-Ni) 2.0/4.0/6.0/60/three exhibits~160 times better corrosion resistance than monolayer coating, deposited from same bath for same time. Better corrosion protection was attributed to the increased effect of interface, arising from the exceptional thinness of the layers. As composition of alloys in successive layers were varied, consequent to the deposition current density (c.d.), the change in phase structure of the deposits were observed, confirmed by X-ray diffraction (XRD) study. Layer formation and surface after corrosion tests were examined by scanning electron microscopy (SEM) and optical profilometer, and reasons responsible for better protection were analyzed. © 2013 by CEE.Item Production of layered coatings of Fe-Ni alloy for enhanced corrosion protection(2013) Pavithra, G.P.; Hegde, A.C.Layered Fe-Ni alloy coatings have been galvanostatically developed on copper using dual and triple square current pulse from acid sulfate bath. The cyclic cathode current density (CCCD) and number of layers have been optimized for enhanced performance of the coatings against corrosion. Corrosion behavior of the coatings is evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy methods in 1 M HCl solution. The polarization study confirms that coatings developed using triple square pulses are more corrosion resistant than those deposited by dual square pulses. The improved corrosion behavior of layered coatings is due to the changed intrinsic electric properties evidenced by the electrochemical impedance spectroscopy. Under optimal conditions, the coatings developed using dual and triple square current pulse have been found to be by about 23 and 57 times, respectively, more corrosion resistant than the monolithic alloys. Surface morphology and layered coatings have been examined by scanning electron microscopy. Saturation of corrosion resistance at a high degree of layering was found, which is attributed to a shorter relaxation time for redistribution of metal ions during plating. © 2013 Allerton Press, Inc.Item Synergistic effect of gelatin and glycerol on electrodeposition of Zn-Ni alloy(2013) Rao, V.R.; Hegde, A.C.The use of organic compounds which improves corrosion resistance has attracted growing interest in electroplating technology. In this direction, this article presents the experimental results of electrodeposition of Zn-Ni alloy on mild steel (MS) from acid chloride bath using gelatin and glycerol as additives. The bath composition and operating parameters have been optimized by the conventional Hull cell method. The effect of gelatin and glycerol, individually and in combination on the deposition process, was identified by a cyclic voltammetry (CV) study at different scan rates. Bright deposition of Zn-Ni alloy was found at optimal current density (c.d.) due to the preferential deposition of gelatin and glycerol by controlling the Ni content of the alloy. The CV study demonstrated that alloy deposition is diffusion controlled when additives were used individually and is adsorption controlled when used in combination. Corrosion behaviors at different current densities (c.d.s) were evaluated by potentiodynamic polarization and electrochemical impedance (EIS) methods. The surface morphology and phase structure of the coatings were analyzed by field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) studies. The experimental results revealed that both gelatin and glycerol have synergistic effects in improving the electrocrystallization process and, hence, the corrosion stability of the coatings. At an optimal c.d. (3.0 A dm-2), the Zn-Ni alloy coating showed peak performance against corrosion with the least corrosion rate. Better corrosion protection at optimal c.d., which was attributed to specific Zn(101), ?-(411,330), and Zn(103) reflections, is evidenced by the XRD study. © 2013 The Minerals, Metals & Materials Society and ASM International.Item Electrofabrication of multilayer Fe-Ni alloy coatings for better corrosion protection(Springer Verlag service@springer.de, 2014) Ullal, Y.; Hegde, A.C.Electrofabrication of multilayer Fe-Ni alloy coatings were accomplished successfully on mild steel and their corrosion behaviors were studied. Multilayer comprised of alternatively formed 'nano-size' layers of Fe-Ni alloy of different composition have been produced from a single bath having Fe 2+and Ni2+ ions using modulated (i.e. periodic pulse control) current density (cd). The deposition conditions were optimized for both composition and thickness of individual layers for best performance of the coatings against corrosion. The deposits were analyzed using scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), Hardness Tester, electrochemical AC and DC methods respectively. The multi layered deposits showed better corrosion resistances compared to the monolayer Fe-Ni (CR = 3.77 mm year-1) coating deposited using DC from the same bath; the maximum corrosion resistance being shown by the coating having 300 layers, deposited at cyclic cathodic current densities of 2.0 and 4.0 A dm-2 (CR = 0.03 mm year-1). Drastic improvement in the corrosion performance of multilayer coatings were explained in the light of changed kinetics of mass transfer at cathode and increased surface area due to modulation and layering. © 2014 Springer-Verlag Berlin Heidelberg.