Faculty Publications
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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 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 Composition modulated multilayer Zn-Fe alloy coatings on mild steel for better corrosion resistance(2011) Venkatakrishna, K.; Hegde, A.C.Composition modulated alloy (CMA) of Zn-Fe coatings were developed on mild steel galvanostatically from chloride bath containing sulphanilic acid (SA) and ascorbic acid (AA) through single bath technique (SBT). The properties of CMA coatings were found to depend on the thickness of individual layers and switching cathode current densities (SCCDs). The CMA (Zn-Fe) coating, having 120 layers, deposited at 20 and 50mAcm-2, were found to show the least corrosion rate (1.545 × 10-2mmy-1) compared to monolithic alloy (32.5 × 10-2mmy-1) of the same thickness. The improved corrosion resistance of multilayered coatings was due to the fact that the defects and failures occurring in a single layer in the deposition process is covered by the successively deposited coating layers, and hence the corrosive agent path is extended or blocked. Further, the high corrosion resistance of CMA Zn-Fe coatings was attributed to the "dielectric barrier" of the coatings, evidenced by dielectric spectroscopy and Mott-Schottky's plot. The corrosion rate was found to increase at high degree of layering, and is attributed to less relaxation time for redistribution of metal ions in diffusion layer, during plating. In other words, at higher layer thickness, the CMA coating tends to become a monolithic. CMA coatings were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). © Taylor & Francis Group, LLC.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 Effect of TiO2 nanoparticles on hydrogen evolution reaction activity of Ni coatings(University of Science and Technology Beijing, 2018) Kullaiah, R.; Elias, L.; Hegde, A.C.The electrocatalytic activity of electrodeposited Ni and Ni–TiO2 coatings with regard to the alkaline hydrogen evolution reaction (HER) was investigated. The Ni coatings were electrodeposited from an acid chloride bath at different current densities, and their HER activities were examined in a 1.0-mol·L-1 KOH medium. The variations in the HER activity of the Ni coatings with changes in surface morphology and composition were examined via the electrochemical dissolution and incorporation of nanoparticles. Electrochemical analysis methods were used to monitor the HER activity of the test electrodes; this activity was confirmed via the quantification of gases that evolved during the analysis. The obtained results demonstrated that the Ni–TiO2 nanocomposite test electrode exhibited maximum activity toward the alkaline HER. The surface appearance, composition, and the phase structure of all developed coatings were analyzed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD), respectively. The improvement in the electrocatalytic activity of Ni–TiO2 nanocomposite coating toward HER was attributed to the variation in surface morphology and increased number of active sites. © 2018, University of Science and Technology Beijing and Springer-Verlag GmbH Germany, part of Springer Nature.Item Electrochemical studies on the corrosion resistance of Zn–Ni–Co coating from acid chloride bath(Springer, 2020) Bhat, R.S.; Manjunatha, K.B.; Prasanna Shankara, R.; Venkatakrishna, K.; Hegde, A.C.Anticorrosive deposits are a valuable approach to defending against corrosion from mild steel structures/machinery equipment. The Zn–Ni–Co coating has been deposited on low carbon steel surfaces using environment friendly optimized acidic chloride bath with ZnCl2·6H2O, NiCl2·6H2O, CoCl2·6H2O, sulphanilic acid (C6H7NO3S) and gelatin (C6H8O6). The standard Hull cell technique has been adopted for the optimization of bath components and experimental conditions, for the superior corrosion resistant coating. The corrosion test with potentiodynamic polarization method was performed to investigate the role of pH on the film quality and corrosion performances of the films. Further, the effect of current densities on corrosion resistance, thickness and hardness, have been investigated. Cyclic voltammetry technique has been used to test the electrochemical properties of the Zn–Ni–Co coating in acidic solutions. The results revealed that the increase in the current density favoured the increase in Ni and Co content in the deposit, showed higher corrosion resistance and higher cathodic current efficiency. The structural and morphological characteristics of the alloy coating have been obtained through scanning electron microscopy and X-ray diffraction techniques. The atomic force microscope was used to examine the topographic structure of the coating. X-ray Photoelectron spectroscopy was used to determine the chemical composition of alloy coatings and verified by energy dispersive X-ray analysis. The results indicate that a new and low-cost chloride bath for Zn–Ni–Co coating exhibit superior corrosion resistance properties and can be implement in various industrial applications such as automobiles, machine tools etc.[Figure not available: see fulltext.]. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.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.