Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
11 results
Search Results
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 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 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.Item Development of nano-structured Zn-Ni multilayers and their corrosion behaviors(2011) Yogesha, S.; Bhat, R.S.; Venkatakrishna, K.; Pavithra, G.P.; Ullal, Y.; Hegde, A.C.Composition modulated multilayer alloy (CMMA) coatings of Zn-Ni was developed using single bath technique (SBT). CMMA coatings were developed galvanostatically using square current pulses. The cyclic cathode current densities (CCCDs) and number of layers were optimized for highest corrosion resistance. Experimental results showed that CMMA coating, developed at 2.0/5.0 A/dm2, having 300 layers is ?29 times higher corrosion resistant than monolithic alloy of same thickness. Tafel and impedance data revealed its good protection ability. The improved corrosion behavior exhibited by multilayers was explained using dielectric spectroscopy. The formation of multilayer and corrosion mechanism was analyzed using scanning electron microscopy (SEM). Copyright © Taylor & Francis Group, LLC.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 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 Compositionally Modulated Multilayered Zn-Co Deposits for Better Corrosion Resistance(Springer, 2020) Bhat, R.S.; Venkatakrishna, K.; Nayak, J.; Hegde, A.C.Zn-Co compositionally modulated multilayer alloy (CMMA) deposits have been developed onto mild steel using single bath technique. Multilayer alloy coatings have been galvanostatically produced using square current pulses. The switched cathode current density and number of layers have been designed for improved corrosion resistance. Experimental data revealed that multilayer coating with 120 layers at 10/30 mA/cm2 demonstrated ~ 125 times higher resistance to corrosion than monolayer alloy coating of the same thickness. The improved corrosion resistance of multilayer coatings is due to small changes in the wt.% cobalt, leading to change in the phase structure of deposit in alternate layers. The defects and failures occurring in a single layer in the deposition process are covered by the alternatively deposited coating layers. Therefore, the direction of the corrosive agent is extended or blocked. Further, the better corrosion resistances afforded by Zn-Co CMMA coatings were explained through changes in electronic properties at the interface, supported by Mott-Schottky’s plot. However, the decrease of corrosion resistance at a high degree of layering is attributed to the less relaxation time for redistribution of solutes in the diffusion layer, during plating. Potentiodynamic polarization and electrochemical impedance data showed its good protection ability. The enhanced corrosion resistance of multilayered deposits is due to small change in cobalt content, leading to alter the phase structure of the alternate-layers of the deposits. The structural morphology and the topographical structure of the coating were analyzed by scanning electron microscopy and atomic force microscopy. Evaluation of the chemical composition of the alloy coatings was carried out by x-ray photoelectron spectroscopy. © 2020, ASM International.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.