Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
4 results
Search Results
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 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 Surface Structure and Electrochemical Behavior of Zinc-Nickel Anti-Corrosive Coating(Center of Excellence in Electrochemistry, Univ. of Tehran, 2023) Bhat, R.S.; Venkatakrishna, K.; Hegde, A.C.We report on the electrodeposition of a zinc-nickel alloy using a sulphate bath on mild steel (MS) substrate. The Hull cell experiment was used to optimize the bath composition and operating conditions. Sulphanilic acid (SA) was used as an additive for the coatings. The bath demonstrated an abnormal co-deposition with more zinc being deposited over nobler nickel. The effect of temperature and current density on the coating thickness, hardness, corrosion resistance, and weight % of Ni content in the coating was investigated. The corrosion behaviour of coated zinc-nickel alloy film in sodium chloride (wt.% 3.5) solution was investigated using potentiodynamic polarization and electrochemical impedance spectroscopic approaches. The nickel content in the coatings was determined through the colorimetric method and verified by the energy dispersive X-ray spectroscopy (EDX) technique. Atomic force microscopy (AFM) and Scanning electron microscopy (SEM) techniques were used to determine the surface roughness and surface topography, of the coatings. The results show that the zinc-nickel coatings had the highest corrosion resistance (0.213 mm y-1) at optimal current density (3A dm-2). Thus, due to their superior corrosion resistance Zn-Ni coatings have been largely used to protect the mild steel components in many industries including the automotive, military, and aerospace segments. © 2023 by CEE (Center of Excellence in Electrochemistry).