Faculty Publications
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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 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 Corrosion resistant Zn-Co alloy coatings deposited using saw-tooth current pulse(2011) Yogesha, S.; Hegde, A.Micro/nanostructured multilayer coatings of Zn-Co alloy were developed periodically on mild steel from acid chloride bath. Composition modulated multilayer alloy (CMMA) coatings, having gradual change in composition (in each layer) were developed galvanostatically using saw-tooth pulses through single bath technique (SBT). CMMA coatings were developed under different conditions of cyclic cathode current densities (CCCDs) and number of layers, and their corrosion resistances were evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) method. Optimal configuration, represented as (Zn-Co)2 0/4.0/300 was found to exhibit ? 89 times better corrosion resistance compared to monolithic (Zn- Co)3 0 alloy deposited for same time, from same bath. The better corrosion resistance of CMMA coatings was attributed to changed interfacial dielectric properties, evidenced by dielectric spectroscopy. Improved corrosion resistance was attributed to formation of n-type semiconductor film at the interface, supported by the Mott-Schottky plot. Further, the formation of multilayer and corrosion mechanism was analysed using scanning electron microscopy (SEM). © Indian Academy of Sciences.Item Surface modification by multilayered Zn-Co alloy coatings(2012) Yogesha, S.; Udupa, K.R.; Hegde, A.Nanostructured multilayer alloy or composition modulated multilayer alloy coatings of Zn-Co have been developed, and their corrosion behaviours were studied by potentiodynamic polarization and electrochemical impedance spectroscopy methods. The coatings were developed galvanostatically using square, triangular and sawtooth current pulses through single bath technique. The cyclic cathode current density and the numbers of layers have been optimised for peak performance of the coatings against corrosion. Under optimal conditions, the coatings developed using square, triangular and sawtooth current pulses were found to be respectively y100, 80 and 90 times more corrosion resistant than monolithic alloy of same thickness. The better corrosion resistances of the composition modulated multilayer alloy coatings were attributed to the dielectric barrier at the interface, as evidenced by dielectric spectroscopy. Surface morphology, multilayer formation and surface after corrosion tests were examined by scanning electron microscopy. © 2012 Institute of Materials, Minerals and Mining.Item Magnetic property and corrosion resistance of electrodeposited nanocrystalline iron-nickel alloys(Elsevier B.V., 2012) Pavithra, G.P.; Hegde, A.In the present investigation we have galvanostatically synthesized nanocrystalline Fe-Ni alloys on copper substrate. The effect of current density (c.d.) on composition, surface morphology and phase structure were studied for explaining the magnetic and electrochemical properties of the nanocrystalline alloy. The bath found to exhibit the preferential deposition of less noble Fe than Ni, and at no conditions of c.d., the deposition has changed from anomalous to normal type. Surface morphology and structural characteristics of the deposits were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. As composition of the alloy varied, consequent to the current density a change of body centered cubic structure (bcc) to face centered cubic structure (fcc) was observed for nanocrystalline materials. Finally, the conditions responsible for peak magnetic property and corrosion resistance were optimized. Factors responsible for improved functional properties were explained in terms of surface morphology and crystalline grain size of the coatings. © 2012 Elsevier B.V.Item Production of layer by layer Zn-Fe compositional multilayer alloy coatings using triangular current pulses for better corrosion protection(Maney Publishing, 2015) Bhat, R.S.; Hegde, A.Multiple-layer coatings of Zn-Fe alloy having alternatively the same compositions have been developed galvanostatically on mild steel (MS) from a single plating bath using triangular current pulses. Thiamine hydrochloride (THC) and citric acid (CA) were used as additives. Multiple-layer coatings were developed under different conditions of cyclic cathode current density (CCCD) and number of layers. Cyclic voltammetry demonstrated that the addition of THC and CA improves the deposit character by increasing the Ni content (through suppressing the deposition of Zn) via preferential adsorption on the cathode surface. The corrosion behaviours of the coatings were evaluated by electrochemical AC and DC methods. The optimum multiple-layer coating, represented as (Zn-Fe)3.0/5.0/300, was found to exhibit about four to five times better corrosion resistance when compared with monolayer (Zn-Fe)3.0 alloy, developed from the same bath for the same duration. Distinct phase structures responsible for interface formation between successive layers (which changes alternatively) were confirmed by X-ray diffraction analysis. Better corrosion resistance afforded by multiple-layer coating was attributed to the increased specific surface area of the coating because of layering. A synergistic effect of both structural difference between layers and individual layer thickness is responsible for enhanced corrosion resistance of the multiple-layer coatings. The formation of multiple layers and corrosion mechanism were analysed by scanning electron microscopy. © 2015 Institute of Materials Finishing.Item Electrodeposition of laminar coatings of Ni-W alloy and their corrosion behaviour(Elsevier, 2015) Elias, L.; Hegde, A.The attractiveness of electroplating for the synthesis of advanced materials is linked to large selection of plating conditions coupled with different mass transfer processes towards the cathode, and this allows the tailoring of different properties of many electrodeposited coatings. This theme has been exploited effectively in the development of a new class of coatings; called composition modulated multilayered (CMM), or in short laminar coatings. The work embodied in this paper is to demonstrate how the corrosion resistance of monolayer Ni-W alloys can be increased to many fold of its magnitude by multilayer deposition. Ni-W coatings have been deposited on mild steel (MS) in a laminar multilayer pattern from a citrate bath using single bath technique (SBT). Electrodeposits having alternate layers of alloys, having different compositions were developed by modulating the direct current (DC). CMM coating configurations have been optimized from a newly developed bath, in terms of current pulse height and thickness of each layer to maximize its corrosion protection ability, in relation to its monolayer coating, developed from same bath for same time. The process and product of the Ni-W coatings have been characterized using different instrumental methods, such as cyclic voltammetry (CV), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) study. The better corrosion resistance behaviour of CMM Ni-W coatings has been analysed in the light of increased surface areas of the coatings due to layering, and results are discussed. © 2015 Elsevier B.V.Item Development of nanolaminated multilayer Ni-P alloy coatings for better corrosion protection(Royal Society of Chemistry, 2016) Elias, L.; Bhat, K.U.; Hegde, A.Nanolaminated multilayer Nickel-Phosphorous (Ni-P) alloy coatings were developed on mild steel from a citrate bath using glycerol as an additive. Multilayer Ni-P alloy coatings having nanolaminated layers of alloys of alternatively different compositions have been developed using pulsed direct current (DC) by cyclic modulation of the cathode current density. The composition and number (hence thickness) of the layers were tailored by periodic modulation of the current density (c.d.) and time using a programmable power source. The deposition conditions were optimized for both the composition and thickness of the individual layers for the best performance of the coatings against corrosion. Electrochemical corrosion study, evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) demonstrated that the multilayer Ni-P alloy coating with 300 nanolaminated layers, represented as (Ni-P)1.0/4.0/300 showed several fold better corrosion resistance compared to its monolayer counterpart (deposited using regular DC) from the same electrolytic bath. Drastic improvement in the corrosion protection efficacy of the nanolaminated multilayer Ni-P alloy coatings were attributed to an increase in number of interfaces, separating layers of alloys having different morphologies, compositions and phase structures, which was supported by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analyses, respectively. The corrosion rates of the multilayer Ni-P alloy coatings were decreased with increasing number of layers, only up to an optimal level and then increased. The increase in corrosion rates at a higher degree of layering were attributed to the diffusion of layers, due to the very short deposition time of each layer. © The Royal Society of Chemistry 2016.Item Ultrasound induced multilayer Ni-Co alloy coatings for better corrosion protection(Elsevier B.V., 2017) Shetty, A.R.; Hegde, A.Ultrasound induced multilayer Ni-Co alloy coatings have been developed galvanostatically by periodic modulation of ultrasound effect, parallel to the process of conventional electroplating. Multilayer Ni-Co alloy having alternative layers of different composition were developed by turning the sonicator probe, ON and OFF periodically, while keeping the current density (c.d.) constant. The deposition conditions, in terms of pulsing power density (p.d.) and degree of layering have been optimized for the highest performance of coating against corrosion, evaluated by electrochemical testing methods. Corrosion data revealed that under optimal conditions, multilayer Ni-Co alloy coating having 150 layers, represented as (Ni-Co)2/2/150 is about 11 times more corrosion resistant than its homogeneous coating, represented as (Ni-Co)4.0 A dm ? 2, deposited from the same bath for same duration of time. Improved corrosion resistance of multilayer Ni-Co alloy coatings was attributed to an increase in the number of interfaces, separating the layers of alloys of different composition, affected due to periodic pulsing of the sonicator. The dependence of corrosion behaviors at different combination of c.d. and p.d., on surface morphology, composition and phase structures were analyzed, using scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS) and X-ray diffraction (XRD) technique, respectively. Experimental results are compared, and discussed. © 2017 Elsevier B.V.