Faculty Publications

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Development of multilayer Sn-Ni alloy coating by pulsed sonoelectrolysis for enhanced corrosion protection
(Royal Society of Chemistry, 2016) Shetty, S.; Mohamed, M.J.; Bhat, D.; Hegde, A.C.
Multilayer Sn-Ni alloy coating has been developed electrochemically on mild steel using an ultrasound effect, as a tool to modulate mass transfer process at electrical double layer, during deposition. Sn-Ni coatings having alternate layers of alloys of different compositions were developed on a nano/micrometric scale by pulsing sonicator ON (tON) and OFF (tOFF), periodically. The composition modulated multilayer alloy (CMMA) Sn-Ni coatings have been deposited by inducing the ultrasound field periodically at optimal current density. Corrosion performances of ultrasound-assisted multilayer Sn-Ni alloy coatings have been evaluated by electrochemical methods. Corrosion data revealed that CMMA Sn-Ni coating, developed using pulsed ultrasonic field and having 150 layers, represented as (Sn-Ni)2/2/150, is the most corrosion resistant, compared to its monolayer alloy coatings developed by both with/without ultrasound effect. Corrosion protection efficacy of multilayer coatings was found to be decreased at high degree of layering due to diffusion of layers. Improved corrosion resistance of multilayer Sn-Ni coatings is attributed to an increase in the number of layers, or interfaces separating alloys of the same metals, but of different composition, surface morphologies and phase structures, supported by energy dispersive spectroscopy, field emission scanning electron microscopy and X-ray diffraction study, respectively. The better corrosion protection of CMMA Sn-Ni coatings, compared to monolayer counterparts, is attributed to an increase in the number of layers, hence phase boundaries between layers, and experimental results are discussed. © 2018 The Royal Society of Chemistry.
Effect of magnetic field on corrosion protection efficacy of Ni-W alloy coatings
(Elsevier Ltd, 2017) Elias, L.; Hegde, A.C.
High corrosion resistant Ni-W alloy coatings were developed using magnetoelectrodeposition (MED) approach for the protection of mild steel substrates. The conditions for the development of more corrosion resistant MED Ni-W alloy coatings were optimized by inducing a magnetic field (B) during deposition, in terms of intensity and direction. The applied magnetic field was used as a tool to alter the crystallinity, composition and thereby the corrosion resistance of the coatings. It was demonstrated that the corrosion resistance of Ni-W alloy coatings can be improved to many folds of its magnitude by MED approach. Significant increase in corrosion resistance exhibited by MED coatings (under both parallel and perpendicular magnetic field, B) is attributed to the increased W content of the alloy affected by an increase in limiting current density (iL). The high corrosion resistance of the MED Ni-W alloy coatings was explained in the light of magnetohydrodynamic (MHD) effect, responsible for the increased W content, brought about by the enhanced mass transport. The inherent limitations of the bath like low iL and induced type of codeposition which impedes the development of W rich alloy coatings has been successfully resolved by MED method. Drastic improvement in corrosion resistance is ascribed to the basic difference in the process of electrocrystallization and phases formed during MED, confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) study. The results are discussed with greater insight into binary alloy deposition and mass transfer process at cathode/electrolyte interface. © 2017 Elsevier B.V.
Effect of Potassium Sodium Tartrate on Composition and Corrosion Performance of Ni–W Alloy Coatings
(Pleiades journals, 2021) Neethu Raveendran, M.; Hegde, A.C.
Abstract: In this communication, the effect of potassium sodium tartrate as complexing agent on the composition, phase structure, surface morphology, and corrosion performance of electrodeposited nickel-tungsten alloy coatings is reported. The deposition conditions were optimized for the best performance of the coatings against corrosion. Ni–W coatings were developed at different current densities and their corrosion behaviour was studied. Compositional data revealed that the noble metal tungsten content of the alloy decreased with growing cathodic current densities. Characteristics responsible for the best anticorrosion performance of Ni–W alloy coatings were compared with those of a citrate bath, earlier reported by the authors and their colleagues. The experimental study in this paper demonstrated an inverse dependency of the W content of Ni–W alloy on a current density, compared to that in a citrate bath. The X-ray diffraction study revealed that anticorrosion performance is driven by the W content of the alloys, not by the current density at which they are deposited. An inverse dependency of the W content on a current density, is discussed in the light of the theory of the mass transfer controlled M-complex ions (where M = W/Ni), associated in the deposition. It is supposed that a decrease/an increase of the W content in a tartrate or a citrate bath with the current density is afforded by a lower limiting current density (iL) of the W/Ni-complex ion, depending on the stability of the M-tartrate/citrate complex formed. The experimental results were discussed with the help of different analytical techniques, like scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometry. © 2021, Allerton Press, Inc.

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