Browsing by Author "Hegde, A. Chitharanjan"

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Electrochemical Development and Characterization of Mutual Alloys of Iron Group Elements
(National Institute of Technology Karnataka, Surathkal, 2013) G.P., Pavithra; Hegde, A. Chitharanjan
This thesis titled ‘Electrochemical development and characterization of mutual alloys of iron group elements’ details a comprehensive approach for electrodepositon mutual alloys of Fe-group metals by a relatively inexpensive, but advanced method called composition modulated multilayer alloy (CMMA) coating method. The coating has been accomplished galvanostatically on copper using Single Bath Technique (SBT). The essential feature of this method is their tailored micro/nano structured layers with alternatively changing composition is responsible for improved corrosion resistance of the coatings. The project involves optimization of three new binary baths of mutual alloys Fe-group metals and their multilayer coatings using direct current (DC) and pulsed current, respectively. The plating conditions and operating parameters have been optimized for best magnetic and corrosion performance of monolayer (non-nanostructured, or bulk) alloy coatings. As an attempt to increase the corrosion resistance of the monolayer coatings of Fe-group metals, namely Fe-Ni, Co-Ni and Fe-Co and multilayer coatings, represented as CMMA (Fe-Ni), (Co-Ni) and (Fe-Co) have been accomplished using square current waves having dual and triple pulses from respective baths (optimized). Multilayer coatings with different configurations have been developed with different combination of current densities, called cyclic cathode current densities (CCCD’s) and number of layers. All depositions were carried out galvanostatically on copper from the respective baths for 10 minutes. Boric acid (BA), ascorbic acid (AA) and sulphanilic acid (SA) were used, as common additives to impart better appearance. The corrosion behaviors of the coatings were evaluated in 1M HCl, as representative aggressive corrosion medium by electrochemical AC and DC techniques. The surface morphology, composition and phase structure of the coatings were characterized by SEM, EDX and XRD methods respectively. The experimental results revealed that CMMA coatings developed using dual and triple current pulses exhibit better (by several fold) corrosion resistance compared to monolayer alloys, developed from same bath for same time. The significant improvement in corrosion performance of CMMA coatings was attributed to small compositional difference in alternate layers, due to change in deposition current density. The formation of layers and their corrosion mechanism have been identified by SEM analysis. The improved corrosion protection of multilayer coatings was found to be the combined effect of compositional modulation of the individual layers and increased number of interfaces due to layering. The experimental data were analyzed, and results were discussed with Tables and Figures.
Electrofabrication of Ni-Based Alloy Coatings for Anticorrosion and Water Splitting Applications
(National Institute of Technology Karnataka, Surathkal, 2023) Gonsalves, Cindrella Nishmitha; Hegde, A. Chitharanjan
This thesis titled ‘Electrofabrication of Ni-based alloy coatings for anticorrosion and water splitting applications’ presents a comprehensive study on development and characterization of two Ni-based alloy coatings from newly formulated baths, namely (Ni-Mo) and (Ni-Fe). Standard Hull cell method was used to optimize bath constituents and operating conditions for best performance of alloy coatings against corrosion, as well as for good electrocatalytic activity for water electro-splitting applications. The corrosion protection efficacy of monolayer Ni-based alloy coatings were improved further by modern methods of electroplating, namely magneto-electrodeposition (MED) and composition modulated multilayer electrodeposition (CMM-ED) approach. Poor corrosion resistance of (Ni-Mo) alloy coatings, limited by the low concentration of metal ions was successfully alleviated by taking the advent of magnetic field (B) effect, applied simultaneously to the process of deposition. Experimental investigation revealed that corrosion protection efficacy of monolayer (Ni-Mo) alloy coatings can be improved about 5 times and 8 times better, through MED technique by superimposing the B, parallel and perpendicular (to the direction of movement of metal ions), respectively. The attractiveness of electroplating linked to the cathode current density has been explored effectively for the development of multilayer (Ni-Fe) alloy coatings of better corrosion resistance, compared to their monolayer counterpart. The multilayer (Ni-Fe) alloy coatings of much higher corrosion resistance were developed by proper manipulation of composition and thickness of alternate layers of alloys by proper modulation of amplitude and duration of current pulse, respectively. In addition, the electro-catalytic activity of (Ni-Mo) and (Ni-Fe) alloy coatings have been tested for their efficacy for both HER and OER in water splitting applications in 1.0 M KOH. The effect of composition, surface morphology and phase structure of alloy coatings on their electro-catalytic efficacies have been studied, using CV and CP methods. The effect of addition of redox-active polyoxometalates (POM), and Ag-nanoparticles into electrolytic baths of (Ni-Mo) and (Ni-Fe) on electro-catalytic activities of their coatings were studied, and reasons responsible for improved activities were discussed. Corrosion performance of all coatings were studied by electrochemical AC and DC methods in 3.5 % NaCl, and results were compared. The process and product of electrodeposition were characterized using SEM, EDS, AFM and XRD techniques. The performance of alloy coatings developed under different conditions of current density are compared, and results are discussed with Tables and Figures.
Electrolytic Synthesis and Characterization of Binary Alloy Coatings for Different Applications
(National Institute of Technology Karnataka, Surathkal, 2024) G, Harshini Sai; Hegde, A. Chitharanjan
This thesis titled ‘Electrolytic synthesis and characterization of binary alloy coatings for different applications’ presents a comprehensive study on development and characterization of Ni/Co-based alloy coatings from newly formulated baths, namely Ni-Ti, Co-P and Co-Fe. Standard Hull cell method was used to optimize bath constituents and operating conditions for best performance of alloy coatings against corrosion, and electro-catalytic activity of water electrolysis. The corrosion protection efficacy of monolayer Ni/Co-based alloy coatings were improved further by modern methods of electroplating, namely composition modulated multilayer (CMM) and magneto-electrodeposition (MED) approaches. The attractiveness of electroplating linked to the cathode current density has been explored effectively for the development of multilayer Ni-Ti and Co-Fe alloy coatings for better corrosion resistance, compared to their monolayer counterpart. The multilayer Ni-Ti and Co-Fe alloy coatings of higher corrosion resistance were developed by proper manipulation of cyclic cathode current densities (for change of composition of layers) and duration of current pulse (for change of layers thickness). Corrosion performance of alloy coatings, were studied by electrochemical AC and DC methods in 3.5 % NaCl solution. Poorer corrosion resistance of (Ni-Ti) alloy coatings, inherited by its bath composition was successfully improved by inducing magnetic field (B), parallel to the process of deposition. Effect of both intensity and direction of B (both parallel and perpendicular) were tested. Experimental investigation revealed that corrosion protection efficacy of monolayer Ni-Ti alloy coatings can be increased seven fold better through MED technique. In addition, the electro-catalytic activity of Ni-Ti and Co-P alloy coatings have been tested for their efficacy for water splitting applications in 1.0 M KOH. The effect of addition of Ag-nanoparticles into baths of Ni-Ti and Co-P on electro-catalytic activities of their coatings were studied. The effect of composition, surface morphology and phase structure of alloy coatings on their electro-catalytic efficacies have been studied, using CV and CP methods. The process and product of electrodeposition were characterized using SEM, EDS, AFM and XRD techniques. The performance of different alloy coatings developed for same duration (10 min) through different methods (monolayer, CMM, and MED) were compared, and experimental results are discussed with Tables and Figures.
Electrolytic Synthesis of Nickel Based Alloys and Their Characterization
(2018) S, Sandhya; Hegde, A. Chitharanjan
This thesis titled, Electrolytic synthesis of nickel based alloys and their characterization details a comprehensive approach for improving the corrosion resistance and electrocatalytic activity of Ni–M (where M = Sn and Mo) alloys through an inexpensive, yet advanced electrodeposition method. The coating properties have been improved by regulating the mass transfer process at cathode film, parallel to the process of deposition. The modulation in the mass transfer was affected by pulsing the current density (c.d.), magnetic field intensity (B) and ultrasonic power density (p.d.). The thesis comprises the optimization of two new binary alkaline baths, namely Sn–Ni and Ni–Mo using direct current (DC) for highest performance of corrosion resistance and electrocatalytic activity for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The corrosion behaviors were evaluated in 5% NaCl solution using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods. Experimental results revealed that corrosion resistance of multilayer Sn–Ni alloy coatings developed by pulsing ultrasound p.d. is many folds better than its monolayer counterpart. The kinetic parameters for HER and OER were determined by cyclic voltammetry (CV) and chronopotentiometry (CP) methods in 1.0 M KOH medium. The electrocatalytic activity of magneto-electrodeposited Ni–Mo alloy coatings were improved, due to changed limiting c.d. (iL) of more readily deposit-able metal, explained by the hydrodynamic effect. Effect of addition of reduced graphene oxide (rGO) into the alloy matrix and the anodic dissolution of the as-deposited coating as a tool to enhance the electrocatalytic activity of Ni–M alloys has also been examined. The changed property of alloy coatings was found to bear a close relationship with their composition, phase structure, surface morphology and roughness, confirmed by EDX, XRD, SEM and AFM analyses, respectively. The experimental data are compared, and results are discussed with Tables and Figures, a note for future work is mentioned at the end.
Synthesis and Characterization of Electrodeposited Nickel Based Alloys and Their Nanocomposite Coatings
(National Institute of Technology Karnataka, Surathkal, 2017) Elias, Liju; Hegde, A. Chitharanjan
This thesis titled ‘Synthesis and Characterization of Electrodeposited Nickel Based Alloys and Their Nanocomposite Coatings’ is a comprehensive approach for improving the corrosion resistance and electrocatalytic activity of binary alloys, namely Ni-W and Ni-P. New alkaline citrate baths have been optimized for the electrodeposition of Ni-W and Ni-P alloy coatings through standard Hull cell method, using glycerol as a common additive. The effect of bath composition, deposition current density (c. d.), pH and concentration of additive on the coating properties were studied. The corrosion resistance of monolayer alloy coatings were improved to many folds of its magnitude through multilayer approach by depositing in layers, having alternatively different composition. Further, the benefit of magnetoelectrodeposition (MED) has been explored for improving the coating characteristics of Ni-W alloy. The conditions of MED have been optimized for maximizing the corrosion protection efficacy of Ni-W alloy coatings. The effect of magnetic field (B) on coating characteristics, in both intensity and direction have been tested. A significant change in the deposit characters have been observed due to increase in the limiting current density (iL), explained by the magnetohydrodynamic (MHD) effect. The electrocatalytic activity of the alloy coatings towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) were tested using electrochemical methods. The HER efficiency of the coatings was further enhanced by different methods such as electrochemical dissolution, MED, magnetic field induced HER (MFI-HER), and by nanoparticles incorporation. All depositions were carried out for the same duration (10 min) for comparison purpose. The corrosion resistance and electrocatalytic activity of Ni-based alloy coatings and their nanocomposite coatings were compared in relation to their composition, surface morphology and phase structure. The process and product of electrodeposition were characterized using different analytical techniques, like SEM, XRD, EDS etc. The performance of the coatings have been compared and discussed with Tables and Figures, supported by plausible mechanism.