Electrochemical Development and Characterization of Mutual Alloys of Iron Group Elements

Abstract

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.