The influence of electrolysis parameters on the composition and morphology of Co–Ni alloys

Abstract

The influence of cathodic current density, the concentration of Co 2+ ions in the electrolyte, and additional substances (saccharin and sodium lauryl sulfate) on the composition and morphology of Co–Ni alloys were investigated. Research was carried out in a Watts-type bath in the presence of boric acid, as a buffer substance. The circulation speed of the electrolyte was 40 dm 3 h −1. Cathodic polarisation curves were determined for parent metals and the Co–Ni alloy. It was established that the presence of additives shifts the cathodic potential of alloy deposition towards more negative values. An increase in the cobalt content in the alloy was observed with decreasing of the cathodic current density and increasing of the Co 2+ ions concentration in the bath. Results obtained confirmed the anomalous character of deposition of the Co–Ni alloy. The cathodic current efficiency is dependent mainly on the current density applied, but the direction of changes has not been precisely determined, for it depends on the composition of the electrolyte. Using diffractional X-ray and micro X-ray analyses, it was determined that single-phase deposits with an fcc lattice for the whole investigated range of current density and electrolyte composition were obtained. In the presence of additives there were obtained fine-grained, bright alloys which adhered well to the substrate.