A contribution to the knowledge of electrochemical deposition of W induced by Ni

It was found that codeposition of Ni and W from an ammonia and citrate-containing electrolyte, is very sensitive to changes in operating conditions. The Ni-W alloy deposit exhibited sensitivity of chemical composition and phase structure on the composition of the electrolyte, pH in particular, as well as on the current density (cd), hydrodynamic conditions and quantity (thickness) of the deposit. Thus, small changes in pH, which arise during the process of bath utilization, are found to change the relationships between peaks in anodic dissolution voltammograms reflecting the existence of different phases. The anodic Linear sweep voltammograms (ALSV) of the alloys deposited at medium cds, pH lower than 8.4 and a high rate of rotation of the RDE contained two peaks. The first one could be ascribed to some tungsten oxide species while the appearance of the second one basically reflects the presence of solid solution of W in Ni, but also points to some other phases. The increase in pH, increase in ed, and the decrease in the rate of rotation of the RDE all lead to ALSV with a single peak with a peak potential shifted in the negative direction. i.e, towards the dissolution peak of pure Ni. Analysis confirmed a decrease of W content in that shift. Still a somewhat more noble behavior than that of Ni points out that some W still remains in the Ni. (C) 2000 Elsevier Science B.V. All rights reserved.