The Influence of Weak Ionic Interactions on Electrode Reactions during Electrodeposition of Re-Ni Alloys

Abstract

The electroplating of Re-Ni alloys in citrate electrolytes of different compositions was studied by cyclic voltammetry and by anodic stripping voltammetry, following galvanostatic deposition. The faradaic efficiency of the deposition process and the composition of the deposits were determined. Increasing the concentrations of either the nickel or the perrhenate ion in the electrolytes was shown to enhance the rate of deposition of the Re-Ni alloy. The process is influenced by mass transport and by concentration of citric acid in the electrolytes. Conductometry, UV-Vis and Raman spectroscopy were used for studying the ionic interactions in electrolytes. No evidence of the existence of perrhenate complexes with other components of the electrolyte was found. However, an increased deformation of the perrhenate ions with increasing molar ratio of [NiCit]−/ReO−4 was clearly shown by Raman spectroscopy. Hence, a weak interaction is definitely observed, which is enough to distort the shapes of the ReO−4 and [NiCit]− or [NiHCit] species, thus enhancing the deposition rate of the Re-Ni alloy. The induced co-deposition is believed to be a catalytic process, including the stage of simultaneous reduction of ReO−4 and [NiCit]− or [NiHCit] species, which influences each other by weak interaction.