Kinetics of induced electrodeposition of alloys containing Mo from citrate solutions

Abstract

Abstract The kinetics of Ni‐Mo alloy electrodeposition from complex citrate‐sulphate baths has been investigated by means of steady‐state polarization measurements in a system with a rotating disk electrode (RDE). The partial current densities for deposition of Ni and Mo as a function of the solution composition, the cathode potentials and the rate of mass transport were determined. Strong interaction between the discharging metal ions occur: nickel induces molybdenum deposition, but its discharge is markedly inhibited by molybdenum. This effect, related to the formation of intermediate molybdenum oxides, becomes less pronounced when the rotation speed was increased. Hydrogen evolution is associated with molybdenum deposition. An increase of the molybdate ions concentration in the bath, as well as an increase in the rate of mass transport lead to an increase in Mo content in deposits and to the reduction of current efficiency. The surface morphology as a function of the content of molybdenum in the alloy were also investigated. Crack‐free, compact, semi‐bright Ni‐Mo coatings, containing up to about 40 wt% of Mo, characterized by good adhesion to steel substrate were obtained. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)