Solid-Phase Diffusion at a Galvanostatic Anodic Dissolution of Zn
Ag and Cu
Au Alloy
O. A. Kozaderov, E. V. Bobrinskaya, T. V. Kartashova, and A. V. Vvedenskii
Voronezh State University, Universitetskaya pl. 1, Voronezh, 394006 Russia
Received August 17, 2004
Abstract — The ionization stages of copper and zinc at a galvanostatic anodic dissolution of Zn–Ag and Cu–Au alloys in acidic chloride environment are found to be electrochemically nonequilibrium. Selective dissolution of the alloys is limited by the transient mutual diffusion of components within a nonequilibrium surface layer. In terms of diverse theoretical models of the solid-phase mass transfer, the effects of the electrode surface microroughness, the apparent shift of the alloy–electrolyte interface boundary, and the relaxation of the vacancy subsystem are analyzed. The parameters of the diffusion layer, namely, its thickness, diffusivities, mutual diffusivities, and the over-equilibrium vacancy concentration were found. The latter characteristic is determined by the dissolution rate of the electrochemically negative alloy component, and, hence, the diffusivities and the Sand parameter of the diffusion kinetics substantially increase with an increase in the current density.