Kinetics of the selective dissolution of Cu-Au alloys under conditions of copper passivation

An appearance of the film of difficultly soluble products of the copper anodic dissolution from Cu-Au alloys (0.1 to 30 at. % Au) in a chloride-containing universal buffer solution (pH 1.25 to 11.90) does not affect the kinetics of the process, which is diffusionally controlled. However, depending on the chemical nature of the product (CuCl or Cu2O), predetermined by the potential of dissolution and the pH, the rate-determining diffusion transport takes place either in Cu(I) oxide at pH greater than or equal to 8.7 or in the surface layer of the alloy at pH less than or equal to 6.00, despite the formation of CuCl. Accordingly, in the former case, the cyclic voltammograms of Cu and Cu-Au alloys practically coincide, whereas, in the latter case, the dissolution of copper from alloys is substantially decelerated.