On Preferential Anodic Dissolution of Alloys in the Low-Current Region and the Nature of the Critical Potential

Abstract

Previous investigations on and alloys have shown that the polarization curves for anodic dissolution of the less noble metal are complex, that the mechanism of preferential anodic dissolution involves the interdiffusion of the components in an alloy layer next to the surface, and that appreciable surface roughening occurs. In the present paper the mechanism of preferential anodic dissolution at lower overpotentials and the nature of the transition (current increases sharply) which occurs at a certain (more noble or oxidizing) potential, , are examined. Results of electrochemical investigations on polycrystalline alloys at indicate that Cu atoms in direct contact with the electrolyte readily dissolve, and that a Cu‐depleted layer forms both above and below . At potentials more noble than appreciable transport of Cu through the Cu‐depleted layer occurs as a result of the onset at of gross surface roughening which provides for a relatively short and time‐independent, interdiffusion distance. The change in diffusion conditions which leads to a surface instability at is reasoned to be related to a potential‐dependent concentration of excess (di) vacancies in the interdiffusion layer.