Kinetics of Phase Transformations during Selective Dissolution of Cu5Zn8

Abstract

The study determined the kinetics of the selective anodic dissolution of the copper-zinc intermetallic compound Cu5Zn8 (gamma-phase) in an acetate buffer solution. Microscopic and X-ray analysis methods demonstrated the selective nature of the corrosive dissolution of Cu5Zn8. The dissolution results in the dezincification of the intermetalic compound and morphological development of its surface accompanied by the formation of the copper phase. A theoretical model of the transition of the electrode surface to the critical state together with the experimental concentration dependencies of the critical potential and critical overvoltage demonstrated that the dissolution of zinc from Cu5Zn8 is most probably limited by the non-stationary diffusion mass-transfer in the solid phase of the intermetallic compound. The study also demonstrated that the phase transformation during the overcritical selective anodic dissolution of the gamma-phase of Cu5Zn8 in an acetate environment accelerates following the growth of the anodic potential and is controlled by the surface diffusion of adatoms towards the three-dimensional nucleus of the copper phase with instantaneous nucleation.

Keywords

• copper-zinc alloy
• gamma phase
• selective dissolution
• phase transformation
• surface development
• heterogeneous nucleation.