Rate controlling reactions for copper corrosion in anaerobic aqueous sulphide solutions

Abstract

The long term corrosion behaviour of copper in anoxic aqueous sulphide solutions has been studied using corrosion potential and electrochemical impedance spectroscopy measurements and scanning electron microscopy on corroded surfaces and cross-sections of surfaces prepared using a focused ion beam. Experiments were conducted in solutions containing either 5×10^?4 or 5×10^?5 mol L^?1 sulphide for 1691 and 4000 h respectively. In the more concentrated solution, a coherent, compact and crystalline chalcocite (Cu₂S) film accumulated on the corroding copper surface. A parabolic growth law was obtained, and the kinetics were controlled by Cu(I) ion transport either through the Cu₂S matrix or along crystalline grain boundaries in the film. In the more dilute solution, the growth of a less crystalline, porous chalcocite layer followed approximately the linear growth kinetics controlled by sulphide ion transport through the pores. If the sulphide was allowed to deplete in the dilute solution, rate control switched to sulphide diffusion in the bulk solution. The implications for waste container corrosion in a nuclear waste repository are discussed.