Key parameters determining structure and properties of sulphide films formed on copper corroding in anoxic sulphide solutions

The corrosion behaviour of copper was studied in anoxic solutions containing different concentrations of sulphide (10(-5)-10(-3) mol L-1) and chloride (0.1-5 mol L-1) under stagnant and controlled convective conditions. The main determinants of the structure and properties of the copper sulphide (Cu2S) films formed are the rate of sulphide transport to the surface relative to the rate of its interfacial reaction with copper, and competition between sulphide and chloride for surface adsorption sites. When sulphide diffusion is rate limiting, the sulphide film formed is porous and non-protective, whereas when film growth is not limited by mass transport of sulphide, the sulphide film is compact and protective. The results indicate that, under Swedish repository conditions, the film formed on copper will be porous and non-protective and its growth diffusion controlled.