Temperature effects on the passivity breakdown of copper in chloride‐containing borate buffer solution

Abstract

Passivity and passivity breakdown of pure copper were studied in alkaline chloride‐containing borate buffer solution from 25°C to 80°C by electrochemical measurements and scanning electron microscopy. The corresponding E–pH diagrams were also calculated. Increased temperatures make the open circuit potential and formation potential for cuprous oxide (Cu2O) shift in a negative direction. The mean breakdown potential shifts in a positive direction and the distribution of breakdown potential has a wider width, while the minimum breakdown potential decreases slightly at higher temperature. The anodic passive film formed at 0.4 V versus Ag/AgCl for 6 h in a chloride‐free solution at T ≥ 40°C can maintain passivity after the addition of 0.1 M NaCl, but cannot maintain passivity at 25°C at the same concentration. High temperature benefits the growth of copper oxide over the formation of copper chloride species. Cu2O and CuO have excellent corrosion resistance to 0.1 M NaCl and passivity can be maintained well above the CuO/Cu2O equilibrium at pH > 8.