Passivation and its stability on copper in alkaline solutions containing carbonate and chloride ions

Abstract

The anodic polarization curve of copper in borate buffer solution at pH 11 shows two anodic current peaks at −0.26V(Pa a1) and −0.03V(P a2) and a passive region with a small hump at a more positive potential. It is found from the result of a channel flow electrode that P a1 corresponds to the formation of Cu 2O, while P a2 seems to be related with the formation of Cu(OH) 2. The presence of carbonate ion hinders protective Cu(OH) 2 passive layer formation. The addition of chloride ion (>0.5 mol/l) causes pitting corrosion at a potential close to oxygen evolution. The stability of the passive film in alkaline solution is lowered by the presence of carbonate or chloride ion. The anodic polarization curve obtained in concentrated carbonate-chloride solution (>1mol/l) at pH11 shows two Tafel regions, the slope of which has 60 and 40 mV/decade, proceeding P a1 and P a2, respectively. Active dissolution model in both Tafel regions have been proposed.