THE PITTING CORROSION OF PURE AND LOW ALLOYED COPPER IN CHLORIDE-CONTAINING BORATE BUFFERED SOLUTIONS

The pitting corrosion of pure and low alloyed copper in chloride-containing borate buffered solutions has been investigated by statistical analysis of pit induction times. The pitting susceptibility is quantified by the pit generation rate. lambda, deduced from the pit induction time distributions. When there is not sufficient time for the passive film to change during the tests (short induction times), its resistance to pitting does not vary significantly and the pit generation rate remains constant. For experimental conditions producing larger induction times, a decrease of pit generation rate is observed. A model, based on the observed influence of the prepolarization time, is proposed for describing such variations of lambda over time. The variations of lambda over time show that the evolution of the passive film in the presence of chloride ions is more favourable in regard to pitting resistance than that observed in absence of these species. Chloride ions incorporated in the passive film appear to have an inhibitive effect towards pitting corrosion.