AN OVERVIEW ON THE PASSIVITY OF METALS

A review is made of some essential subjects on the passivtion process, the passive film, and the film breakdown. Passivation of metals results from the formation of a condensed phase of continuous oxide layer on the metal surface. The electrochemical stability of passivated metals depends not only on the chemical property but also on the electronic property of the passive films. The electronic avalanche breakdown of passive film occurs when the film is thick, while the ionic breakdown emerges with thin oxide films in the presence of aggressive anions. The film breakdown is followed either by repassivation or by pitting corrosion depending on the degree of metal salt enrichment at the film breakdown sites. © 1990.