Passivity and its Breakdown: From Iron to Gold

Passivity, resulting from the direct oxidation of a metal by its environment, is observed not only for ferrous metals, nickel, aluminum, etc., but also for noble metals and other electronic materials ranging from superconductors, such as NbN, to magneto-optic alloys, such as Tb-Fe and Gd-Co. The passivating films on these metals are, however, subject to chemical and electrochemical attack that is followed by corrosion of the underlying metal. Conditions leading to passivation and to its breakdown, as well as the phenomonology and mechanisms of these processes, will be discussed.