Passivity breakdown, pit initiation and propagation of pits in metallic materials - Review

The article presents a review of literature which covers aspects of pitting corrosion observed in metallic materials, focussing on events associated with nucleation of pits, i.e. passivity breakdown, initiation of pits and their propagation stage. It is highlighted that there is a clear separation of the passivity breakdown/pit initiation process from the pit propagation, which can be considered in terms of the localised acidification model of Galvele. The process of passivity breakdown is more diverse and remains still the least understood. Relevant appears the recent argument of Burstein about the state of passivity and its continuous process of breakdown and repair. Under such conditions and using the localised acidification as a criterion, the likelihood of stable pits is then only a question of how good the repair process is.