The nucleation and growth of corrosion pits on stainless steel

The nucleation and growth of corrosion pits on stainless steels in chloride is described. Pits arise from distinct sites on the surface that are destroyed after reaction. Metastable and stable pits grow at a diffusion-controlled rate. In the metastable state metal dissolution occurs through a perforated cover: the pit only achieves stability when this cover is no longer necessary to maintain the diffusion barrier. The growth of the pit and the transition from metastability to stability is described by the pit stability product. Recent results show that nucleation of the corrosion pit occurs by a microscopically violent event, observed as a sharp tiny current transient which initiates metastable pit growth. Many such nucleation events do not achieve metastability, however, and die immediately after nucleation.