THE NUCLEATION AND GROWTH OF CORROSION PITS ON STAINLESS-STEEL

The nucleation and growth of corrosion pits on stainless steels in chl oride is described. Pits arise from distinct sites on the surface that are destroyed after reaction. Metastable and stable pits grow at a di ffusion-controlled rate. In the metastable state metal dissolution occ urs through a perforated cover: the pit only achieves stability when t his cover is no longer necessary to maintain the diffusion barrier. Th e growth of the pit and the transition from metastability to stability is described by the pit stability product. Recent results show that n ucleation of the corrosion pit occurs by a microscopically violent eve nt, observed as a sharp tiny current transient which initiates metasta ble pit growth. Many such nucleation events do not achieve metastabili ty, however, and die immediately after nucleation.