Nucleation and Repassivation of Corrosion Pits for Pitting on Iron and Nickel

Pit nucleation and repassivation on iron and nickel has been examined by potentiostatic transient measurements. Very short times for the nucleation of corrosion pits of some ms to some 100 ms for prepassivated specimens have been observed. Addition of picrate to the electrolyte can stop pit nucleation for well prepassivated specimens at all potentials completely, but cannot prevent the corrosion of already existing pits. The results are explained by the adsorption‐ and film breaking theory but give contradiction to the penetration mechanism. The repassivation of corrosion pits in an early stage of development takes Δ Tr = 1 ms to some 100 ms according to the pitting time Δ tp and the pit current density. A relation Δ Tr = k(Δtp)2 has been found. The transport of the accumulated aggressive anions from the pit electrolyte to the bulk solution is postulated as the rate determining process for repassivation.