Local Corrosion Chemistry—A Review

The localized chemistry in pits, crevices, and cracks has been studied since the middle of the 1920’s. Galvele introduced a quantitative framework for localized corrosion through his paper on acidification in pits. He developed a concept that required that the arithmetic product of pit depth and current density (x·i) must attain a critical value in order to sustain this local acidification. This framework, introduced in 1976, is still useful today. However, advances in modeling and analytical techniques have provided an expanded view of Galvele’s approach. Two criteria are generally used for solution-chemistry effects on localized corrosion initiation and repassivation: the critical pH and the critical concentration of metal-anion complexes. The paper discusses the results of different experimental and modeling approaches in understanding local chemistry changes during repassivation, with an emphasis on the role of metal-anion complexes in localized corrosion. Finally, the gaps in understanding and future research areas are discussed.