On a Recent Quantitative Framework Examining the Critical Factors for Localized Corrosion and Its Impact on the Galvele Pit Stability Criterion

A quantitative framework examining the Galvele pit stability criterion in the context of repassivation using information from experiments on 1D stainless steel artificial pit electrodes and mass transport modeling is discussed. The framework is built principally upon three studies that have systematically evaluated the critical electrochemical conditions describing the transition of a corroding surface from active dissolution to repassivation. First, the applicability of the Galvele pit stability product for the interpretation of the results of artificial pit experiments was assessed by analyzing the 1D flux as a function of pit geometry, which delineated the parameter space for appropriate data collection and analysis. Mass transport modeling of the 1D pit in combination with experimental measurements of the pit stability product and the repassivation potential provided an estimate of the critical concentration of metal ions at the corroding surface of the pit as it transitioned from stability to repassivation. This estimate was confirmed by separate concentration-dependent anodic kinetics experiments. Finally, this framework was extended to include the critical pH associated with the transition, which was evaluated based on the increasing influence of the cathodic reaction inside the pit as repassivation was approached. Applying mixed potential theory to these results provided the mechanistic rationale that validated this framework to describe repassivation. This framework advanced the idea that critical conditions for pit stability and repassivation were fundamentally independent of geometry.