The Location of Cathodic Reaction during Localized Corrosion

Abstract

A theoretical model for predicting the current and potential distribution within a prototypic pit was used to estimate conditions under which cathodic reaction occurs in the occluded region. The model is developed for a long, narrow occluded cell where the anode is localized in the tip region. Cathodic reaction (hydrogen reduction) on the side walls and external surface is predicted by assuming metal‐ion hydrolysis, diffusion of hydrogen ions, Ohm's law, cathodic reduction via Tafel kinetics, and constriction of current lines entering the occluded region. Results indicate that cathodic reaction within occluded regions is favored for deep narrow regions in solutions of low hydrogen ion concentration. Dimensionless groupings of system parameters are used to scan behavior over wide ranges of parameter space and to compile conditions under which appreciable cathodic reaction can be anticipated within occluded cells.