Electrochemical Behavior of Iron Within Crevices in Nearly Neutral Chloride Solutions

Abstract

In crevices where the internal iron is not short‐circuited to external metal, the corrosion rate is determined by the limiting cathodic current for oxygen reduction. This limiting current, and accordingly the corrosion rate, is independent of pH and Cl− concentration but is suppressed to a constant value when the height of the crevice is less than the thickness of the oxygen diffusion layer. When iron in the crevice is short‐circuited to external, open platinum, the initial crevice corrosion rate is independent of crevice height but increases with increasing Cl− concentration and area of external electrode. At constant Cl− concentration, the crevice corrosion rate of internal iron short‐circuited to open external iron decreases with increasing chromate ion concentration. At a constant chromate ion concentration which does not give protection, the crevice corrosion rate is greater the greater the chloride ion concentration for short times, but at longer times the rates are essentially independent of bulk chloride concentration.