The Limiting IR Voltage within Electrolyte in Cavities during Localized Corrosion and Hydrogen Charging of Metals

摘要

In-place gas bubbles within pits, crevices and cracks often cause large differences in electrode potential between the base of the cavity (E sub x=L) and the sample surface (E sub x=o). These potential changes are much greater than predicted by existing theoretical calculations which ignore the possibility of a constricted current path. In this paper, a limiting electrode potential, E sub LIM, within the cavity is identified. It is the potential at which the net current, with respect to that available for flow in (or out of) the cavity, is zero. (1) In the case of a single current-producing reaction within the cavity, E sub LIM is the equilibrium potential of this reaction. (2) For more than one reaction of the same sign, E sub LIM will be the least noble equilibrium potential in the case of anodic polarization, and the most noble for cathodic reactions. (3) When reactions of opposite sign occur in the cavity E sub LIM will be the mixed potential of these reactions.