A Simple Phase Transition Model for Metal Passivation Kinetics

Abstract

We present a minimal parameter kinetic model which describes the corrosion and passivation of metal surfaces. Two elementary steps are included, namely, the oxidation of surface metal atoms to produce adsorbed cations, and the subsequent dissolution of these cations into the electrolyte. Oxide layer formation is represented by two‐dimensional condensation of adsorbed cations to produce a continuous phase; statistics of the condensation process are treated at the mean field level. The structure and magnitude of the i‐V curve in the active‐passive transition region is calculated for two cases: the limit of maximum passivation hysteresis (spinodal decomposition of the oxide phase), and the limit of zero hysteresis (equilibrated phase transition). Methods for analyzing experimental i‐V curves to yield the rate constants associated with the model are presented.