DEFECT FORMATION AND PHASE-TRANSFORMATIONS IN OXIDE-FILMS ON IRON IN ANODIC POLARIZATION IN A NEUTRAL SOLUTION

The role of nonstoichiometry of oxide films in the mechanism and kinetics of anodic behavior of iron in a neutral solution has been studied. Anodic dissolution of iron proceeds in the presence of a nonstoichiometric oxide film with participation of oxygen vacancies and defect-ions Fe2+, the active centers of metal dissolution. The potential of iron transition to the state of passivity corresponds to the anodic boundary of the region of oxide stability as viewed from the oxygen deficiency and critical concentration of nonstoichiometry defects. Oxygen stoichiometrization of the oxide and its ordering at the subsequent solid-phase transformation provide passivity of iron. The necessary amount of oxygen comprises the monolayer fractions.