Quantitative analysis of iron dissolution during repassivation of freshly generated metallic surfaces

A channel flow double electrode was coupled with the pulsed laser depassivation technique to investigate the repassivation kinetics on iron in sulfuric acid (pH 1 to 3). The amount of ferrous ion dissolved from the activated iron electrode during repassivation was measured. The total charge for repassivation is separated into partial charges for dissolution of ions, Q(d), and formation of adsorbed species, Q(f). The charge Q(d) decreases with the electrode potential. The charge Q(f) does not depend on the electrode potential. Its value corresponds to the formation of a monolayer of trivalent oxide film. A reaction model for repassivation of iron involving two adsorbed species was simulated numerically in good agreement with the experimental results. The actual rate of repassivation was characterized by the fractional coverage of passivating species.