Kinetics and Mechanism of Passive Film Formation on Iron in 0.05M   NaOH

Abstract

Simultaneous electrochemical and ellipsometric studies of the anodic film growth on iron in have revealed that passivation occurs in two stages. During the first stage, which lasts for about 2s, the anodic current is consumed only for film growth, whereas in the second stage release of iron cations into the electrolyte also occurs. The chemical composition of the passive film formed for times longer than 2s corresponds to with a constant density and a complex index of refraction of . During the first stage of film formation , the film density and the complex index of refraction change from values characteristic of the electrolyte to those of, which is probably related to the fact that the amount of water occluded in the passive film decreases with time. The film thickness increases with increasing anodic potential. A major increase in film thickness occurs during the first 0.2–0.5s.