Determination of the diffusivity of point defects in passive films on carbon steel

Abstract Mott–Schottky analysis is performed for passive films formed on carbon steel in borate solution. It is shown that the calculated donor density decreases exponentially with increasing film formation potential. The experimental data are interpreted in terms of the point defect model for passivity of carbon steel, assuming that the donors are oxygen vacancies and cation interstitials. The diffusivity of the donors D0 is calculated to be in the range of 10−16–10−15 cm2 s−1.