Formation and growth processes of electrochemical passive layers (borate medium: pH 9.2) and electron stimulated oxidized films (5.10~(-6) Pa O_2) formed on Fe-Cr alloys

摘要

Internal composition of passive layers (borate buffer pH 9.2, 0.3V/_(sce)) and Electron Stimulated Oxidized (ESO) layers formed on a series of Fe-Cr alloys (5 - 30 at%) was determined during ageing by quantitative AES depth profiling to approach and compare their film growth processes. ESO films were "in-situ" prepared by high (AES) electron irradiation under low oxygen pressures. In both cases, the film growth process seems to result of an outward cations migration (Fe Cr) under electric field (Cabrera-Mott model). Slow down of growth kinetics occurs beyond a critical chromium bulk concentration of 10-15 at% and may be attributed to an improved efficiency of inner Cr_2O_3 layers acting like a diffusion barrier for the Fe cations transport.