A study of the structure of a passive film using angle-resolved X-ray photo-electron spectroscopy

Angle-resolved X-ray photo-electron spectroscopy (ARXPS) measurements were performed in order to characterize the in-depth distribution of constituents in the passive film formed on amorphous Al-36Cr-9Mo alloy in 1 M HCl. The result showed that chromium cations were enriched in the exterior of the passive film and aluminum cations were rich in the interior. A model of in-depth distribution of constituents in the passive film considering migration and diffusion of cations was proposed. Experimental data by ARXPS were in agreement with the exponential concentration in-depth distribution of cations of the passive film. The analysis indicated that the migration and diffusion of chromium cations in the passive film were faster than those of aluminum cations. The enrichment of chromium at the outermost surface of the passive film was attributed to the faster dissolution of aluminum cations into the solution in comparison with that of chromium cations. Copyright (C) 1996 Elsevier Science Ltd.