Effect of the surface segregation of chromium on oxidation of high-purity Fe-Cr alloys at room temperature

Angle-resolved X-ray photoelectron spectroscopy (AR-XPS) has been used for investigating the effect of the surface segregation of chromium on oxide films formed on the surface of high-purity iron-13% and 25% chromium alloys at room temperature (298 K). The chromium segregation in the surface was confirmed by in-situ heating at 973 K under ultra high vacuum. The effective thickness of its segregated zone was evaluated to be less than 1 nm, from the relationship between the concentration of iron and chromium and the take-off angle in AR-XPS. The effective concentration of segregated chromium was estimated a few times as much as the bulk concentration. The surface with the chromium segregation was subsequently exposed to air, and an oxide film formed on the surface was also characterized. The oxide film formed on the surface with the chromium segregation was found to be thinner than the case without segregation. These results on the surface layer were consistent with spectral information of the chemical state denoted by Fe2p and Cr2p.