THE OPTIMAL FORMATION CONDITION OF CHROMIUM OXIDE THIN FILM ON STAINLESS-STEEL SURFACE

We investigated the various oxidation conditions of stainless-steel surface using synchrotron radiation photoemission spectroscopy. Stainless-steel samples are oxidized at 450-550degreesC in various oxygen partial pressures. Increasing the annealing temperature from 450degreesC to 550degreesC, the trivalent chromium concentration in the surface increased and iron oxides decreased. The PES spectra from stainless steels oxidized at 550degreesC show that there exists the critical oxygen partial pressure, p'(c) similar to 5 x 10(-7) Torr. Below this critical pressure, the oxide formed mainly consists of chromium oxide, while the oxide formed mainly consists of iron oxide above the critical pressure. The oxidation behavior is in good agreement with the Ellingham diagram (a free-energy/temperature diagram).