Identification by photoelectrochemistry of oxide phases grown during the initial stages of thermal oxidation of AISI 441 ferritic stainless steel in air or in water vapour

Abstract: Room temperature photoelectrochemistry was used to characterise oxide phases grown during the initial stages of oxidation of the ferritic stainless steel AISI441 at 650°C and 850°C in synthetic air or in water vapour. Grazing incidence X-ray diffraction and Raman spectroscopy were additionally used to discuss PEC results. Haematite Fe2O3 (∼2.0eV), chromia Cr2O3 (3.0 and 3.5eV) and their mutual solid solution (∼ 2.5eV) were detected by their respective bandgap values determined from photocurrent vs. energy curves. The Cr/Fe ratio of the films increased with time/temperature and was higher in air-grown than in H2O-grown oxides. Observation of photocurrent vs. potential curves indicated that chromia was N-type in all specimens, resulting from thermodynamic equilibrium with the metallic substrate and not with the gas phase. [Copyright &y& Elsevier]