A preliminary study of the corrosion films of stainless steel SUS304 was carried out by X-ray photoemission spectroscopy for supercritical water having no oxidant or reactant. The corrosion films produced by the supercritical water at 450°C and 50 MPa were compared with those by anodic polarization in H 2SO 4 aqueous solution. The chemical states in the films were determined by factor analysis of Fe, Cr, and Ni 2p X-ray photoelectron spectra. Factor analysis of the passivated SUS304 surface was successfully carried out using four reference spectra, Fe metal, Fe 3O 4, Fe 2O 3, and FeOOH, with careful treatment excluding wüstite Fe 1-xO phase from the standpoint of thermochemistry. In the surface treated by supercritical water, the ratio of iron and nickel increased even when compared to the bulk composition of SUS304 and the major component of nickel was attributed to NiFe 2O 4. In contrast, the content of chromium decreased remarkably. This was explained by effective removal of CrO 4 2- and its protonated form, HCrO 4 -, which are predicted in the Pourbaix diagram prepared for chromium in supercritical water (450°C and 50 MPa).
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry