In SR-GIXRD Study of Oxide Film Evaluation on AISI 304 Stainless Steel in High Temperature Water

Oxide films on AISI 304 stainless steel in high temperature and high pressure water were detected by a new method that synchrotron radiation grazing incidence X-ray diffraction. The morphology, phase structure, thickness and electrochemical corrosion resistance of the oxide films were illustrated. A empirical equation for oxide growth is applied to evaluate the changes in film thickness. Observations suggest that small irregular granular (Fe, Cr)₂O₃ oxides and polyhedral block (Fe, Cr)₃O₄ oxides are grown on stainless steel surface. The fine inner (Fe, Cr)₂O₃ particles preferentially form, and the part is precipitated by the (Fe, Cr)₃O₄ structure for the diffusion outward, leading to the formation of external coarse grain oxides. The average size of (Fe, Cr)₂O₃ is slightly oscillated with the oxidation time, and that of (Fe, Cr)₃O₄ oxides increases with the increasing exposure time. The oxide film thickness is less than 500 nm for 24 h oxidation in high temperature water, and for 240 h oxidation the thickness is less than 800 nm. Polarization and EIS test results indicate that the oxide films of (Fe, Cr)₂O₃ and (Fe, Cr)₃O₄ provides corrosion resistance for stainless steel.