Non-destructive analysis on oxidation states of Ti atoms in the passivation film formed on SUS321 using hard X-ray photoelectron spectroscopy

Abstract

An oxidation state of a small amount of Ti in the naturally formed passivation film on stainless steel (Fe-Cr alloy, SUS321) was non-destructively evaluated using angle resolved hard X-ray photoelectron spectroscopy (HX-PES) at BL46XU in SPring-8. The synchrotron radiation with photon energy of 7942.5 eV was used as an excitation source. The intensity of Cr 1s peak assigned to metallic state gradually increased with increasing of take-off angle θ from 15° to 30°. It drastically increased at larger take-off angle region (30~80°). The results clearly suggest a formation of passivation film on SUS321 and enough large probing depth of HX-PES to evaluate the chemical states of elements placed below the passivation film. Ti 1s spectra collected at take-off angles from 15 to 80° revealed only Ti in tetravalent state. Taking an inelastic mean free path length of Ti 1s photoelectrons into account, it suggests that only Ti in tetravalent state exists in and below the passivation film.