Photocathodic protection of oxide films formed on 304 stainless steel by hightemperature oxidation

Purpose This study aims to prepare in situ on 304 stainless steel by using the high-temperature oxidation at 350°C, 550°C and 750°C of oxide films and analyze the semiconductor properties and photoelectrochemical cathodic protection (PCP) of oxide films. Design/methodology/approach Photocathodic protection of oxide films in situ on 304 stainless steel in air at 350°C, 550°C and 750°C in 3.5 wt.% NaCl solution has been investigated by using electrochemical techniques to analyze the semiconductor properties and using UV-visible spectroscopy to evaluate optical properties, with bandgaps estimated via the Kubelka–Munk function. SEM, XPS and XRD have been also used to characterize the oxide films. Findings The results show that the Cr/Fe atomic ratio in the surface oxide film increases from 0.29 to 0.4 with the increase of temperature. The oxide film formed at 550°C consist of Fe2O3/Cr2O3 and with highest carrier concentration. The oxide film formed at 350°C contain main phase of Cr2O3 and the oxide film at 750°C with main phase Fe3O4. Furthermore, the charge transfer resistance (Rct) value of the oxide film at 550°C was 27% of that of oxide film at 350°C and 72% of that of oxide film at 750°C. Originality/value The oxide film formed at 550°C had significantly highest PCP. The oxide film at 550°C exhibited tremendous PCP performance may attribute to p-n heterojunction consist of Fe2O3/Cr2O3, thereby accelerating electron transfer efficiency.