Influence of Zn injection on characteristics of oxide film on 304 stainless steel in borated and lithiated high temperature water

► ZnCr 2O 4 became dominate in oxide film after long-term immersion under ZWC condition. ► ZnCr 2O 4 shows wide E-pH region and low solubility under the simulated primary condition. ► Zn effects were rationalized by thermodynamic calculations and crystallographic analysis. The oxide film on 304 stainless steel exposed to the hydrothermal environments at 573.15 K up to 20 days without/with 10 ppb Zn injection has been investigated ex situ by X-ray photoelectron spectroscopy (XPS). ZnFe 2O 4 and ZnCr 2O 4 were found to be formed in the oxide film at the initial stage of immersion by substitution reaction between Zn 2+ and Fe 2+, and ZnCr 2O 4 became dominant after long-term immersion. The calculations of potential-pH diagrams, solubilities and crystallographic features of spinels have been done to evaluate the oxide film structure and the inhibition mechanism caused by Zn injection.