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

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). ZnFe2O4 and ZnCr2O4 were found to be formed in the oxide film at the initial stage of immersion by substitution reaction between Zn2+ and Fe2+, and ZnCr2O4 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.

► ZnCr2O4 became dominate in oxide film after long-term immersion under ZWC condition.
► ZnCr2O4 shows wide E-pH region and low solubility under the simulated primary condition.
► Zn effects were rationalized by thermodynamic calculations and crystallographic analysis.