Electrochemical and surface analytical investigation of the effects of Zn concentrations on characteristics of oxide films on 304 stainless steel in borated and lithiated high temperature water

• Zn injection changed composition and structure of oxide films on 304 SS.
• A few ppb Zn altered electrochemical behaviour, more Zn injection had little effect.
• ≤50 ppb Zn injection could significantly affect formation of Zn-bearing oxides.
• A modified PDM is proposed to explain inhibition mechanism of Zn injection.

The characteristics of oxide films formed on 304 stainless steel (SS) in borated and lithiated high temperature water with Zn injection of 0 ppb to100 ppb were investigated using in-situ potentiodynamic polarization curves, electrochemical impedance spectra at 573.15 K and ex-situ X-ray photoelectron spectroscopy (XPS). There was a high inhibition effect of Zn injection on the growth of oxide films in the testing solution. The lowest growth rate was corresponding to the highest Zn-injected level. The ≤50 ppb Zn injection based on plant experience could significantly affect the formation of Zn-bearing oxides on the surfaces, while >50 ppb Zn injection showed no obvious influence on the oxide films. A modified point defect model was proposed to discuss the effects of injected Zn concentrations on the oxide films on 304 SS in high temperature water.