Influence of Zn on oxide films on Alloy 690 in borated and lithiated high temperature water

To clarify the corrosion control effect of Zn injection into hydrothermal environments, the oxide films on Alloy 690 in the deaerated borated and lithiated water have been investigated using potentiodynamic polarization curves, electrochemical impedance spectra at 300 °C and ex-situ X-ray photoelectron spectroscopy. With Zn injection in the solution, ZnCr2O4 and ZnFe2O4 were formed in the inner and outer layers of the oxide films on Alloy 690, respectively, through exchange reactions between Zn2+ and Fe2+/Ni2+. A simple model for oxide film structure change and the mechanism of corrosion inhibition by Zn injection is proposed and discussed.

► Resistance of oxide film increased and passive current density decreased with Zn injection.
► A stable oxide film composed of ZnCr2O4 and ZnFe2O4 was formed with Zn injection.
► A model for oxide film characteristics and inhibition mechanism by Zn injection is proposed.