Effects of pH value on characteristics of oxide films on 316L stainless steel in Zn-injected borated and lithiated high temperature water

• Fe oxides increase and Cr oxides decrease in oxide films as pH increases.
• Corrosion rate of 316L SS decreases with joint Zn injection and elevated pH value.
• Solubilities of oxides at 573.15 K are calculated using thermodynamic approach.
• A modified duplex-layer model is proposed to describe the evolvement of oxide films.
• An optimized water chemistry with low Zn and elevated pH is recommended.

The effects of pH values from 6.9 to 7.4 on oxide films for 316L stainless steel in borated and lithiated high temperature water at 573.15 K without and with Zn injection were examined by in situ potentiodynamic polarization curves, electrochemical impedance spectra and ex situ X-ray photoelectron spectroscopy (XPS) analysis. The composition of oxide films appears slightly pH dependent: rich in chromites and ferrites at pH = 6.9 and pH = 7.4, respectively. The corrosion rate decreases significantly in the high pH value solution with Zn injection due to the formation of compact oxide films. The solubilities and structural model of oxides are proposed and discussed.