Passive film growth and oxide layer restructuring on stainless steel in a high-temperature borate electrolyte

The oxide films formed on AISI 316L(NG) in the temperature range 150-300°C in a simulated light water reactor coolant have been characterised by impedance spectroscopy and ex-situ analysis using Auger electron spectroscopy. The results show that the nature of the barrier layer does not change drastically with temperature, although the growth mechanism of the oxide film is different at 150…300°C than at room temperature. A procedure for the calculation of the kinetic constants of the interfacial reactions, as well as the diffusion coefficients of ionic / electronic defects in the oxide has been developed on the basis of the Mixed-Conduction Model for passive films. The effect of temperature on the parameters has been quantified, and their relevance for the corrosion behaviour of stainless steel in a high-temperature electrolyte is discussed