Influence of mechanical surface treatments on oxide properties formed on 304L stainless steel in simulated BWR and PWR primary water

Abstract

• Influence of surface treatment on the oxidation features in LWR environment was evaluated. • Oxide properties were determined by a recently developed electrochemical method . • Microstructural modifications affect slightly the oxides structure and properties. • The test environment plays a more significant role on the oxidation mechanism. The effect of dry grinding on the oxidation features of 304L stainless steel (SS) in simulated primary water of BWR and PWR was studied. The objective is to demonstrate the influence of mechanical surface treatments on surface state and oxidation behavior of the SS. Thus, the oxide formed on a ground surface and two polished surfaces (down to 2400 with SiC emery paper and with colloidal silica) had been compared. Subsurface characterizations were first performed to describe the microstructural modification induced by the surface treatment. Then, the morphology and the composition of the oxides' duplex structure were characterized by either scanning electron microscopy, transmission electron microscopy or X-Ray photoelectron spectrometry. Finally, the reactivity of the oxidized surfaces was determined ex-situ by a recently developed electrochemical technique based on electrochemical Impedance spectroscopy and Mott-Schotcky approach. The mechanical surface treatment mainly influences the thickness and doping density of the inner oxide; and the composition and morphologies of the outer oxide-hydroxide precipitates in terms of shape and size. This work evidences that the thinner the inner oxide, the higher the doping density. Besides, the impact of the considered environment on oxidation features is also discussed.