Active dissolution of a silicon-rich austenitic stainless steel in nitric acidic investigated through atomic emission spectroelectrochemistry

Abstract : Austenitic stainless steels (SS) with silicon additions are used for some equipment containing nitric acid in the spent nuclear fuel reprocessing plant. This work aimed at studying the corrosion behavior of this SS in such acid media. For that purpose, two kinds of electrochemical experiments were performed linear polarizations from active to transpassive domains to study the oxidation/dissolution behavior as a function of potential and alternative polarizations between active and passive states to study the passive layer formation/dissolution kinetics. In both cases, the measurement was followed using in-situ Atomic Emission Spectro ElectroChemistry (inductive coupled plasma atomic emission spectroscope real time connected to a potentiostat) and chemical surface evolution was characterized with ex-situ X-ray photoelectron spectroscopy. An accumulation on surface (resulting from a selective dissolution) of several elements was found as a function of potential. In the active domain, metallic copper accumulates on surface, which impacts the cathodic reaction kinetics. In the passive domain, surface accumulation of chromium was observed (reversible phenomenon when polarized again in the active domain), which is found to directly control the SS global dissolution rate. Eventually, accumulation of silicon at the surface was found in both active and passive domains. This phenomenon appears as irreversible and consequently could affect the SS long term corrosion behavior.