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Corrosion behavior of a silicon enriched austenitic stainless steel in hot and concentrated nitric acid media

Abstract : This work aims at understanding the corrosion behavior of the Uranus S1N stainless steel (SS) in hot and concentratred nitric acid. The Uranus S1N SS is a 304L type SS (18Cr-15Ni) added by 4 wt.% of Si. In pure nitric acid, the 304L SS dissolves slower. In other words, Si enhances the corrosion rate of the SS. But when oxidizing species are added, the 304L dissolves at a much higher rate than the Uranus S1N. Mecanisms involving Si that bring to this phenomenon are not clearly established. The purpose of this thesis project is to elucidate the role of Si in the spontaneous corrosion of the SS in pure nitric acid and in presence of oxidizing species. Reduction and oxydation phenomena are compared, through I-V curves measurements, between both steels, for different conditions : pure nitric acid, presence of pentavalent vanadium, hexavalent chromium. It was shown that Si diminishes the reduction kinetics and prevents the Uranus S1N SS to be shifted to its transpassive domain even when conditions are largely oxidizing. Then the oxide layer was investigated through three sets of experiments. Firstly, thermodynamics of the oxides where characterized by measuring the activation potential of the SS. Secondly, their chemical composition, thickness and structure were investigated coupling congruent in-situ and ex-situ measurements. Eventually, high potential passivity breakdown was investigated to understand why Si inhibits the intergranular attack at the surface. These three investigations rely on coupling original in-situ techniques as the atomic emission spectroelectrochemistry (electrochemical measurements coupled to elemental on line analysis) and ex-situ surface analysis as X-Ray photoelectron spectroscopy or Energy dispersive X-ray spectroscopy on cross-section thin blades.
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Submitted on : Wednesday, May 16, 2018 - 11:49:08 AM
Last modification on : Wednesday, October 14, 2020 - 4:00:58 AM
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  • HAL Id : tel-01793175, version 1



Barbara Laurent. Corrosion behavior of a silicon enriched austenitic stainless steel in hot and concentrated nitric acid media. Analytical chemistry. Université Paris sciences et lettres, 2017. English. ⟨NNT : 2017PSLEC003⟩. ⟨tel-01793175⟩



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