In-depth corrosion mechanisms of Fe- and Ni-based alloys in molten solar salt with varying extents of chloride and sulfate impurities

Solar salt is currently used in concentrated solar power plants with thermal energy storage. Thermal decomposition of nitrates increases the concentration of oxidizing agents and melt basicity, leading to accelerated corrosion of containment materials. This is further complicated by the impurities in industrial-grade salts. In this study, the corrosion behavior of X20CrMoV12-1, Alloy 800 H, and Haynes-230 is investigated at 600 degrees C in different solar salt mixtures with varying impurity contents. Corrosion mechanisms, including aspects of salt decomposition, impurities, and Cr-dissolution, are discussed in detail. It is proposed that the reactants for oxidation, fluxing, and nitridation are generated from either nitrate or nitrite anions at the alloy/scale interface.