Corrosion behavior of alloys in Li2CO3-K2CO3 eutectic salt under an Air-then-Argon condition

Molten carbonates are among the ideal candidate materials for high-temperature thermal energy storage, but with high corrosiveness. In this study, a novel corrosion mitigation strategy, termed Air-then-Argon (AA) treatment, is proposed. This study investigates the corrosion behavior of three alloys (SS310, In625, and In601) in Li 2 CO 3 -K 2 CO 3 (28.5–71.5 wt%) carbonate melt under different gas conditions. The effect of the AA condition on the corrosion behavior of the immersed alloys was tested and compared with alloys directly immersed under argon (Ar) and air. Via weight loss method, it was shown that SS310 exhibited very low corrosion rates under both conditions, with slightly better performance under the Ar condition. In contrast, In625 showed much higher weight loss (146.6 ± 26.8 mg/cm 2 , for 200h) under argon compared to the AA condition. Under the AA condition, SS310 exhibited 84.8 % less weight loss than in air, while In625 had 90.1 % reduction compared to Ar atmosphere. For In601, the weight loss under Ar was the smallest among the samples tested. The microstructure and elemental distribution of the corrosion layers were analyzed with thermodynamic calculations of metal oxidation. The study summarizes the corrosion mechanisms of alloys in different gas environments and it reveals that the abnormal weight loss of In625 under inert conditions is mainly due to the oxidation and dissolution of Mo and Nb, which disrupted the protective LiCrO 2 layer. SS310 and In625 were tested under the AA condition in more challenging 700 °C carbonate melt. Weight loss data after 500 h confirmed effective corrosion mitigation. The corrosion bilayers formed on alloys exposed to carbonate melt in air exhibited excellent corrosion resistance when subsequently in argon, suggesting that controlling the gas environment could be an economical and effective method for mitigating carbonate corrosion.