Impact of Chloride Impurities on the Corrosion Behavior of Stainless Steel in Molten Alkali Carbonate Salts for Concentrated Solar Power Systems

This study clarifies the catalytic role of chloride ions on the corrosion performance of SS316L alloy immersed in molten LiNaK carbonate salt at 700 °C. Accordingly, isothermal static immersion corrosion tests were systematically conducted under different experimental conditions. Our results revealed that the presence of Cl significantly accelerates the corrosion process: the rate constant of the corroded samples increased from 11.3 × 10−2 mg/cm2 to 13.8 × 10−2 mg/cm2 with the addition of Cl. Continuous migration of Cl2 and volatile metal chlorides leads to the formation of obvious pores, transverse cracks along grain boundaries, surface wrinkles, and partial spalling of the oxide scale, thereby severely aggravating substrate degradation. Notably, no chlorine-containing compounds or chlorine-rich regions were detected in the corroded samples, confirming that chlorine is not consumed in the corrosion process, rather it acts as an autocatalyst through the cyclic process of “oxidation–diffusion–reaction–regeneration”.