Electrochemical study on the corrosion behaviors of 316 SS in HITEC molten salt at different temperatures

Corrosion of 316 SS in HITEC molten salt was investigated at 450 degrees C, 600 degrees C, and 680 degrees C by electrochemical methods including potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. Corrosion products were investigated by XRD and SEM equipped with EDS. Corrosion of 316 SS in HITEC molten salt exhibited active corrosion characteristics at these temperatures. 316 SS exhibited resistance to corrosion in HITEC molten salt at 450 degrees C, suffered severe corrosion at 680 degrees C, and demonstrated discontinuously increasing corrosion rate from 600 degrees C to 680 degrees C. A thin layer of Cr2O3 and Fe-based oxides formed at 450 degrees C. At 600 degrees C and 680 degrees C three distinct oxide layers could be distinguished with a loose outer Fe-based oxide layer. After corrosion at 600 degrees C and 680 degrees C for 200 h, Na2O and K2O were detected in the HITEC molten salts, which caused the decomposition of the protective Cr2O3 layer and enhanced corrosion of 316 SS. EIS results show that the corrosion processes of 316 SS in molten salt at 450 degrees C and 600 degrees C are controlled by outward diffusion of metal ions and oxygen vacancies, while corrosion mechanism at 680 degrees C change to was inward diffusion of oxygen ions. The change in corrosion mechanism became more prominent when corrosion time was prolonged to 197 h.