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

Abstract

Corrosion of 316 SS in HITEC molten salt was investigated at 450 °C, 600 °C, and 680 °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 °C, suffered severe corrosion at 680 °C, and demonstrated discontinuously increasing corrosion rate from 600 °C to 680 °C. A thin layer of Cr2O3 and Fe-based oxides formed at 450 °C. At 600 °C and 680 °C three distinct oxide layers could be distinguished with a loose outer Fe-based oxide layer. After corrosion at 600 °C and 680 °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 °C and 600 °C are controlled by outward diffusion of metal ions and oxygen vacancies, while corrosion mechanism at 680 °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.