Corrosion behavior and mechanism of 316 stainless steel in NaCl-KCl-ZnCl2 molten salts at high temperature

The corrosion behavior and mechanism of 316SS alloy in NaCl-KCl-ZnCl2 molten salts were investigated at 500°C under Ar by static corrosion experiment. The annual corrosion rate was evaluated by weight loss. The morphology and microstructure changes of 316SS alloy after exposure in the chloride salt were analyzed by scanning electron microscopy with energy dispersion spectroscopy and X-ray diffraction techniques. The annual corrosion rate increased with time, then decreased to attain a steady rate of 195 µm/a after 240 h. No obvious pitting and intergranular corrosion occurred. An oxide layer composed of the oxides of Zn, Fe, Cr and Ni formed on the surface of the 316SS samples. The corrosion mechanism was further discussed. It was closely related to hygroscopicity of ZnCl2 which led to the formation of Zn(OH)2 or basic zinc chloride, then Fe, Cr involved in the reactions. With corrosion proceeding, nickel oxide also formed by reaction with Fe3+. The Zn(OH)2 or basic zinc chloride in NaCl-KCl-ZnCl2 should be further removed before commercial application.