Improved corrosion resistance of SS316L in molten nitrates containing chloride ions: Pre-oxidation treatment

This study investigates the influence of pre-oxidation treatment on the corrosion of SS316L in molten solar salt with added chloride ions. The results show that bare SS316L is subjected to severe corrosion in a molten solar salt containing a large amount of chloride ions, with a loose oxide layer forming on the surface and exhibiting pronounced delamination. However, after being pre-oxidised at 800 °C for 5 h, a continuous and dense oxide layer on the surface of SS316L was formed. The pre-formed Fe 3 O 4 and Cr 2 O 3 oxide layer enables the oxide/matrix interface to maintain low oxygen and chlorine pressure, thereby slowing down the oxidation–chlorination reaction rate. Finally, corrosion products with a three-layered structure consisting of Fe 2 O 3 , Fe 3 O 4 , FeCr 2 O 4 and NiFe 2 O 4 are formed, which maintains the integrity structure during the whole immersion and improves the corrosion resistance of SS316L. Roles of the pre-oxidation mechanism give new insights into alloy protection in molten nitrates with chloride ions. It offers a novel approach to enhancing the corrosion resistance of next-generation concentrated solar power equipment.