Corrosion mechanism of SS316L exposed to NaCl/Na2CO3 molten salt in air and argon environments

Molten salts are potential energy storage media for solar thermal power, but can be highly corrosive. To investigate molten salt corrosion mechanisms, the oxidation state and structure of SS316L exposed to salt in air and argon environments was investigated using SEM and XANES techniques. It was determined that iron formed mixed Fe2+ and Fe3+ states in both environments, with lower oxidation states deeper into the corrosion. Cr2+ was the primary oxidation state present in the scale for chromium. Reduced salt basicity with lower oxygen concentration favoured the lower oxidation state, whilst Cr3+ ions were dissolved by the salt. •SS316L was corroded in both air and argon environments, argon environments were more aggressive.•Cross sections were analysed with SEM-EDS, XANES and XFM.•Fe2+ and Fe3+ oxidation states were present in both environments.•Cr2+ was the only oxidation state detected in argon, due to reduced salt basicity.•In air, Cr3+ was detected close to the metal but dissolved into the salt leaving a Cr2+ outer layer.