Influence of carbon dioxide on corrosion behavior of stainless steel in molten lithium-sodium carbonate

The corrosion behavior of type 316L stainless steel in a molten Li2CO3-Na2CO3 eutectic had been investigated using an electrochemical method in the temperature range of 823K - 973K. An anodic polarization curve of 316L showed the passive behavior under the Ar gas atmosphere at 923K. When CO2 was added in the atmosphere, the active current peak was shifted to the noble direction with increasing current. The corrosion rate of 316L increased with temperature in Ar. A similar behavior was seen under Ar+30%CO2 from 923K to 973K. However, the transition of the active-passive behavior did not appear at 823K, and a lot of corrosion pits were observed on the surface after the test. This anomalous corrosion, so-called hot corrosion, at 823K seems to be caused by the instability of an outer scale under the CO2 contained atmosphere, and by the difficulty in forming a continuous inner oxide scale at this temperature.