Effect of lithium on the atmospheric corrosion characteristics of TZM as the first-wall material in EAST

The effect of Lithium (Li) coating on the corrosion behavior of molybdenum-titanium-zirconium (TZM) alloy was investigated in low- and high-humidity air at room temperature (RT). Additionally, the corrosion mechanism was also studied through immersion tests in deionized water and LiOH solution. The test results confirm that the corrosion of the TZM alloy depends on the presence of H2O and O2, particularly H2O. In environments with high humidity, the TZM surface without Li coating easily undergoes oxidation, resulting in the formation of dark-green MoO3·xH2O. The Li coating significantly accelerates the surface oxidation of the TZM alloy because of its high absorptive properties for H2O, O2, and CO2, thereby generating Li2O, LiOH, and Li2CO3. These processes lead to a high content of O2 and H2O near the TZM surface, facilitating the formation of MoO3·xH2O. The immersion of TZM in water also leads to oxidative corrosion, which is more severe than that in high humidity air because of the dissolution of MoO3, causing the water to become dark-green. The oxidation of TZM in LiOH solution exhibits a behavior similar to that of water immersion. However, the corrosion in the LiOH solution is more severe because of the reaction between the surface oxide MoO3 and LiOH, which forms a colorless Li2MoO4, accelerating the corrosion process. This study offers valuable insights into the effective anti-corrosion strategies for the cleaning and storage of the TZM wall material in the EAST tokamak.