Corrosion Behavior of Si3N4 Ceramic in High-temperature Molten Salt-water Vapor Environment

Molten salt electrolysis is the key technology for dry reprocessing of spent fuel in the nuclear energy industry. High-temperature molten salt can cause severe corrosion to crucible materials used for spent fuel, so the selection of the crucible material with good resistance to high temperature and corrosion is crucial for the development of the dry reprocessing method. Si3N4 is considered as a promising candidate for the crucible used in dry reprocessing, primarily due to its excellent high-temperature thermal and mechanical properties. However, its resistance to high-temperature molten salts and water vapor has not been fully investigated. In this work, the corrosion behavior of Si3N4 in LiCl-KCl and NaCl-2CsCl molten salt under Ar atmosphere and water vapor (5%H2O-10%O-2-85%Ar) was investigated. The results show that in argon atmosphere, Si3N4 undergoes slight grain boundary corrosion in LiCl-KCl molten salt, while NaCl-2CsCl molten salt presents weak corrosion on Si3N4. In 5%H2O-10%O-2-85%Ar water vapor environment, LiCl-KCl molten salt prefers to attack the grain boundary phase. Si3N4 shows serious corrosion degradation in the NaCl-2CsCl molten salt compared with the corrosion level in argon atmosphere. The water vapor environment significantly promotes the corrosion of Si3N4 in the molten salt environment, while the grain boundary phase is the most susceptible site for the corrosion of Si3N4. In addition, no direct correlation is found between the wettability and corrosion resistance of LiCl-KCl and NaCl-2CsCl molten salts. Results of this work elucidate the mechanism of high-temperature molten salt-water vapor-induced degradation of Si3N4, offering guidelines for the selection of crucibles in the dry reprocessing of spent fuel.