Corrosion behavior of ceramic structural materials in an electrolytic reduction process

The electrolytic reduction of spent oxide fuel involves the liberation of oxygen in a molten LiCl electrolyte, which results in a chemically aggressive environment that is too corrosive for typical alloying structural materials. Therefore, the choice of the optimum material for the processing equipment that handles molten salt is critical. We investigated the corrosion behaviors of CaO-stabilized ZrO₂ (CSZ) and mullite (Al₆Si₂O₁₃) at 650°C for 168 h in molten (1, 3) wt% Li₂O–LiCl. The as-received and tested specimens were examined by scanning electron microscopy/X-ray energy dispersive spectrometry and X-ray diffraction. CSZ showed a much better hot-corrosion resistance in the presence of Li₂O–LiCl molten salt than mullite. The surface corrosion layers of mullite consisted of LiAlSiO₄ in 1 wt% Li₂O–LiCl, and a LiAlO₂ phase appeared as the Li₂O concentration increased to 3 wt%. Furthermore, Li₂SiO₃ was the only corrosion product observed at 3 wt% Li₂O–LiCl. The surface corrosion layers of CSZ were composed mainly of tetragonal-ZrO₂ with partial monoclinic-ZrO₂ in 1 wt% Li₂O–LiCl, and a Li₂ZrO₃ phase appeared at 3 wt% Li₂O–LiCl. There was no corrosion product detached from the surface for those specimens. CSZ was beneficial for increasing the hot-corrosion resistance of the structural materials that handle high-temperature molten salts containing Li₂O.