Corrosion behavior of ceramic structural materials in an electrolytic reduction process

Abstract

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.