High-Temperature Corrosion Behavior of Al-Coated Ni-Base Alloys in Lithium Molten Salt for Electroreduction

The electrolytic reduction of a spent oxide fuel involves the liberation of oxygen in a molten salt LiCl–Li2O electrolyte, which creates a corrosive environment for typical structural materials. In this study, the corrosion behaviors of Al–Y-coated specimens in a Li molten salt kept under an oxidizing atmosphere at 650 °C for 72 and 168 h were investigated. The weight loss fraction of the coated specimen to bare specimen was approximately 60% for 3% Li2O and 54% for 8% Li2O at 72 h, and approximately 38% for 3% Li2O and 30% for 8% Li2O at 168 h. Corrosion was induced in the LiCl–Li2O molten salt by the basic oxide ion O2− via the basic flux mechanism, and the corrosion product was found to be dependent on the activity of the O2− ion. The increase in weight loss may have been caused by the increase in the O2− concentration due to the increase in the Li2O concentration rather than being because of the increased reaction time. The Al–Y coating was found to be beneficial for hot corrosion resistance, which can be useful for handling high-temperature lithium molten salt under an oxidizing atmosphere.

Alloy Design of New Ni-Based Structural Materials for Electrolytic Reduction and its Corrosion Behavior in Lithium Molten Salt

In this study, the corrosion behavior of new Ni-based structural materials was studied for electrolytic reduction after exposure to LiCl-Li2O molten salt at 650°C for 24-216h under an oxidizing atmosphere. The new alloys with Ni, Cr, Al, Si, and Nb as the major components were melted at 1700°C under inert atmosphere. The corrosion products and fine structures of the corroded specimens were characterized by SEM, EDS, and XRD. The corrosion rate of 12wt% Cr-2wt% Si alloys and 12wt% Cr-5wt% Si alloys are below 0.3mm/year. However, the corrosion rate of 20wt% Cr-5wt% Si is 0.6mm/year. Also, the corrosion products of 12wt% Cr alloys were Cr2O3, NiCr2O4, Ni, and NiO; those of 20wt% Cr alloys were Cr2O3, LiAl2Cr3O8, and NiO. The higher corrosion rate of 20wt% Cr-5wt% Si could be the higher solute concentration which leads to an unstable alloy formation. As confirmed by the pseudo binary phase diagram of (Ni-Cr-Al-Nb)-Si, the solubility of the silicon with 20 wt% of Cr decreased to 4 wt% from 5 wt% with 12 wt% of Cr.