Erosion resistance evaluation of ceramic crucible in oxide-fluoride slags: Application to high-temperature molten oxide electrolysis

Compared to conventional carbothermic reduction or aqueous electrolysis, molten oxide electrolysis (MOE) promises efficient metal extraction, improved environmental outcomes, and adaptability to diverse mineral feedstocks. A critical challenge is identifying refractory ceramics that enable a feasible, durable MOE process. In this work, the erosion behaviors of four refractories, BN, Si 3 N 4 , ZrO 2 , and SiC, are investigated in a molten CaO-SiO 2 -TiO 2 -Nb 2 O 5 -Fe 2 O 3 -CaF 2 slag from Bayan Obo tailings. Combining thermodynamic calculations with in situ observation via high-temperature confocal laser scanning microscopy, the erosion resistance of four ceramic materials was evaluated. It is found that ZrO 2 , BN, and Si 3 N 4 ceramics suffer severe degradation in the molten slags, whereas SiC maintains better stability. SiC was fabricated into crucibles to study the erosion process by the static crucible method. It is found that a dense protective layer dominated by TiC/NbC is formed on the surface of SiC, effectively inhibiting further penetration and erosion of molten slags. This explains why the actual corrosion resistance of silicon carbide in molten slag significantly outperforms theoretical predictions based on thermodynamic equilibrium calculations. The erosion rate of the SiC crucible is calculated to be 4.78 mg h −1 . These findings provide direct guidance for selecting refractories for MOE and advancing sustainable metallurgy.