Crystal-phase-mediated synthesis of niobium carbide from model niobium-bearing phases via a pyrochlore intermediate

This study proposes a crystal-phase-mediated strategy for the efficient synthesis of niobium carbide (NbC) from model niobium-bearing phases. By investigating the different carbonization behaviors of four representative niobium phases (niobium oxide, pyrochlore, columbite, and aeschynite), pyrochlore exhibited optimal carbonization capability due to its lowest activation energy (84.4 kJ·mol −1 ) and low Nb-O bond strength. We employed CaF 2 and Na 2 CO 3 as additives to convert refractory phases into a highly reactive pyrochlore intermediate (NaCaNb 2 O 6 F), achieving a conversion ratio of over 93% below 1100 ℃. This intermediate enables the efficient in situ synthesis of NbC with a carbonization ratio exceeding 92% at 1100 ℃ (based on selective leaching, estimated error ± 5%), about 200 ℃ lower than in direct carbonization. This additive-induced phase transformation pathway significantly lowers the energy barrier for NbC production, demonstrating a potential low-temperature pathway that may inform future strategies for the synthesis of niobium carbide, though further validation on natural ores is required.