Synthesis of high purity nano-sized transition-metal carbides

Nano-sized transition-metal carbides with high purities were synthesized by vacuum carbothermal reduction coupled with a novel method for the removal of free carbon by molten calcium treatment. Transition-metals oxides were firstly reduced by excessive carbon black under vacuum condition, and then the obtained product was treated in molten calcium to remove the free carbon. After acidic leaching the product, pure carbides were obtained. The excess carbon in the carbothermic reduction stage could not only increase the contact between reactants and make the reduction more thorough, but also act as barrier to restrict the grain growth of the products. The effects of carbothermic reduction temperature, calcium treatment temperature and particle sizes of oxides on the reaction products were discussed in detail. It was concluded that after carbothermic reduction of corresponding oxides at 1823 K in vacuum and the following calcium treatment at 1173 K, TiC, ZrC, HfC, V8C7, NbC and TaC with the particle sizes of 100 nm, 70 nm, 130 nm, 200 nm, 150 nm and 120 nm, could be prepared, respectively.