Electrochemical Synthesis of Nano-Metallic Carbides from the Mixtures of Metal Oxide and Graphite

Abstract

Nanocrystalline transition metal carbides (TMCs, M = Ti, Zr, Hf, Nb and Ta) have been synthesized by direct electrochemical reduction of solid mixture precursors composed of transition metal oxides and graphite powder (TMOs-C) in molten CaCl2 at 850°C. The synthesis temperature is much lower than that of the conventional carbothermic reduction process. SEM analysis showed that the particle sizes of the as-prepared TMCs powders were about 15–30 nm. The formation processes of nanocrystalline TMCs monitored by analyzing partially reduced samples were confirmed to be similar to each other and could be divided into three steps: TMOs-C first to CaMaOb and MCxOy, then to pure MCxOy and last to MC. It has been found that the electrolysis production of TMVCs is much faster than that of TMIVCs. The formation of intermediate MCxOy during the electrolysis processes was investigated and their stability should be the key influence factor of the electro-deoxidation rate of the mixtures.