Preparation of Ultrafine W Powder via Carbothermic Prereduction of Tungsten Oxide Followed by Deep Reduction with Hydrogen

A two-step reduction method to synthesize tungsten powder with controllable size is proposed. Firstly, precursors composed of W and WO2 were synthesized via carbothermic prereduction of tungsten trioxide with different C/WO3 ratios at 1323 K, then the precursors were completely reduced by hydrogen to remove residual oxygen at 1023 K and 1223 K,respectively. It was observed that increasing the C/WO3 molar ratio in the prereduction stage was beneficial to decrease the particle size of the W powder. In the subsequent hydrogen reduction stage, the presence of the gaseous intermediate phase W-O-H had a great influence on the morphology of the final product. Tungsten powders with particle size ranging from micron to nanometer range could be prepared by controlling the C/WO3 ratio and hydrogen reduction temperature.