Synthesis of tungsten carbide through gas-solid reaction at low temperatures

Conventionally, WC powders are produced heating a mixture of W powder and carbon black. This method is based on solid state reaction controlled by diffusion and phase transformations. Thus high temperatures ( > 1400 degreesC) and long times are necessary. This paper presents a method able to synthesize WC at low temperatures (similar to 850 degreesC) in 2 h. It is based on a gas-solid reaction between a W source and a C-containing gas. The gas phase is a mixture of H-2 and CH4. Ammonium paratungstate and tungsten blue oxide are used as the tungsten source. The higher reactivity of the precursor material and the better contact between the gas-solid reactants explain the lower temperatures and higher reaction rates of this method compared to the conventional one. Very fine WC crystallites ( < 1 mum) can be produced, but the particle size, shape and porosity depend on the precursor type and particle size. (C) 2001 Elsevier Science B.V. All rights reserved.