Preparation of molybdenum and tungsten carbides from solution derived precursors

Synthesis principles have been developed for the preparation of solution derived precursors that can be selectively converted to desired refractory materials, as powders, fibres or thick films. The precursors are prepared from aqueous or ethylene glycol solutions containing a pyrolysable organic compound (carbonaceous gel or saccharose) and a soluble molybdenum or tungsten compound (peroxo acid or ethylene glycolate). The concentrated solutions exhibit rheological properties that allow fibre drawing and production of thick films. The sequence of the high temperature reactions - pyrolysis, reduction, carburization - was investigated by thermal gravimetric analysis (TGA), X-ray analysis and nitrogen adsorption. Because of the high homogeneity of the reactants, carbon and transition metal suboxides in the pyrolysed precursors, the observed carburization temperatures (800-1200 degrees C) are lower than those used industrially. Most of the intermediate and final products - carbon/oxide composites, Mo(C,O), Mo2C, W2C, and WC - are materials of a high Brunauer-Emmett-Teller (BET) surface area (50-200m(2) g(-1)). (C) 1998 Chapman & Hall.