Study of the Preparation of Bulk Powder Tungsten Carbides by Temperature Programmed Reaction with CH4+ H2Mixtures

Abstract The synthesis of bulk tungsten carbides by carburization of W metal or of WO 3 with mixtures of CH 4 in hydrogen at various pressures has been studied in temperature programmed experiments. The resulting solids have been characterized by elemental analysis, X-ray diffraction, XPS analysis, and specific surface area measurements. The carburization occurs in two distinct steps: W 2 C is formed in the first step taking place at about 650°C at atmospheric pressure with a 20% CH 4 –H 2 mixture, while the formation of WC occurs only at higher temperatures. During carburization some free carbon is deposited, the importance of which is very much dependent on CH 4 partial pressure and on the temperature of carburization. It has also been shown that direct carburization of WO 3 by CH 4 –H 2 does not take place, but that the carburization occurs via the reduction of WO 3 to W metal. The rate of reduction of WO 3 and that of carburization of W metal are very much dependent on, respectively, hydrogen partial pressure and CH 4 partial pressure. The extent of reduction of WO 3 into W metal required for carburization which takes place also depends on CH 4 partial pressure, indicating a competition between carburization of W metal at the surface and diffusion of W metal into the bulk of the solid.