GB890757A - Improvements in or relating to the production of tungsten and molybdenum carbides - Google Patents

Abstract

<PICT:0890757/III/1> Tungsten or molybdenum carbides are prepared by contacting H2 with particles of tungsten, or molybdenum, oxide, a tungsten, or molybdenum, compound decomposable to oxide below the reduction temperature, or mixtures thereof, fluidized in a gas phase heated to at least 400 DEG C., initiating a flow of a carburizing gas into the gas phase when the bed is at least 800 DEG C., but before there has been any reduction of the oxide beyond the dioxide, and continuing the flow of carburizing gas and H2, while maintaining the bed at at least 800 DEG C., until the carbide is formed. Oxides may be trioxides or dioxides, and compounds may be ammonium, tungstates or, molybdates, or molybdic, or tungstic, acids. Carburizing gases are methane, ethane, propane, butane, ethylene, propylene, benzene, toluene, CO, natural gas, or town gas. The oxide or compound is fed to reactor 1 heated by furnace 9 from bin 2 and fluidization of bed 7 is initially effected by He, A, Kn, or N2, or mixtures thereof entering through 4 and distributer 5 and withdrawn at 6 to remove air, and H2 is added subsequently. Alternatively, air may be evacuated through 6 before fluidization with inert gas or H2. Disengaging zone 10 and filters 11 remove entrained solid. During reduction gases are withdrawn through 6, and methane is added at any time prior to, or during, reduction to the dioxide, or when this reduction is complete, as determined by monitoring the partial pressure of H2O in the exit gases. During carburization temperature, 800-1000 DEG C., and pressure, atmospheric and 2 atms. are referred to, are controlled to prevent excess free C deposition, and gases may be recycled through 12. To aid control a temperature gradient may be maintained in the bed, and methane may be added at intermediate points. Carbide is removed at 16.