The U.S. Bureau of Mines conducted a bench-scale study to delineate the important parameters in a three-step process to produce commercial-quality tungsten carbide (wc) directly from tungsten minerals. In the process, tungsten concentrates of wolframite or wolframite and scheelite are decomposed at 1,050 deg c in a molten mixture of nacl and na2sio3 that forms two immiscible phases. Tungsten, as sodium tungstate, reports to the halide phase and is separated from the gangue constituents, which report to the silicate phase. After decanting to separate the two phases, natural gas is sparged into the molten halide phase at 1,070 deg c. Submicrometer crystals of wc are initially produced. These crystals grow into thin, triangular-shaped plates up to 100 um on a side or into popcorn-shaped conglomerates. Sparged wc was examined for its suitability for use in sintered carbide products. In physical evaluations, sparged wc ground to an average particle size of 1.52 Um and compacted with 10 pct CO binder into standard 6- by 6- by 22- mm test bars had a density of 14.35 and a rockwell a hardness of 89.6. This compared favorably with 14.39 and 89.7, Respectively, for test bars made from a standard commercial 1.52-Um wc powder. Test bars made from Bureau of Mines wc had no "c" porosity or eta phase.
Int. Acad. Publ., Beijing, 1988, V. 2, PP. 626-633