Novel Route to Submicrometer Tungsten Carbide

Abstract

A mixture of graphite and scheelite (CaWO4) have been mechanically milled together for 40 h. The resultant powder and an unmilled powder were examined by thermal analysis, isothermal annealing, and X-ray diffraction to determine the effect of milling on the reduction of scheelite to tungsten carbide. The milled powder underwent a rapid reduction reaction at 800°C- 300°C lower than the unmilled powder. The reduction sequence to WC was shown to differ for the two powders with W2C intermediate in the milled powder and W in the unmilled powder. The milled powder showed complete reduction to WC in 1 h at 1,000°C, whereas the unmilled powder was incompletely reduced, even after 1 h at 1,200°C. Separation of the final phases was readily achieved by a simple acid leach, leaving WC grains around 200 nm in size.