Room temperature reduction of scheelite (CaWO4)

Abstract

A mixture of scheelite and magnesium has been mechanically milled together for 100 h, either with graphite or in a nitrogen atmosphere, with the intention of forming tungsten carbide or nitride. The resultant powders were examined by thermal analysis, isothermal annealing, and x-ray diffraction to determine the effect of milling on the reduction of scheelite. With graphite, nanocrystallite W2C was the exclusive tungsten product; WC was not detected even after annealing at 1000 °C. No nitride formed in the system milled with nitrogen; however, 10 nm crystallites of elemental tungsten were formed. The unwanted phases, MgO and CaO, were readily removed by leaching in acid, leaving a fine powder composed of impact welded aggregates of either carbide or 99% pure tungsten metal.