The self-propagation high-temperature synthesis of ultrafine high purity tungsten powder from scheelite

High-purity tungsten was prepared by the self-propagating high-temperature synthesis (SHS) process from a mixture of CaO . WO3 and Mg. The complete reduction of CaO . WO3 required a 33% excess of magnesium over the stoichiometric molar ratio Mg/CaO . WO3 of 3: 1. The MgO and CaO in the product were leached with an HCl solution. The product tungsten had a purity of 99.980% which was higher than that of the reactants. The high purity results because the nontungsten reactants and products are volatilized by the high temperatures generated during the rapid exothermic SHS reaction and are dissolved during HCl leaching of the product.