Influence of the chemical composition of precursors and reduction conditions on the properties of magnesiothermic tungsten powders

We have studied tungsten powders prepared by reducing the tungsten oxide compounds WO3, MgWO4, CaWO4, and Ca3WO6 with magnesium vapor in the temperature range 700-800A degrees C. In the case of the reduction of WO3 and MgWO4, we observed segregation of reaction products: removal of most of the forming magnesium oxide from the reaction zone. The powders prepared by reducing WO3, MgWO4, and CaWO4 consisted of alpha-W, whereas the reduction of Ca3WO6 at temperatures below 740A degrees C led to the formation of both alpha-W and beta-W. The use of tungsten precursors containing refractory oxides (MgWO4, CaWO4, and Ca3WO6) allowed us to obtain tungsten powders with specific surface areas at a level of 20 m(2)/g and mesoporous structures.