Crystal growth of tungsten during hydrogen reduction of tungsten oxide at high temperature

Crystal growth of tungsten during hydrogen reduction of tungsten oxide (WO3) to prepare coarse grain tungsten powder at high temperature (950 degrees C) was studied. The phase composition and morphologies of products were investigated by means of XRD and SEM. The results show that the reduction sequence of hydrogen reduction Of WO3 is WO3 -> WO2.9 -> W18O49 -> WO2 -> W. The step of WO2 -> W is the critical step which determines the grain size of tungsten powder. The partial pressure (p(H2O)/pH(2)) of H2O within powder layer shows strong effect on the nucleation and grain growth of tungsten. By increasing the p(H2O)/p(H2) within powder layer, well-developed coarse grain tungsten powder with particle size above 15 mu m is obtained. After carburizing, the powder can be used to produce ultra-coarse grain cemented carbide with grain size above 5 mu m.