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

Trans. Nonferrous Met. Soc. China. 19(2009). - P. 785−789.Abstract: Crystal growth of tungsten during hydrogen reduction of tungsten oxide (WO₃) to prepare coarse grain tungsten powder at high temperature (950 ℃) 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→WO_2.9→W₁₈O₄₉→WO₂→W. The step of WO₂→W is the critical step which determines the grain size of tungsten powder. The partial pressure (pH₂O/pH₂) of H₂O within powder layer shows strong effect on the nucleation and grain growth of tungsten. By increasing the pH₂O/pH₂ within powder layer, well-developed coarse grain tungsten powder with particle size above 15 μm is obtained. After carburizing, the powder can be used to produce ultra-coarse grain cemented carbide with grain size above 5 μm.