Regulation of particle size and morphology of tungsten powders in bottom-blowing hydrogen reduction process

Particle size and morphology of tungsten powders determine the processing properties of tungsten products. The thermodynamic analysis indicates that the partial pressure of water vapor is an essential factor to regulate the hydrogen reduction of tungsten oxides. The investigation proposed a method of changing the particle size of tungsten powders by bottom blowing hydrogen pretreated by water bath at various temperatures. The experimental results manifested that the bottom-blowing hydrogen could eliminate discrepancies of the water vapor partial pressure in the solid powder layers, thus improving the uniformity of the tungsten powders in a crucible. The partial pressure of water vapor increased with temperatures of water bath increasing. As the water bath temperature raised from 50 degrees C to 80 degrees C, the average particle size of tungsten powders increased significantly from 3.8 mu m to 12.0 mu m. Chemical vapor transport was responsible for the increase in the average particle size of tungsten powders under the higher partial pressure of water vapor. In addition, the oxygen content of tungsten powders produced remained relatively stable at a lower level with the partial pressure of the water vapor increasing. This study provided theoretical foundation and technological reference for preparing the tungsten powders with superior properties (desirable homogeneity in the particle size and shape and low oxygen content).