Reduction of ultra-fine tungsten powder with tungsten (vi) oxide in a vertical tube reactor

Abstract

The reduction of WO(3) with hydrogen in a vertical tube reactor is a new approach to the reduction of tungsten oxide compared to conventional procedures in a stationary layer. The advantage of this method is the intensive contact between the reducent and the oxide particles, a higher degree and a shorter time of reduction of only a few seconds, compared to the several hours processing time in a horizontal tube reactor. The characterization of the WO(3) powder and of the tungsten powder included a SEM microstructural examination and DT/TG analyses. The SEM examination of the tungsten powder indicates the presence of small particles with a size of about 1 mu m, also within an agglomerated porous foam structure. Tungsten powder with a particle size of less than 1 mu m is obtained at an optimal temperature with a suitable flow of hydrogen, as a result of stretching and the cracking of large particles, first in the reaction zone, and then, due to appropriate shock of the temperature, outside of this zone. Using an appropriate mathematical model, the degree of reduction and the time required for the formation of tungsten particles during the hydrogen reduction of WO(3) in a vertical tube reactor were determined. Experimental studies have shown that the degree of reduction of WO(3) with hydrogen in a vertical tube reactor increases with the temperature and the flow of hydrogen.