Tungsten Trioxide Reverting Ultrafine Tungsten Powder

The reduction method of tungsten trioxide (WO₃) is also known as tungsten trioxide carbonization, the method can be used to restore high-quality ultrafine tungsten powder, the process is needed by the mixer, pellet mill dryer and two rotary kiln components.

Firstly, we take the tungsten trioxide (mass fraction, 84%) and carbon black powder (mass fraction, 16%) to mix the grains in order to have a diameter of 3mm ball, and then to have two successive reduction in a rotary kiln. Continuously during the reaction through a series of intermediate products:
WO₃ → WO_2.9 → WO_2.72 → WO_2.0 → W → W₂C → WC.

Heating WO₃ in the first furnace at 1247 ℃ in N₂, the heating reaction products are WO_2.72, mixture of WO₂ and W, and the ultra-fine grain nucleation occurs in the intermediate product of the transformation. The process WO_2.72 and WO₂ are due to a sharp contraction in the volume of fine grain, and the transition time of WO_2.72 transferring to WO₂, which has a significant increase in density. Two compounds promote grain growth WO₂ (OH) is not formed in the case of materials containing carbon black. Fine WO₂ particles do not thicken into ultrafine grain. Secondly, putting kiln at 1500 ℃ in the rotary, and hydrogen atmosphere ultrafine W are directly restored. Finally, we usually add a small amount of grain growth inhibitor to prevent the ultra-fine carbide grain growth.

Experiments show that in the direct reduction process, original tungsten trioxide and carbon black play an important role in the performance characteristics of tungsten reduction. the size of carbon is reduced in the order of C → B → A. When the original tungsten trioxide particle size is 2.60 micron to 1.80 micron, the tungsten grain size reduction is hardly affected by the particle size of carbon black, in this case of the tungsten powder particle size are reduced about 0.50 microns. When using a particle size of 1.00 micron, tungsten trioxide fine particles and carbon are reduced, the reduction of tungsten particle size is 0.36 micrometers, this depends on the original particle size reduction of tungsten trioxide, and the size and reduction of tungsten powder are prepared by WC- CO alloy.