Usually,APT at 500℃ can be completely removed from water and get into WO₃ , this process seems not complex, but actually the key point at the second reduction step of preparation of tungsten powder. APT in different atmosphere calcination will produce oxides of different intermediate states, WO₃ (yellow tungsten oxide), WO_2.9 (blue tungsten oxide) and WO_2.72(violet tungsten oxide). The three tungsten activity gradually increased in the order like this: yellow tungsten oxide→blue tungsten oxide→violet tungsten oxide. Generally, intermediate with high activity easy to get fine particle tungsten powder; on the contrary, we get coarse tungsten powder.

 

A great deal of hydrosphere will be produced in the reduction of tungsten powder from ammonium paratungstate, and they come from two aspects:
First one, also the majority one is water removed from APT in the process crystallization;
The second one takes a small part, water comes from the reduction of WO3 to blue tungsten oxide and violet tungsten oxide. Generally believed that the crystal rifted after dehydration and deamination which will help hydrogen enter the crystal, thus help the reduction of tungsten powder.

 

There are three factors influence the morphology of tungsten powder in the process of one-step reduction method.
First, temperature, hydrogen in the high volatility and temperature helps to produce coarse grain tungsten powder of complete crystal forms and uniform and dispersed.
Second, reduction time, effect on the size of tungsten powder, tungsten powder has a trend of growing up with the increasing hydrogen reduction time goes.
Third, shipping amount, the big boat loading cause depth of material becoming thicker, and then do harm to tungsten oxide and water vapor to diffusion and crystal growth in the reduction process. So, reduce the amount of shipping will help producing tungsten powder with uniform size.

 

4. Conclusions

Compared with traditional two-step reduction, one step reduction preparing tungsten powder basically gets the same grain from APT, and the size controllable. The products can meet quality requirements in the existing market.