1. VTO were first reduction in hydrogen, along a first temperature of 640 ℃, the second temperature of 760 ℃, third temperature of 860 ℃, when the temperature reaches 860 ℃ heat preservation for 20min.
2. in the air at 500 ℃ making tungsten powder to oxidation with slowly heated for the first time, then heat preservation for 10min.
3. Replace the first step and second to continuous cycle reduction reaction.
4. Using alcohol on the analytical results above steps were dispersed pattern, then using BT-9600 laser particle size analyzer and JXA-840A electron probe scanner to analysis particle size and morphology of samples.