Fine violet tungsten oxide may be prepared by direct reduction of ammonium paratungstate (APT) under wet hydrogen conditions. The process is short and the equipment is simple.
Adopting APT with particle size of 10μm as raw material, under the conditions of pH2O:pH2=1.7:1, the temperature is raised to 1173K in two hours, keeping 1.5h, directly reducing to obtain violet tungsten oxide with particle size of 2.2μm.
The grain size of the prepared fine violet tungsten oxide depends on the factors such as reduction temperature, hydrogen humidity, heating rate, grain size of raw material and material thickness. The grain size of the violet tungsten oxide increases with the rise of reduction temperature, the increase of hydrogen humidity, heating rate, grain size and thickness of the raw material.
In other words, it is favorable for the preparation of the fine grain size violet tungsten oxide if:
1. The reduction temperature is low;
2. The hydrogen humidity is small;
3. The heating rate is slow;
4. The grain size of raw material is small;
5. The material thickness is thin.
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