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Violet tungsten oxide which is abbreviated as VTO, is a kind of tungsten oxide. Violet tungsten oxide is finely crystalline powder having high activity and strong fissile octahedral structure. The appearance of violet tungsten like needle and rod. The surface area, grain size and apparent density of violet tungsten oxide are smaller when compared to blue tungsten oxide and yellow tungsten oxide. So its property is also quite different from other tungsten oxides.
Violet tungsten oxide is reduced by ammonium paratungstate under a certain temperature. Chemical formula of violet tungsten oxide is WO2.72 or W18O49.
Violet tungsten oxide is very suitable for the production of tungsten metal powder and tungsten carbide.
The preparation method can be divided into following types:
1. The reduction of APT hydrogen: put APT into the boat and the reduction happens in the wet hydrogen environment.
2. The rotary furnace method: in the presence of ammonia, APT decomposition calcination in mild reducing atmosphere, and finally reduce into violet tungsten oxide.
3. Direct synthesis method: mix WO3 with W according to the stoichiometry and then prepare the violet tungsten oxide at 890 degrees Celsius with pure agron gas.
The study shows that most of the manufacturers are using the industrial rotary furnace, and need to meet the conditions as follows:
1. The rotary furnace should be sealed, the gas should flow through the furnace tube, and fully contact the material. Meanwhile the external furnace should heat equally.
2. Furnace tube has a certain temperature gradient, that is, the furnace can be divided into different temperature to make sure the temperature of the furnace tube on each section is stable and to avoid heating blind area, affecting the quality of products.
3. The inner wall of the furnace tube should be smooth, and avoid reacting material sticking to the inner wall of the furnace tube.
4. Have a good exhausting performance, the reaction generated water vapor can be discharged in time to facilitate the realization of mechanization and automation.
Its main operation steps are as follows:
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First, put APT into the furnace using the screw feeder with certain feed speed under a certain temperature calcining. After NH3 decomposes and produces H2, it starts calcining in a reducing environment and gradually reduces into violet tungsten oxide. After baked violet tungsten oxide over 80 mesh sieve, the experimental sample properties, phase composition and morphology are measured by some instruments, such as X-ray diffraction, field emission scanning electron microscopy (SEM),and WLP-208 average particle size measuring instrument. | | 