Ultrafine grain size violet tungsten oxide may be prepared by different production processes.
At present, violet tungsten oxide (VTO) is generally produced by using ammonium paratungstate (APT) as raw material, and calcining APT with the injection of ammonia gas (NH3) in a rotary furnace. However, the VTO powder prepared by this method has large particle size and high impurity content, that is, it is difficult to obtain VTO powder with higher purity.
Research also shows that a method for preparing VTO powder is to mechanically mix ammonium metatungstate (AMT) and glucose through grinding method, and calcine the mixture to obtain tungsten oxide powder. The process is simple and efficient. However, phase purity of the reaction product is insufficient as the mixing is not uniform by mechanical mixing. In addition, the calcination temperature is high. So, particles of the obtained product are larger.
It has also been found that VTO powder may be prepared by hydrothermal synthesis method, by mixing WCl6 and ethanol, reaction in a reactor at 180°C for 24h. Although VTO can be produced by this method, it takes a long time to react, and the quantity of VTO prepared is small each time.
Therefore, it is necessary to develop a new efficient and simple production method for producing violet tungsten oxide to provide raw materials for the preparation of ultrafine powders such as ultrafine tungsten powder and tungsten carbide powder.
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