Nanometer Tungsten Trioxide Preparation by Ultrasonic Spray Drying

Nano-tungsten trioxide powder is an important industrial raw material, which can be used to prepare nano-tungsten powder and nano-tungsten carbide powder. In addition, nano-WO₃ has strong absorption ability to electromagnetic wave, can be used as excellent absorption material in the utilization of solar energy, and can be used as important invisible material in the military. Nano-WO₃ powder has a huge specific surface, significant surface effect, and is a good catalyst. As a transition metal compound, nano-WO₃ has semiconductor properties and is a potential sensitive material. It is sensitive to many gases such as NO_x, H₂S, NH₃ and so on.

A method of preparing nanometer tungsten trioxide (WO₃) powder by ultrasonic spray drying is developed. It can effectively solve the problems of low drying efficiency, large powder consumption and large equipment in the old spray heat transfer technology.

The method of preparing nanometer WO₃ powder by ultrasonic spray drying is using industrial ammonium tungstate solution (tungstic acid content of 100 ~ 600g/ litre) as raw material, using ultrasonic spray device (frequency 1000KHz to 4000KHz) to atomized the ammonium tungstate solution to form tiny droplets. Droplets are transported to the microwave dryer, and the ammonium tungstate droplets are heated rapidly under the action of microwave. Evaporation, ammonium tungstate decomposition, solid particles precipitation; under the action of gravity, particles settle down, and finally gather at the bottom of the silo, through the screw aggregator to collect the finished powder WO₃.

Because of the obvious selectivity of microwave heating, and the physical process of microwave heating is carried out in three-dimensional form, it can achieve simultaneous heating inside and outside, no longer by three simple ways of heat conduction, radiation and convection. Microwave penetration into processed materials is a kind of bulk heating through the overall dissipation of microwave power. Sometimes the processed materials can be regarded as heat source and heater. These characteristics are incomparable with any traditional thermal heating. Therefore, nano-sized tungsten trioxide can be easily prepared. The product particles are uniform and stable, and its adaptability is good. It can be industrialized and mass-produced.

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