Extraction of Violet Tungsten with Ammonium Metatungstate Evaporation Reduction

As a semiconductor material (its band gap can be 2.4 to 2.8eV), tungsten oxide is widely used in photoelectrochemistry. The violet tungsten WO_2.72 has been paid special attention to by the researchers because of its unique properties and structures.

Monoclinic violet tungsten has the largest oxygen defect structure. Compared with yellow tungsten (WO₃) and blue tungsten (WO_2.9), violet tungsten has the highest surface structure and the highest chemical activity. It is suitable for the production of ultrafine particles of tungsten powder and various kinds of tungsten compounds. On the other hand, violet tungsten can be applied to biomedicine as a carrier for cancer cell drugs. It can shield light waves starting from near infrared light and achieve intelligent insulation. It can also be applied to photocatalytic degradation of organic pollutants to purify the environment.

The preparation method of violet tungsten powder is usually made of ammonium partrungstate as raw material, and calcined with ammonia in rotary kiln. The time and temperature setting of calcination are the key to making high quality violet tungsten. However, there are many difficulties in the preparation of nano violet tungsten by calcining reduction of ammonium parotungstate. The resulting violet tungsten particles are larger and more impurities. Therefore, some scholars have proposed that the evaporation process is different from the traditional ammonium metatungstate evaporation reduction method.

1.According to the reaction measurement ratio, ammonium partial tungstate 0.01mol, ammonium nitrate 0.24mol, thiourea 0.05mol.

2.Solution preparation: mix the selected raw materials in a certain proportion, the mixture is uniform, the molar ratio of ammonium nitrate to ammonium metatungstate is 12~36, the molar ratio of the auxiliary agent to ammonium metatungstate is 5~15.

3.Heating the solution at constant temperature of 200 degrees, evaporating and condensing to form colloidal substances, then decomposing, producing a large amount of gas, and then obtaining nano needle like violet tungsten powder by oxidation-reduction reaction.

ammonium metatungstate is used as the raw material in the evaporation reduction process of ammonium metatungstate. It has the advantages of short process, low cost, simple process, easy scale production, and a large amount of gas discharged by severe redox reaction, the fluffy porous powder is prepared easily and quickly in less than ten minutes. The produced needle-shaped purple tungsten has fine particle size, large specific surface area, large surface activity and excellent performance.

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