Violet Tungsten Oxide Prepared from Ammonium Partrungstate

Generally, violet tungsten oxide is obtained by calcining ammonium paratungstate in a rotary furnace. The prepared violet tungsten oxide is ultrafine and of good quality. During the preparation process, furnace temperature, furnace tube speed and feeding speed are the three factors that affect the properties of violet tungsten oxide.

Preparation of reagents

Ammonium paratungstate and liquid nitrogen are needed in this preparation process.

1.  Ammonium paratungstate was prepared by ion exchange method. Its chemical formula is 5 (NH₄) ₂O · 12WO₃ · 5H₂O. The mass ratio of contained WO₃ is 88.96%.

2. The mass ratio of NH₃ contained in liquid nitrogen is greater than or equal to 99.8%, and that of impurity is less than or equal to 0.2%.

Preparation process

The preparation is carried out in an improved rotary furnace. Liquid nitrogen is introduced into the rotary furnace after vaporization. Then ammonium paratungstate is put into the rotary furnace by a screw feeder at a certain speed. It is calcined at a certain temperature. Hydrogen is produced by the decomposition of NH₃. Therefore, violet tungsten oxide can be obtained by calcining ammonium paratungstate in presence of hydrogen.

Analysis of preparation and product

1. Furnace temperature, furnace tube speed and feeding speed are three important factors affecting the performance of violet tungsten oxide. During the preparation process, excessive reduction of the materials will be caused by high temperature of furnace as well as slow speed of furnace tube and feeding, resulting in the increase of WO₂ phase and W phase. And ammonium paratungstate can’t be completely converted into W₁₈O₄₉ phase, which leads to the increase of W₂₀O₅₈ and other phases. Only by coordinating the three factors can violet tungsten oxide (W₁₈O₄₉) be successfully prepared.

2. The prepared violet tungsten oxide is in a color of blue purple or purple red. It is ultrafine and of high quality. Violet tungsten oxide has unique needle structure and distribution of particles is loose.

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