Violet Tungsten Oxide APT Hydrogen Reduction Method

Violet tungsten oxide (WO_2.72) is one of the most widely used raw materials in the production of tungsten powder. Usually ammonium paratungstate is as raw material calcined in a rotary kiln derived. Violet tungsten oxide is an intermediate product with a special surface, fine needle structure and high chemical activity of tungsten. Because tungsten carbide (WC) powder prepared by using violet tungsten oxide has fine and uniform particle size, narrow particle size distribution and no structural agglomeration, it is a product with uniform properties and high quality. Therefore, violet tungsten oxide is suitable for the production of fine tungsten powder.

The preparation of violet tungsten oxide is mainly based on APT hydrogen mild reduction method, using a modified industrial rotary kiln (ZW-001- & 300mmX6700mm) for reduction. Liquid ammonia is passed into the rotary kiln after being vaporized, the APT is fed into the furnace by a screw feeder at a certain feeding speed, and calcined at a certain temperature. As the NH₃ is decomposed to produce H₂, the APT is calcined and decomposed in the reducing gas Violet tungsten oxide. The most important parameters influencing the production of violet tungsten oxide are: furnace temperature, furnace tube speed, feed rate and NH₃ flow rate. If the temperature is too high, the feed rate is too low, the tube speed is too slow will lead to over-reduction of the material, resulting in increased WO₂ phase content or W phase appears. Therefore, only the relationship between the three can produce a single phase of violet tungsten oxide.

NH₃ can be decomposed into N₂ and H₂ at high temperature, can make APT mildly reduce and decompose to produce W_2.72 phase. After the decomposition of NH₃ volume increases, you can take away the large amount of water vapor generated by the reaction. However, if the flow rate of NH₃ is too large, the partial pressure of H2 in the furnace will increase, resulting in the increase of WO₂ content in the product, which will affect the quality of the product. Therefore, the exhaust system should be rationally used to ensure the pressure stability in the furnace.

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