Tungsten Powder Preparation by One-step Reduction Method

In order to prepare tungsten powder from ammonium paratungstate, tungsten oxide should be burned in a weak reduction atmosphere before hydrogen reduction is a common method in industry. The tungsten powder prepared by this process is mostly polycrystalline, which is the main material for preparing tungsten alloy and tungsten carbide.

However, some scholars believe that the traditional process is long, easy to introduce impurities, and the production cost is relatively high. Therefore, he proposed a one-step reduction method for the direct preparation of tungsten powder from ammonium paratungstate through tungsten peroxide process.

The main process of one-step reduction is as follows: 1. In the first step of controlling the formation of blue tungsten-like intermediates, a certain proportion of hydrogen and nitrogen mixed gas is introduced into the reduction furnace to replace ammonia. 2. Loading capacity 50 g, hydrogen flow 32/h, heating rate 10 ℃/min, 500 ℃ for 200 min, 900 ℃ for 1.5 h, air-cooled to 100 ℃ for removal.

During the hydrogen reduction reaction, it was found that the morphology of the particles from ammonium paratungstate to blue tungsten did not change significantly, but there were obvious cracks on the surface of the particles. In the reduction process, a large amount of water vapor is produced, which mainly comes from two aspects: first, the crystalline water removed by APT, which accounts for the majority of the water; second, due to the existence of weak reduction atmosphere, a small amount of tungsten trioxide is reduced to blue tungsten or violet tungsten in the reduction process.

The results show that one-step reduction of tungsten powder by ammonium paratungstate is feasible, and the yield of tungsten powder prepared under the optimum conditions is more than 98.5%. Moreover, the reduction temperature can be controlled to control the particle size of tungsten powder. The longer reduction time, the larger the grain size of tungsten powder and the more complete polygon the grain size of tungsten powder. The lower the initial hydrogen reduction temperature is, the better the formation of fine tungsten powder. The larger the loading capacity, the worse the uniformity of tungsten powder. Therefore, although the one-step reduction method is operable, it is not perfect. Firstly, its process requirements are very strict, and its purity requirements for ammonium paratungstate are very high.

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