2020年10月28日星期三

Tungsten Powder Prepared by One Step Reduction Method

The preparation of tungsten powder from APT is usually calcined in the weak reducing atmosphere to produce yellow tungsten, blue tungsten or purple tungsten.

Then, the reduction of hydrogen to produce tungsten powder is a commonly used method in industry. The tungsten powder prepared by this process is a kind of very regular polycrystal, which is the main raw material for preparing tungsten alloy and tungsten carbide.

But some scholars believe that the traditional process is long, easy to bring in impurities, production costs are relatively high, so he proposed a step through tungsten oxide process, the direct preparation of tungsten powder from ammonium paratungstate one step reduction method.

The main process of one-step reduction method is as follows: 1. In the first step to control the formation of the intermediate of blue tungsten, a certain proportion of hydrogen and nitrogen mixed gas is replaced into ammonia in the reduction furnace. 2. Loading the amount of 50g, hydrogen flow 32 / h, heating rate of 10 °C / min, 500 °C insulation 200min, 900 °C insulation 1.5h, air-cooled to 100 °C out. In the hydrogen reduction reaction, it is found that the particle morphology of ammonium paratungstate to blue tungsten has no obvious change, but there is obvious crack on the surface of the particle. 




In the reduction process, there are a large number of water vapor generated, this part of water vapor mainly comes from two aspects: first, APT removal of crystalline water, this part of water accounted for most; In the reduction process, there are a large number of water vapor generated, this part of water vapor mainly comes from two aspects: first, APT removal of crystalline water, this part of water accounted for most; Second, due to the presence of weak reducing atmosphere, a small amount of tungsten trioxide in the reduction process was reduced to blue tungsten or purple tungsten produced when the water appears.

It is generally believed that this crack is due to the dehydration of APT and the cracks caused by ammonium removal, which is more conducive to the entry of hydrogen. In addition, the larger particle APT particles gap, will also be more conducive to hydrogen through and reduction of tungsten powder. Therefore, under the same reduction condition, the loading capacity of large particle APT can be more relatively.

The results show that the stepwise reduction of tungsten powder by ammonium paratungstate is feasible, and the yield of tungsten powder obtained under the optimum process conditions is more than 98.5%. It can also control the reduction temperature to control the particle size of tungsten powder. Prolonging the reduction time will cause the tungsten powder to grow up, and the grain of tungsten powder tends to be a complete polygon. The lower the initial hydrogen reduction temperature, the more conducive to the formation of fine tungsten powder; the larger the loading amount, the uniformity of tungsten powder will become worse.

Therefore, although the one-step reduction method has operability, but it is not perfect, first of all, the process requirements are very strict, and it is also required for the purity of ammonium paratungstate. Second, at the moment of nearly one hundred thousand yuan per ton of tungsten powder, the loss benefit of the law is almost equal to the cost of the traditional method.

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