The quality parameters of tungsten powder are powder size and purity. Although the essence of the growth of tungsten particles is the volatile deposition during the reduction process, there are many factors that affect the quality of tungsten power, including raw materials, hydrogen flow rate and technological conditions.
In the preparation of ultrafine tungsten powder, the selection of powder materials has different influences on the quality of tungsten powder.
Ultrafine tungsten powder can be produced by blue tungsten and violet tungsten under certain reduction conditions. Due to its special pore structure, violet tungsten has good permeability and can quickly remove water vapor from the reducing atmosphere, so as to produce fine and uniform tungsten powder, and has a comparative advantage in productivity.
In addition, violet tungsten can be reduced in dry hydrogen without going through the intermediate phase of tungsten dioxide, resulting in a fine and uniform tungsten powder. During the reduction process, the technological conditions should be controlled to avoid the formation of tungsten dioxide aggregates.
The particle size of the reduced tungsten powder is affected by the flow rate of hydrogen, the direction of hydrogen flow and the humidity. The higher the hydrogen humidity and the smaller the airflow, the finer the powder will be. In general, the flow direction of hydrogen in production is opposite to the direction of the material, that is, the reverse flow of hydrogen.
The effects of the reduction process on tungsten particle size include reduction temperature, boat speed, and material thickness.
If the temperature is too low, the reduction will not be sufficient, and the tungsten powder particles will grow when the temperature is too high. If the boat is pushed too fast, the tungsten oxide will be pushed into the high-temperature zone before it can be reduced in the low-temperature zone, which will make the tungsten powder particles grow up or increase the oxygen content. The thinner the material in the vessel, the finer the tungsten powder, but the yield will decline.
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