Violet tungsten oxide is kind of short rod fine crystal and between these short rod fine crystals there have many voids, particle size distribution is relatively loose. Which are conducive to discharge water and help hydrogen into the crystal particles, therefore, not only the restore process can take place inside also can restore on the surface, violet tungsten oxide advantageous for the producing ultrafine tungsten powder. Besides the reduction process conditions during the reaction should able to better control, such as low dew point of hydrogen, flow rate, amount of loading the boat.
After studies showed with the development of reduction reaction, the oxygen atom reduce and oxygen vacancies increase of violet tungsten oxide, tungsten dioxide particles becomes more dense than γ- tungsten oxide’s. This is bad for hydrogen gas get into interior particles and the water which producing by reaction particles are not easily discharged. During the restore process, the reaction only happens on violet tungsten oxide surface but hardly occurs at particle interior. According to tungsten oxide reduction - precipitation growth mechanism, since violet tungsten oxide reduced to tungsten dioxide will lead to the production of tungsten powder particles grow up, so to produce ultra-fine tungsten powder or nano tungsten powder, so in the reduction process is best not restore to tungsten dioxide.
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