Tungsten Trioxide Hydrogen Reduction

Producing tungsten trioxide can use ammonium tungsten or tungsten acid by dried and calcined. First it will be at 100 ℃ removed moisture from tungsten acid or ammonium paratungstate. Then removed water and ammonium compounds by calcination . Tungsten acid at a temperature of 773 ~ 873 ℃ calcined product is still less than 0.5% of water, and at a temperature of 973 ~ 1023 ℃ calcined only less than 0.1% water. Tungsten acid reaction formula is: H2WO4 = WO3 +H2O; however ammonium paratungstic (APT) can be reacted at temperatures higher than 523 ℃, ammonium tungsten reaction formula is: 5 (NH4) 2O · 12WO3 · NH2O = 12WO3 + 10NH3 ↑ + (n + 5) H2O ↑. Calcination temperature and speed which has a significant impact on the product, the higher the calcination temperature, the coarser granularity WO3 are. And a sharp rise in the temperature of the system the specific surface area of WO3 is large. On the contrary, slowly heated then WO3’crystal morphology will more complete so that the small specific surface area WO3 has. China will divided WO3 into three levels, first level was 99.95%, secondary 99.9% purity, the third levels of 99.5%. Particle size is generally used for the production of bulk density of WO3 tungsten products or specific surface area, said the finer the particle size, the smaller the bulk density, the greater specific surface area. Ammonium paratungstate or tungsten acid job is usually calcined in a rotary tube furnace for firing, furnace tube made of stainless steel pipe external resistance wire heating, calcining furnace tube when constant rotation speed of approximately 2.5r/min. Tungsten acid calcination temperature is 1023 ~ 1123K, ammonium paratungstate calcination temperature is 873 ~ 973K, the specific choice of the calcination temperature depends on the product requirements.

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