Coarse tungsten trioxide has an apparent density of 1.2~1.6g/cm3. Coarse WO3 has greater apparent density as its particle size is larger than fine tungsten trioxide of 0.5~0.7g/cm3.
Producing Method
The production of coarse WO3 is treating "ammonium paratungstate - sodium paratungstate complex salt" with saturated ammonium chloride solution, the specific steps are shown as follows:
Add complex salt and saturated ammonium chloride solution with a solid-to-liquid ratio of 1: 5.5 in a reaction vessel equipped with a high speed stirrer. Stir 1~2h at the temperature range of 90~95°C. At this moment, NH+4 in the system replaces Na+ in the complex salt molecule to generate ammonium paratungstate precipitate. After centrifugation, the mother liquor can be reused to produce complex salt; the obtained ammonium paratungstate was carefully washed in deionized water.
The method for determining the end of washing is shown as follows:
Take 20mL sample which need washing. Pour 1 mL AgNO3 solution acidified with nitric acid beforehand into the sample. It means the ending of washing if there is no turbidity within 10 minutes after shaking. The mixture is dried after centrifugal dewatering. And it calcines at 600~700°C to form blue tungsten oxide (WO2.72~2.9), which will be further transformed into tungsten trioxide.
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