Blue Tungsten Oxide Producing Method
Blue tungsten oxide preparing method mainly is ammonium paratungstate (APT) closed calcination, APT hydrogen mild reduction and internal reduction method, the front two are mostly used in industrial of China. In addition, blue tungsten oxide can be obtained by mild hydrogen reducing tungsten trioxide (WO3), but the quality is not as good as with APT for raw materials; hydrogen reduction of tungsten solvent to extract tungsten organic phase can also prepare blue tungsten oxide of O: W = 2.82; internal reduction method can get BTO with main phase of WO2.90.
Research of ammonium paratungstate decomposed to blue tungsten oxide under a reducing atmosphere and found that the decomposition of APT has experienced three stages:
1.APT loses part of crystal water at temperature range of 90-180℃;
2.In the temperature range of 180-260℃, ammonia began to escape from the ammonium paratungstate to generate ammonia metatungstate (AMT) which is soluble in water and can produce high purity ammonium paratungstate after reconstitution, and the loss rate is accelerated with temperature increasing;
3.AMT begin to decompose at temperatures within the range of 260-350℃, the further loss of water molecules and ammonia to give the blue tungsten oxide, and also, decomposition products include ammonium tungsten bronze (ATB).
The above three phases can be simply described as: APT→AMT→blue tungsten oxide.