APT calcination method producing yellow tungsten oxide is calcinating APT in the air, after it reaches to certain temperature, the decomposed material is yellow tungsten oxide. When calcinating APT in the air, it will have different phase under different temperature. When it reaches 500℃, it converts to yellow tungsten oxide. The process of APT calcination was analyzed by differential thermal analysis (DSC) and X-ray diffraction (XRD). It was found that the phase change of APT in air was:
1.When temperature is lower than 240℃, APT converts to AMT.
2.When it reaches 300~350℃, it converts to amorphous substance (ammonium tungsten bronze).
3.When it goes up to 400℃, hexagonal structure of WO3 is obtained.
4.When it heats up to 500℃, triclinic crystalline model of yellow tungsten oxide is obtained.
Besides that, ammonium paratungstate purity determines yellow tungsten oxide purity, also crystalline form. So control APT crystalline and purity will have ideal crystalline form and purity of yellow tungsten oxide.