Abstract
During thermal decomposition of ammonium paratungstate (Monoclinic and Orthorhombic AP T), study on formation process of very fine grain tungsten oxide particle was carried out by thermobalance in nitrogen atmosphere. Thermogravimetric analysis, X-ray diffraction, scanning electron microscopy and specific surface area measurement have been used to make clear the thermal decomposition process. The results obtained are as follows.
(1) Both monoclinic and orthorhombic APT decompose into WO3 through the following order:
5(NH4)2O⋅12WO3⋅5H2O→X(NH4)2O⋅12WO3→12WO3
5(NH4)2O⋅12WO3⋅11H2O→X(NH4)2O.12WO3→12WO3
(2) Crystal system of X(NH4)2O⋅12WO3 changed along the following step.
APT→Amorphous→Hexagonal ammonium tungsten bronze (→Monoclinic WO3)
(3) Ultrafine individual particles are formed on the original APT particle changed like spongy at around 773K, and the particles were uniform in size and shape.
