Abstract
The crystals of ammonium paratungstate were thermally decomposed in both air and vacuum, and the process of thermal decomposition of this salt and the formation of tungsten trioxide particles were studied by means of following measurements, (i) weight (ii) determination of the evolved ammonia gas, (iii) the differential thermal analysis, (iv) the X-ray analysis, (v) the surface area measurement and also (vi) the observation by electron microscope.
The result obtained are as follows;
(1) The dehydration of the crystal takes place completely below 250°C. The evolution of ammonia occurs in several stages extending to 420°C.
(2) The a-tungsten trioxide are obtained at the temperatures above 420°C by the decomposipion in air. The particle of a-tungsten trioxide consists of small unit particles which are linked with each other, forming an aggregate whose shape are resemble that of the mother salt.
(3) When the salts are decomposed in vacuum, 7-tungsten oxide are obtained at the temperature ranging from 400-500°C, and 8-tungsten oxide at the temperature higher than 500°C. The shape of the particle thus obtained was somewhat different from that of a-tungsten obtained in air.
Experimental results, and the considerations on the mechanism of decomospition and also the formation of tungsten trioxide are described in detail.
