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Journal of the Korean Chemical Society (JKCS)

ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 7, Number 1
February 20, 1963 

The Study of Thermal Decomposition of Polyacids by Differential Thermal Analysis: Ammonium Paratungstate
Yungpil Ahn
The thermal decomposition process of ammonium paratungstate 5(NH4)2O·12WO3·5H2O was analysed by the methods of thermogravimetric analysis, differential thermal analysis, quantitative analysis of the ammonia which is released during heating and X-ray powder diffraction in air and in vacuo. There are several endothermic peaks which indicate release of ammonia and exothermic peaks which indicate crystal growth and oxidation of decomposed products in air. After water is driven off the ammonia is released at intervals corresponding to the endothermic peaks. The highest temperature at which ammonia is released is about 420℃ in air and 480℃ in vacuo. In air the crystal structure of paratungstate is conserved up to a temperature of 300℃ at which the remaining ammonia is about 4 mols. At 320℃ the remaining ammonia becomes less than 2 mols and the paratungstate structure changes into the amorphous state. After that γ oxide is produced and is oxidized to α oxide in the temperature range of 400-500℃ in air. In vacuo however the endothermic peaks and structural changes occur at lower temperatures and the structure of γ oxide is conserved up to temperatures higher than 500℃.
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