| The thermal decomposition process of ammonium paratungstate (A.P.T.), 5(NH₄)₂O ·5H₂O, was studied by differential thermal analysis, thermogravimetry, and X-Ray power diffraction. A small quantity of water and ammonia was released below 250℃ and most of water and ammonia was driven off rapidly about 305℃. At 320℃, the ammonia remained 1 mole and the compound changed into amorphous state and γoxide, followed by the formation of αoxide at about 440℃. The shape of tungstic oxide particles was similar to that of APT and tungstic oxide particles were smaller than APT particles because of fracture of the latter during decomposition. Tungstic oxide particles were annealed for various periods of time (1 hr. to 10 hrs.) over the temperature range of 500 to 1000℃. The particles became finer due to further fracture at higher temperatures. The particles were composed of fine grains, the growth of which increased with increasing time and temperature. The color of the oxide powder changed from yellow to green with increasing temperature due to the formation of WO_(2.9). |
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