Abstract
The thermal decomposition of ammonium tetrathiotungstate (ATT), (NH4)2WS4, was studied by SEM, FTIR, XRD, EDX and TG/DTA-MS. The decomposition of ATT involved three steps in inert atmosphere: (1) release of free water between 30 and 140 °C; (2) formation of an amorphous WS3 phase between 170 and 280 °C, from which (3) a slightly crystalline WS2 formed between 330 and 470 °C. As a difference compared to inert atmosphere, in air in the second step, the ATT decomposed into directly WS2 instead of WS3. This WS2 phase was amorphous and still contained traces of ATT. Between 260 and 500 °C from the WS2, monoclinic tungsten oxide crystallized in two steps: at 302 °C a slightly crystalline m-WO3 formed, which became more crystalline at 471 °C. During the investigation of the effect of the particle size, it was found that the thermal behaviour of ATT crystals was similar to ATT powder, with some shift in the decomposition temperature. The XRD results showed that the WS2 formed from the ATT powder in N2 had a higher level of crystallization, compared to the WS2 obtained from ATT crystals.
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