Abstract:The thermal decomposition mechanism of ammonium thiotungstate of granularity 62~74μm in N2was investigated by means of DTA and XRD methods. The thermal decomposition reaction occurs in three steps: (NH₄)₂WS₄H₂O→(NH₄)₂WS₄+H₂O→2NH₃+H₂+2S+WS₂→2NH3+H₂S+S+WS₂. The thermal decomposition activation energy and orders of (NH₄)₂WS₄H₂O in granularity of 62~74μm in three steps were calculated according to Kissinger, Freeman-Carrol, Coasts-Redfern methods from the DTA curves. The value of activation energy and the orders of reactions is 551.87 kJ/mol and 1.4 in the first step, 125.65 kJ/mol and 0.52 in the second step as well as 277.69kJ/mol and 0.8 in the third step respectively. The reaction rate in every step has also been given.

Key words: (NH₄)₂WS₄·H₂O　thermal decomposition kinetics　N2　DTA　XRD