Thermal decomposition of (NH4)2MoO2S2, (NH4)2MoS4, (NH4)2WO2S2 and (NH4)2WS4

The thermal decomposition of (NH4)2MoO2S2,(NH4)2MoS4, (NH4)2WO2S2 and (NH4)2WS4 has been studied by DTA and TGA methods. All compounds decompose in two steps. The tetrathio compounds decompose as represented by the equations, (NH4)2MeS4 → 2NH3 + H2O + MeS3 MeS3 → MeS2 + S (Me  Mo, W). The thermal decomposition of the dithio salts is very complex. It is presumed that mixtures of oxysulphides and sulphides are formed as intermediate compounds. The final product of decomposition of the dithio-molybdate is very close to MoS2, the final product of the decomposition of the dithio-tungstate yielding a mixture of WS2 and WO2 of the average composition WO0·5S1·75. The formal energies of activation which qualitatively describe the thermal properties of the compounds and heats of decomposition for the first reaction step were calculated from the thermal decomposition curves.