APT decomposition

Non-isothermal kinetic (k, A and ΔE) and thermodynamic (ΔH, C_p and ΔS) parameters of ammonium paratungstate decomposition to the onset of formation of WO₃, were determined by analysing thermogravimetry (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC) curves recorded at various heating rates (1–30°C min⁻¹). Thermal events encountered throughout the decomposition course were due to three endothermic (at 120 ° C (I), 195 ° C (II) and 359 ° C (IV)) and two exothermic (at 265 ° C (III) and 386 °C (V)) processes. The events I–IV were accompanied by weight losses resulting from the elimination of volatile components [(NH₄)₂O, NH₃ and H₂O] leading to the formation of intermediate solid products (metatungstate and polytungstate), whereas event V was due to the crystallization of WO₃ in the immediate vicinity of its formation (at 370 ° C).

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