Thermal decomposition mechanism of ammonium phosphotungstate hydrate in air atmosphere

► Water soluble PhTA was formed by solving CaWO4 in HCl solutions containing H3PO4. ► In the first thermal decomposition step, APhT losses its crystal water. ► In the second thermal decomposition step, APhT transforms to PhT. ► At elevated temperatures, PhT is decomposed gradually to WO3 and P2O518WO3. ► The activation energy of dehydration reaction was calculated to be 53.45 kJ mol− 1.