Thermal and thermo-oxidative decomposition of ammonium–iron(II) phosphate monohydrate

The thermal and thermo-oxidative decompositions of NH4FePO4·H2O were studied by means of a combination of classical thermal analysis techniques (TG and DSC) with MS and powder XRD analysis. The experiment was run in two different (inert and oxidizing) atmospheres. In an inert (N2) atmosphere, thermal decomposition occurs in three steps at 265, 350 and 420 °C related to the evacuation of H2O (steps 1 and 3) and NH3 (steps 1–3). In an oxidizing (O2) atmosphere, thermal evacuation is coupled with the oxidation from Fe(II) to Fe(III). In addition, application of Vyazovkinʹs model-free kinetic method to three TG curves obtained at different heating rates (5, 10 and 20 °C/min) allows the activation energy to be calculated as a function of the extent of conversion. This helps to disclose the kinetic scheme that facilitates understanding of the mechanism of these reactions.