Phase changes on heating ammonium magnesium phosphate hydrates

DTA and TG curves of NH4MgPO4 · H2O, NH4MgPO4 · H2O and (NH4)2Mg(HPO4)2 · 4H2O are complex because of several overlapping reactions and different reaction paths, dependent on the combination of phases present and the experimental variables, especially the atmosphere. By heating samples to various temperatures, quenching to room temperature and examining the reaction products by X-ray diffraction, the phases formed after various heat treatments have been identified. The most important reaction sequence on heating in the presence of excess MgO is