Thermochemical Properties and Decomposition Kinetics of Ammonium Magnesium Phosphate Monohydrate

Abstract Ammonium magnesium phosphate monohydrate NH 4 MgPO 4 ·H 2 O was prepared via solid state reaction at room temperature and characterized by XRD, FT‐IR and SEM. Thermochemical study was performed by an isoperibol solution calorimeter, non‐isothermal measurement was used in a multivariate non‐linear regression analysis to determine the kinetic reaction parameters. The results show that the molar enthalpy of reaction above is (28.795±0.182) kJ/mol (298.15 K), and the standard molar enthalpy of formation of the title complex is (−2185.43±13.80) kJ/mol (298.15 K). Kinetics analysis shows that the second decomposition of NH 4 MgPO 4 ·H 2 O acts as a double‐step reaction:an n th‐order reaction ( F n ) with n= 4.28, E 1 =147.35 kJ/mol, A 1 =3.63×10 13 s −1 is followed by a second‐order reaction ( F 2 ) with E 2 =212.71 kJ/mol, A 2 =1.82×10 18 s −1 .