Kinetics and Thermodynamics of the Formation of MnFeP4O12

The kinetics and thermodynamics of dehydration and intermolecular polycondensation reactions of Mn 1/2 Fe 1/2 (H 2 PO 4 ) 2 ·H 2 O and Mn 1/2 Fe 1/2 (H 2 PO 4 ) 2 were studied under nonisothermal heating by thermogravimetry (TG). On the basis of three calculation procedures and 24 kinetic mechanism functions, kinetic triplets ( E, A, kinetic model) using the Arrhenius equation were calculated for both processes. The comparison of the results obtained with these calculation procedures show a strong dependence on the selection of the mechanism function for the process. The thermodynamic functions (Δ H *, C p, Δ G *, and Δ S *) of both reactions are calculated from differential scanning calorimetry (DSC) experiments. Kinetic and thermodynamic results indicate that the polycondensation step has a lower rate and is a stronger reaction than the dehydration step and corresponds to the breaking of the strong hydrogen-bonded P−OH group, in connection with the polycondensation reaction, which confirms that the decomposition product (manganese iron cyclotetraphosphate, MnFeP 4 O 12 ) was obtained.