Study of kinetics and thermodynamics of the dehydration reaction of AlPO4 • H2O

The kinetics and thermodynamics of the thermal dehydration of aluminum phosphate monohydrate, AlPO4 center dot H2O were studied using thermogravimetry (TG-DTG-DTA) at four heating rates in dry air atmosphere. The activation energies of the dehydration step of AlPO4 center dot H2O were calculated through the methods of Friedman (FR) and Flynn-Wall-Ozawa (FWO) and the possible conversion function has been estimated through the Achar and Li-Tang equations. The independent activation energies on extent of conversions and the better kinetic model of the dehydration reaction for AlPO4 center dot H2O indicate single kinetic mechanism and the F-2.05 model as a simple n-order reaction of "chemical process or mechanism no-invoking equation'', respectively. The positive values of Delta H-# and Delta G(#) for the dehydration reaction show that it is endothermic and non-spontaneous process and it is connected with the introduction of heat. The kinetic and thermodynamic functions calculated for the dehydration reaction by different techniques and methods were found to be consistent.