Kinetics and thermodynamics of thermal decomposition of synthetic AlPO 4•2H2O

The non-isothermal kinetics of dehydration of AlPO4•2H 2O was studied in dynamic air atmosphere by TG-DTG-DTA at different heating rates. The result implies an important theoretical support for preparing AlPO4. The AlPO4•2H2O decomposes in two step reactions occurring in the range of 80-150 °C. The activation energy of the second dehydration reaction of AlPO4•2H2O as calculated by Kissinger method was found to be 69.68 kJ mol^-1, while the Avrami exponent value was 1.49. The results confirmed the elimination of water of crystallization, which related with the crystal growth mechanism. The thermodynamic functions (ΔH*, ΔGand ΔS) of the dehydration reaction are calculated by the activated complex theory. These values in the dehydration step showed that it is directly related to the introduction of heat and is non-spontaneous process. © 2009 Akadémiai Kiadó, Budapest, Hungary.