Kinetics of Thermal Transformation of Mg3(PO4)2 · 8H2O to Mg3(PO4)2

Abstract

The kinetics of thermal dehydration of Mg3(PO4)2 · 8H2O was investigated using thermogravimetry at four different heating rates. The activation energies of the dehydration step of Mg3(PO4)2 · 8H2O were calculated through the isoconversional Ozawa and Kissinger-Akahira-Sunose (KAS) methods and iterative methods, which were found to be consistent and indicate a single mechanism. The possible conversion function of the dehydration reaction for Mg3(PO4)2 · 8H2O has been estimated through the Coats and Redfern integral equation, and a better kinetic model such as random nucleation of the “Avrami–Erofeev equation (A 3/2 model)” was found. The thermodynamic functions (ΔH*, ΔG*, and ΔS*) of the dehydration reaction are calculated by the activated complex theory and indicate that it is a non-spontaneous process when the introduction of heat is not connected.