Thermal kinetics and thermodynamics of the dehydration reaction of Mg3(PO4)2·22H2O

Mg3(PO4)2•22H2O lost its crystal water in the temperature range of 40 -200°C and the calcined sample was identified as Mg3(PO4)2, was a notable for its further treatments in optical and electrical applications.Dehydration process was studied using non-isothermal thermogravimetry (TG) applying model-fitting method.Different mechanism models (chemical reaction order, diffusion and phase interfacial reaction) were applied.The activation energies calculated for the dehydration reaction; and average of activation energy was found as 160 kJ/mol.The better kinetic model of the dehydration reaction for Mg3(PO4)2•22H2O was selected as F3 (chemical reaction -third order).The thermodynamic functions (ΔH, ΔG and ΔS) of the dehydration reaction were calculated by the activated complex theory and found that the process was endothermic, non-spontaneous and fast.