Thermal decomposition kinetics and reversible hydration study of the Li 2Zn(HPO 4) 2·H 2O

Abstract

The dilithium zinc hydrogen phosphate monohydrate (Li 2Zn(HPO 4) 2·H 2O) was synthesized at the ambient temperature by using zinc acetyl acetonate monohydrate, phosphoric acid and lithium hydroxide monohydrate. The thermal stability of the Li 2Zn(HPO 4) 2·H 2O was studied by non-isothermal kinetic method (Ozawa and Kissinger) from the differential scanning calorimetric (DSC) data. The studied hydrate undergoes two endothermic thermal transformations, which the first transformation is due to the release of water molecule of crystallization and the second one is due to the release of water of constituent from HPO 4 2− anions and transforms to P 2O 7 4−. The activation energies ( E a) calculated for the dehydration step and decomposition step of the Li 2Zn(HPO 4) 2·H 2O from different methods were found to be consistent. The dehydration and rehydration processes of the synthesized compound were investigated and found that the water of crystallization can be removed and rehydrated without the disrupting the structure of the material, provided it is not heated beyond 200 °C. The dehydration and rehydration processes of the synthesized Li 2Zn(HPO 4) 2·H 2O exhibits similar property to the zeolite.