Preparation of LiZnPO4·H2O via a novel modified method and its non-isothermal kinetics and thermodynamics of thermal decomposition

Abstract

The single phase α-LiZnPO4·H2O was directly synthesized via solid-state reaction at room temperature using LiH2PO4·H2O, ZnSO4·7H2O, and Na2CO3 as raw materials. XRD analysis showed that α-LiZnPO4·H2O was a compound with orthorhombic structure. The thermal process of α-LiZnPO4·H2O experienced two steps, which involved the dehydration of one crystal water molecule at first, and then the crystallization of LiZnPO4. The DTA curve had the one endothermic peak and one exothermic peak, respectively, corresponding to dehydration of α-LiZnPO4·H2O and crystallization of LiZnPO4. Based on the iterative iso-conversional procedure, the average values of the activation energies associated with the thermal dehydration of α-LiZnPO4·H2O, was determined to be 86.59 kJ mol−1. Dehydration of the crystal water molecule of α-LiZnPO4·H2O is single-step reaction mechanism. A method of multiple rate iso-temperature was used to define the most probable mechanism g(α) of the dehydration step. The dehydration step is contracting cylinder model (g(α) = 1−(1−α)1/2) and is controlled by phase boundary reaction mechanism. The pre-exponential factor A was obtained on the basis of Ea and g(α). Besides, the thermodynamic parameters (ΔS≠, ΔH≠, and ΔG≠) of the dehydration reaction of α-LiZnPO4·H2O were determined.