Determination of kinetic triplet of the synthesized Ni3(PO4)2·8H2O by non-isothermal and isothermal kinetic methods

Abstract

The nickel phosphate octahydrate (Ni3(PO4)2·8H2O) was synthesized by a simple procedure and characterized by FTIR, TG/DTG/DTA, AAS, and XRD techniques. The morphologies of the title compound and its decomposition product were studied by the SEM method. The dehydration process of the synthesized hydrate occurred in one step over the temperature range of 120–250 °C, and the thermal decomposition product at 800 °C was found to be Ni3(PO4)2. The kinetic parameters (E and A) of this step were calculated using the Ozawa–Flynn–Wall and Kissinger–Akahira–Sunose methods. The iterative methods of both equations were carried out to determine the exact values of E, which confirm the single-step mechanism of the dehydration process. The non-isothermal kinetic method was used to determine the mechanism function of the dehydration, which indicates the contracting disk mechanism of R1 model as the most probable mechanism function and agrees well with the isothermal data. Besides, the isokinetic temperature value (Ti) was calculated from the spectroscopic data. The thermodynamic functions of the activated complex (ΔS≠, ΔH≠, and ΔG≠) of the dehydration process were calculated using the activated complex theory of Eyring. The kinetic parameters and thermodynamic functions of the activated complex for the dehydration process of Ni3(PO4)2·8H2O are reported for the first time.