Authors:Rattanai Baitahe, Naratip Vittayakorn and Banjong Boonchom
Copper hydrogenphosphate monohydrate, CuHPO4·H2O, was synthesized for the first time through simple and rapid method using the mixing of copper carbonate and phosphoric acid in acetone medium at ambient temperature. The obtained CuHPO4·H2O decomposed in three stages via dehydration and deprotonated hydrogenphosphate reactions, revealed by TG/DTG and DSC techniques. The kinetic triplet parameters (Ea, A, and n) and thermodynamic functions (ΔH∗, ΔG∗, and ΔS∗) for the first two decomposed steps were calculated from DSC data. All the obtained functions indicate that the deprotonated HPO42− reaction for the second step occurs at a higher energy pathway than the dehydration reaction for the first step. The calculated wavenumbers based on DSC peaks were comparable with FTIR results, which support the breaking bonds of OH (H2O) and P-OH (HPO42−) according to decomposed mechanisms. All the calculated results are consistent and in good agreement with CuHPO4·H2O's thermal transformation mechanisms.
The thermal transformation of Na2C2O4 was studied in N2 atmosphere using thermo gravimetric (TG) analysis and differential thermal analysis (DTA). Na2C2O4 and its decomposed product were characterized using a scanning electron microscope (SEM) and the X-ray diffraction technique (XRD). The non-isothermal kinetic of the decomposition was studied by the mean of Ozawa and Kissinger–Akahira–Sunose (KAS) methods. The activation energies (Eα) of Na2C2O4 decomposition were found to be consistent. Decreasing Eα at increased decomposition temperature indicated the multi-step nature of the process. The possible conversion function estimated through the Liqing–Donghua method was ‘cylindrical symmetry (R2 or F1/2)’ of the phase boundary mechanism. Thermodynamic functions (ΔH*, ΔG* and ΔS*), calculated by the Activated complex theory and kinetic parameters, indicated that the decomposition step is a high energy pathway and revealed a very hard mechanism.