The thermal decomposition of magnesium hydrogen phosphate trihydrate MgHPO4 · 3H2O was investigated in air atmosphere using TG-DTG-DTA. MgHPO4 · 3H2O decomposes in a single step and its final decomposition product (Mg2P2O7) was obtained. The activation energies of the decomposition step of MgHPO4 · 3H2O were calculated through the isoconversional methods of the Ozawa, Kissinger–Akahira–Sunose (KAS) and Iterative equation,
and the possible conversion function has been estimated through the Coats and Redfern integral equation. The activation energies
calculated for the decomposition reaction by different techniques and methods were found to be consistent. The better kinetic
model of the decomposition reaction for MgHPO4 · 3H2O is the F1/3 model as a simple n-order reaction of “chemical process or mechanism no-invoking equation”. The thermodynamic functions (ΔH*, ΔG* and ΔS*) of the decomposition reaction are calculated by the activated complex theory and indicate that the process is non-spontaneous
without connecting with the introduction of heat.
The thermal decomposition kinetics of nickel ferrite (NiFe2O4) precursor prepared using egg white solution route in dynamical air atmosphere was studied by means of TG with different
heating rates. The activation energy (Eα) values of one reaction process were estimated using the methods of Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS),
which were found to be consistent. The dependent activation energies on extent of conversions of the decomposition reaction
indicate “multi-step” processes. XRD, SEM and FTIR showed that the synthesized NiFe2O4 precursor after calcination at 773 K has a pure spinel phase, having particle sizes of ~54 ± 29 nm.
The kinetics and thermodynamics of the thermal dehydration of aluminum phosphate monohydrate, AlPO4 · H2O were studied using thermogravimetry (TG-DTG-DTA) at four heating rates in dry air atmosphere. The activation energies of the dehydration step of AlPO4 · H2O were calculated through the methods of Friedman (FR) and Flynn–Wall–Ozawa (FWO) and the possible conversion function has been estimated through the Achar and Li–Tang equations. The independent activation energies on extent of conversions and the better kinetic model of the dehydration reaction for AlPO4 · H2O indicate single kinetic mechanism and the F2.05 model as a simple n-order reaction of “chemical process or mechanism no-invoking equation”, respectively. The positive values of ΔH& and ΔG& for the dehydration reaction show that it is endothermic and non-spontaneous process and it is connected with the introduction of heat. The kinetic and thermodynamic functions calculated for the dehydration reaction by different techniques and methods were found to be consistent.
Authors:Banjong Boonchom and Chanaiporn Danvirutai
The binary manganese and calcium dihydrogen phosphate monohydrate Mn0.5Ca0.5(H2PO4)2 · H2O was synthesized by a rapid and simple co-precipitation method using phosphoric acid, manganese metal, and calcium carbonate
at ambient temperature. Thermal transformation shows complex processes and the final decomposed product was the binary manganese
calcium cyclotetraphosphate MnCaP4O12. The activation energies of some decomposed steps were calculated by Kissinger method. Activated complex theory has been
applied to each step of the reactions and the thermodynamic functions are calculated. These values for transformation stages
showed that they are non-spontaneous processes without the introduction of heat. The differences of physical and chemical
properties of the synthesized compound and its decomposed product are compared with M(H2PO4)2 · H2O and M2P4O12 (M = Mn and Ca), which indicate the effects of the presence of Ca ions in substitution of Mn ions and confirm the formation
of solid solution.
Authors:Banjong Boonchom and Chanaiporn Danvirutai
The non-isothermal kinetics of dehydration of AlPO4·2H2O was studied in dynamic air atmosphere by TG–DTG–DTA at different heating rates. The result implies an important theoretical
support for preparing AlPO4. The AlPO4·2H2O decomposes in two step reactions occurring in the range of 80–150 °C. The activation energy of the second dehydration reaction
of AlPO4·2H2O as calculated by Kissinger method was found to be 69.68 kJ mol−1, while the Avrami exponent value was 1.49. The results confirmed the elimination of water of crystallization, which related
with the crystal growth mechanism. The thermodynamic functions (ΔH*, ΔG* and ΔS*) of the dehydration reaction are calculated
by the activated complex theory. These values in the dehydration step showed that it is directly related to the introduction
of heat and is non-spontaneous process.
Authors:Banjong Boonchom, Chanaiporn Danvirutai and Montree Thongkam
The thermal decomposition of synthetic serrabrancaite (MnPO4 · H2O) was studied in N2 atmosphere using TG-DTG-DTA. Thermal analysis results indicate that the decomposition occurs in two stages, which are assigned
to the dehydration and the reduction processes and the final product is Mn2P2O7. X-ray powder diffraction, FT-IR and FT-Raman techniques were used for identification of the solid decomposition product.
The decomposition kinetics analysis of MnPO4 · H2O was performed under non-isothermal condition through isoconversional methods of Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose
(KAS). The dependences of activation energies on the extent of conversions are observed in the dehydration and the reduction
reactions, which could be concluded the “multi-step” processes.
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.