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  • Author or Editor: Sen Liao x
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Abstract

Nanocrystalline NH4ZrH(PO4)2·H2O was synthesized by solid-state reaction at low heat using ZrOCl2·8H2O and (NH4)2HPO4 as raw materials. X-ray powder diffraction analysis showed that NH4ZrH(PO4)2·H2O was a layered compound with an interlayer distance of 1.148 nm. The thermal decomposition of NH4ZrH(PO4)2·H2O experienced four steps, which involves the dehydration of the crystal water molecule, deamination, intramolecular dehydration of the protonated phosphate groups, and the formation of orthorhombic ZrP2O7. In the DTA curve, the three endothermic peaks and an exothermic peak, respectively, corresponding to the first three steps' mass losses of NH4ZrH(PO4)2·H2O and crystallization of ZrP2O7 were observed. Based on Flynn–Wall–Ozawa equation and Kissinger equation, the average values of the activation energies associated with the NH4ZrH(PO4)2·H2O thermal decomposition and crystallization of ZrP2O7 were determined to be 56.720 ± 13.1, 106.55 ± 6.28, 129.25 ± 4.32, and 521.90 kJ mol−1, respectively. Dehydration of the crystal water of NH4ZrH(PO4)2·H2O could be due to multi-step reaction mechanisms: deamination of NH4ZrH(PO4)2 and intramolecular dehydration of the protonated phosphate groups from Zr(HPO4)2 are simple reaction mechanisms.

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Abstract

The single phase NH4NiPO4·6H2O was synthesized by solid-state reaction at room temperature using NiSO4·6H2O and (NH4)3PO4·3H2O as raw materials. XRD analysis showed that NH4NiPO4·6H2O was a compound with orthorhombic structure. The thermal process of NH4NiPO4·6H2O experienced three steps, which involves the dehydration of the five crystal water molecules at first, and then deamination, dehydration of the one crystal water, intramolecular dehydration of the protonated phosphate groups together, at last crystallization of Ni2P2O7. In the DTA curve, the two endothermic peaks and an exothermic peak, respectively, corresponding to the first two steps’ mass loss of NH4NiPO4·6H2O and crystallization of Ni2P2O7. Based on Flynn–Wall–Ozawa equation, and Kissinger equation, the average values of the activation energies associated with the thermal decomposition of NH4NiPO4·6H2O, and crystallization of Ni2P2O7 were determined to be 47.81, 90.18, and 640.09 kJ mol−1, respectively. Dehydration of the five crystal water molecules of NH4NiPO4·6H2O, and deamination, dehydration of the crystal water of NH4NiPO4·H2O, intramolecular dehydration of the protonated phosphate group from NiHPO4 together could be multi-step reaction mechanisms. Besides, the thermodynamic parameters (ΔH , ΔG , and ΔS ) of the decomposition reaction of NH4NiPO4·6H2O were determined.

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Abstract

MgFe2(C2O4)3·6H2O was synthesized by solid-state reaction at low heat using MgSO4·7H2O, FeSO4·7H2O, and Na2C2O4 as raw materials. The spinel MgFe2O4 was obtained via calcining MgFe2(C2O4)3·6H2O above 500 °C in air. The MgFe2(C2O4)3·6H2O and its calcined products were characterized by thermogravimetry and differential scanning calorimetry (TG/DSC), Fourier transform FT-IR, X-ray powder diffraction (XRD), and vibrating sample magnetometer (VSM). The result showed that MgFe2O4 obtained at 800 °C had a specific saturation magnetization of 40.4 emu g−1. The thermal process of MgFe2(C2O4)3·6H2O experienced three steps, which involves the dehydration of the six waters of crystallization at first, and then decomposition of MgFe2(C2O4)3 into amorphous MgFe2O4 in air, and at last crystallization of MgFe2O4. Based on Flynn–Wall–Ozawa equation, the average values of the activation energies associated with the thermal decomposition of MgFe2(C2O4)3·6H2O were determined to be 148.45 ± 25.50 and 184.08 ± 7.64 kJ mol−1 for the first and second decomposition steps, respectively. Dehydration of the six waters of MgFe2(C2O4)3·6H2O is multi-step reaction mechanisms. Decomposition of MgFe2(C2O4)3 into MgFe2O4 could be simple reaction mechanisms, kinetic model that can better describe the thermal decomposition of MgFe2(C2O4)3 is the F 3/4 model, and the corresponding function is g(α) = 1 − (1 − α)1/4.

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Abstract

The MnV2O6·4H2O with rod-like morphologies was synthesized by solid-state reaction at low heat using MnSO4·H2O and NH4VO3 as raw materials. XRD analysis showed that MnV2O6·4H2O was a compound with monoclinic structure. Magnetic characterization indicated that MnV2O6·4H2O and its calcined products behaved weak magnetic properties. The thermal process of MnV2O6·4H2O experienced three steps, which involves the dehydration of the two waters of crystallization at first, and then dehydration of other two waters of crystallization, and at last melting of MnV2O6. In the DSC curve, the three endothermic peaks were corresponding to the two steps thermal decomposition of MnV2O6·4H2O and melting of MnV2O6, respectively. Based on the Kissinger equation, the average values of the activation energies associated with the thermal decomposition of MnV2O6·4H2O were determined to be 55.27 and 98.30 kJ mol−1 for the first and second dehydration steps, respectively. Besides, the thermodynamic function of transition state complexes (ΔH , ΔG , and ΔS ) of the decomposition reaction of MnV2O6·4H2O were determined.

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Abstract

The precursor of nanocrystalline BiFeO3 was obtained by solid-state reaction at low heat using Bi(NO3)3·5H2O, FeSO4·7H2O, and Na2CO3·10H2O as raw materials. The nanocrystalline BiFeO3 was obtained by calcining the precursor. The precursor and its calcined products were characterized by differential scanning calorimetry (DSC), Fourier transform-infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). The data showed that highly crystallization BiFeO3 with rhombohedral structure (space group R3c (161)) was obtained when the precursor was calcined at 873 K for 2 h. The thermal process of the precursor experienced three steps, which involve the dehydration of adsorption water, hydroxide, and decomposition of carbonates at first, and then crystallization of BiFeO3, and at last decomposition of BiFeO3 and formation of orthorhombic Bi2Fe4O9. The mechanism and kinetics of the crystallization process of BiFeO3 were studied using DSC and XRD techniques, the results show that activation energy of the crystallization process of BiFeO3 is 126.49 kJ mol−1, and the mechanism of crystallization process of BiFeO3 is the random nucleation and growth of nuclei reaction.

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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 E a and g(α). Besides, the thermodynamic parameters (ΔS , ΔH , and ΔG ) of the dehydration reaction of α-LiZnPO4·H2O were determined.

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Nanocrystalline Zn0.5Ni0.5Fe2O4

Preparation and kinetics of thermal process of precursor

Journal of Thermal Analysis and Calorimetry
Authors: Wenwei Wu, Yongni Li, Kaiwen Zhou, Xuehang Wu, Sen Liao, and Qing Wang

Abstract

Zn0.5Ni0.5Fe2(C2O4)3·6H2O was synthesized by solid-state reaction at low heat using ZnSO4·7H2O, NiSO4·6H2O, FeSO4·7H2O, and Na2C2O4 as raw materials. The spinel Zn0.5Ni0.5Fe2O4 was obtained via calcining Zn0.5Ni0.5Fe2(C2O4)3·6H2O above 773 K in air. The Zn0.5Ni0.5Fe2(C2O4)3·6H2O and its calcined products were characterized by thermogravimetry and differential scanning calorimetry (TG/DSC), Fourier transform FT-IR, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), and vibrating sample magnetometer (VSM). The result showed that Zn0.5Ni0.5Fe2O4 obtained at 1073 K had a saturation magnetization of 86.7 emu g−1. The thermal process of Zn0.5Ni0.5Fe2(C2O4)3·6H2O experienced three steps, which involved the dehydration of the six crystal water molecules at first, and then decomposition of Zn0.5Ni0.5Fe2(C2O4)3 into Zn0.5Ni0.5Fe2O4 in air, and at last crystallization of Zn0.5Ni0.5Fe2O4. Based on KAS equation, and OFW equation, the values of the activation energies associated with the thermal process of Zn0.5Ni0.5Fe2(C2O4)3·6H2O were determined to be 126.02 ± 23.93, and 259.76 ± 18.67 kJ mol−1 for the first, and second thermal process steps, respectively. Dehydration of the six waters of Zn0.5Ni0.5Fe2(C2O4)3·6H2O is multi-step reaction mechanisms. Decomposition of Zn0.5Ni0.5Fe2(C2O4)3 into Zn0.5Ni0.5Fe2O4 could be simple reaction mechanism, probable mechanism function integral form of thermal decomposition of Zn0.5Ni0.5Fe2(C2O4)3 is determined to be g(α) = [−ln(1 − α)]4.

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