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Abstract  

The thermal decomposition mechanism of hydrazine 3-nitro-1,2,4-triazol-5-one (HNTO) compound was studied by means of differential scanning calorimetry (DSC), thermogravimetry and derivative thermogravimetry (TG-DTG), and the coupled simultaneous techniques of in situ thermolysis cell with rapid scan Fourier transform infrared spectroscopy (in situ thermolysis/RSFTIR). The thermal decomposition mechanism is proposed. The quantum chemical calculation on HNTO was carried out at B3LYP level with 6-31G+(d) basis set. The results show that HNTO has two exothermic decomposition reaction stages: nitryl group break first away from HNTO molecule, then hydrazine group break almost simultaneously away with carbonyl group, accompanying azole ring breaking in the first stage, and the reciprocity of fragments generated from the decomposition reaction is appeared in the second one. The C–N bond strength sequence in the pentabasic ring (shown in Scheme 1) can be obtained from the quantum chemical calculation as: C3–N4 > N2–C3 > N4–C5 > N1–C5. The weakest bond in NTO is N7–C3. N11–N4 bond strength is almost equal to N4–C5. The theoretic calculation is in agreement with that of the thermal decomposition experiment.

Scheme 1 
Scheme 1 

Scheme of HNTO

Citation: Journal of Thermal Analysis and Calorimetry 100, 2; 10.1007/s10973-009-0416-6

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Abstract  

The single crystal of lead salt of 3-nitro-1,2,4-triazol-5-one (NTO), [Pb(NTO)2(H2O)] was prepared and its structure was determined by a four-circle X-ray diffractometer. The crystal is monoclinic, its space group is P21/n with crystal parameters of a=0.7262(1) nm, b=1.2129(2) nm, c=1.2268(3) nm, =90.38(2)°, V=1.0806(2) nm3, Z=4, D c=2.97 g cm–3, µ=157.83cm–1, F(000)=888. The final R is 0.027. By using SCF-PM3-MO method we obtained optimized geometry for [Pb(NTO)2 H2O] and particularly positions for hydrogen atoms. Through the analyses of MO levels and bond orders it is found that Pb atom bond to ligands mainly with its 6pz and 6py AOs. The thermal decomposition experiments are elucidated when [Pb(NTO)2 H2O] is heated, ligand water is dissociated first and NO2 group has priority of leaving. Based on the thermal analysis, the thermal decomposition mechanism of [Pb(NTO)2 H2O] has been derived. The lattice enthalpy and its lattice energy were also estimated.

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Abstract  

An attempt to estimate the thermal decomposition mechanism of polymers using the simultaneous TG-DTA/FT-IR system was summarized. The library search of FT-IR spectra at various temperatures and of the subtraction spectrum obtained by subtracting the spectra at different temperatures were used to determine the types of evolved gases from poly(ethylene terephthalate) and poly(butylene terephthalate) at given stages of decomposition. The quantitative analysis of evolved gases was carried out using the specific gas profiles at the specific absorption band. The kinetic parameters were estimated from both TG and spectroscopic curves measured at various heating rates.

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Abstract  

[Cd(NTO)4Cd(H2O)6]4H2O was prepared by mixing the aqueous solution of 3-nitro-1,2,4-triazol-5-one and cadmium carbonate in excess. The single crystal structure was determined by a four-circle X-ray diffractometer. The crystal is monoclinic, space group C2/c with crystal parameters of a=2.1229(3) nm, b=0.6261(8) nm, c=2.1165(3) nm, β=90.602(7), V=2.977(6) nm3, Z=4, Dc=2.055 gcm−3, μ=15.45 cm−1, F(000)=1824, λ(MoKα)=0.071073 nm. The final R is 0.0282. Based on the results of thermal analysis, the thermal decomposition mechanism of [Cd(NTO)4Cd(H2O)6]4H2O was derived. From measurements of the enthalpy of solution of [Cd(NTO)4Cd(H2O)6]4H2O in water at 298.15 K, the standard enthalpy of formation, lattice energy, lattice enthalpy and standard enthalpy of dehydration have been determined as -(1747.84.8), -2394, -2414 and 313.6 kJ mol−1 respectively.

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Three new rare-earth metal (Pr, Nd and Sm) salt hydrates of 3-nitro-1,2,4-triazol-5-one (NTO) were prepared and characterized. The thermal behaviour of the three salt hydrates, M(NTO)3·nH2O (M=Pr and Nd,n=9;M=Sm,n=8) were studied by means of TG and DSC under conditions of linear temperature increase. The thermal decomposition intermediates were determined by means of IR, MS and X-ray diffraction spectrometry. The thermal decomposition mechanisms of these hydrates were proposed as follows:

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The activation energy for thermal dehydroxylation in vacuum of alkaline-earth hydroxides has been calculated from thermogravimetric data. The experimental results of Mg(OH)2 Ca(OH)2 and Sr(OH)2 are in agreement with an unimolecular decay law and their activation energies are similar to the values of enthalpies of decomposition. In contrast, as the dehydroxylation process of Ba(OH)2 takes place in liquid phase and the BaO does not dissolve into the molten Ba(OH)2, a kinetic of zero order describes the reaction rate and the activation energy is lower than the enthalpy of decomposition.

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Interpretation of partial thermal decomposition mechanism of Dy2(SO4)3·8H2O

Thermal, electrical and spectroscopic techniques

Journal of Thermal Analysis and Calorimetry
Authors: S. Basavaraja, A. Venkataraman, and Arabinda Ray

Abstract  

Partial dehydration of Dy2(SO4)3·8H2O was studied employing TG, DSC, D.C. electrical conductivity and spectroscopic techniques. The possible mechanism for the loss of water molecules (partial dehydration) was found to be random nucleation obeying Mapel equation based on TG trace. The DSC traces are supports the results of TG traces and are also utilized to understand the enthalpy changes accompanying the partial dehydration and phase transition accompanying the dehydrated samples. D.C. electrical conductivity studies are attempted to supplement these TG studies. Attempts are made to explain the structural changes accompanying dehydration on the basis of infrared spectra and X-ray diffraction and scanning electron microscopic studies.

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Abstract  

Thermal decomposition of polyurethane, epoxy, poly(diallyl phthalate), polycarbonate, and poly(phenylene sulfide) was examined using a combination of thermal and chemical analysis techniques. Thermal gravimetric analysis with simultaneous analysis of evolved gases by Fourier transform infrared spectroscopy, differential scanning calorimetry, and gas chromatography coupled with Fourier transform infrared spectroscopy were used to obtain rate data, determine enthalpy changes, and identify decomposition products. Examination of the evolved decomposition products indicated a common set of chain scission mechanisms involving the aromatic moieties in each of the polymer materials studied.

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Abstract

A series of Mg/Al hydrotalcites with tailored content of carbonate and nitrate anions was prepared using precipitation method. A part of the obtained materials was additionally crystallized in hydrothermal conditions. Different hydrotalcite phases or domains may co-exist within one sample obtained at controlled conditions. Decomposition mechanism studied in situ (DRIFT, XRD) was different for the samples with high concentration of interlayer nitrate anions than for carbonate-containing sample. TG-QMS study of hydrothermally treated samples provided more precise data for quantitative description of decomposition steps of Mg/Al hydrotalcites containing different mixtures of nitrate and carbonate anions.

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Abstract  

The two complexes of [Ln(CA)3bipy]2 (Ln = Tb and Dy; CA = cinnamate; bipy = 2,2′-bipyridine) were prepared and characterized by elemental analysis, infrared spectra, ultraviolet spectra, thermogravimetry and differential thermogravimetry techniques. The thermal decomposition behaviors of the two complexes under a static air atmosphere can be discussed by thermogravimetry and differential thermogravimetry and infrared spectra techniques. The non-isothermal kinetics was investigated by using a double equal-double steps method, the nonlinear integral isoconversional method and the Starink method. The mechanism functions of the first decomposition step of the two complexes were determined. The thermodynamic parameters (ΔH , ΔG and ΔS ) and kinetic parameters (activation energy E and the pre-exponential factor A) of the two complexes were also calculated.

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