Dehydration kinetics of ulexite from thermogravimetric data

In the present study, the kinetic parameters of the thermal decomposition of ulexite were investigated by using TGA data. For the kinetic analysis, the Suzuki and Coats-Redfern methods were applied. It was determined that the process fits a first-order kinetic model, and the value of the activation energies and frequency factors decreased with decreasing particle size, which can be attributed to the increasing particle internal resistance to the escape of water as the grain size increases. The activation energy values were found to be 47.34–60.01 kJ mol^–1 for region I and 0.225–1.796 kJ mol^–1 for region II for the range of particle size fraction used. The frequency factors were calculated to be 9821.8–524.9 s^–1 for region I and 3.05×10^–44–2.807×10^–5 for region II for the same conditions.     

Thermal decomposition kinetics of natural fibers: Activation energy with dynamic thermogravimetric analysis

Dynamic TG analysis under nitrogen was used to investigate the thermal decomposition processes of 10 types of natural fibers commonly used in the polymer composite industry. These fibers included wood, bamboo, agricultural residue, and bast fibers. Various degradation models including the Kissinger, Friedman, Flynn-Wall-Ozawa, and modified Coats-Redfern methods were used to determine the apparent activation energy of these fibers. For most natural fibers approximately 60% of the thermal decomposition occurred within a temperature range between 215 and 310 °C. The result also showed that an apparent activation energy of 160-170 kJ/mol was obtained for most of the selected fibers throughout the polymer processing temperature range. These activation energy values allow developing a simplified approach to understand the thermal decomposition behavior of natural fibers as a function of polymer composite processing.     

Thermal decomposition kinetics of solids from DDTA curves

It is shown that the activation energy for solid thermal decompositions which follow a first order kinetic equation can be determined in a very simple manner from a single derivative differential thermal analysis (DDTA) curve. The experimental results are in good agreement with those obtained by other workers.     

Thermal decomposition reactions of solids controlled by diffusion and phase-boundary processes: possible misinterpretation of the mechanism from thermogravimetric data

A comparative study of phase -boundary and diffusion-controlled reactions has been carried out using thermogravimetric data. The results reported support the hypothesis that a single TG diagram does not allow the determination of whether a solid decomposition reaction is controlled by a diffusion mechanism or governed by the movement of an interface coming from a nucleation process. However, the analysis of both a single TG diagram and an isothermal curve might be a quick and valid way for discerning between these mechanisms. These statements are confirmed by studying the thermal decomposition kinetics of Ba(OH)₂ and CaCO₃.     

Energy of activation for the decomposition of the alkaline-earth carbonates from thermogravimetric data

Activation energies for the vacuum thermal decomposition of calcium, strontium and barium carbonates have been determined from thermogravimetric data, using the Coats and Redfern equation. A computer program, written in 4100 Algol, was used to process the data and to obtain the order (n) of the decomposition reactions. In all three cases, a value ofn=2/3 was in closest agreement with the experimental results, suggesting that decomposition occurs at a progressively shrinking spherical interface. The energies of activation obtained were in close agreement with the corresponding values of the enthalpy of decomposition, calculated at the temperature at which half of the sample had decomposed.     

Thermal decomposition and non-isothermal decomposition kinetics of carbamazepine

The thermal stability and kinetics of isothermal decomposition of carbamazepine were studied under isothermal conditions by thermogravimetry (TGA) and differential scanning calorimetry (DSC) at three heating rates. Particularly, transformation of crystal forms occurs at 153.75°C. The activation energy of this thermal decomposition process was calculated from the analysis of TG curves by Flynn-Wall-Ozawa, Doyle, distributed activation energy model, ?atava-?esták and Kissinger methods. There were two different stages of thermal decomposition process. For the first stage, E and logA [s^?1] were determined to be 42.51 kJ mol^?1 and 3.45, respectively. In the second stage, E and logA [s^?1] were 47.75 kJ mol^?1 and 3.80. The mechanism of thermal decomposition was Avrami-Erofeev (the reaction order, n = 1/3), with integral form G(α) = [?ln(1 ? α)]^1/3 (α = ～0.1–0.8) in the first stage and Avrami-Erofeev (the reaction order, n = 1) with integral form G(α) = ?ln(1 ? α) (α = ～0.9–0.99) in the second stage. Moreover, ΔH ^≠, ΔS ^≠, ΔG ^≠ values were 37.84 kJ mol^?1, ?192.41 J mol^?1 K^?1, 146.32 kJ mol^?1 and 42.68 kJ mol^?1, ?186.41 J mol^?1 K^?1, 156.26 kJ mol^?1 for the first and second stage, respectively.     

Thermal behavior and decomposition kinetics

The thermal behaviors of [1,1,1-trifluro-3-(2-thenoyl)-acetonato]copper(II) Cu(TTA)₂ and its adducts with pyridine Cu(TTA)₂(Py)₂, 2,2'-bipyridine Cu(TTA)₂(Bpy), quinoline Cu(TTA)₂(Ql)₂, and dimethyl sulfoxide Cu(TTA)₂(DMS) in a nitrogen atmosphere were studied under the non-isothermal conditions by simultaneous TG-DTG-DSC technique. The results showed that the evolution of the solvent molecules generally proceeded before the release of TTA in different ways according to their structures. The Cu(TTA)₂(Bpy) exhibited a unique decomposition pattern due to its distinctive structure. The dependences of activation energy on extent of reaction for all the stage of each compound were determined by using an isoconversional method, Flynn-Wall-Ozawa equation, which show E values varied with reaction progress, indicating the complexity of these decomposition reactions. In addition, the values of activation energy E for TTA molecules evolution are generally higher than that for the solvent molecules release. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal decomposition kinetics of strontium oxalate

The thermal decomposition behavior in air of SrC₂O₄ · 1.25H₂O was studied up to the formation of SrO using DTA-TG-DTG techniques. The decomposition proceeds through four well-defined steps. The first two steps are attributed to the dehydration of the salt, while the third and fourth ones are assigned to the decomposition of the anhydrous strontium oxalate into SrCO₃ and the decomposition of SrCO₃ to SrO, respectively. The exothermic DTA peak found at around 300°C is ascribed to the recrystallization of the anhydrous strontium oxalate. On the other hand, the endothermic DTA peak observed at 910°C can be attributed to the transition of orthorhombic-hexagonal phase of SrCO₃. The kinetics of the thermal decomposition of anhydrous strontium oxalate and strontium carbonate, which are formed as stable intermediates, have been studied using non-isothermal TG technique. Analysis of kinetic data was carried out assuming various solid-state reaction models and applying three different computational methods. The data analysis according to the composite method showed that the anhydrous oxalate decomposition is best described by the two-dimensional diffusion-controlled mechanism (D₂), while the decomposition of strontium carbonate is best fitted by means of the three-dimensional phase boundary-controlled mechanism (R₃). The values of activation parameters obtained using different methods were compared and discussed.     

Thermal decomposition kinetics of potassium iodate

The effect of gamma ray irradiation on the rate and kinetics of thermal decomposition of potassium iodate (KIO₃) has been studied by thermogravimetry (TG) under non-isothermal conditions at different heating rates (3, 5, 7, and 10 K min^?1). The thermal decomposition data were analyzed using isoconversional methods of Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, and Friedman. Irradiation with gamma rays increases the rate of the decomposition and is dependent on the irradiation dose. The activation energy decreases on irradiation. The enhancement of the rate of the thermal decomposition of KIO₃ upon irradiation is due to the combined effect of the production of displacements and extended lattice defects and chemical damage in KIO₃. Non-isothermal model fitting method of analysis showed that the thermal decomposition of irradiated KIO₃ is best described by the contracting sphere model equation, with an activation energy value of ~340 kJ mol^?1.     

Thermal decomposition kinetics of potassium iodate

The thermal decomposition of potassium iodate (KIO₃) has been studied by both non-isothermal and isothermal thermogravimetry (TG). The non-isothermal simultaneous TG–differential thermal analysis (DTA) of the thermal decomposition of KIO₃ was carried out in nitrogen atmosphere at different heating rates. The isothermal decomposition of KIO₃ was studied using TG at different temperatures in the range 790–805 K in nitrogen atmosphere. The theoretical and experimental mass loss data are in good agreement for the thermal decomposition of KIO₃. The non-isothermal decomposition of KIO₃ was subjected to kinetic analyses by model-free approach, which is based on the isoconversional principle. The isothermal decomposition of KIO₃ was subjected to both conventional (model fitting) and model-free (isoconversional) methods. It has been observed that the activation energy values obtained from all these methods agree well. Isothermal model fitting analysis shows that the thermal decomposition kinetics of KIO₃ can be best described by the contracting cube equation.     

Thermal decomposition kinetics of sodium metaperiodate

Aged and fresh samples of sodium metaperiodate are subjected to thermal decomposition studies in air by TG, DTG and DTA techniques. The kinetic parameters for their decomposition have been evaluated by weighted least squares method using equations of Coats-Redfern, Horowitz-Metzger and Freeman-Carroll. The results indicate that, within the limits of experimental error, ageing did not change the E^* values considerably.

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过氧化二异丙苯的热分解动力学研究

过氧化二异丙苯(DCP)是一种有广泛用途的过氧化物交联剂,具有高的交联效率和优良的交联性能.其分解温度较低,热分解速度较快,即使没有外界能量的作用,在自然储存的条件下也会发生化学反应,放出热量[1,2].     

Thermal decomposition kinetics of potassium iodate

The rate and kinetics of the thermal decomposition of potassium iodate (KIO₃) has been studied as a function of particle size, in the range 63?C150???m, by isothermal thermogravimetry at different temperatures, 790, 795, 800 and 805?K in nitrogen atmosphere. The theoretical and experimental mass loss data are in good agreement for the thermal decomposition of all samples of KIO₃ at all temperatures studied. The isothermal decomposition of all samples of KIO₃ was subjected to both model-fitting and model-free (isoconversional) kinetic methods of analysis. It has been observed that the activation energy values are independent of the particle size. Isothermal model-fitting analysis shows that the thermal decomposition kinetics of all the samples of KIO₃ studied can be best described by the contracting cube equation.     

Thermal decomposition kinetics of aluminum sulfate hydrate

The kinetics of individual stages of thermal decomposition of Al₂(SO₄)₃·18H₂O were studied by TG method. It is found that Al₂(SO₄)₃·18H₂O decomposes to Al₂O₃ in four major stages, all of endothermic. Some of these major stages are formed by sub-stages. The first three major stages are dehydration reactions in which two, ten and six moles water are lost, respectively. The last major stage is sulfate decomposition. In this study the kinetic parameter values of these major and sub-stages were calculated by integral and differential methods. The alterations of activation energies with respect to the decomposition ratio and to the method were investigated.     

Thermal decomposition kinetics of nickel fluorenone semicarbazone

Thermal decomposition of nickel fluorenone-semicarbazone has been studied by TG. Thermoanalytical data (TG and DTG) of the chelate are presented. Mass loss considerations at the main decomposition stages indicate conversion of the complex to oxide. Mathematical analysis of TG data shows that first order kinetics is applicable for the first stage and second order to the second stage. Kinetic parameters (energy and entropy of activation and preexponential factor) are reported.

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Thermal decomposition kinetics of some aromatic azomonoethers

Thermal analysis of three azomonoether dyes, exhibiting liquid-crystalline properties, was performed in dynamic air atmosphere. Thermal stability studies and the evaluation of the kinetic parameters of each physical or chemical transformations are essential for a full characterization, before attempting accurate thin films’ depositions of such materials used in non-linear optical applications. New synthesized dyes with general formula: where R is a nematogenic group: CN, CF₃ or a highly polarizable group: NO₂ were investigated using TG, DTG, DTA and DSC techniques, under non-isothermal regime. The evolved gases were analyzed by FTIR spectroscopy. The activation energies of the first decomposition step were evaluated for each compound, the obtained results revealing complex mechanisms.     

Thermal decomposition kinetics of some aromatic azomonoethers

The non-isothermal kinetic parameters corresponding to the decomposition of 4-[(4-chlorobenzyl)oxy]-4’-nitro-azobenzene were evaluated. The kinetic analysis was performed by means of different multi-heating rates methods: isoconversional (‘model-free’) methods (Flynn–Wall–Ozawa) and invariant kinetic parameters method (IKP) associated with the criterion of the independence of activation parameters on the heating rate. The values of the obtained non-isothermal kinetic parameters are in satisfactory agreement.     

Thermal decomposition kinetics of some aromatic azomonoethers

Thermal analysis of 4-[(4-chlorobenzyl)oxy]-4′-chloro-azobenzene dye, exhibiting liquid crystalline properties, was performed in dynamic air atmosphere. The compound behavior was investigated using TG, DTG, DTA and DSC techniques, under non-isothermal linear regime. The evolved gases were analyzed by FTIR spectroscopy. Kinetic parameters of the first decomposition step were obtained by means of multi-heating rates methods, such as isoconversioanl methods, IKP method and Perez-Maqueda et al. criterion.     

Thermal decomposition of polystyrene,polyoxyethylene glycol and their mixtures by thermogravimetric techniques

The thermal decompositions of polystyrene, polyoxyethylene glycol and mixtures of the two have been studied by thermogravimetry. The composition of the mixtures both before and after decomposition, as well as changes in the molecular weights and polydispersities of the polystyrene components, were followed by gel permeation chromatography. Ultra-violet spectrophotometry also served to determine the polystyrene contents of the mixtures after decomposition. The presence of polyoxyethylene glycol as a reaction promoter was found to have a pronounced effect on the decomposition of polystyrene, believed to be initiated, in large part, by intermolecular transfer. The depolymerization that follows takes place more rapidly probably because of the presence of a large number of active fragments. The overall activation energy, calculated by the method of Flynn and Wall, supports this hypothesis, being lower in the presence of polyoxyethylene glycol and higher in its absence.