共查询到20条相似文献,搜索用时 25 毫秒
1.
M. TunÇ H. ErŞahan S. Yapici S. Şolak 《Journal of Thermal Analysis and Calorimetry》1997,48(2):403-411
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. 相似文献
2.
Thermal decomposition kinetics of natural fibers: Activation energy with dynamic thermogravimetric analysis 总被引:2,自引:0,他引:2
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. 相似文献
3.
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. 相似文献
4.
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. 相似文献
5.
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. 相似文献
6.
Zhen-li Qi Duan-feng Zhang Fei-xiong Chen Jun-yan Miao Bao-zeng Ren 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2014,88(13):2308-2313
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. 相似文献
7.
Lu Zhenrong Ding Yuanchen Xu Ying Chen Shuhua Yu Yunpeng 《Journal of Thermal Analysis and Calorimetry》2003,73(1):333-340
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. 相似文献
8.
F. A. Al-Newaiser S. A. Al-Thabaiti A. O. Al-Youbi A. Y. Obaid M. A. Gabal 《Chemical Papers》2007,61(5):370-375
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. 相似文献
9.
K. Muraleedharan 《Journal of Thermal Analysis and Calorimetry》2013,114(2):491-496
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. 相似文献
10.
K. Muraleedharan M. P. Kannan T. Ganga Devi 《Journal of Thermal Analysis and Calorimetry》2011,103(3):943-955
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. 相似文献
11.
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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14.
K. Muraleedharan 《Journal of Thermal Analysis and Calorimetry》2012,109(1):237-245
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. 相似文献
15.
《Journal of Thermal Analysis and Calorimetry》2009,98(3):855-861
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. 相似文献
16.
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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17.
A. Rotaru Anna Kropidłowska Anca Moanţă P. Rotaru E. Segal 《Journal of Thermal Analysis and Calorimetry》2008,92(1):233-238
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. 相似文献
18.
A. Rotaru Anca Moanta I. Sălăgeanu P. Budrugeac E. Segal 《Journal of Thermal Analysis and Calorimetry》2007,87(2):395-400
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. 相似文献
19.
A. Rotaru Anca Moanţă P. Rotaru E. Segal 《Journal of Thermal Analysis and Calorimetry》2009,95(1):161-166
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. 相似文献
20.
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. 相似文献