MgAl-水滑石热分解过程动力学研究

类水滑石化合物Hydrotalcite-like Compounds(简称HTLcs)又称阴离子粘土,是由带正电荷的氢氧化物层和层间阴离子构成[1]。由于在类水滑石结构中含有大量的结构羟基和层间可分解的阴离子,所以其热稳定性较差,易于分解形成具有一定酸碱性及大比表面的复合氧化物,该复合氧化物由于具有晶粒小、活性元素分布均匀、比表面积大等特点,表现出了优异的催化性能[2~5]。近年来,以HTLcs为前体经高温焙烧制备双金属复合氧化物备受关注[6]。揭示类水滑石热解机理、选择焙烧条件是催化剂制备的关键所在。本文利用TG-DTA技术详细研究了不同镁铝比HTL…     

Effect of some ammonium salts on thermal decomposition of impregnated wood and properties of activated carbons

Methods of chemical, thermal, IR spectral, and X-ray phase analysis were used to study the effect of ammonium additives NH₄Cl + NH₄NO₃ introduced into a phosphorus-nitrogen formulation on the thermal decomposition of impregnated wood in the temperature range 20–700°C and on adsorption characteristics of the resulting activated carbon.     

Effect of thermal transport mechanisms on the thermal decomposition of CaCO3

Isothermal and dynamic techniques were employed to examine the rate of weight loss of CaCO₃. Thermogravimetric studies were conducted in atmospheres of He, N₂, Ar, and various percentage of CO₂ in Ar. Three methods for deriving kinetic parameters from thermogravimetric data were used and these results were then compared with data obtained from isothermal investigations done on identical samples. It was found that the higher the thermal conductivity of the atmosphere, the more repidly the reaction proceeded. Also, as the percentage of CO₂ in Ar increased, the temperature range of the decomposition became higher and narrower, resulting in a higher activation energy.     

Effect of gamma-irradiation on the thermal decomposition of potassium chlorate

The thermal decomposition of -irradiated KClO₃ was studied by dynamic thermogravimetry. The reaction order, activation energy, frequency factor and entropy of activation were computed using the Coats-Redfern, Freeman-Carroll and Horowitz-Metzger methods and were compared with those of the unirradiated salt. The decomposition increases with the irradiation dose. The energy of activation decreases on irradiation. The mechanism for the decomposition of unirradiated and irradiated KClO₃ follows the Avrami model equation, 1-(1-)^1/3, and the rate controlling process is a phase boundary reaction assuming spherical symmetry.     

Effect of lignin content on thermal degradation of wood pulp

A series of pulps containing between 3.6 and 23% of lignin was prepared by a careful delignification of a high-yield bisulfite pulp. The pulps were subjected to isothermal pyrolysis in a Perkin-Elmer TGS-1 thermobalance. The measurements were carried out at 8 different temperatures from 325 to 360°C under nitrogen atmosphere. The results obtained indicate that the effect of lignin on degradation depends strongly on temperature. Below 330°C, the rate of degradation varied only little with lignin. This variation becomes more important at temperatures above 330°C in that the rate of degradation increases with decreasing lignin content. The apparent activation energy of degradation ranges from 41.4 kcal mol^?1 at 23% of lignin to 67.0 kcal mol^?1 at 3.7% of lignin.     

Effect of gamma-irradiation on the thermal decomposition of barium oxalate hemihydrate

The effect of -irradiation (1.0–4.0 MGy) on the thermal decomposition of barium oxalate hemihydrate has been studied at 723K by a gas evolution method. Decomposition isotherms of unirradiated and irradiated crystals are characterized by (i) rapid initial gas evolution, (ii) acceleratory and (iii) decay stages. Irradiation enhances the rate of decomposition without altering the mechanism of the process, the effect being higher at higher irradiation doses. The analysis of the data reveal that the two-dimensional phase boundary reaction model gives the best fit to the results.     

Effect of electric fields on the thermal decomposition of calcium carbonate

The thermal decomposition of CaCO₃ powder and single crystal samples to CaO has been shown by X-ray diffraction and ESCA to be assisted by the application of external DC electric fields during the reaction. The effect is particularly marked at the positive electrode. The results are discussed in terms of both ionic migration effects and the field-induced electro-adsorption/electro-desorption of gaseous CO₂ at the surface of a semiconductor. Approximate calculations based on both theories show that ionic migration cannot account for the magnitude of the observed effects, but a reasonably satisfactory explanation is provided by the application of semi-conductor surface theory to the system.     

Effect of γ-irradiation on the thermal decomposition of strontium bromate

The effect of irradiation on the thermal decomposition of strontium bromate has been studied by dynamic thermogravimetry. Irradiaton enhances the decomposition and decreases the energy of activation but does not change the mechanism of decomposition.     

Effect of heating rate on the thermal decomposition of lead dioxide

Experimental data are presented on the kinetics and mechanism of PbO₂ decomposition at heating rates varying from 0 to 2.5 · 10³ °/sec. The studies were carried out with a time-of-flight mass spectrometer MSKH-4, a Paulik-Paulik-Erdey derivatograph and an X-ray diffractometer DRON-0.5At low heating rates (0 to 0.2 °/s) oxygen is evolved in four stages: PbO₂ PbO_1.56 PbO_1.44 PbO. At extremely high heating rates (2 · 10²–2.5 · 10³ °/s) the number of stages is reduced to two: PbO₂ PbO_1.4 PbO. An attempt is made to connect the observed change in the decomposition mechanism of PbO₂ with the crystal structure formation of the lead oxides.

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Zusammenfassung Versuchsergebnisse bezüglich der Kinetik und des Mechanismus der Zersetzung von PbO₂ bei Aufheizgeschwindigkeiten zwischen 0 und 2.5 · 10³°/s werden mitgeteilt. Die Untersuchungen wurden mittels eines time-of-flight Massenspektrometers MSKH-4, eines Derivatographen des Typs Paulik-Paulik-Erdey und eines Röntgendiffraktometers DRON-0.5 durchgeführt.Bei niedrigen Aufheizgeschwindigkeiten (0 bis 0.2 °/sec) wird Sauerstoff in vier Stufen entwickelt: PbO₂ PbO_1.56 PbO_1.44 PbO. Bei extrem hohen Aufheizgeschwindigkeiten (2 · 10² – 2.5 · 10³°/s) wird die Zahl der Stufen auf zwei herabgesetzt: PbO₂ PbO_1.4 PbO. Es wird versucht die beobachtete Ánderung in dem Zersetzungsmechanismus von PbO₂ mit der Kristallstrukturbildung der Bleioxide in Verbindung zu bringen.

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Résumé On présente des résultats expérimentaux concernant la cinétique et le mécanisme de la décomposition de PbO₂ pour des vitesses de chauffage allant de 0 à 2.5 · 10³°/s. Les études ont été effectuées à l'aide d'un spectromètre de masse du type MSKH-4, d'un Dérivatograph du type Paulik-Paulik-Erdey et d'un diffractomètre des rayons X du type DRON-0,5.Aux faibles vitesses de chauffage (0 à 0.2°/s) l'oxygène se dégage en quatre étapes: PbO₂ PbO_1.56 PbO_1.44 PbO. Aux vitesses de chauffage très élevées (2 · 10² à 2.5 · 10³°/s) le nombre des étapes se réduit à deux: PbO₂ PbO_1.4 PbO. On essaye de relier le changement observé dans le mécanisme de décomposition de PbO₂à la structure cristalline des oxydes de plomb.

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PbO₂ 2.5 · 10³°/c. — — MCX — 4, — — — 0.5. (0–0.2°/c) : PbO₂ PbO_1.56. PbO_1.44 PbO. (2 · 10²–2.5 · 10³°/c) : PbO₂ PbO_1.4 PbO. PbO₂ .

     

Effect of radiation dose on the thermal decomposition of sodium bromate

Influence of radiation dose in the range of 0.5–2.0 MGy of⁶⁰Co -rays on the isothermal decomposition of sodium bromate at 633.0 K shows that irradiation increases the initial gas evolution {ie37-1}, shortens the induction period (I), enhances the rate of reaction in the accelerating and decay stages. The data fit well the Prout-Tompkins relationship, indicating that nucleation occurs in a chain branching manner during the process. The fraction decomposed, , increases with increasing radiation dose.     

Effect of plasticizer dibutyl phthalate on the thermal decomposition of nitrocellulose

This paper aims to investigate the effects of plasticizer dibutyl phthalate (DBP) on the thermal decomposition of nitrocellulose (NC) by using a series of analytical apparatuses. In the present study, the detailed structures of pure NC (NC-P) and NC with DBP (NC-D) were revealed by scanning electron microscope. It was found that the fibers in NC-D are more closely aligned than those in NC-P, which makes the thermal behaviors of NC-D different from NC-P. The thermal stability of both NC-P and NC-D was examined by means of simultaneous TG-DSC apparatus (STA). Three different kinetic methods (Kissinger–Akahira–Sunose method, Ozawa–Flynn–Wall method, and Friedman method) were applied for determining the activation energy E of these two NC samples. Moreover, the experimental data were compared with sigmoidal models and pre-exponential factor was calculated by compensation effect. Besides, in situ Fourier transform infrared (FTIR) and a TGA instrument coupled with Frontier FTIR spectrometer were employed to investigate the characteristic functional groups of decomposition residues and gaseous products at different temperatures, respectively. The results show that NC-P and NC-D have similar decomposition products and decomposition mechanisms.     

Effect of water vapor on the thermal decomposition process of zinc hydroxide chloride and crystal growth of zinc oxide

Thermal decomposition process of zinc hydroxide chloride (ZHC), Zn₅(OH)₈Cl₂·H₂O, prepared by a hydrothermal slow-cooling method has been investigated by simultaneous X-ray diffractometry and differential scanning calorimetry (XRD-DSC) and thermogravimetric-differential thermal analysis (TG-DTA) in a humidity-controlled atmosphere. ZHC was decomposed to ZnO through β-Zn(OH)Cl as the intermediate phase, leaving amorphous hydrated ZnCl₂. In humid N₂ with P_H2O=4.5 and 10 kPa, the hydrolysis of residual ZnCl₂ was accelerated and the theoretical amount of ZnO was obtained at lower temperatures than in dry N₂, whereas significant weight loss was caused by vaporization of residual ZnCl₂ in dry N₂. ZnO formed by calcinations in a stagnant air atmosphere had the same morphology of the original ZHC crystals and consisted of the c-axis oriented column-like particle arrays. On the other hand, preferred orientation of ZnO was inhibited in the case of calcinations in 100% water vapor. A detailed thermal decomposition process of ZHC and the effect of water vapor on the crystal growth of ZnO are discussed.     

Effect of aluminum morphology on thermal decomposition of ammonium perchlorate

Journal of Thermal Analysis and Calorimetry - In this paper, two kinds of flake aluminum powder are prepared by bidirectional rotation mill using the spherical aluminum powder (Al-1) as raw...     

Effect of catocene on the thermal decomposition of ammonium perchlorate and octogen

Simultaneous TG/DSC-FT-IR was employed to study the effect of catocene with a high concentration (5, 15, and 25 %) on the thermal decomposition of ammonium perchlorate (AP) and octogen (HMX) with different particle sizes. The experimental results show that catocene has effect on the thermal decomposition of AP and HMX, but the role that catocene playing changes with the concentration of catocene and the particle size of AP and HMX. High concentration of catocene (more than 15 %) benefits the decomposition of fine AP and HMX at low temperature, but has little effect on the decomposition of median and coarse AP. The thermal decomposition of HMX is affected by catocene mainly through increasing the heat release of the first decomposition step, while through both increasing the heat release and decreasing the decomposition temperature of the first decomposition step for the thermal decomposition of AP.     

Effect of rare earth oxides on the thermal decomposition of barium oxalate

Catalytic activity of rare earth oxides (REO); La₂O₃, Sm₂O₃, Gd₂O₃ and Ce₂O₃ on the isothermal decomposition of barium oxalate has been studied at 723 K. The α?t plots for pure salt as well as mixtures indicate that the process follows: initial gas evolution, a short acceleratory and a long decay stages. The results of the kinetic analysis show that Prout-Tompkins relationship and two-dimensional phase boundary reaction give best fit of the data for both pure salt as well as mixtures. The rate constants of acceleratory and decay periods are enhanced remarkably by adding REO admixtures and their catalytical activity is in the order La₂O₃>Sm₂O₃>Gd₂O₃ >Ce₂O₃. The plausible mechanism of decomposition and the role of admixture there on has been discussed in the light of electron transfer process.     

Effect of the solvent on the kinetics of thermal decomposition of acetylcyclohexylsulfonyl peroxide

The kinetics of the decomposition of acetylcyclohexylsulfonyl peroxide (ACSP) in CCl₄, benzene, toluene, ethylbenzene, cumene, acetonitrile, ethanol, and 2-propanol in an atmosphere of O₂ were studied at 40–70 °C. The rate constants (k ₀) and activation parameters of the monomolecular decomposition of ACSP were determined. A linear dependence between logA ₀ and activation energyE ₀ (compensation effect) was established. The dependence ofk ₀ on the nature of a solvent is described by the four-parameter Koppel-Palm equation. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 935–937, May 1997.     

Effect of stearates on the thermal oxidation process of paraffin

Journal of Thermal Analysis and Calorimetry - Thermal reaction process of paraffin/stearate mixtures was studied by thermogravimetric–differential scanning calorimetry–Fourier transform...     

Effect of sample mass on the kinetics of thermal decomposition of a solid

Effects of sample mass on the kinetics of isothermal dehydration of crushed crystals of Li₂SO₄·H₂O were investigated using conventional TG. The process was characterized by a combination of Avrami-Erofeyev and contracting geometry models. Distribution of the fractional reaction, α, in particles within the sample assembly as well as the change in the rate of gross diffusion of the evolved water vapour appear responsible for the sample-mass-dependent kinetic parameters obtained for the system.