Search Results

You are looking at 51 - 60 of 275 items for :

  • "reaction kinetics" x
  • All content x
Clear All

Abstract  

The non-parametric kinetics (NPK) method has been recently developed for the kinetic treatment of thermoanalytical data. The most significant feature of this method is its ability to provide information about the reaction kinetics without any assumptions either about the functionality of the reaction rate with the degree of conversion or the temperature. This paper presents the results of the application of the method to adiabatic calorimetry. Some data have been obtained by numerical simulation, but also the thermal decomposition of DTBP, a well known first order reaction, has been studied, being the obtained results in good agreement with literature.

Restricted access

Abstract  

The formation of alkali metal alcoxides by an alcohol reacting on the elemental metal itself cannot be completed under stoichiometric conditions. As a consequence of solvation, the chemical activity of the reacting alcohol is drastically reduced. Thus, the reaction cannot undergo completion without a large excess of alcohol with respect to the alkali metal. Moreover, solvation processes can drop the reaction kinetics down to nearly zero. When an excess of alkali metal is reacted with alcohol, the heat accumulated by solvation can be suddenly released by an addition of pure alcohol. Extremely dangerous thermal runaways can be started this way.

Restricted access

Isothermal cure characterization of dicyclopentadiene

The glass transition temperature and conversion

Journal of Thermal Analysis and Calorimetry
Authors: X. Liu, X. Sheng, J. Lee, and M. Kessler

Abstract  

Conversion (α) and the glass transition temperature (T g) were investigated during the isothermal cure of endo-dicyclopentadiene (DCPD) with a Grubbs catalyst for different temperatures using differential scanning calorimetry. Conversion vs. In (time) data at an arbitrary reference temperature were superposed by horizontal shift and the shift factors were used to calculate an Arrhenius activation energy. Glass transition temperature vs. conversion data fell on a single curve independent of cure temperature, implying that reaction of the norbornene and cyclopentene ring of DCPD proceeds in a sequential fashion. Implications of the isothermal reaction kinetics for self-healing composites are discussed.

Restricted access

Abstract  

Reaction kinetics of the formation of TiC by calciothermic reduction of TiO2 in presence of carbon have been investigated using thermal analysis (TG-DTA) of a powder mixture of TiO2, Ca, and C in argon atmosphere at different heating rates. Both the reaction initiation and the peak temperatures are found to increase with heating rates. The appearance of exothermic peaks in the DTA plots after Ca melting indicates the reduction of TiO2 by liquid calcium and formation of TiC by in-situ reaction of Ti with C. The apparent activation energy of the process has been found to be 170.80.5 kJ mol-1.

Restricted access

The structural changes occurring during the dehydroxylation of kaolinite have been followed using flash calcination to produce kinetically frozen calcines. The percentage of dehydroxylation was varied by changing the furnace residence time or temperature and/or heating speed. These calcination conditions affected the reaction kinetics, but the products depended only on the extent of dehydroxylation.

Restricted access

Summary The aim of this work is to develop a simplified, though rigorously based thermogravimetric analysis (TG) method to estimate intrinsic reactivity parameters (activation energy, E, and pre-exponential factor, A) for the oxidation in air of engineering carbonaceous materials. To achieve this aim, a modified Coats-Redfern method for analysing linear curves has been devised. The new method assumes first-order reaction kinetics with respect to carbon, and uses a statistical criterion to estimate an ‘optimum’ heating rate. For the oxidation in air of a model carbon, an optimum rate of 27 K min-1 was determined, at which E=125.8 kJ mol-1. This is in good agreement with activation energies obtained using established, though more limited model-free or isoconversional methods.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: Yuh Kumekawa, Motohiro Hirai, Yuhki Kobayashi, Satoshi Endoh, Eri Oikawa, and Takuya Hashimoto

Abstract  

Thermodynamic and kinetic stabilities of CuAlO2 and CuGaO2 have been evaluated by using thermogravimetry and thermodynamic calculations. It has been revealed that CuAlO2 and CuGaO2 are not thermodynamically stable in air below 800 °C and 1,200 °C, respectively, and that the oxidation reaction, 4CuMO2 + O2 → 2CuO + 2CuM2O4 (M = Al, Ga), should occur if the reaction kinetics are high enough. However, rate constants and activation energies indicated slow kinetics of the oxidation reaction, showing kinetic stability of CuMO2 even under some thermodynamically unstable temperatures and atmospheres. It was also concluded that CuAlO2 showed higher thermodynamic and kinetic stability than CuGaO2.

Restricted access

Abstract

This article described the synthesis and mesomorphic behavior transition of a novel liquid crystalline (LC) epoxy resin 4-(2,3-epoxypropoxy)biphenyl,4″-(2,3-epoxypropoxy)phenyl-4′carboxylate (EBEPC), which combined a hydroxyl benzoic aromatic ester and biphenol rigid-rod group. EBEPC showed a clear nematic schlieren texture under curtain conditions. The reaction kinetics of EBEPC cured by 4,4′-diaminodiphenyl-methane (DDM) was studied by using an isoconversional method under isothermal conditions with differential scanning calorimetry (DSC). The isothermal DSC data can be fitted reasonably by an autocatalytic curing model. Smectic phases had been observed in the EBEPC/DDM curing system. The results of DSC showed that the formation of the LC phase had pronounced influence on the curing reaction.

Restricted access

Abstract  

In this study, a new mathematical model was suggested to account for the effect of internal and external diffusion on fluid–solid noncatalytic reactions. The special features of this model are the combination of the transport processes and the chemical reaction kinetics with the added factor due to the structural properties of the solid reactant. The model was examined theoretically and experimentally. A reactive cloth filter that separates radionuclides from radioactive waste solutions is used as a practical application for the model. Analyses of the respective rate data in accordance with another two theoretical models showed that process is controlled by the rate of the diffusion step. The external and internal mass transfer constants across the liquid film and the resin matrix were determined from the graphical representation of the proposed model. The practical validation with the theoretical results offered satisfactory agreement at most of the process stages.

Restricted access

Abstract  

The thermal decomposition of ammonium perchlorate (AP)/hydroxyl-terminated-polybutadiene (HTPB), the AP/HTPB solid propellant, was studied at different heating rates in dynamic nitrogen atmosphere. The exothermic reaction kinetics was studied by differential scanning calorimetry (DSC) in non-isothermal conditions. The Arrhenius parameters were estimated according to the Ozawa method. The calculated activation energy was 134.5 kJ mol-1, the pre-exponential factor, A, was 2.04×1010 min-1 and the reaction order for the global composite decomposition was estimated in 0.7 by the kinetic Shimadzu software based on the Ozawa method. The Kissinger method for obtaining the activation energy value was also used for comparison. These results are discussed here.

Restricted access