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Sylvain Marinel – One of the best experts on this subject based on the ideXlab platform.

  • microwave versus conventional sintering estimate of the Apparent Activation Energy for densification of α alumina and zinc oxide
    Journal of The European Ceramic Society, 2014
    Co-Authors: Alexandre Badev, Sebastien Saunier, Dominique Goeuriot, Romain Heuguet, Sylvain Marinel

    Abstract:

    Abstract A comparative study between the conventional and 2.45 GHz microwave multimode sintering behavior of insulator (α-Al2O3) and semi-conductive ceramic (ZnO) was systematically investigated. The Apparent Activation Energy of nonisothermal sintering was determined by way of the Arrhenius plot of densification data at constant heating rates (CHR) and the concepts of Master Sintering Curves (MSCs), respectively. During microwave densification process, the Apparent Activation Energy was about 90 kJ/mol less than the value for conventional sintering of Al2O3 applying these two estimation methods. However, an opposite result was obtained in the case of ZnO, although its densification process had been also accelerated by microwave as well as Al2O3. The significant differences in Activation Energy give a good proof of the difference in diffusion mechanism induced by the electromagnetic field underlying microwave sintering.

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  • Microwave versus conventional sintering: Estimate of the Apparent Activation Energy for densification of alpha-alumina and zinc oxide
    Journal of the European Ceramic Society, 2014
    Co-Authors: Fei Zuo, Alexandre Badev, Sebastien Saunier, Dominique Goeuriot, Romain Heuguet, Sylvain Marinel

    Abstract:

    A comparative study between the conventional and 2.45 GHz microwave multimode sintering behavior of insulator (alpha-Al2O3) and semi-conductive ceramic (ZnO) was systematically investigated. The Apparent Activation Energy of nonisothermal sintering was determined by way of the Arrhenius plot of densification data at constant heating rates (CHR) and the concepts of Master Sintering Curves (MSCs), respectively. During microwave densification process, the Apparent Activation Energy was about 90 kJ/mol less than the value for conventional sintering of Al2O3 applying these two estimation methods. However, an opposite result was obtained in the case of ZnO, although its densification process had been also accelerated by microwave as well as Al2O3. The significant differences in Activation Energy give a good proof of the difference in diffusion mechanism induced by the electromagnetic field underlying microwave sintering. (C) 2014 Elsevier Ltd. All rights reserved.

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Bojan Jankovic – One of the best experts on this subject based on the ideXlab platform.

  • distribution of Apparent Activation Energy counterparts during thermo and thermo oxidative degradation of aronia melanocarpa black chokeberry
    Food Chemistry, 2017
    Co-Authors: Bojan Jankovic, Milena Marinoviccincovic, Marija M Jankovic

    Abstract:

    Kinetics of degradation for Aronia melanocarpa fresh fruits in argon and air atmospheres were investigated. The investigation was based on probability distributions of Apparent Activation Energy of counterparts (ea). Isoconversional analysis results indicated that the degradation process in an inert atmosphere was governed by decomposition reactions of esterified compounds. Also, based on same kinetics approach, it was assumed that in an air atmosphere, the primary compound in degradation pathways could be anthocyanins, which undergo rapid chemical reactions. A new model of reactivity demonstrated that, under inert atmospheres, expectation values for ea occured at levels of statistical probability. These values corresponded to decomposition processes in which polyphenolic compounds might be involved. ea values obeyed laws of binomial distribution. It was established that, for thermo-oxidative degradation, Poisson distribution represented a very successful approximation for ea values where there was additional mechanistic complexity and the binomial distribution was no longer valid.

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  • the pyrolysis process of wood biomass samples under isothermal experimental conditions Energy density considerations application of the distributed Apparent Activation Energy model with a mixture of distribution functions
    Cellulose, 2014
    Co-Authors: Bojan Jankovic

    Abstract:

    This work deals with the isothermal pyrolysis of Pine and Beech wood samples and kinetic studies, using the thermo-analytical technique, at five different operating temperatures. Pyrolysis processes were investigated by using the distributed Apparent Activation Energy model, which involves the complex mixture of different continuous distribution functions. It was found that decomposition processes of wood pseudo-components take place in different conversion areas during entire pyrolyses, whereby these areas, as well as the changes in Apparent Activation Energy (E a) values, are not the same for softwood and hardwood samples. Bulk density (Bden) and Energy density (ED) considerations have shown that both biomass samples suffer from low Bden and ED values. It was concluded that pyrolysis can be used as a means of decreasing transportation costs of wood biomass materials, thus increasing Energy density. The “pseudo” kinetic compensation effect was identified, which arises from kinetic model variation and wood species variation. In the current extensive study, it was concluded that primary pyrolysis refers to decomposition reactions of any of three major constituents of the considered wood samples. Also, it was established that primary reactions may proceed in parallel with simultaneous decomposition of lignin, hemicelluloses and cellulose in the different regions of wood samples, depending on the operating temperature. It was established that endothermic effects dominate, which are characterized with devolatilization and formation of volatile products. It has been suggested that the endothermic behavior that arises from pyrolyses of considered samples may indicate the endothermic depolymerization sequence of cellulose structures.

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  • thermal characterization and kinetic analysis of non isothermal decomposition process of bauxite red mud estimation of density distribution function of the Apparent Activation Energy
    International Journal of Mineral Processing, 2013
    Co-Authors: Bojan Jankovic, Ivana Smiciklas, Jasna Stajictrosic, Dusan G Antonovic

    Abstract:

    Abstract Thermal characterization and kinetic analysis of non-isothermal decomposition process of Bauxite red mud were carried out using thermogravimetry (TG), derivative thermogravimetry (DTG), differential scanning calorimetry (DSC), differential thermal analysis (DTA) and Fourier transform infrared spectroscopy (FTIR). It was found that the investigated decomposition was a complex heterogeneous process, which included two main decomposition stages and one sub-stage. The overall decomposition process consisted of the series of parallel and competitive reactions, which originated from the decomposition of various chemical species and solid-state transformations. This behavior was confirmed by the appearance of different forms of density distribution functions of Apparent Activation Energy values. Furthermore, the conversion range of 0.10 ≤ α ≤ 0.30, with a constant value of the Apparent Activation Energy (146.4 kJ mol− 1) for the second stage of the overall process, belongs to calcite decomposition, which takes place through a two-dimensional diffusion mechanism.

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Günter Borchardt – One of the best experts on this subject based on the ideXlab platform.

  • oxygen exchange at gas oxide interfaces how the Apparent Activation Energy of the surface exchange coefficient depends on the kinetic regime
    Physical Chemistry Chemical Physics, 2016
    Co-Authors: P Fielitz, Günter Borchardt

    Abstract:

    In the dedicated literature the oxygen surface exchange coefficient KO and the equilibrium oxygen exchange rate 0O are considered to be directly proportional to each other regardless of the experimental circumstances. Recent experimental observations, however, contradict the consequences of this assumption. Most surprising is the finding that the Apparent Activation Energy of KO depends dramatically on the kinetic regime in which it has been determined, i.e. surface exchange controlled vs. mixed or diffusion controlled. This work demonstrates how the diffusion boundary condition at the gas/solid interface inevitably entails a correlation between the oxygen surface exchange coefficient KO and the oxygen self-diffusion coefficient DO in the bulk (“on top” of the correlation between KO and 0O for the pure surface exchange regime). The model can thus quantitatively explain the range of Apparent Activation energies measured in the different regimes: in the surface exchange regime the Apparent Activation Energy only contains the contribution of the equilibrium exchange rate, whereas in the mixed or in the diffusion controlled regime the contribution of the oxygen self-diffusivity has also to be taken into account, which may yield significantly higher Apparent Activation energies and simultaneously quantifies the correlation KO ∝ DO1/2 observed for a large number of oxides in the mixed or diffusion controlled regime, respectively.

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  • Oxygen exchange at gas/oxide interfaces: how the Apparent Activation Energy of the surface exchange coefficient depends on the kinetic regime.
    Physical Chemistry Chemical Physics, 2016
    Co-Authors: P Fielitz, Günter Borchardt

    Abstract:

    In the dedicated literature the oxygen surface exchange coefficient KO and the equilibrium oxygen exchange rate 0O are considered to be directly proportional to each other regardless of the experimental circumstances. Recent experimental observations, however, contradict the consequences of this assumption. Most surprising is the finding that the Apparent Activation Energy of KO depends dramatically on the kinetic regime in which it has been determined, i.e. surface exchange controlled vs. mixed or diffusion controlled. This work demonstrates how the diffusion boundary condition at the gas/solid interface inevitably entails a correlation between the oxygen surface exchange coefficient KO and the oxygen self-diffusion coefficient DO in the bulk (“on top” of the correlation between KO and 0O for the pure surface exchange regime). The model can thus quantitatively explain the range of Apparent Activation energies measured in the different regimes: in the surface exchange regime the Apparent Activation Energy only contains the contribution of the equilibrium exchange rate, whereas in the mixed or in the diffusion controlled regime the contribution of the oxygen self-diffusivity has also to be taken into account, which may yield significantly higher Apparent Activation energies and simultaneously quantifies the correlation KO ∝ DO1/2 observed for a large number of oxides in the mixed or diffusion controlled regime, respectively.

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