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Sylvain Marinel - One of the best experts on this subject based on the ideXlab platform.
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microwave versus conventional sintering estimate of the Apparent Activation Energy for densification of α alumina and zinc oxide
Journal of The European Ceramic Society, 2014Co-Authors: Alexandre Badev, Sebastien Saunier, Dominique Goeuriot, Romain Heuguet, Sylvain MarinelAbstract: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, 2014Co-Authors: Fei Zuo, Alexandre Badev, Sebastien Saunier, Dominique Goeuriot, Romain Heuguet, Sylvain MarinelAbstract: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.
Bojan Jankovic - One of the best experts on this subject based on the ideXlab platform.
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distribution of Apparent Activation Energy counterparts during thermo and thermo oxidative degradation of aronia melanocarpa black chokeberry
Food Chemistry, 2017Co-Authors: Bojan Jankovic, Milena Marinoviccincovic, Marija M JankovicAbstract: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, 2014Co-Authors: Bojan JankovicAbstract: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, 2013Co-Authors: Bojan Jankovic, Ivana Smiciklas, Jasna Stajictrosic, Dusan G AntonovicAbstract: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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the kinetic analysis of isothermal curing reaction of an unsaturated polyester resin estimation of the density distribution function of the Apparent Activation Energy
Chemical Engineering Journal, 2010Co-Authors: Bojan JankovicAbstract:Abstract The kinetic process of isothermal curing of an unsaturated polyester resin samples has been studied. The differential isoconversional method is used to yield dependency of the Apparent Activation Energy, E a , on the degree of cure. It was found that the dependence of E a on α is complex, but in the conversion range α = 0.10–0.50, E a is practically constant. It was found that the gelling stage of curing process is mainly controlled chemically which can be best described by two-parameter autocatalytic model. At higher values of α , when vitrification point is reached, the change in rate-limiting step was observed. As the consequence of shifting effect from the kinetics to diffusion control, the kinetic law equation is modified with additional diffusion term. It was found that the experimentally obtained density distribution function of the Apparent Activation Energy can be approximate by unbalanced modified Gaussian distribution function with quite satisfactory precision.
Günter Borchardt - One of the best experts on this subject based on the ideXlab platform.
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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, 2016Co-Authors: P Fielitz, Günter BorchardtAbstract: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, 2016Co-Authors: P Fielitz, Günter BorchardtAbstract: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.
Takashi Murakami - One of the best experts on this subject based on the ideXlab platform.
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effects of atmospheric composition on Apparent Activation Energy of silicate weathering ii implications for evolution of atmospheric co2 in the precambrian
Geochimica et Cosmochimica Acta, 2018Co-Authors: Yoshiki Kanzaki, Takashi MurakamiAbstract:Abstract The Apparent Activation Energy of silicate weathering is a key parameter for understanding the regulation of atmospheric CO2 and surface-temperature of the Earth. Combining the atmospheric composition effects on the Apparent Activation Energy with the compensation law for silicate-weathering flux, the relationship between the temperature dependence of atmospheric CO2 ( Δ H C O 2 ′ ), temperature (T) and silicate-weathering flux ( F C O 2 ) has been recently established ( Kanzaki and Murakami, 2018 ). The present study examined the effects of atmospheric CO2 and CH4 on silicate weathering in the Precambrian based on the above T- Δ H C O 2 ′ - F C O 2 relationship and the greenhouse effects of CO2, which represent Δ H C O 2 ′ on the global scale, with and without the presence of CH4. Calculation of the ratio of the change in F C O 2 to the corresponding change in the partial pressure of atmospheric CO2 ( P C O 2 ) as an indicator of the silicate-weathering feedback on CO2 revealed hitherto unknown weathering-climate interplays. The states where P C O 2 ∼30 °C are unstable due to the positive feedback, and immediately change with slight CO2 changes to either the states of P C O 2 > 10−0.5 atm or those of P C O 2 The temperature and P C O 2 transitions in the Precambrian were finally calculated based on the relationship between Δ H C O 2 ′ , T and F C O 2 and the greenhouse effects of CO2. The calculated CO2 levels are high enough that the temperature could have been maintained at >0 °C only by CO2 through the Precambrian. The consistent P C O 2 estimates from paleosols (fossil weathering profiles) in the literature support the argument. The calculated temperatures suggest that the Earth could have been cool to hot until around the end of Archean and cool to moderate afterwards.
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Effects of atmospheric composition on Apparent Activation Energy of silicate weathering: I. Model formulation
Geochimica et Cosmochimica Acta, 2018Co-Authors: Yoshiki Kanzaki, Takashi MurakamiAbstract:Abstract We have developed a weathering model to comprehensively understand the determining factors of the Apparent Activation Energy of silicate weathering in order to better estimate the silicate-weathering flux in the Precambrian. The model formulates the reaction rate of a mineral as a basis, then the elemental loss by summing the reaction rates of whole minerals, and finally the weathering flux from a given weathering profile by integrating the elemental losses along the depth of the profile. The rate expressions are formulated with physicochemical parameters relevant to weathering, including solution and atmospheric compositions. The Apparent Activation energies of silicate weathering are then represented by the temperature dependences of the physicochemical parameters based on the rate expressions. It was found that the interactions between individual mineral-reactions and the compositions of solution and atmosphere are necessarily accompanied by those of temperature-dependence counterparts. Indeed, the model calculates the Apparent Activation Energy of silicate weathering as a function of the temperature dependence of atmospheric CO2 ( Δ H CO 2 ′ ) . The dependence of the Apparent Activation Energy of silicate weathering on Δ H CO 2 ′ may explain the empirical dependence of silicate weathering on the atmospheric composition. We further introduce a compensation law between the Apparent Activation Energy and the pre-exponential factor to obtain the relationship between the silicate-weathering flux ( F CO 2 ), temperature and the Apparent Activation Energy. The model calculation and the compensation law enable us to predict F CO 2 as a function of temperature, once Δ H CO 2 ′ is given. The validity of the model is supported by agreements between the model prediction and observations of the Apparent Activation Energy and F CO 2 in the modern weathering systems. The present weathering model will be useful for the estimation of F CO 2 in the Precambrian, for which Δ H CO 2 ′ can be deduced from the greenhouse effect of atmospheric CO2.
Alexandre Badev - One of the best experts on this subject based on the ideXlab platform.
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microwave versus conventional sintering estimate of the Apparent Activation Energy for densification of α alumina and zinc oxide
Journal of The European Ceramic Society, 2014Co-Authors: Alexandre Badev, Sebastien Saunier, Dominique Goeuriot, Romain Heuguet, Sylvain MarinelAbstract: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, 2014Co-Authors: Fei Zuo, Alexandre Badev, Sebastien Saunier, Dominique Goeuriot, Romain Heuguet, Sylvain MarinelAbstract: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.
