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An important consequence of the expanding study of the nanocrystallinestate is the recognition of new behavior that is exposed at the nanometer length scale,but this also requires the recognition of the scaling of conventional beh...
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An important consequence of the expanding study of the nanocrystallinestate is the recognition of new behavior that is exposed at the nanometer length scale,but this also requires the recognition of the scaling of conventional behavior. The syn-thesis pathways further emphasize the importance of reaction kinetics and especiallynucleation processes where the nanometer length scale is central to the kinetics. Si-milarly, the observed phase selection during nanostructure synthesis is often differentthan that expected from the thermodynamics of bulk phase stability, but can be ana-lyzed in terms of a scaling of the hierarchy of equilibrium and the influence of largecharacteristic driving free energies. At the same time, the reaction pathways that yielddifferent phase states and microstructures can be described in terms of open or closedsystem conditions that reflect the manner in which the excess free energy is developedduring synthesis. The principles that govern the genesis of nanostructured materialsand the key issues concerning the reaction kinetics and stability are illustrated fromthe observed behavior in specific amorphous alloys, but the treatment also applies ingeneral to materials systems.
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There is an increasing demand from the food industry for complex products with controlled nutritional and
sensorial properties (vitamins, antioxidants or flavour compounds contents). Many of these properties result
from chemical...
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There is an increasing demand from the food industry for complex products with controlled nutritional and
sensorial properties (vitamins, antioxidants or flavour compounds contents). Many of these properties result
from chemical reactions induced in food by the technological treatments. The conception of foods and the
reappraisal of the products and processes require strategies allowing the appearance and the protection of
valuable compounds to be controlled.
The reactions in a food system are described as a complex network of many chemical reactions. But only a
small part of all the molecules consumed or synthesized by these reactions can be experimentally observed.
A major stake of this study was to propose a methodology to extract a simplified (so-called apparent)
identifiable reaction pathway which could give a reliable representation of the complex reaction system
occurring during cooking of a bakery product. Such a methodology was based on theoretical knowledge of
the system, taking into account the experimental constraints and the available information. A limited number
of observable chemical markers were selected according to their ability to point out different advancement
steps of the reactions (Maillard reaction, caramelization, lipid oxidation). The use of statistical methods made
it possible to extract an apparent reaction pathway from available information. The representation of the
reaction system as a stoichio-kinetic model, combined with mass balance and enthalpy equations, can provide
a better knowledge of the transfer-reaction coupling and its consequences on the final products
characteristics.
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The molecular dynamics (MD) is applied to discuss the combustion reaction rates in a simplified system, consisting of well-stirred mixtures of combustible gases. The chemical reactions are postulated to occur among the colliding m...
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The molecular dynamics (MD) is applied to discuss the combustion reaction rates in a simplified system, consisting of well-stirred mixtures of combustible gases. The chemical reactions are postulated to occur among the colliding molecules having the higher energies compared with a prescribed threshold level. The calculated results shows the reaction rate k expressed in Arrhenius formulae seemingly to be valid for a certain range of temperature and also the activation energy E{sub}a to be closely related not only to the threshold but exothermic heating values.
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Reaction kinetics of metallurgical physical chemistry which was successfully applied in metallurgy (as ferrous metallurgy, non-ferrous metallurgy) became an important theoretical foundation for subject system of traditional metall...
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Reaction kinetics of metallurgical physical chemistry which was successfully applied in metallurgy (as ferrous metallurgy, non-ferrous metallurgy) became an important theoretical foundation for subject system of traditional metallurgy. Not only the research methods were very perfect, but also the independent structures and systems of it had been formed. One of the important tasks of metallurgical reaction engineering was the simulation of metallurgical process. And then, the mechanism of reaction process and the conversion time points of different control links should be obtained accurately. Therefore, the research methods and results of reaction kinetics in metallurgical physical chemistry were not very suitable for metallurgical reaction engineering. In order to provide the definite conditions of transmission, reaction kinetics parameters and the conversion time points of different control links for solving the transmission and reaction equations in metallurgical reaction engineering, a new method for researching kinetics mechanisms in metallurgical reaction engineering was proposed,which was named stepwise attempt method. Then the comparison of results between the two methods and the further development of stepwise attempt method were discussed in this paper. As a new research method for reaction kinetics in metallurgical reaction engineering, stepwise attempt method could not only satisfy the development of metallurgical reaction engineering, but also provide necessary guarantees for establishing its independent subject system.
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摘要 :
Reaction kinetics of metallurgical physical chemistry which was successfully applied in metallurgy (as ferrous metallurgy, non-ferrous metallurgy) became an important theoretical foundation for subject system of traditional metall...
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Reaction kinetics of metallurgical physical chemistry which was successfully applied in metallurgy (as ferrous metallurgy, non-ferrous metallurgy) became an important theoretical foundation for subject system of traditional metallurgy. Not only the research methods were very perfect, but also the independent structures and systems of it had been formed. One of the important tasks of metallurgical reaction engineering was the simulation of metallurgical process. And then, the mechanism of reaction process and the conversion time points of different control links should be obtained accurately. Therefore, the research methods and results of reaction kinetics in metallurgical physical chemistry were not very suitable for metallurgical reaction engineering. In order to provide the definite conditions of transmission, reaction kinetics parameters and the conversion time points of different control links for solving the transmission and reaction equations in metallurgical reaction engineering, a new method for researching kinetics mechanisms in metallurgical reaction engineering was proposed, which was named stepwise attempt method. Then the comparison of results between the two methods and the further development of stepwise attempt method were discussed in this paper. As a new research method for reaction kinetics in metallurgical reaction engineering, stepwise attempt method could not only satisfy the development of metallurgical reaction engineering, but also provide necessary guarantees for establishing its independent subject system.
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摘要 :
Reaction kinetics of metallurgical physical chemistry which was successfully applied in metallurgy (as ferrous metallurgy, non-ferrous metallurgy) became an important theoretical foundation for subject system of traditional metall...
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Reaction kinetics of metallurgical physical chemistry which was successfully applied in metallurgy (as ferrous metallurgy, non-ferrous metallurgy) became an important theoretical foundation for subject system of traditional metallurgy. Not only the research methods were very perfect, but also the independent structures and systems of it had been formed. One of the important tasks of metallurgical reaction engineering was the simulation of metallurgical process. And then, the mechanism of reaction process and the conversion time points of different control links should be obtained accurately. Therefore, the research methods and results of reaction kinetics in metallurgical physical chemistry were not very suitable for metallurgical reaction engineering. In order to provide the definite conditions of transmission, reaction kinetics parameters and the conversion time points of different control links for solving the transmission and reaction equations in metallurgical reaction engineering, a new method for researching kinetics mechanisms in metallurgical reaction engineering was proposed, which was named stepwise attempt method. Then the comparison of results between the two methods and the further development of stepwise attempt method were discussed in this paper. As a new research method for reaction kinetics in metallurgical reaction engineering, stepwise attempt method could not only satisfy the development of metallurgical reaction engineering, but also provide necessary guarantees for establishing its independent subject system.
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It may be possible to lower costs of Carbon Capture and Sequestration by keeping constituents such as sulfur dioxide (S02) in the flue gas stream. The reactive behavior of pure CO_2 and CO_2 + SO_2 mixtures within a geologically r...
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It may be possible to lower costs of Carbon Capture and Sequestration by keeping constituents such as sulfur dioxide (S02) in the flue gas stream. The reactive behavior of pure CO_2 and CO_2 + SO_2 mixtures within a geologically realistic environment was examined. The experimental apparatus consisted of a series of four high-pressure reactors operated at different conditions and with different feed gas compositions to observe changes in both the rock and water compositions. The rock consisted of equal proportions of quartz, calcite, andesine, dolomite, chlorite and magnesite (constituents in arkose or dirty sand stone). The brine was prepared from laboratory grade sodium chloride and by varying the amount of magnesium concentration in the brine. Several long term batch experiments with pure C0_2 were carried out at different temperatures. Each mineral in the mixture showed evidence of participating in the geo-chemical reactions. Layers of calcite were seen growing on the surface of the arkose. Analcime deposits were omnipresent, either occurring as large connected aggregates or as deposits on the surfaces of other minerals (Quartz). Ankerite and calcite depositions were observed as amorphous masses intergrown with the feed. The CO_2 + SO_2 mixture experiments showed growth of euhedral anhydrite crystals and pronounced dissolution patterns over the examined surfaces. The growth of these new phases would lead to significant changes in the petrophysical properties of the rock. The trends in ionic concentration changes in the aqueous phase complemented the changes in the rock chemistry. The rates of these reactions were computed by measuring the changes in the compositions of the initial and the final samples. The rates of these reactions were computed by computing the changes in the compositions of the initial and the final rock samples (both individual and mixture) provided by the XRD analyses and were observed to be lower than expected.
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Laboratoire de Chimie et Microbiologie de l'Eau (CNRS UMR 6008), Université de Poitiers - ENSIP, 40 Avenue du Recteur Pineau, 86022 Poitiers Cedex, France
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The imidization kinetics for AFR700B polyimide were determined using Fourier transfore infrated spectroscopy (FTIR) by following the increase in imide groups as tracked with the 1360 cm~-1 band over several isotherms. Imidization ...
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The imidization kinetics for AFR700B polyimide were determined using Fourier transfore infrated spectroscopy (FTIR) by following the increase in imide groups as tracked with the 1360 cm~-1 band over several isotherms. Imidization occurs at an rapid initial rate, followed by a slow rate. The reaction rates for both the fast and slow regions were found to be first order with respect to the increase in the 1360 cm~-1 band. The activeation energy and preexponetial fctor were found for each region. The formation of imide rings in AFR700B was found to occur until approximately 300degC. This was confirmed by the rpesence of water up to 300degC in thermogravimetric analysis-mass spectroscopy data. Literature has shown that imidization is mass transfer limited. Thus, the kinetics should be coupled with a mass transfer relation to accurately describe the imidization reaction.
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摘要 :
The imidization kinetics for AFR700B polyimide were determined using Fourier transfore infrated spectroscopy (FTIR) by following the increase in imide groups as tracked with the 1360 cm~-1 band over several isotherms. Imidization ...
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The imidization kinetics for AFR700B polyimide were determined using Fourier transfore infrated spectroscopy (FTIR) by following the increase in imide groups as tracked with the 1360 cm~-1 band over several isotherms. Imidization occurs at an rapid initial rate, followed by a slow rate. The reaction rates for both the fast and slow regions were found to be first order with respect to the increase in the 1360 cm~-1 band. The activeation energy and preexponetial fctor were found for each region. The formation of imide rings in AFR700B was found to occur until approximately 300degC. This was confirmed by the rpesence of water up to 300degC in thermogravimetric analysis-mass spectroscopy data. Literature has shown that imidization is mass transfer limited. Thus, the kinetics should be coupled with a mass transfer relation to accurately describe the imidization reaction.
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