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Dissertations / Theses on the topic 'Diffusing Diffusivity'

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Author: Grafiati

Published: 6 September 2023

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1

Chmelik, Christian, Pavel Kortunov, Sergey Vasenkov, Taro Ito, Jörg Kärger, Jan Konatowski, Jens Weitkamp, and Douglas M. Ruthven. "Transport diffusivity in zeolites." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-196446.

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2

Larsen, Ryan J., and Charles F. Zukoski. "Self-diffusivity and free volume." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-188864.

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3

Heber, André, Markus Selmke, and Frank Cichos. "Thermal diffusivity measurements with a single nanoparticle." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-183781.

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4

Kremer, Heiko, Cristina Botero, Andreas P. Fröba, and Alfred Leipertz. "Thermal diffusivity of fluids by dynamic light scattering." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-196289.

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5

Rudakova, Maya, and Andrey Filippov. "Diffusivity of water in a biological model membrane." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-197030.

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6

Heber, André, Markus Selmke, and Frank Cichos. "Thermal diffusivity measurements with a single nanoparticle." Diffusion fundamentals 20 (2013) 89, S. 1, 2013. https://ul.qucosa.de/id/qucosa%3A13676.

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7

Kremer, Heiko, Cristina Botero, Andreas P. Fröba, and Alfred Leipertz. "Thermal diffusivity of fluids by dynamic light scattering." Diffusion fundamentals 2 (2005) 72, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14405.

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8

Larsen, Ryan J., and Charles F. Zukoski. "Self-diffusivity and free volume: an ideal binary mixture." Diffusion fundamentals 11 (2009) 8, S. 1-2, 2009. https://ul.qucosa.de/id/qucosa%3A13928.

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9

Nechaev, Yury S. "Mechanisms of hydrogen sorption, solubility and diffusivity in carbon nanomaterials, relevance to the on-board storage problem: Mechanisms of hydrogen sorption, solubility and diffusivityin carbon nanomaterials, relevance to the on-board storage problem." Diffusion fundamentals 2 (2005) 100, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14437.

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10

Rudakova, Maya, and Andrey Filippov. "Diffusivity of water in a biological model membrane: an NMR study." Diffusion fundamentals 2 (2005) 130, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14472.

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11

Ruthven, Douglas M. "Adsorption and desorption kinetics for diffusion controlled systems with a strongly concentration dependent diffusivity: Adsorption and desorption kinetics for diffusion controlledsystems with a strongly concentration dependent diffusivity." Diffusion fundamentals 6 (2007) 51, S. 1-11, 2007. https://ul.qucosa.de/id/qucosa%3A14230.

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The formal solution to the diffusion equation for transient adsorption in a semiinfinite medium with a strongly concentration dependent diffusivity, originally derived by Fujita ( 3 ), has been extended to desorption. Profiles for adsorption and desorption are compared and simplified asymptotic expressions which are useful when the diffusivity ratio is large are derived. The effect of a strongly concentration dependent diffusivity on adsorption and desorption kinetics is briefly considered.

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12

Mi, Xi, and Yunfeng Shi. "On the measurement of surface diffusivity in disordered nanoporous carbon via molecular dynamics simulations." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-185894.

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Gas diffusion in nanoporous carbon includes distinct diffusion modes: surface diffusion on the pore walls and non-surface diffusion away from pore walls. We have performed molecular dynamics (MD) simulations of Ar diffusion in disordered nanoporous carbon. The main objective of this work is to separate the surface diffusion and non-surface diffusion contributions so as to comprehend their respective dependency on the porous structure and testing conditions. The nanoporous carbon sample is obtained using the quenched molecular dynamics (QMD) method. Gas flows are generated by applying a constant external force on each Ar atom, mimicking a constant chemical potential gradient. The contributions from surface diffusion and non-surface diffusion are separated according to the distance of the gas atoms away from the pore wall. We show that the surface diffusivity is affected by the interactions between gas atoms and the pore walls, the temperature, and the loading.

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13

Ruthven, Douglas M. "Adsorption and desorption kinetics for diffusion controlled systems with a strongly concentration dependent diffusivity." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-193874.

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The formal solution to the diffusion equation for transient adsorption in a semiinfinite medium with a strongly concentration dependent diffusivity, originally derived by Fujita ( 3 ), has been extended to desorption. Profiles for adsorption and desorption are compared and simplified asymptotic expressions which are useful when the diffusivity ratio is large are derived. The effect of a strongly concentration dependent diffusivity on adsorption and desorption kinetics is briefly considered.

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14

Čapek, Pavel, Vladimír Hejtmánek, Libor Brabec, Arlette Zikánová, Milan Kočiřík, and Bohumil Bernauer. "3D stochastic replicas of porous solids: a way to improve predicted diffusivity." Diffusion fundamentals 11 (2009) 79, S. 1-2, 2009. https://ul.qucosa.de/id/qucosa%3A14044.

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15

Hejtmánek, Vladimír, Pavel Čapek, Libor Brabec, Arlette Zikánová, Milan Kočiřík, and Bohumil Bernauer. "3D stochastic replicas of porous solids: a way to improve predicted diffusivity." Diffusion fundamentals 11 (2009) 91, S. 1-4, 2009. https://ul.qucosa.de/id/qucosa%3A14064.

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The goal of our contribution was to develop a method providing morphological (microstructural) descriptors whose values would match total porosity and specific surface obtained other independent methods. The model obtained from limited amount of statistical information, accessible by image analysis of cross-sections, offers an attractive way for the prediction of equilibrium and transport phenomena in natural and man-made macroporous media.

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16

Chmelik, Christian, Pavel Kortunov, Sergey Vasenkov, Taro Ito, Jörg Kärger, Jan Konatowski, Jens Weitkamp, and Douglas M. Ruthven. "Transport diffusivity in zeolites: possible reasons for misleading results of macroscopic techniques." Diffusion fundamentals 2 (2005) 86, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14421.

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17

Bassett, John. "Assessing the Spatial Diffusivity of Sound Fields in Rooms using Ambisonic Techniques." Thesis, The University of Sydney, 2012. http://hdl.handle.net/2123/8255.

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This thesis explores the means of objectively measuring diffuse sound fields contained within music performance auditoria. Although the diffuse field is considered to be an important component of the reverberant sound field there is currently no widely accepted method for its measurement. A review of methods shows that attempts to characterize the field may be divided into those methods that seek to directly measure the state of the field and those that indirectly indicate the existence of the state. The primary focus of this thesis is the application of Ambisonic techniques to capture the spatial aspects of the sound field. Initial work explores the rotation of a directional microphone in three measurement spaces. The results and modeling in idealised simulated sound fields indicate that the method may have some efficacy. The method is extended through the application of signal processing to the output of an Ambisonic microphone array. The method is tested firstly in a reverberation room that is modified progressively to produce a series of room states with incrementally increasing reverberation time. The extents of the measurement system were tested by measuring the degrees of diffusivity reached in a reverberation room. Diffusing panels were progressively added in the expectation the increases in diffusivity would be detected. The measurement was carried out in conjunction with standard absorption coefficient measurements outlined in Appendix A of ISO 354. Comparison was made between the measured field and the standard method for achieving a diffuse field in a reverberation room test facility. The final stage attempts to find correlation between physical measures of diffuse fields and listener’s subjective assessment of those fields. To that end a paired comparison test was conducted where listeners were presented music samples rendered through simulated halls where the scattering coefficients and consequently the sound field diffusivity was varied. Subjects were asked to choose which pair they preferred.

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18

Chiu, Ka Lok. "Thermal diffusion of organic semiconductors determined by scanning photothermal deflection (SPD) technique." HKBU Institutional Repository, 2020. https://repository.hkbu.edu.hk/etd_oa/843.

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Thermal diffusivity (D), measuring how fast heat propagates in a medium, is an important quantity in heat conduction. For a medium with great thermal diffusivity, it will reach thermal equilibrium in shorter time. In the field of solid state materials, thermal diffusivity can give information about the quality and morphology of solid, since D is very sensitive to microstructures. However, studies on the thermal diffusion of organic semiconductors are very scarce. In this thesis, the thermal diffusion of different classes of photovoltaic polymers and their blends with molecular electron acceptors were studied by scanning photothermal deflection (SPD) technique. The reliability of the technique was confirmed by the good matching between the SPD derived experimental D values and the nominal D values of different reference materials obtained from literatures. To illustrate that determination of thermal diffusivity is a possible method for studying microscopic properties of organic photovoltaic materials, SPD technique was applied to various films of photovoltaic polymers with different crystallinities. It is observed that photovoltaic polymers always possess small D values in the range of 0.3mm2/s to 2.3mm2/s. It is also discovered that photovoltaic polymers with more planar molecular structure, stronger π-π stacking and higher crystallinity would possess larger D values. When photovoltaic polymers are blended with small molecular acceptors bulk heterojunctions (BHJs), the thermal diffusivity is always reduced due to disrupted polycrystalline structure and increase probability of intermolecular phonon transport. However, for all-polymer BHJs with polymeric acceptor, the reduction in thermal diffusivity can be moderate as the proportion of ultrafast intramolecular phonon transport is SPD technique was also applied to PBDB-T:(ITIC-M+N2200) ternary BHJs with different ITIC-M to N2200 weight ratio. The thermal diffusivity of the ternary blend increases with the weight percentage of N2200 polymeric acceptor. It is observed that PBDB:(ITIC-M+N2200) ternary photovoltaic devices with enhanced thermal diffusion can possess enhanced photostability. Such enhancement in photostability is attributed to the reduced heat trapping at the area being illuminated due to the improved thermal diffusion.

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19

Sharma, Manju, and Subramanian Yashonath. "Size dependence of solute diffusivity and Stokes-Einstein relationship: effect of van der Waals interaction." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-193071.

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Size dependence of solute diffusivity has been investigated using molecular dynamics simulations for a range of solute radii in a binary mixture consisting of solute and solvent species. We demonstrate that the Stokes-Einstein relationship between self diffusivity and solute radius breaks down over a range of solute-solvent size ratios. This is a result of the previously known Levitation Effect. Three distinct regimes can be seen depending on the solute-solvent size ratio. Several properties have been computed to understand the nature of solute motion in the three regimes.

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20

Selezneva, Liudmila V., and Andrei V. Nazarov. "The influence of interstitial impurity atom – vacancy complex on diffusivity of interstitial atom in alpha-iron." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-193608.

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21

Mi, Xi, and Yunfeng Shi. "On the measurement of surface diffusivity in disordered nanoporous carbon via molecular dynamics simulations." Diffusion fundamentals 16 (2011) 84, S. 1-8, 2011. https://ul.qucosa.de/id/qucosa%3A13829.

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Gas diffusion in nanoporous carbon includes distinct diffusion modes: surface diffusion on the pore walls and non-surface diffusion away from pore walls. We have performed molecular dynamics (MD) simulations of Ar diffusion in disordered nanoporous carbon. The main objective of this work is to separate the surface diffusion and non-surface diffusion contributions so as to comprehend their respective dependency on the porous structure and testing conditions. The nanoporous carbon sample is obtained using the quenched molecular dynamics (QMD) method. Gas flows are generated by applying a constant external force on each Ar atom, mimicking a constant chemical potential gradient. The contributions from surface diffusion and non-surface diffusion are separated according to the distance of the gas atoms away from the pore wall. We show that the surface diffusivity is affected by the interactions between gas atoms and the pore walls, the temperature, and the loading.

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22

Ruprecht, Benjamin, Jessica Heine, Martin Wikening, Sylvio Indris, Joseph Wontcheu, Wolfgang Bensch, Thomas Bredow, and Paul Heitjans. "Influence of anion substitution on the lithium diffusivity in hexagonal Li x TiS 2-y Se y." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-188254.

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23

Nanok, Tanin, O. Sangsawang, Sergey Vasenkov, Frerich J. Keil, and Siegfried Fritzsche. "Molecular dynamics simulation study of the concentration dependence of the self-diffusivity of methanol in NaX zeolite." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-189605.

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24

Nechaev, Yury S. "Mechanisms of hydrogen sorption, solubility and diffusivity in carbon nanomaterials, relevance to the on-board storage problem." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-196620.

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25

Sharma, Manju, and Subramanian Yashonath. "Size dependence of solute diffusivity and Stokes-Einstein relationship: effect of van der Waals interaction." Diffusion fundamentals 7 (2007) 11, S. 1-15, 2007. https://ul.qucosa.de/id/qucosa%3A14168.

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Size dependence of solute diffusivity has been investigated using molecular dynamics simulations for a range of solute radii in a binary mixture consisting of solute and solvent species. We demonstrate that the Stokes-Einstein relationship between self diffusivity and solute radius breaks down over a range of solute-solvent size ratios. This is a result of the previously known Levitation Effect. Three distinct regimes can be seen depending on the solute-solvent size ratio. Several properties have been computed to understand the nature of solute motion in the three regimes.

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26

Selezneva, Liudmila V., and Andrei V. Nazarov. "The influence of interstitial impurity atom – vacancy complex on diffusivity of interstitial atom in alpha-iron." Diffusion fundamentals 6 (2007) 34, S. 1-2, 2007. https://ul.qucosa.de/id/qucosa%3A14210.

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27

Thermitus, Marc-Antoine. "Nouvelles techniques d'identification de la diffusivité thermique par la méthode Flash." Lyon, INSA, 1997. http://www.theses.fr/1997ISAL0029.

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Ce travail porte sur l'identification de la diffusivité thermique des matériaux opaques et isotropes par la méthode flash. Dans une première approche, on exploite non seulement le thermogramme de la face arrière mais aussi celui de la face qui reçoit l'impulsion thermique. Le rapport des des deux thermogrammes offre l'avantage d’être indépendant de la diffusion radiale de la chaleur dans l’échantillon. La diffusivité peut alors être identifiée par la méthode des moments temporels partiels. Une autre manière de tenir compte des deux thermogrammes est de calculer le rapport de leurs transformées de Laplace. Dans ce cas, en utilisant la méthode des quadripôles thermiques, on montre que l'influence de la durée et de la répartition temporelle de l'impulsion n'intervient pas. La diffusivité est alors identifiée dans le domaine de Laplace par la méthode de Levenberg-Marquardt. Cette méthode convient particulièrement aux films minces. Dans une deuxième approche, on ne considère que le thermogramme de la face arrière auquel on applique une transformation logarithmique. Le nouveau modèle obtenu est peu sensible aux pertes et à la diffusion radiale de la chaleur. On montre de plus que l'échantillon peut être assimilé à un système linéaire représenté par un modèle d'état. La diffusivité est alors identifiée en utilisant le filtre de Kalman. Cette méthode très efficace aux hautes températures et lorsque l'impulsion thermique n'est pas homogène, est bien adaptée au traitement en ligne des données
The aim of this work is to propose new identification techniques of thermal diffusivity with the flash method in the case of isotropic and opaque materials. In the first approach, the temperature histories of the two faces of the sample are considered. It is shown that their ratio doesn’t depend on the radial heat diffusion within the sample. In this case, thermal diffusivity can be identified with an adapted moment method. Another way to take the two thermograms into account, is to compute the ratio of their Laplace transforms. Using the quadrupole method, it is shown that the duration of the pulse has no effect. Thermal diffusivity is then identified with the Levenberg-Marquardt method. This technique is particularly suitable for thin films. In the second approach, the logarithmic transform of the rear face temperature rise is considered. In comparison with other existing techniques, the new obtained regression model has the peculiarity to be less sensible to heat losses and to the non-uniformity of the pulse. Furthermore. A stare model is proposed, allowing the identification of thermal diffusivity with the Kalman filter. This technique is also suitable for on-line data redution

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28

Sahalan, Mariaulpa. "Diffusion-weighted Imaging of Lymph Node Tissue." Thesis, The University of Sydney, 2018. http://hdl.handle.net/2123/20070.

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Purpose: The study investigates the hypothesis of clinically observed decreased apparent diffusion coefficient (ADC) of cancerous lymph nodes can be attributed to increased cellularity. The study characterises the mean diffusivity (MD) of lymph node sub-structures and investigates correlation between MD and cellularity metrics. The study also investigates the theoretical information content of single and multi-biophysical models. Methods:. A 3 mm diameter core sample was extracted from a formalin fixed lymph node tissue post-surgery and imaged using 9.4T and 16.4T Bruker MRI system. Samples were sectioned and stained with haematoxylin and eosin (H&E). Diffusion tensor model was fitted voxelwise and MD values were computed using Matlab. Cellularity metrics includes measurement of nuclear count and nuclear area. Eleven models with combinations of isotropic, anisotropic, and restricted components were tested for diffusion modelling and ranked using the Akaike information criterion (AIC). Results: The findings showed distinct diffusivities of lymph node sub-structures (capsule and parenchyma). Parenchyma in normal lymph node tissues had higher MD (0.71 ± 0.17 µm2/ms) than metastatic parenchyma (0.52 ± 0.08 µm2/ms) and lymphoma (0.47 ± 0.19 µm2/ms). No correlation were observed between MD and nuclear count (r = 0.368) and nuclear area (r = 0.368) respectively at 95 % confidence intervals. The single biophysical models (ADC and DTI) were ranked lowest by AIC. Multi-biophysical models consist of anisotropic and restricted diffusion (Zeppelin-sphere, Ball-stick-sphere, and Ball-sphere) were ranked highest in the majority of voxels of the tissue samples. Conclusion: A distinct diffusivity value were found in lymph node sub-structures with no correlation to cellularity. Multi-biophysical models were ranked highest and extract more information from the measurement data than simple single biophysical models.

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29

Ruprecht, Benjamin, Jessica Heine, Martin Wikening, Sylvio Indris, Joseph Wontcheu, Wolfgang Bensch, Thomas Bredow, and Paul Heitjans. "Influence of anion substitution on the lithium diffusivity in hexagonal Li x TiS 2-y Se y." Diffusion fundamentals 12 (2010) 106, 2010. https://ul.qucosa.de/id/qucosa%3A13915.

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30

Nanok, Tanin, O. Sangsawang, Sergey Vasenkov, Frerich J. Keil, and Siegfried Fritzsche. "Molecular dynamics simulation study of the concentration dependence of the self-diffusivity of methanol in NaX zeolite." Diffusion fundamentals 11 (2009) 33, S. 1-2, 2009. https://ul.qucosa.de/id/qucosa%3A13977.

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31

Boumaaza, Mouna. "Experimental investigation of gas diffusivity and CO2-binding capacity of cementitious materials." Thesis, La Rochelle, 2020. https://tel.archives-ouvertes.fr/tel-03285120.

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Actuellement, les méthodes d’essais normalisées, couramment utilisées pour étudier la carbonatation du béton, s’appuient sur l’évaluation de la chute du pH (<9) de la solution interstitielle d'un échantillon de béton exposé à des concentrations ambiantes ou très élevées de CO2 (2% à 50% en volume). Ces méthodes sont souvent critiquées car soit, elles nécessitent beaucoup de temps (plus d’une année pour la carbonatation naturelle), soit elles sont coûteuses et d’une faible fiabilité (la carbonatation accélérée, notamment quand la concentration de CO2 est supérieure à 3% CO2). Deux mécanismes principaux pilotent la carbonatation: le transport diffusif du dioxyde de carbone gazeux, qui est régi par le coefficient de diffusion effectif de cette espèce dans le milieu poreux, et la consommation de CO2 par la quantité de produits carbonatables présente dans la matrice cimentaire. Ces deux propriétés du matériau sont requises pour les modèles prédictifs de la profondeur de carbonatation des matériaux cimentaires. L’objectif de ce travail est donc de développer deux méthodes d’essai simples et fiables pour déterminer ces deux propriétés.D’abord, nous avons développé et validé une méthode d’essai permettant de déterminer le coefficient de diffusion effectif d’oxygène (De,O2) de neufs pâtes de ciment durcies et 44 bétons pré-conditionnés à différentes humidités relatives. L'influence de la durée d'hydratation, du rapport eau sur liant, de la carbonatation accélérée (1% CO2) et du type de liant sur la diffusivité de l'oxygène est étudiée sur des bétons et pâtes de ciment durcies. L’influence de l’épaisseur de l’échantillon de béton testé sur le De,O2 est évaluée à l'état sec et après conditionnement des bétons à une humidité relative de 93%. La corrélation entre la perméabilité à l'oxygène et le coefficient de diffusion effective d’oxygène est étudiée sur 44 mélanges de béton.Une deuxième méthode d’essai est développée pour étudier le taux instantané de fixation de CO2 et la quantité de produits carbonatables de pâtes de ciment hydratées, de phases pures d’hydrates et anhydres synthétisées. Les échantillons ont été carbonatés dans des systèmes ouverts sous humidités relatives contrôlées et concentration ambiante de CO2, puis le système bascule en configuration fermée pour mesurer la quantité de CO2 fixée par le matériau testé pendant une courte période. Cette méthode d’essai permet de déterminer l’évolution en fonction de temps du taux instantané de réaction de carbonatation et de la capacité de fixation de CO2 sous différents environnements. Un bon accord entre les résultats de la nouvelle méthode d’essai et l'analyse thermogravimétrique a été observé, ce qui met en évidence la fiabilité et la précision de la méthode de test développée.Les résultats obtenus des essais de diffusion et les quantités de produits carbonatables sont intégrés dans des modèles de prédiction de la profondeur de carbonatation. Ces profondeurs de carbonatation ont été comparées aux profondeurs de carbonatation déterminées directement sur les mêmes matériaux par pulvérisation de phénolphtaléine, en carbonatation naturelle et accélérée
The current standardized methods used to investigate the carbonation performance of concrete are based on the direct determination of the pH variation on the surface of a concrete specimen exposed to ambient or higher CO2 concentration. These methods are either time-consuming (natural carbonation) or of a questionable accuracy (accelerated carbonation). The carbonation physicochemical process involves two major mechanisms: gaseous CO2 diffusion into the cementitious material’s porous network and its dissolution and reaction with CaO of the hardened cement paste. Most carbonation depth prediction models require the CO2-effective diffusion coefficient and the amount of carbonatable products as input parameters. Hence the aim of this work is to develop two simple and reliable test methods to determine these two properties in a reliable and cost-effective manner.First we developed and validated a test method to determine the oxygen-effective diffusion coefficient (De,O2) of nine different hardened cement pastes preconditioned at different relative humidity levels, and 44 concrete mixtures. The influence of the hydration duration, water-per-binder ratio, accelerated carbonation, and binder type on the oxygen diffusivity was investigated. The dependence of the De,O2 on the tested concrete specimen thickness was investigated at the dry state and after conditioning at 93%RH. The De,O2 was determined before and after full carbonation of six concrete mixtures previously conditioned at different RH. A correlation between oxygen permeability and diffusivity is investigated on 44 concrete mixtures.A second test method is developed to determine the instantaneous CO2 binding rate and the amount of carbonatable products of powdered hydrated cement pastes and synthetic anhydrous and hydrates. The samples were carbonated in open systems at ambient CO2 concentration and controlled relative humidity, and then the system switches into a closed configuration while the measurement of the CO2-uptake is performed over a short period of time. The test method allows for the measurement of the carbonation reaction rate and capacity; and their evolution as function of time under different RH. The developed method shows advantages for being nondestructive, allowing the samples to carbonate at controlled CO2 concentration and humidity, and providing measurements with low cost equipment. A good agreement between the test method results and thermogravimetric analysis was observed, which highlights the reliability and accuracy of the developed test method.The results obtained from the gaseous diffusion coefficient and carbonatable products test methods were used as inputs for carbonation depth prediction models. A correlation was investigated between the measured carbonation depth on different concrete and hydrated cement pastes mixtures by means of phenolphthalein solution under both natural and accelerated exposure. The results were compared with the calculated carbonation depth using our experimental results
Die zurzeit verwendeten Methoden zur Untersuchung des Karbonatisierungs-widerstandes von Beton basieren auf der direkten Bestimmung des pH-Wertes der oberflächennahen Betonrandzone, die zuvor einer bestimmten Prüflagerung ausgesetzt war (relative Luftfeuchte, spezifische CO2-Konzentrationen). Diese Methoden sind jedoch entweder sehr zeitaufwändig (natürliche Karbonatisierung) oder von fraglicher Praxisnähe (beschleunigte Karbonatisierung). Der physikalisch-chemische Karbonatisierungsprozess beinhaltet zwei Hauptmechanismen: die Diffusion von gasförmigem CO2 in das poröse Netzwerk des Betons und dessen Auflösung und Reaktion mit CaO der ausgehärteten Zementsteins. Die meisten Modelle zur Vorhersage der Karbonatisierungstiefe erfordern den effektiven CO2-Diffusionskoeffizienten und die Menge an karbonatisierbarer Masse als Eingabeparameter. Ziel dieser Arbeit ist es, zwei einfache und zuverlässige Testmethoden zu entwickeln, um diese beiden Eigenschaften zuverlässig und kostengünstig zu bestimmen.Nach Entwicklung und Validierung einer geeigneten Testmethode zur Messung von Sauerstoffdiffusionskoeffizienten (De,O2), wurden diese an neun verschiedenen Zementproben gemessen, die bei unterschiedlichen relativen Luftfeuchten vorkonditioniert wurden. Anschließend wurden 44 verschiedene Betonmischungen geprüft. Bei diesen wurde die Hydratationsdauer und der Wasserbindemittelwert variiert. Die Abhängigkeit des Sauerstoffdiffusionskoeffizienten De,O2 von der getesteten Betonprobendicke wurde im trockenen Zustand und nach Konditionierung bei 93% relativer Luftfeuchtigkeit untersucht. Der Sauerstoffkoeffizient De,O2 wurde vor und nach der vollständigen Carbonisierung von sechs Betonmischungen bestimmt, die zuvor bei unterschiedlicher relativer Luftfeuchtigkeit vorkonditioniert worden waren. Eine zweite Testmethode wurde entwickelt, um die momentane CO2-Bindekapazität und die Menge an karbonatisierbarer Masse aus pulverförmigen Zementhydratpasten und synthetischen wasserfreien Produkten und Hydraten zu bestimmen. Die Proben wurden zunächst in offenen Systemen bei einer CO2-Konzentration in der Umgebung und einer kontrollierten relativen Luftfeuchtigkeit gegeben, um danach dann in eine geschlossene Konfiguration umzuwechseln. So konnte man die CO2-Aufnahme über einen kurzen Zeitraum nachverfolgen. Die Testmethode ermöglicht die Messung der Karbonatisierungsreaktionsrate und –kapazität in Abhängigkeit der Zeit unter verschiedenen relativen Luftfeuchten der Umgebungsluft. Es wurde eine gute Übereinstimmung zwischen den Ergebnissen der Testmethode und der thermogravimetrischen Analyse festgestellt, was die Zuverlässigkeit und Genauigkeit der entwickelten Untersuchungsmethodik unterstreicht.Die Ergebnisse beider Tests wurden als Input für Vorhersagemodelle für den zeitabhängigen Karbonatisierungsfortschritt von Beton verwendet. Es wurde eine Korrelation zwischen der gemessenen Karbonatisierungstiefe an verschiedenen Beton- und Zementhydratmischungen mittels Phenolphthaleinlösung untersucht, wobei u. a. Karbonatisierungstiefen bestimmt nach natürlicher Lagerung mit berechneten/vorhergesagten Karbonatisierungstiefen, die mithilfe der vorgestellten Modellierung und Inputdaten aus Test miteinander verglichen wurden

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Wirbeleit, Frank. "Arsenic diffusivity study by comparison of post-Surface and post-implant diffusion in silicon with Local Density Diffusion (LDD-) model approximation." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-186124.

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The LDD model was first applied to Arsenic concentration profiles determined in surface diffusion experiments by Yoshida and Arai [1]. The new method presented is based on a mathematical convolution with a delta-function-like concentration profile. By comparing the LDD approximation of post-surface diffusion with post-implant diffusion experiments, the same LDD model parameter r is found to hold for both experimental arrangements. This work found that post-implant diffusivity is concentration dependant and this might indicate an anomalous diffusion mechanism for Arsenic.

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Wirbeleit, Frank. "Arsenic diffusivity study by comparison of post-Surface and post-implant diffusion in silicon with Local Density Diffusion (LDD-) model approximation." Diffusion fundamentals 15 (2011) 3, S. 1-10, 2011. https://ul.qucosa.de/id/qucosa%3A13836.

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The LDD model was first applied to Arsenic concentration profiles determined in surface diffusion experiments by Yoshida and Arai [1]. The new method presented is based on a mathematical convolution with a delta-function-like concentration profile. By comparing the LDD approximation of post-surface diffusion with post-implant diffusion experiments, the same LDD model parameter r is found to hold for both experimental arrangements. This work found that post-implant diffusivity is concentration dependant and this might indicate an anomalous diffusion mechanism for Arsenic.

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Martins, Bingre Do Amaral Rogéria Paula. "Porosity design of a shaped zeolite for improved effective diffusivity." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAF025.

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Les zéolithes sont des catalyseurs à base d’aluminosilicates largement utilisées dans l’industrie, particulièrement remarquables dans la catalyse. Ces matériaux sont synthétisés dans un laboratoire sous forme de poudre et doivent être mis en forme pour pouvoir être utilisés à grande échelle. Ce procédé est réalisé par l’ajout d’un liant, dans ce cas, la boehmite, pour conférer la résistance mécanique requise. Cette Thèse décrit l’introduction d’une porosité supplémentaire dans la zéolithe mise en forme en utilisant des agents porogènes. Ces catalyseurs ont été testés dans différentes réactions catalytiques et dans l’adsorption du toluène afin d’évaluer l’effet de la présence de méso- et/ou de macropores dans le liant. Une amélioration de la performance des échantillons a été vérifiée lors de l’augmentation du volume macroporeux. Les zéolithes ont été testées en RMN à gradient de champ pulsé, en mesures d’adsorption et en chromatographie en phase gazeuse inverse pour déterminer la diffusivité effective de molécules sondes. Les résultats ont permis de corréler les performances catalytiques avec une diffusion améliorée
Zeolites are aluminosilicate catalysts widely used in industrial processes, with paramount importance in catalysis area. These materials are synthesized in a laboratory in a form of a powder and have to be shaped into centimeter-sized bodies to be implemented at large scale. This process is performed by the addition of a binder, in this case boehmite, to confer the mechanical strength required. The work described in this Thesis aimed to introduce additional porosity in shaped zeolite by means of pore former agents. These catalysts were tested in different catalytic reactions and toluene adsorption to assess the effect of meso- and/or macropores presence in the binder. It was verified an improvement of the performance of the samples with a raise in the macropore volume. The samples were also tested in pulsed-field gradient NMR, uptake measurements and inverse gas chromatography to determine the effective diffusivity of probe molecules. The results allowed to establish a correlation between the catalytic performance and an improved diffusion

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35

Nechaev, Yury S. "On the physics of the apparent solubility and diffusivity of hydrogen in metals and alloys, relevance for revealing the hydrogen-assisted damage micromechanisms." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-196064.

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Kechaou, Nabil. "Séchage de gels fortement déformables : étude de la diffusion interne de l'eau et modélisation." Vandoeuvre-les-Nancy, INPL, 1989. http://www.theses.fr/1989NAN10063.

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Séchage par convection de deux milieux modèles de produits alimentaires, la gélatine et un gel de polyacrylamide. Séchage dans une boucle permettant le relevé de la masse en continu et le traitement des données en garantissant des exigences extrêmement fines de la régulation en température et en humidité de l'air

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Du, Plessis Elsa. "Modelling of single phase diffusive transport in porous environments." Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/4323.

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Thesis (MSc (Applied Mathematics))--University of Stellenbosch, 2010.
ENGLISH ABSTRACT: Macroscopic diffusion through porous media is considered in systems where this process does not occur along with or induce bulk convective flow of the diffusing species. The diffusion coefficient present in the governing equations of suchmacroscopic diffusion is unique to a pair of species in a binary system. This coefficient may be determined experimentally, but such experimentation must be carried out for every different pair of species. Taking this into consideration, a deterministic pore-scale model is proposed to predict the effective diffusivity of homogeneous and unconsolidated porous media which ultimately depends solely on the porosity of the media. The approach taken is to model a porous medium as either a fibre bed or an array of granules through which the diffusive process is assumed to be homogenous and transversally isotropic. The fibre bed and granular modelsmay be viewed as two-dimensional and three-dimensional models respectively, and may also be combined to form a weighted average model which adjusts to differing diffusive behaviour at different porosities. The model is validated through comparison with published analytical and numerical models as well as experimental data available in the literature. A numerical program is implemented to generate further data for various arrangements of homogeneous, anisotropic and transversely isotropic porous media. The numerical results were validated against an analytical model from the literature which proved to be inapplicable to a specific case. The weighted average analytical model is proposed for this case, instead. The results of this study indicate that the weighted average analytical model is in good agreement with the numerical and experimental data and as such may be applied directly to a binary system of which the porosity is known in order to predict the effective diffusivity.
AFRIKAANSE OPSOMMING: Makroskopiese diffusieprosesse deur poreuse media word oorweeg in sisteme waar geen konveksie van die diffunderende stof plaasvind of geïnduseer word nie. Die wiskundige beskrywing van hierdie prossese bevat die sogenaamde diffusiekoëffisïent, ’n konstante wat uniek is tot ’n tweeledige sisteem. Dié konstante kan eksperimenteel bepaal word, maar as gevolg van die uniekhied daarvan tot verskillende sisteme moet dit vir elke tweeledige sisteem bepaal word. Op grond hiervan word ’n deterministiese model voorgestel om die effektiewe diffusiwiteit vir diffusie deur homogene en losstaande poreuse media te voorspel. Die model hang slegs af van die porositeit van die poreuse medium wat benader word as ’n veselbed of korrelstruktuur. Die diffusieproses deur dergelike strukture word beskou as homogeen en isotroop in die dwarsstroomrigting. Die veselbed- en korrelmodelle word beskou as twee- en driedimensionele modelle onderskeidelik en word gekombineer om ’n geweegde gemiddelde model te vorm wat dus by enige porositeit die verlangde porositeit gee. Die model is geverifieer deur vergelyking met analitiese- en numeriese modelle asook eksperimentele data vanuit die literatuur. ’n Numeriese program is gebruik om verdere resultate te verkry vir verskeie skikkings van homogene, anisotrope en dwarsverskuifde poreuse media. Die numeriese resultate is gekontroleer deur vergelyking met ’n analitiese model vanuit die literatuur. ’n Spesifieke geval is uitgewys waarvoor hierdie model nie toepasbaar is nie, maar waarvoor die voorgestelde geweegde gemiddelde model goeie resultate lewer. Die uitkomste dui aan dat die analitiese model goed ooreenstem met die numeriese en eksperimentele data en kan dus direk toegepas word om die effektiewe diffusiwiteit te verkry van ’n tweeledige sisteem waarvan die porositeit bekend is.

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Bensetiti, Zouhir. "Compétition réaction-diffusion estimation de la diffusivité effective du réactif et de l'efficacité du catalyseur." Vandoeuvre-les-Nancy, INPL, 1993. http://www.theses.fr/1993INPL134N.

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Le concept de la diffusivité effective dans les catalyseurs poreux est largement utilisé pour mettre en évidence l'importance de la diffusion à la réaction chimique. Plusieurs modèles sont utilisés pour estimer cette quantité. Dans ce travail, nous avons introduit une nouvelle diffusivité effective qui fait intervenir la distribution des tailles de pore et la distribution des sites catalytiques appelée diffusivité en catalyse. Nous avons trouvé que les valeurs de cette diffusivité sont inferieures à celles estimées par les modèles de Wakao et Smith et Johnson et Stewart. Nous comparons dans ce travail les modèles de diffusion en essayant d'interpréter les taux de conversion expérimentaux avec un ajustement des paramètres cinétiques intrinsèques. Sur la base des résultats d'ajustements, nous conclurons sur la validité des différents modèles. Pour être efficace, cette méthode doit être appliquée aux résultats expérimentaux en régime diffusionnel et chimique. Nous avons étudié la réaction de déshydratation du méthanol en dimethylether et eau et la réaction d'isomérisation du n-butène sur alumine gc070. Après avoir déterminé l'ordre des réactions et résolu l'équation du bilan de matière pour le réactif. Nous avons trouvé que le modèle de la diffusivité en catalyse donne une meilleure estimation de la diffusivité effective que les modèles de Johnson-Stewart et Wakao-Smith. Dans notre travail nous avons aussi essaye de montrer l'influence de la structure réelle du catalyseur sur l'estimation de la diffusivité effective

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39

Nechaev, Yury S. "On the physics of the apparent solubility and diffusivity of hydrogen in metals and alloys, relevance for revealing the hydrogen-assisted damage micromechanisms." Diffusion fundamentals 2 (2005) 53, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14386.

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40

Lyashenko, Yu O., and L. I. Gladka. "Determination of effective diffusion coefficients for inhomogeneous media." Thesis, Sumy State University, 2011. http://essuir.sumdu.edu.ua/handle/123456789/20690.

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A new model of effective medium is proposed for the transition zone located between two diffusion-interacting phases. In the model the effective diffusivity depends on the kinetic coefficients in each phase, volume fractions of phases and on the additional parameter, which generally characterizes the structure type of the two-phase zone. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/20690

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41

Do, Amaral Sobral Paulo José. "Diffusivité de l'eau dans le gel polyacrylamide-eau autour de la transition vitreuse." Vandoeuvre-les-Nancy, INPL, 1992. http://docnum.univ-lorraine.fr/public/INPL_T_1992_DO_AMARAL_SOBRAL_J.pdf.

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Pour de multiples applications industrielles: mise en forme, séchage, il est nécessaire de prévoir le transfert de matière dans les milieux polymériques déformables. Notre choix du gel de polyacrylamide et d'eau: système simple à deux constituants et une même phase, a été guidé par son caractère très complexe: milieu gonflant, existence d'une transition vitreuse-caoutchoutique dans la région hygroscopique et présence permanente d'un phénomène de relaxation moléculaire. Notre travail a consisté à mettre au point une balance précise à 0,01 mg permettant d'établir des cinétiques de sorption dans la vapeur pure. Nous l'avons équipé de contrôle de température à 0,03°C avec acquisition de toutes les données en temps réel. Les résultats montrent pour la première fois l'incidence de la transition vitreuse à température fixée: la diffusivité de l'eau subit un saut d'un facteur deux dans la région de la transition qui divise l'ensemble de la variation de diffusivité entre une phase de croissance ralentie et une phase quasi-constante (4. 35 10-¹¹ m². S-¹ à 20-40°C). On compare ces résultats de diffusivités au modèle prédictif du volume libre de Vrentas et Dudda. Sur un vaste domaine de concentration, le comportement général du transfert de matière peut s'interpréter par l'existence d'une diffusion non-fickienne associée au comportement viscoélastique selon le modèle de Durning et Tabor

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42

Nelson, George J. "Computational characterization of diffusive mass transfer in porous solid oxide fuel cell components." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31660.

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Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2010.
Committee Co-Chair: Haynes, Comas; Committee Co-Chair: Wepfer, William; Committee Member: Fedorov, Andrei; Committee Member: Liu, Meilin; Committee Member: Paredis, Chris; Committee Member: Teja, Amyn. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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43

Calderan, Christelle. "Contribution à l'étude de la diffusion de la chaleur dans les barrières thermiques à structure hétérogène par microanalyse photothermique." Perpignan, 1999. http://www.theses.fr/1999PERP0386.

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44

Prillieux, Aurélien. "Hydrogen and water vapour effects on oxygen solubility and diffusivity in high temperature Fe-Ni alloys." Phd thesis, Toulouse, INPT, 2017. http://oatao.univ-toulouse.fr/18676/1/PRILLIEUX_Aurelien.pdf.

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It is a worldwide priority to reduce emissions of greenhouse gases such as CO2. One solution for reducing these emissions is to improve the efficiency of energy production units by increasing their operating temperature. However, in order to increase operating temperature, new austenitic materials based on the Fe-Ni-Cr system have to be designed. In addition, these materials need to exhibit good protection against high temperature oxidation, which is achieved by the formation of a slow growing chromium oxide or alumina scale on the metal. However, to predict the formation of a protective scale, knowledge of the oxygen permeability, the product of oxygen solubility and diffusivity, in the base alloy is required. The objective of this study is to measure the permeability, solubility and diffusivity of oxygen in Fe- Ni alloys at temperatures above 1,000°C. In order to obtain the best results, the formation of an external oxide layer during the experiment has to be avoided. To achieve this, the oxygen partial pressure was fixed at the Fe/FeO equilibrium pressure in all experiments. In addition, two types of atmospheres were used: one dry and one wet, in order to investigate the effect of water vapour on oxygen permeability, solubility and diffusivity. The dry atmosphere was achieved using the Rhines Pack technique. The samples were oxidised in vacuum-sealed quartz capsules, which contained a mixture of powdered iron and wüstite. The humid atmosphere was obtained by using H2/H2O gas mixtures with the appropriate water vapour to hydrogen ratio to fix oxygen partial pressure at the Fe/FeO equilibrium. The maximum oxygen solubility was found in pure iron, and decreased continuously with nickel additions to the alloy. The dependence of solubility on alloy composition is non-ideal, and cannot be predicted from simple models. Moreover, the presence of water vapour in the atmosphere seems to increase the solubility by a factor of 2 in alloys with nickel content lower than 80 at.% at temperatures near 1,000°C. However, at 1,150°C the solubility of the oxygen is independent of the environment. The oxygen permeability was determined by measuring the internal oxidation kinetics of Fe-Ni-Cr alloy. These kinetics were evaluated by measuring the internal oxidation zone depth by optical microscopy, or by continuous and discontinuous thermogravimetry. Results showed that the oxygen permeability exhibits the same variation with alloy composition as the oxygen solubility, independent of the atmosphere. In particular, no significant effect of water vapour on oxygen permeability values was observed. In the present study, the oxygen diffusion coefficient was also determined using permeability, in addition to the independent measurement of the oxygen solubility carried out in the present study. For temperature above 1,000°C, the variation of oxygen diffusion coefficient with the alloy composition is similar in all environments tested, and a maximum is observed for alloys with a nickel content of 40 at.%. However, for a given nickel content up to 60 at.%, the presence of water vapour in the atmosphere decreases the value of the oxygen diffusion coefficient by a factor of 2-3 at 1,000°C. In addition, this difference between diffusion coefficients measured in a dry and wet atmosphere increases as the temperature decreases. Overall, it was found that the water vapour has no effect on the way in which oxygen permeability, solubility and diffusivity vary with the alloy composition. However, the presence of water vapour in the environment appears to increase the oxygen solubility and decrease the oxygen diffusivity in iron-rich alloys, the effect being more significant at low temperatures. These results suggest further research into interactions between O, H and metal vacancies, particularly for temperature around 1,000°C and below, as the latter defect is thought to change the diffusion and solubility properties of interstitial species.

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Citron, Alberto <1988&gt. "Studio di processi elettrodici non diffusivi mediante nanoelettrodi di platino e applicazioni in elettroanalisi." Master's Degree Thesis, Università Ca' Foscari Venezia, 2014. http://hdl.handle.net/10579/5667.

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In questo lavoro di tesi sono stati preparati e caratterizzati nanoelettrodi di platino a forma di disco con raggi elettrodici variabili tra 20 e 600 nm. Per confronto sono stati anche preparati, con la stessa metodologia, e impiegati microelettrodi a disco di platino di 12,5 μm di raggio. Gli elettrodi sono stati fabbricati mediante una tecnologia basata sull’impiego di un “laser puller” a partire da fibre di platino di 25 μm di diametro e capillari di quarzo. I nanoelettrodi presentano inaspettatamente elevate superfici reali (fino a 4-5 ordini di grandezza superiori rispetto alla superficie geometrica del microdisco di base), che risultano vantaggiose per la determinazione di specie elettroattive di processi non diffusivi. La superficie reale degli elettrodi è stata determinata per via voltammetrica sfruttando i processi di under potential deposition (UPD) sia dell’idrogeno che del bismuto. La superficie geometrica è stata determinata impiegando specie elettroattive caratterizzate da processi elettrodici reversibili e operando in condizioni diffusive. Applicazioni analitiche hanno riguardato la determinazione di acqua ossigenata e acido ascorbico. Quest’ultima specie è stata impiegata per confronto, in quanto il suo processo elettrodico non è catalizzato dal platino.

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46

Rambaks, Andris, Filipp Kratschun, Carsten Flake, Maren Messirek, Katharina Schmitz, and Hubertus Murrenhoff. "Computational approach to the experimental determination of diffusion coefficients for oxygen and nitrogen in hydraulic fluids using the pressure-decay method." Technische Universität Dresden, 2020. https://tud.qucosa.de/id/qucosa%3A71099.

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In the presented paper, the applicability of pressure-decay methods to determine the diffusivities of gases in hydraulic fluids is analysed. First, the method is described in detail and compared to other measurement methods. Secondly, the thermodynamics and the mass transfer process of the system are studied. This results in four different thermodynamic models of the gaseous phase in combination with two diffusion models. Thirdly, the influence of the models on the pressure-decay method is evaluated computationally by examining the diffusion process of air in water as all system parameters are available from literature. It is shown that ordinary pressure-decay methods are not applicable to gas mixtures like air and therefore a new method for calculating the diffusivities is suggested.

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47

Simoni, Giulia. "Modelli diffusivi ed effetti di ritardo nella conduzione del calore e nella dinamica delle popolazioni." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/6934/.

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Abstract:

In questi tesi viene studiata la teoria classica di diffusione del calore come modello parabolico per cui viene calcolata una soluzione attraverso il metodo di separazione delle variabili e il metodo delle onde dispersive. Viene poi affrontata la teoria alternativa proposta da Cattaneo del modello iperbolico del calore, allo scopo di superare il paradosso di velocità di propagazione infinita. Si conclude con alcuni esempi in cui lo stesso ragionamento viene applicato in diverse teorie diffusive e di reazione-diffusione in ambiti bio-matematici, come ad esempio la dinamica delle popolazioni.

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48

Chen, Zhangqi. "A Comprehensive Study of Diffusion and Modulus of Binary Systems within the Ti-Mo-Nb-Ta-Zr System." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1562224291399741.

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49

André, Stéphane. "Identification de la diffusivité phonique du verre par méthode flash de 20°C à 500°C." Vandoeuvre-les-Nancy, INPL, 1992. http://docnum.univ-lorraine.fr/public/INPL_T_1992_ANDRE_S.pdf.

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La méthode flash est étendue à la gamme de températures 20°C-600°C. Appliquée aux milieux semi-transparents (M. S. T. ), et couplé à une étude théorique du transfert combiné conduction/rayonnement, elle permet d'accéder directement à la mesure de la diffusivité phonique des verres. Pour cela, le rôle des conditions aux limites radiatives (noires ou réfléchissantes), de l'épaisseur de l'échantillon, du degré de semi-transparence du matériau (coefficient d'absorption) a été mis en évidence. Une étude expérimentale portant sur cinq verres à teneur en Fe₂O₃ différente, a confirmé les prédictions théoriques établies dans le cas du milieu gris. La prise en compte de la dépendance spectrale du coefficient d'absorption, par un modèle multi-bandes (milieu non-gris), reste sans influence sur la mesure de diffusivité phonique dans les cas indiqués. Nous proposons finalement une nouvelle expression de la conductivité phonique des verres flottés en fonction de la température
The flash method is extended to the 300K to 800K temperature range. Applied to semi-transparent media (S-T-M) and associated to a theoretical study of the coupled Conductions-Radiation 1-D transient heat transfer, it allows the direct measurement of the phonic diffusivity of glass. For this reason, the contribution of either the radiative boundary conditions (black or reflecting), the sample’s thickness, or the degree of semi-transparency (absorption coefficient) has been underscored. An experimental study has been carried out on five different glasses of various Fe2O3 content and has confirmed the theoretical predictions yielded by simulations made in the case of the gray medium. The spectral dependence of the absorption coefficient (“non-gray” medium) has been taken into-account through a multi-band model. It has no influence on the measurement of the phonic diffusivity in the prescribed conditions. Finally, we propose a new expression for the phonic conductivity of float glasses as a function of temperature

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Sposini, Vittoria [Verfasser], Ralf [Akademischer Betreuer] Metzler, Gianni [Akademischer Betreuer] Pagnini, Ralf [Gutachter] Metzler, Arkady [Gutachter] Pikovsky, and Stas [Gutachter] Burov. "The random diffusivity approach for diffusion in heterogeneous systems / Vittoria Sposini ; Gutachter: Ralf Metzler, Arkady Pikovsky, Stas Burov ; Ralf Metzler, Gianni Pagnini." Potsdam : Universität Potsdam, 2020. http://d-nb.info/1226217214/34.

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