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Antoine Blondel – One of the best experts on this subject based on the ideXlab platform.

  • Effets de la température et de l’irradiation sur le comportement du chlore 37 dans le Graphite nucléaire : Conséquences sur la mobilité du chlore 36 dans les Graphites irradiés
    , 2013
    Co-Authors: Antoine Blondel
    Abstract:

    Ce travail s’inscrit dans le cadre des études sur la gestion des déchets graphités issus du démantèlement des centrales UNGG (Uranium Naturel Graphite Gaz). Les déchets graphités contiennent, entre autres, du 36Cl, radionucléide de longue période dimensionnant pour le stockage, car très mobile dans les ouvrages cimentaires et formations argileuses. Or, à ce jour, peu de données sont disponibles sur la localisation du 36Cl et sa spéciation dans le Graphite nucléaire irradié. Ces informations sont nécessaires pour le dimensionnement d’un site de stockage adapté aux déchets graphités et leur obtention constitue l’objectif de ma thèse, réalisée en partenariat avec EDF, CEA et Andra. Dans ce contexte, nous avons mis en œuvre des études expérimentales permettant de simuler et d’évaluer l’impact de la température, de l’irradiation et de la radiolyse à l’interface gaz/Graphite sur le comportement en réacteur du 36Cl. La présence de 36Cl dans le Graphite est simulée par l’implantation ionique de 37Cl dans des échantillons de Graphite nucléaire vierge ce qui permet de nous affranchir des contraintes liées à l’utilisation de Graphite irradié. En extrapolant nos résultats aux déchets graphités, nos études sur les effets comparatifs de la température et de l’irradiation montrent que la température tend à appauvrir l’inventaire en chlore 36 des Graphites irradiés et que l’irradiation en régime mixte, tel qu’elle a lieu dans les réacteurs UNGG, renforce cet effet d’appauvrissement

  • Effets de la température et de l’irradiation sur le comportement du chlore 37 dans le Graphite nucléaire : conséquences sur la mobilité du chlore 36 dans les Graphites irradiés
    , 2013
    Co-Authors: Antoine Blondel
    Abstract:

    Ce travail s’inscrit dans le cadre des études sur la gestion des déchets graphités issus du démantèlement des centrales UNGG (Uranium Naturel Graphite Gaz). Les déchets graphités contiennent, entre autres, du 36Cl, radionucléide de longue période dimensionnant pour le stockage, car très mobile dans les ouvrages cimentaires et formations argileuses. Or, à ce jour, peu de données sont disponibles sur la localisation du 36Cl et sa spéciation dans le Graphite nucléaire irradié. Ces informations sont nécessaires pour le dimensionnement d’un site de stockage adapté aux déchets graphités et leur obtention constitue l’objectif de ma thèse, réalisée en partenariat avec EDF, CEA et Andra. Dans ce contexte, nous avons mis en oeuvre des études expérimentales permettant de simuler et d’évaluer l’impact de la température, de l’irradiation et de la radiolyse à l’interface gaz/Graphite sur le comportement en réacteur du 36Cl. La présence de 36Cl dans le Graphite est simulée par l’implantation ionique de 37Cl dans des échantillons de Graphite nucléaire vierge ce qui permet de nous affranchir des contraintes liées à l’utilisation de Graphite irradié. En extrapolant nos résultats aux déchets graphités, nos études sur les effets comparatifs de la température et de l’irradiation montrent que la température tend à appauvrir l’inventaire en chlore 36 des Graphites irradiés et que l’irradiation en régime mixte, tel qu’elle a lieu dans les réacteurs UNGG, renforce cet effet d’appauvrissement

Charles A. Wilkie – One of the best experts on this subject based on the ideXlab platform.

  • expandable Graphite polyamide 6 nanocomposites
    Polymer Degradation and Stability, 2005
    Co-Authors: Fawn Marie Uhl, Qiang Yao, Hiroyoshi Nakajima, Evangelos Manias, Charles A. Wilkie
    Abstract:

    Polyamide-6 (PA-6)/Graphite nanocomposites were prepared by melt blending, using a variety of Graphites, including virgin Graphite, expandable Graphites and expanded Graphite. The resulting nanocomposites were characterized by X-ray diffraction, thermogravimetric analysis, cone calorimetry, and tensile mechanical analysis. Nanocomposite formation does occur, as denoted by the nanometre dispersion of Graphite layers in the polymer matrix, and the dispersion depends on the Graphite treatment. The material properties of the resulting composites are improved relative to the virgin/unfilled polymer; in particular, there is an enhancement of the thermal stability without any significant deterioration of the mechanical properties.

  • Expandable Graphite/polyamide-6 nanocomposites
    Polymer Degradation and Stability, 2005
    Co-Authors: Fawn Marie Uhl, Qiang Yao, Hiroyoshi Nakajima, Evangelos Manias, Charles A. Wilkie
    Abstract:

    Polyamide-6 (PA-6)/Graphite nanocomposites were prepared by melt blending, using a variety of Graphites, including virgin Graphite, expandable Graphites and expanded Graphite. The resulting nanocomposites were characterized by X-ray diffraction, thermogravimetric analysis, cone calorimetry, and tensile mechanical analysis. Nanocomposite formation does occur, as denoted by the nanometre dispersion of Graphite layers in the polymer matrix, and the dispersion depends on the Graphite treatment. The material properties of the resulting composites are improved relative to the virgin/unfilled polymer; in particular, there is an enhancement of the thermal stability without any significant deterioration of the mechanical properties.

  • studies on the mechanism by which the formation of nanocomposites enhances thermal stability
    Chemistry of Materials, 2001
    Co-Authors: Alexander B Morgan, Charles A. Wilkie
    Abstract:

    Polystyrene-clay and polystyreneGraphite nanocomposites have been prepared and used to explore the process by which the presence of clay or Graphite in a nanocomposite enhances the thermal stability of polymers. This study has been designed to determine if the presence of paramagnetic iron in the matrix can result in radical trapping and thus enhance thermal stability. Nanocomposites were prepared by bulk polymerization using both iron-containing and iron-depleted clays and Graphites, and they were characterized by X-ray diffraction, transmission elecelectron microscopy, thermogravimetric analysis, and cone calorimetry. The presence of structural iron, rather than that present as an impurity, significantly increases the onset temperature of thermal degradation in polymer-clay nanocomposites. Intercalated nanocomposites show an iron effect, but this is less important for exfoliated systems. PolymerGraphite nanocomposites show no difference between iron-free and iron-containing nanocomposites, presumably because the iron is not nanodispersed in the Graphite.

S. Mukhopadhyay – One of the best experts on this subject based on the ideXlab platform.

  • Thermal and thermomechanical characteristics of monolithic refractory composite matrix containing surface-modified Graphite
    Ceramics International, 2016
    Co-Authors: S. Mukhopadhyay, Kaushik Dana, Saibal Moitra, S Basumallick, Tapas Kumar Mukhopadhyay
    Abstract:

    Abstract The thermomechanical analysis (TMA) and thermal characteristics of carbon-containing refractory castable matrix with 20.0 wt% Graphite have been compared with Graphite-free high alumina based similar castable matrix. Graphite has been added both in uncoated and coated forms, the latter having a thin sol–gel calcium aluminate coating on as-received Graphite flakes. The influence of systematic variation of microfine constituents e.g. reactive alumina, high alumina cement etc in the matrix has been investigated in terms of the heat flow studies obtained by differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). The densification behavior of Graphite-free and Graphite-containing castable matrices has been critically estimated by the dimensional changes in dynamic heating regime up to 1500 °C. The role of coated Graphite on improved densification behavior of refractory was explored by microstructure and phase assemblage studies of the respective fired castable. It was further corroborated by the transmission electron microscope (TEM) studies of surface-modified Graphites.

  • in depth studies on cementitious nanocoatings on Graphite for its contribution in corrosion resistance of alumina based refractory composite
    Ceramics International, 2015
    Co-Authors: S. Mukhopadhyay, C Mondal, Arijit Chakraborty, D Mali, Soumya Ghosh
    Abstract:

    Abstract Some newer insights had been reported in this paper on synthesis and application of calcium aluminate coated Graphite in alumina–carbon refractory castables. The course of evolution of AlO 4 (tetrahedral) and AlO 6 (octahedral) units in the nanocoating was investigated by XRD (X-ray diffraction), Raman specspectroscopy and FTIR (Fourier transformed infrared spectroscopy) studies. An extended research on the resemblance and disparity between sol–gel and conventional refractory cements were also explored. FESEM ( Field Emission Scanning Electron Microscopy), XRD of coated and uncoated Graphites had been revisited with a special study on ESEM (environmental scanning electron microscopy) of those two. The hydrophilic thin film containing Ca-doped γ-Al 2 O 3 phases rendered a decisive influence on Graphite retention in castable matrix. A comparison between pore size distribution and thermogravimetric analysis (TGA) of two fired castable refractories advocated the superiority of the one containing coated Graphite. Determination of corrosion and penetration indices by the static slag corrosion test, supplemented with microstructural studies, confirmed that the less porous castable containing coated Graphites excelled again in the harsh environment.

  • comparison of solid state and sol gel derived calcium aluminate coated Graphite and characterization of prepared refractory composite
    Ceramics International, 2012
    Co-Authors: S. Mukhopadhyay, Subir Kumar Dutta
    Abstract:

    Abstract This paper entails an extended investigation on sol–gel thin film of calcium aluminate (CaAl 2 O 4 ) over Graphite flakes that improved their oxidation resistance and water wettability. The commercial preparation of calcium aluminate has been compared with the sol–gel synthesis by differential thermal analysis (DTA) and X-ray diffraction (XRD) to assess the feasibility of the latter for coating preparation. Poorly crystalline nanostructured Ca-doped γ-Al 2 O 3 is considered to be an important intermediate for this preparation. Scanning electron microscopy (SEM) and energy dispersive specspectroscopy (EDS) of the calcined gel have been carried out to ascertain its composition. Quantitative chemical analysis of sol gel derived calcium aluminate was also estimated. Atomic force microscopy (AFM) has been conducted to ensure the evolution of hydrophilic nanosized cementitious phases on Graphite. Zeta potential values of coated and uncoated Graphites with increasing pH have also been determined to distinguish between their compatibility in a refractory castable matrix. Improved physical properties of that high alumina castable containing coated Graphite, e.g. apparent poroporosity (AP), bulk density (BD), cold crushing strength (CCS) have been measured to evaluate the refractory quality. The reasons for its better performance are explored by taking further insight on the microstructural analyses of the fired castable (1500 °C) soaked for an extended period.

Peter J. Uggowitzer – One of the best experts on this subject based on the ideXlab platform.

  • Physical properties of Graphite/aluminium composites produced by gas pressure infiltration method
    Carbon, 2003
    Co-Authors: Thomas Etter, Maria Papakyriacou, Peter Schulz, Peter J. Uggowitzer
    Abstract:

    Abstract Graphite/aluminium composites have been produced by means of gas pressure infiltration method. Two porous Graphite preforms with a porosity of 10 and 13 vol%, respectively, have been infiltrated using either a commercially 99.85 pure aluminium or an AlSi7Mg alloy. Thermal expansion coefficient, electrical conductivity and flexural strength have been determined as a function of Graphite preforms and metal matrices. To investigate the susceptibility of this composite system to thermal damage, specimens were thermally cycled between 60 and 300 °C up to 1020 cycles. Infiltrated Graphites exhibited a significantly higher electrical conductivity (0.34–0.51 m/Ω mm 2 ) compared to porous Graphite preforms depending on Graphite type and metal matrix. Thermal cycling did not influence electrical conductivity. The coefficients of thermal expansion of the composites were at least three times lower than for monolithic aluminium. Thermal cycling has reduced these values even more, most likely due to stress relaxation processes. The infiltration of porous Graphite preforms with AlSi7Mg alloy or Al99.85 has increased the flexural strength of the composites resulting in values up to 105 MPa. The decrease in mechanical strength due to thermal cycling was about 10%.

  • physical properties of Graphite aluminium composites produced by gas pressure infiltration method
    Carbon, 2003
    Co-Authors: Thomas Etter, Maria Papakyriacou, Peter Schulz, Peter J. Uggowitzer
    Abstract:

    Abstract Graphite/aluminium composites have been produced by means of gas pressure infiltration method. Two porous Graphite preforms with a porosity of 10 and 13 vol%, respectively, have been infiltrated using either a commercially 99.85 pure aluminium or an AlSi7Mg alloy. Thermal expansion coefficient, electrical conductivity and flexural strength have been determined as a function of Graphite preforms and metal matrices. To investigate the susceptibility of this composite system to thermal damage, specimens were thermally cycled between 60 and 300 °C up to 1020 cycles. Infiltrated Graphites exhibited a significantly higher electrical conductivity (0.34–0.51 m/Ω mm 2 ) compared to porous Graphite preforms depending on Graphite type and metal matrix. Thermal cycling did not influence electrical conductivity. The coefficients of thermal expansion of the composites were at least three times lower than for monolithic aluminium. Thermal cycling has reduced these values even more, most likely due to stress relaxation processes. The infiltration of porous Graphite preforms with AlSi7Mg alloy or Al99.85 has increased the flexural strength of the composites resulting in values up to 105 MPa. The decrease in mechanical strength due to thermal cycling was about 10%.

Maël Le Guillou – One of the best experts on this subject based on the ideXlab platform.

  • Migration du deutérium dans le Graphite nucléaire : conséquences sur le comportement du tritium en réacteur UNGG et sur la décontamination des Graphites irradiés
    , 2014
    Co-Authors: Maël Le Guillou
    Abstract:

    En France, 23 000 tonnes de Graphites irradiés générés par le démantèlement des réacteurs nucléaires de première génération Uranium Naturel-Graphite-Gaz (UNGG) sont en attente d’une solution de gestion à long terme. Cette thèse porte sur le comportement du tritium, l’un des principaux contributeurs à l’inventaire radiologique des Graphites à l’arrêt des réacteurs. Afin d’anticiper des rejets de tritium lors du démantèlement ou de la gestion des déchets, il est indispensable d’obtenir des données sur sa migration, sa localisation et son inventaire. Notre étude repose sur la simulation du tritium par implantation de l’ordre de 3 % at. de deutérium jusqu’à environ 3 μm dans un Graphite nucléaire vierge. Celui-ci a ensuite subi des recuits jusqu’à 300 h et 1300 ° C sous atmosphère inerte, gaz caloporteur UNGG et gaz humide, dans le but de reproduire des conditions proches de celles rencontrées en réacteur et lors des opérations de gestion des déchets. Les profils et la répartition spatiale du deutérium ont été analysés via la réaction nucléaire 2H(3He,p)4He. Les principaux résultats montrent un relâchement thermique du deutérium se produisant selon trois régimes contrôlés par le dépiégeage de sites superficiels ou interstitiels. L’extrapolation des données au cas du tritium tend à montrer que son relâchement thermique en réacteur pourrait avoir été inférieur à 30 % et localisé à proximité des surfaces libres du Graphite. L’essentiel de l’inventaire en tritium à l’arrêt des réacteurs serait retenu en profondeur dans les Graphites irradiés, dont la décontamination nécessiterait alors des températures supérieures à 1300 °C, et serait plus efficace sous gaz inerte que sous gaz humide