Tuning, Impedance Matching, and Temperature Regulation during High-Temperature Microwave Sintering of Ceramics

International audienceOver the years, microwave radiation has emerged as an efficient source of energy for material processing. This technology provides a rapid and a volumetric heating of material. However, the main issues that prevent microwave technology from being widespread in material processing are temperature control regulation and heating distribution within the sample. Most of the experimental works are usually manually monitored, and their reproducibility is rarely evaluated and discussed. In this work, an originally designed 915MHz microwave single-mode applicator for high-temperature processing is presented. The overall microwave system is described in terms of an equivalent electrical circuit. This circuit has allowed to point out the different parameters which need to be adjusted to get a fully controlled heating process. The basic principle of regulation is then depicted in terms of a block function diagram. From it, the process has been developed and tested to sinter zirconia-and spinel-based ceramics. It is clearly shown that the process can be successfully used to program multistep temperature cycles up to similar to 1550 degrees C, improving significantly the reproducibility and the ease of use of this emerging high-temperature process technology

Development and validation of high-density SNP array in ducks

Development and validation of high-density SNP array in ducks. XIth European symposium on poultry genetics (ESPG

New investigations around CYP11A1 and its possible involvement in an androstenone QTL characterised in Large White pigs

<p>Abstract</p> <p>Background</p> <p>Previously, in boars with extreme androstenone levels, differential expression of the <it>CYP11A1 </it>gene in the testes has been characterised. <it>CYP11A1 </it>is located in a region where a QTL influencing boar fat androstenone levels has been detected in a Large White pig population. Clarifying the role of CYP11A1 in boar taint is important because it catalyses the initial step of androstenone synthesis and also of steroid synthesis.</p> <p>Results</p> <p>A genome-wide association study located <it>CYP11A1 </it>at approximately 1300 kb upstream from SNP H3GA0021967, defining the centre of the region containing the QTL for androstenone variation. In this study, we partially sequenced the <it>CYP11A1 </it>gene and identified several new single nucleotide polymorphisms (SNP) within it. Characterisation of one animal, heterozygous for <it>CYP11A1 </it>testicular expression but homozygous for a haplotype of a large region containing <it>CYP11A1</it>, revealed that variation of <it>CYP11A1 </it>expression is probably regulated by a mutation located downstream from the SNP H3GA0021967. We analysed <it>CYP11A1 </it>expression in LW families according to haplotypes of the QTL region's centre. Effects of haplotypes on <it>CYP11A1 </it>expression and on androstenone accumulation were not concordant.</p> <p>Conclusion</p> <p>This study shows that testicular expression of <it>CYP11A1 </it>is not solely responsible for the QTL influencing boar fat androstenone levels. As a conclusion, we propose to refute the hypothesis that a single mutation located near the centre of the QTL region could control androstenone accumulation in fat by regulating the <it>CYP11A1 </it>expression.</p

Synthèse et frittage par des procédés non conventionnels de composés diélectriques dérivés de la pérovskite de type CaCu3Ti4O12

As the miniaturization of electronic components is becoming a major issue in many business sectors (automotive, aerospace, computer sciences…), the development of new families of materials with a high dielectric constant and low dielectric losses is still a priority line of research. This is the case of CaCu3Ti4O12. This material has been studied extensively since 2000 thanks to its “exceptional” relative permittivity. The work presented in this thesis proposes an original study of the synthesis and sintering of CaCu3Ti4O12 by non-conventional processes and its structural, microstructural and physical characterization.The first study concerns the conventional and microwave synthesis of CaCu3Ti4O12. The interest of microwave heating is the good coupling between microwaves and the dielectric properties of the material. This allows a rapid synthesis of CaCu3Ti4O12 and the control of its particle size. Subsequently, the study focused on a thorough analysis of the natural sintering of this ceramic. Densification is controlled up to 80% of relative density by grain-boundary diffusion. At higher temperature, a liquid phase occurs during the sintering, resulting in abnormal grain growth. Various sintering techniques (controlled atmosphere, SPS, forging) were used to control the microstructure of CaCu3Ti4O12. In the meantime, particular attention was paid to the nanostructural characterization of grain boundaries. For the first time, the transmission electron microscopy analysis reveals the exact nature of the copper-rich phases segregating at the grain boundaries in CaCu3Ti4O12. Finally, the structural, microstructural and physical characterizations of all the polycrystalline ceramics and the single-crystal provide new arguments in the understanding of the dielectric properties of CaCu3Ti4O12.À l’heure où la miniaturisation des composants électroniques devient un enjeu majeur dans de nombreux secteurs d’activités (automobile, aérospatial, informatique…), le développement de nouvelles familles de matériaux présentant une constante diélectrique élevée et de faibles pertes diélectriques constitue, aujourd’hui encore, un axe de recherche privilégié. C’est le cas de CaCu3Ti4O12, matériau très étudié depuis les années 2000, notamment grâce à sa permittivité relative "exceptionnelle". Les travaux présentés dans cette thèse proposent une étude originale de la synthèse et du frittage de CaCu3Ti4O12 par des procédés non-conventionnels ainsi que sa caractérisation structurale, microstructurale et physique.La première étude porte sur la synthèse conventionnelle et micro-ondes de CaCu3Ti4O12. L’intérêt du chauffage micro-ondes est d’exploiter le couplage micro-ondes/propriétés diélectriques afin de permettre une synthèse rapide de la phase tout en contrôlant sa granulométrie. Par la suite, l’étude s’est consacrée à la compréhension approfondie du frittage naturel de CaCu3Ti4O12. La densification est régie jusqu’à 80% de densité par de la diffusion aux joints de grains. Il s’ensuit au cours du processus à haute température (>1000°C) l’apparition d’une phase liquide entraînant un grossissement granulaire anormal. Le recours à différentes techniques de frittage (atmosphère contrôlée, sous charge par Spark Plasma Sintering ou forgeage) a été employé pour maîtriser la microstructure de CaCu3Ti4O12. En parallèle de cette étude, une attention toute particulière a été portée sur la caractérisation nanostructurale des joints de grains. Pour la première fois, l’analyse fine réalisée en microscopie électronique en transmission révèle la nature exacte de l’ensemble des phases riches en cuivre qui ségrégent aux joints de grains de CaCu3Ti4O12. Enfin, les caractérisations structurales, microstructurales et physiques réalisées sur l’ensemble des céramiques polycristallines et monocristaux permettent d’apporter de nouveaux arguments dans la compréhension des propriétés diélectriques de CaCu3Ti4O12

Synthèse et frittage par des procédés non conventionnels de composés diélectriques dérivés de la pérovskite de type CaCu3Ti4O12

As the miniaturization of electronic components is becoming a major issue in many business sectors (automotive, aerospace, computer sciences…), the development of new families of materials with a high dielectric constant and low dielectric losses is still a priority line of research. This is the case of CaCu3Ti4O12. This material has been studied extensively since 2000 thanks to its “exceptional” relative permittivity. The work presented in this thesis proposes an original study of the synthesis and sintering of CaCu3Ti4O12 by non-conventional processes and its structural, microstructural and physical characterization.The first study concerns the conventional and microwave synthesis of CaCu3Ti4O12. The interest of microwave heating is the good coupling between microwaves and the dielectric properties of the material. This allows a rapid synthesis of CaCu3Ti4O12 and the control of its particle size. Subsequently, the study focused on a thorough analysis of the natural sintering of this ceramic. Densification is controlled up to 80% of relative density by grain-boundary diffusion. At higher temperature, a liquid phase occurs during the sintering, resulting in abnormal grain growth. Various sintering techniques (controlled atmosphere, SPS, forging) were used to control the microstructure of CaCu3Ti4O12. In the meantime, particular attention was paid to the nanostructural characterization of grain boundaries. For the first time, the transmission electron microscopy analysis reveals the exact nature of the copper-rich phases segregating at the grain boundaries in CaCu3Ti4O12. Finally, the structural, microstructural and physical characterizations of all the polycrystalline ceramics and the single-crystal provide new arguments in the understanding of the dielectric properties of CaCu3Ti4O12.À l’heure où la miniaturisation des composants électroniques devient un enjeu majeur dans de nombreux secteurs d’activités (automobile, aérospatial, informatique…), le développement de nouvelles familles de matériaux présentant une constante diélectrique élevée et de faibles pertes diélectriques constitue, aujourd’hui encore, un axe de recherche privilégié. C’est le cas de CaCu3Ti4O12, matériau très étudié depuis les années 2000, notamment grâce à sa permittivité relative "exceptionnelle". Les travaux présentés dans cette thèse proposent une étude originale de la synthèse et du frittage de CaCu3Ti4O12 par des procédés non-conventionnels ainsi que sa caractérisation structurale, microstructurale et physique.La première étude porte sur la synthèse conventionnelle et micro-ondes de CaCu3Ti4O12. L’intérêt du chauffage micro-ondes est d’exploiter le couplage micro-ondes/propriétés diélectriques afin de permettre une synthèse rapide de la phase tout en contrôlant sa granulométrie. Par la suite, l’étude s’est consacrée à la compréhension approfondie du frittage naturel de CaCu3Ti4O12. La densification est régie jusqu’à 80% de densité par de la diffusion aux joints de grains. Il s’ensuit au cours du processus à haute température (>1000°C) l’apparition d’une phase liquide entraînant un grossissement granulaire anormal. Le recours à différentes techniques de frittage (atmosphère contrôlée, sous charge par Spark Plasma Sintering ou forgeage) a été employé pour maîtriser la microstructure de CaCu3Ti4O12. En parallèle de cette étude, une attention toute particulière a été portée sur la caractérisation nanostructurale des joints de grains. Pour la première fois, l’analyse fine réalisée en microscopie électronique en transmission révèle la nature exacte de l’ensemble des phases riches en cuivre qui ségrégent aux joints de grains de CaCu3Ti4O12. Enfin, les caractérisations structurales, microstructurales et physiques réalisées sur l’ensemble des céramiques polycristallines et monocristaux permettent d’apporter de nouveaux arguments dans la compréhension des propriétés diélectriques de CaCu3Ti4O12

Non-conventional synthesis and sintering of CaCu3Ti4O12 dielectric materials

À l’heure où la miniaturisation des composants électroniques devient un enjeu majeur dans de nombreux secteurs d’activités (automobile, aérospatial, informatique…), le développement de nouvelles familles de matériaux présentant une constante diélectrique élevée et de faibles pertes diélectriques constitue, aujourd’hui encore, un axe de recherche privilégié. C’est le cas de CaCu3Ti4O12, matériau très étudié depuis les années 2000, notamment grâce à sa permittivité relative "exceptionnelle". Les travaux présentés dans cette thèse proposent une étude originale de la synthèse et du frittage de CaCu3Ti4O12 par des procédés non-conventionnels ainsi que sa caractérisation structurale, microstructurale et physique.La première étude porte sur la synthèse conventionnelle et micro-ondes de CaCu3Ti4O12. L’intérêt du chauffage micro-ondes est d’exploiter le couplage micro-ondes/propriétés diélectriques afin de permettre une synthèse rapide de la phase tout en contrôlant sa granulométrie. Par la suite, l’étude s’est consacrée à la compréhension approfondie du frittage naturel de CaCu3Ti4O12. La densification est régie jusqu’à 80% de densité par de la diffusion aux joints de grains. Il s’ensuit au cours du processus à haute température (>1000°C) l’apparition d’une phase liquide entraînant un grossissement granulaire anormal. Le recours à différentes techniques de frittage (atmosphère contrôlée, sous charge par Spark Plasma Sintering ou forgeage) a été employé pour maîtriser la microstructure de CaCu3Ti4O12. En parallèle de cette étude, une attention toute particulière a été portée sur la caractérisation nanostructurale des joints de grains. Pour la première fois, l’analyse fine réalisée en microscopie électronique en transmission révèle la nature exacte de l’ensemble des phases riches en cuivre qui ségrégent aux joints de grains de CaCu3Ti4O12. Enfin, les caractérisations structurales, microstructurales et physiques réalisées sur l’ensemble des céramiques polycristallines et monocristaux permettent d’apporter de nouveaux arguments dans la compréhension des propriétés diélectriques de CaCu3Ti4O12.As the miniaturization of electronic components is becoming a major issue in many business sectors (automotive, aerospace, computer sciences…), the development of new families of materials with a high dielectric constant and low dielectric losses is still a priority line of research. This is the case of CaCu3Ti4O12. This material has been studied extensively since 2000 thanks to its “exceptional” relative permittivity. The work presented in this thesis proposes an original study of the synthesis and sintering of CaCu3Ti4O12 by non-conventional processes and its structural, microstructural and physical characterization.The first study concerns the conventional and microwave synthesis of CaCu3Ti4O12. The interest of microwave heating is the good coupling between microwaves and the dielectric properties of the material. This allows a rapid synthesis of CaCu3Ti4O12 and the control of its particle size. Subsequently, the study focused on a thorough analysis of the natural sintering of this ceramic. Densification is controlled up to 80% of relative density by grain-boundary diffusion. At higher temperature, a liquid phase occurs during the sintering, resulting in abnormal grain growth. Various sintering techniques (controlled atmosphere, SPS, forging) were used to control the microstructure of CaCu3Ti4O12. In the meantime, particular attention was paid to the nanostructural characterization of grain boundaries. For the first time, the transmission electron microscopy analysis reveals the exact nature of the copper-rich phases segregating at the grain boundaries in CaCu3Ti4O12. Finally, the structural, microstructural and physical characterizations of all the polycrystalline ceramics and the single-crystal provide new arguments in the understanding of the dielectric properties of CaCu3Ti4O12

Polymer Processing under Microwaves

International audienceOver the last decades, microwave heating has experienced a great development and reached various domains of application, especially in material processing. In the field of polymers, this unusual source of energy showed important advantages arising from the direct microwave/matter interaction. Indeed, microwave heating allows regio-, chemio-, and stereo-selectivity, faster chemical reactions, and higher yields even in solvent-free processes. Thus, this heating mode provides a good alternative to the conventional heating by reducing time and energy consumption, hence reducing the costs and ecological impact of polymer chemistry and processing. This review states some achievements in the use of microwaves as energy source during the synthesis and transformation of polymers. Both in-solution and free-solvent processes are described at different scales, with comparison between microwave and conventional heating

Dielectric properties of flash spark plasma sintered BaTiO3 and CaCu3Ti4O12

International audienceFlash sintering is an approach allowing reducing the sintering time to mere seconds. To improve the microstructures and the properties of flash sintered specimens, this process has been successfully adapted to pressure assisted sintering such as the spark plasma sintering. This work is the exploration of the potential of this ultra-rapid sintering process for the improvement of the dielectric properties of well-known materials such as BaTiO 3 and CaCu 3 Ti 4 O 12. In particular, we focus on the potential improvement of the dielectric loss

High-resolution FIB-TEM-STEM structural characterization of grain boundaries in the high dielectric constant perovskite CaCu3Ti4O12

International audienceIn this work, the grain boundaries composition of the polycrystalline CaCu3Ti4O12 (CCTO) was investigated. A Focused Ion Beam (FIB)/lift-out technique was used to prepare site-specific thin samples of the grain boundaries interface of CCTO ceramics. Scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray spectrometry (EDXS) and Electron Energy Loss Spectroscopy (EELS) systems were used to characterize the composition and nanostructure of the grain and grain boundaries region. It is known that during conventional sintering, discontinuous grain growth occurs and a Cu-rich phase appears at grain boundaries. This Cu-rich phase may affect the final dielectric properties of CCTO but its structure and chemical composition remained unknown. For the first time, this high-resolution FIB-TEM-STEM study of CCTO interfacial region highlights the composition of the phases segregated at grain boundaries namely CuO, Cu2O and the metastable phase Cu3TiO4

High-resolution FIB-TEM-STEM structural characterization of grain boundaries in the high dielectric constant perovskite CaCu3Ti4O12

International audienceIn this work, the grain boundaries composition of the polycrystalline CaCu3Ti4O12 (CCTO) was investigated. A Focused Ion Beam (FIB)/lift-out technique was used to prepare site-specific thin samples of the grain boundaries interface of CCTO ceramics. Scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray spectrometry (EDXS) and Electron Energy Loss Spectroscopy (EELS) systems were used to characterize the composition and nanostructure of the grain and grain boundaries region. It is known that during conventional sintering, discontinuous grain growth occurs and a Cu-rich phase appears at grain boundaries. This Cu-rich phase may affect the final dielectric properties of CCTO but its structure and chemical composition remained unknown. For the first time, this high-resolution FIB-TEM-STEM study of CCTO interfacial region highlights the composition of the phases segregated at grain boundaries namely CuO, Cu2O and the metastable phase Cu3TiO4