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31	Investigação do processo de obtenção de aluminatos de bário e cálcio para construção e caracterização de catodos termiônicos impregnados para a aplicação em dispositivos de microondas de potência HIGASHI, CRISTIANE 09 October 2014 (has links) Made available in DSpace on 2014-10-09T12:52:11Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:49Z (GMT). No. of bitstreams: 0 / O presente trabalho descreve os processos de preparação do aluminato de bário e cálcio, material emissor de elétrons, empregados nos catodos do tipo impregnado para utilização em uma válvula de microondas do tipo TWT. Os catodos investigados constituem-se de uma pastilha de tungstênio porosa impregnada com aluminato de bário e cálcio com proporção molar 5:3:2. Para a síntese do aluminato, utilizaram-se três diferentes métodos: reação em estado sólido, precipitação e cristalização. A termogravimetria auxiliou na consolidação dos procedimentos de preparação dos aluminatos de modo a definir os parâmetros de pirólise/calcinação. Verificou-se que a técnica que apresentou melhores características de síntese foi o método da cristalização, pois esta apresentou uma menor temperatura de formação do aluminato (800ºC) em atmosfera oxidante (O2), quando comparada às técnicas de reação em estado sólido e de precipitação (temperatura de 1000ºC em atmosfera redutora H2). Utilizou-se o conceito da distribuição da função trabalho prática (PWFD) de Miram para a caracterização termiônica dos catodos impregnados. Empregando-se este método, foi possível traçar o perfil termiônico do catodo com aluminato de bário e cálcio. As curvas PWFD apresentaram a função trabalho média do catodo aluminato de, aproximadamente, 2,00 eV. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP aluminates barium calcium tungsten cathodes thermionic emitters travelling wave tubes x-ray diffraction infrared spectra spectroscopy thermal gravimetric analysis scanning electron microscopy x-ray fluorescence analysis
32	Vliv velikosti částic a způsobu přípravy na hydrataci vápenato-hlinitých fází / The influence of particle size and methods of preparation of calcium aluminate phases on their hydration Ohaňka, Zdeněk January 2018 (has links) This work focuses on the hydration of four calcium aluminate phases – C3A, C12A7, CA and CA2. Above all, the influence of particle size and method of preparation on hydration behaviour were studied. Influence of these factors on hydration products were also investigated. Calcium aluminates were prepared by solid state synthesis and amorphous citrate method. Both methods were described in detail. The particle size was determined by laser diffraction. Isothermic calorimetry was used to investigate the process of hydration. Hydration products were identified by X-ray diffraction analysis and simultaneous thermogravimetric and differential thermal analysis.
33	Functionalization of carbon-bonded ceramic foam filters with nano-scaled materials for steel melt filtration Storti, Enrico 23 April 2018 (has links) (PDF) In order to improve the purity of steel castings, the use of special reactive coatings on carbon-bonded ceramic foam filters was explored. Carbon nanotubes were dispersed in water by means of ultrasonic treatment, using xanthan gum to stabilize the nanotubes in suspension and control the rheological behavior. The coatings were applied by cold spraying and binding was achieved during heat treatment in reducing atmosphere, thanks to an artificial pitch added to the slurry. The coated filters were successfully immersed in molten steel for different times. The thickness of the first alumina layer generated at the interface was independent of the immersion time: concentration gradients through its thickness suggested that the formation of this structure is limited by diffusion. Investigation of the steel after solidification by means of ASPEX showed that the presence of the coating influenced the size as well as the chemical composition of the remaining inclusions. Nano-coated filters had the best filtration efficiency (up to 95% for alumina inclusions after 10 s), but longer tests resulted in worse performance. In addition, coatings based on calcium aluminates in combination with carbon showed an efficiency greater than 97% for steel samples taken directly from the melt. Filtration Stahlschmelze Einschlüsse Keramikschaumfilter kohlenstoffgebundenes Aluminiumoxid CNTs Calciumaluminate Elektrospinnen Magnesiumborat Filtration Steel melt Inclusions Ceramic foam filters Carbon-bonded alumina CNTs Calcium aluminates Electrospinning Magnesium borate ddc:620 Metallschmelze Filtration Schaumkeramik Aluminiumoxide Kohlenstoff Calciumaluminate
34	Functionalization of carbon-bonded ceramic foam filters with nano-scaled materials for steel melt filtration Storti, Enrico 23 March 2018 (has links) In order to improve the purity of steel castings, the use of special reactive coatings on carbon-bonded ceramic foam filters was explored. Carbon nanotubes were dispersed in water by means of ultrasonic treatment, using xanthan gum to stabilize the nanotubes in suspension and control the rheological behavior. The coatings were applied by cold spraying and binding was achieved during heat treatment in reducing atmosphere, thanks to an artificial pitch added to the slurry. The coated filters were successfully immersed in molten steel for different times. The thickness of the first alumina layer generated at the interface was independent of the immersion time: concentration gradients through its thickness suggested that the formation of this structure is limited by diffusion. Investigation of the steel after solidification by means of ASPEX showed that the presence of the coating influenced the size as well as the chemical composition of the remaining inclusions. Nano-coated filters had the best filtration efficiency (up to 95% for alumina inclusions after 10 s), but longer tests resulted in worse performance. In addition, coatings based on calcium aluminates in combination with carbon showed an efficiency greater than 97% for steel samples taken directly from the melt. info:eu-repo/classification/ddc/620 ddc:620

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