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Estudo de sinterizacao de ceramicas a base de nitreto de silicio utilizando-se como aditivos oxidos de cerio e aluminioMARCHI, JULIANA 09 October 2014 (has links)
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06503.pdf: 8504108 bytes, checksum: e88a1b46ff6da2a80eea392ae1bc6867 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Obtencao e caracterizacao de ceramicas no sistema Si-Al-O-N-C empregando pirolise de misturas de polissiloxano e cargasROCHA, ROSA M. da 09 October 2014 (has links)
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09621.pdf: 29120771 bytes, checksum: 09052cbfc1e575071c4639bed85d4176 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Estudo da influencia das caracteristicas do po de nitreto de silicio sobre a sinterabilidade e propriedades mecanicas do sinterizadoROCHA, JOSE C. da 09 October 2014 (has links)
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06008.pdf: 6005614 bytes, checksum: 5159bd3fe200e19625451d226c3d83a2 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Desenvolvimento de compositos refratarios SiC-AlN e SiC-SiAlONMAKUNTUALA, KEVA 09 October 2014 (has links)
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06875.pdf: 3426497 bytes, checksum: f67e7359c8137f84a2c63219a3f4ce7a (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Efeito da adicao do ferro e do silicio na densificacao microestructura e propriedades mecanicas do nitreto de silicioDUAILIBI FILHO, JAMIL 09 October 2014 (has links)
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05588.pdf: 8394403 bytes, checksum: 33b933f7290f619b3b70e1fecfad5373 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Cinetica e mecanismo de oxidacao de ceramicas a base de nitreto de silicio com adicao de terras rarasMORAIS, DANIEL S. 09 October 2014 (has links)
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06123.pdf: 4547052 bytes, checksum: 48ec616978a4d951011d14b673b5caa2 (MD5) / Dissertacao (Mestrado) / IEA/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Estudos de sinterizacao e caracterizacao de Sisub(3)Nsub(4) tendo como aditivos Ndsub(2)Osub(3)-Ysub(2)Osub(3)-Alsub(2)Osub(3)COUTINHO, ANA C. de S. 09 October 2014 (has links)
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07014.pdf: 5588197 bytes, checksum: b7528ce22235ffd98fe5cb5f8e558a7f (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Current transport in hydrogenated amorphous silicon nitrideMorgan, B. A. January 2000 (has links)
A defect band is formed in hydrogenated amorphous silicon nitride (a-SiNx:H) due to current stressing of the material. This gives rise to an increase in conductivity, referred to as current induced conductivity. This thesis investigates the current transport mechanisms that occur in the induced defect band, by comparing the temperature dependence of the conductivity of several sets of a-SiNx:H thin film diodes. These sets were systematically current stressed to different levels with one set remaining unstressed. Samples with energy gaps of 2.06 eV and 2.28 eV were considered. We show that around room temperature a modified Poole-Frenkel description of conduction (i.e. field enhanced hopping of carriers via charged defect states) provides a good fit to the data. Using this model the activation energy of current transport was calculated and shown to depend on the material band gap. Data fitting to the Poole-Frenkel model provided further support for the field-assisted hopping mechanism. Previous investigations had suggested that the defect band resides in the lower half of the band gap, so that current transport through the defect band was then expected to be due to the movement of holes, in a manner consistent with Poole-Frenkel conduction. By considering samples grown on p-type and n-type substrates, we demonstrated that transport was indeed the result of the movement of holes through the defect states within the induced defect band. At lower temperatures the experimental data is poorly described by a modified Poole-Frenkel type process, so further mechanisms were considered, including variable-range hopping and nearest-neighbour hopping. Due to the similar nature and slight temperature dependence of each process, differentiating between the two mechanisms proved difficult. However, other factors such as the temperature range and defect density favoured variable-range hopping transport. By assuming this form of low temperature hopping transport, conduction through the defect-band of the a-SiNx:H, could then be convincingly explained over the entire temperature range from 320 K to 20 K in terms of two dominant transport mechanisms, Poole-Frenkel conduction and variable-range hopping.
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Desenvolvimento de composito ceramico a partir de mistura de alumina e polimero pecursor ceramico polissilsesquioxano / Development of ceramic composites from mixture of alumina and ceramic precursor polymer poly (silsesquioxane)MACHADO, GLAUSON A.F. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:26:46Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:59:55Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Desenvolvimento de composito ceramico a partir de mistura de alumina e polimero pecursor ceramico polissilsesquioxano / Development of ceramic composites from mixture of alumina and ceramic precursor polymer poly (silsesquioxane)MACHADO, GLAUSON A.F. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:26:46Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:59:55Z (GMT). No. of bitstreams: 0 / O processamento de materiais cerâmicos, a partir de pirólise de polímeros precursores, tem sido intensivamente pesquisado no decorrer das últimas décadas, devido às vantagens que esta via proporciona, como: temperaturas de processo inferiores as das técnicas convencionais; controle da estrutura em nível molecular; possibilidade de síntese de grande variedade de compostos cerâmicos; obtenção de peças semi-acabadas; etc. O processo de pirólise controlada de polímero e carga ativa (AFCOP-active filler controlled polymer pyrolysis) possibilita a síntese de compósitos cerâmicos, por meio de reação entre cargas adicionadas (óxidos, metais, intermetálicos, etc.) e produtos sólidos e gasosos, provenientes da decomposição polimérica. Com base neste processo, no presente trabalho foram confeccionadas amostras de alumina, contendo adições de 10 e 20% em massa, de polímero precursor polissilsesquioxano. Estas foram pirolisadas a 900°C e tratadas termicamente em temperaturas de 1100, 1300 e 1500ºC, empregando-se taxa de aquecimento de 5°C/ min. e atmosfera de N2. As amostras foram caracterizadas em relação à densidade aparente, porosidade e dureza, após cada etapa de tratamento térmico. As transformações estruturais foram analisadas por difração de raios X, microscopia eletrônica de varredura e espectroscopia de infravermelho. As amostras tratadas até 1300°C resultaram em compósitos de alumina e oxicarbeto de silício, enquanto as tratadas a 1500°C, formaram compósitos de mulita e alumina. Na amostra da composição com 20% de polímero, se observou início de densificação em torno de 800°C e alta taxa de retração foi obtida a 1400°C. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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