Thesis (M.S.)--Rochester Institute of Technology, 1991. / Typescript. Includes bibliographical references (leaves 235-252).

Thesis (M.S.)--University of Wisconsin--Madison, 1968. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--Florida State University, 2006. / Advisor: Amy B. Chan-Hilton, Florida State University, College of Engineering, Dept. of Civil and Environmental Engineering. Title and description from dissertation home page (viewed Sept. 18, 2006). Document formatted into pages; contains xiii, 116 pages. Includes bibliographical references.

Made available in DSpace on 2018-08-01T21:58:48Z (GMT). No. of bitstreams: 1 tese_10827_Dissertação Jenifer Rigo Almeida - FINAL.pdf: 2105933 bytes, checksum: 17fccc5751be81765e75282388ce4b0c (MD5) Previous issue date: 2017-03-27 / Baterias de íon-Lítio (LIBs) exauridas são consideradas resíduos sólidos perigosos devido à presença de metais e compostos orgânicos em sua composição, representando desperdício de recursos naturais não renováveis e de metais valiosos quando descartadas. Este trabalho tem por objetivo fornecer dados quantitativos sobre a composição química do material ativo do cátodo (MAC) de diferentes LIBs exauridas visando monitorar variações com o passar dos anos e auxiliar nos processos de reciclagem do material. Os elementos Al, Co, Cr, Cu, Ga, Li, Mg, Mn, Ni, Ti e Zn foram determinados por espectrometria de emissão óptica com plasma indutivamente acoplado (ICP OES) após lixiviação ácida empregando 2,0 mol.L-1 de ácido cítrico (HCit) e H2O2 (0,25 mol.L-1) como alternativa ambientalmente favorável. As condições otimizadas para adequação do meio às curvas analíticas foram: para Al, Cu: Curva de HCit diluído 10 vezes sem padrão interno (PI); para Co, Li, Mn, Ni: Curva de HCit diluído 500 vezes sem PI; para Ga, Zn: Curva de HCit diluído 10 vezes com Y. O procedimento analítico empregado alcançou limites de detecção de 0,01 mg.L-1 para Al; 0,20 mg.L-1 para Co; 0,006 mg.L-1 para Cr; 0,02 mg.L-1 para Cu; 0,004 mg.L-1 para Ga; 0,02 mg.L-1 para Li; 0,0005 mg.L-1 para Mg; 0,07 mg.L-1 para Mn; 0,70 mg.L-1 para Ni; 0,0005 mg.L-1 para Ti e 0,007 mg.L-1 para Zn. A exatidão do procedimento foi confirmada por testes de adição e recuperação dos analitos obtendo-se valores entre 92-113 %. Os elementos majoritários Co (43-67 % m/m), Li (5,3-6,8 % m/m), Mn (0,8-8,2 % m/m), Ni (0,1-11,7 % m/m) e Al (0,06-3,2 % m/m) e os elementos minoritários Cr (0,0005-0,002 % m/m), Cu (0,01-0,05 % m/m), Mg (0,005-0,02 % m/m), Ti (0,001-0,07 % m/m), Ga (0,0009-0,03 % m/m) e Zn (0,009-0,05 % m/m) demonstraram que a composição do MAC pode variar de acordo com a capacidade e ano de fabricação. As baterias mais antigas foram as que apresentaram maiores teores de Co e Li. As baterias de menor capacidade foram as que continham os maiores teores de Mn e Ni, indicando que o Co foi substituído. O pó do MAC e o resíduo após lixiviação foram caracterizados por difratometria de raios X (DRX) obtendo-se LiCoO2 como composto principal, podendo ser reutilizado.

Les systèmes d'imagerie à rayons X (RX) sont des appareils volumineux et contraignants en termes de contrôle du faisceau. L'industrie des tubes électroniques est donc à la recherche de solutions pour assurer la stabilité du courant tout en permettant la miniaturisation du système.Ce travail opte pour l'amélioration de la source d'électrons, en remplaçant l'émission thermoïonique historique par l'émission de champ. En particulier, les cathodes froides à base de nanotubes de carbone possèdent l'avantage de pouvoir délivrer de forts courants (>1A/cm^2), tout en ayant un faible temps de réponse.A travers le développement d'une structure innovante de cathodes à nanotubes de carbone à grille intégrée, l'objectif de cette étude est de réaliser des sources commutables et régulées, pour des sources de rayons X miniatures, portables ou polyvalentes.La modélisation électrostatique de la nouvelle structure a conduit à la fabrication de cathodes à grille optimisées, sur lesquelles est cru un réseau vertical de nanotubes de carbone. L'analyse de défaillance permet finalement d'obtenir des dispositifs isolés fiables. Leur caractérisation en émission de champ indique des performances de modulation de courant inégalées, de l'ordre de 10^6 pour +/-40V de polarisation de grille. La régulation du courant a également été démontrée avec l'obtention d'une stabilité à 0,02% sur 100 h.Pour pallier les limitations rencontrées (courant de fuite et croissance parasite), une structure de grille enterrée a été proposée avec succès, ainsi qu'une nouvelle méthode de fabrication d'émetteurs courts et fins. Ces cathodes fonctionnelles ont finalement été intégrées en tube à rayons X et ont montré pour la première fois une modulation de courant de 2000 à une haute tension fixe de 60 kV. / This work chooses to improve the electron source by replacing thermionic emission with field emission. More especially, carbon nanotubes based cold cathodes stand out by their ability to supply high currents (>1A/cm^2) while responding fast.Through the development of an innovative structure of in-plane gated carbon nanotube based cathode, this study aims at making switchable and regulated sources for miniature, portable or polyvalent X-rays sources.The electrostatic modelling of the new structure led to the fabrication of optimized gated cathodes, where a vertically aligned array of carbon nanotubes is grown. Default analysis allows to get reliable insulated devices.Field emission characterization shows unprecedented current modulation of 10^6 at +/-40V bias voltage. Current regulation is also achieved with a stability of 0.02% over 100 h.Another structure with a burried gate electrode was designed to successfully cope with leak current and parasitic growth. A new way of growing short and thin nanotubes was tackled.Finally, gated cathodes were integrated in a compact X-ray tube and showed a current modulation of 2000 at a high voltage of 60 kV.

Indiana University-Purdue University Indianapolis (IUPUI) / Recent innovations in portable electronics, electric vehicles and power generation by wind and solar have expanded the need for effcient battery storage. Lithium-ion batteries have been the frontline contender of battery storage yet are not able to match current demands. Alternatively, lithium-sulfur batteries are a promising technology to match the consumer demands. Elemental sulfur cathodes incur a variety of problems during cycling including the dissolution of intermediate lithium polysul- fides, an undesirable volume change (~ 80%) when completely reduced and a high dependence on liquid electrolyte, which quickly degrades the cell's available energy density. Due to these problems, the high theoretical capacity and energy density of lithium sulfur cells are unattainable. In this work, A new class of phenyl polysul- fides, C6H5SxC6H5(4 < x <6), are developed as liquid sulfur containing cathode materials. This technology was taken a step further to fulfill and emerging need for exible electronics in technology. Phenyl tetrasulfide (C6H5S4C6H5) was polymerized to form a high energy density battery with acute mobility. Lithium half-cell testing shows that phenyl hexasulfide (C6H5S6C6H5) can provide a specific capacity of 650mAh/g and capacity retention of 80% through 500 cycles at 1C rate along with superlative performance up to 10C. Furthermore, 1, 302W h/ kg and 1, 720W h/L are achievable at a low electrolyte/active material ratio. Electrochemical testing of polymer phenyl tetrasulfide reveals high specific capacities of 634mAh /g at 1C, while reaching 600mAh /g upon mechanical strain testing. This work introduces novel cathode materials for lithium-sulfur batteries and provides a new direction for the development of alternative high-capacity flexible cathode materials.

This is Part B of the Thesis. / <p> The design and performance of a flat emitting ring on-axis electron gun suitable for use in a small reflected beam accelerator was investigated. The design constraints include a low emittance (approximately 5π cm mrad), and a small beam size with a focus approximately 13 cm from the emitting surface.</p> <p> A suitable geometry was determined theoretically and was tested with a dispenser cathode. A beam with a focus at 12.7 ± 1 cm and an emittance of approximately 7π cm mrad was obtained. However, the dispenser cathode response time to heater current changes is too large for the required gun current control.</p> <p> Experiments were done to study the mechanical and thermal properties of flat emitting foil rings, since a directly heated foil has a fast response time. Two foils were tested: 1.27 x 10^-3 cm thick tungsten and 4.57 x 10^-4 cm thick tantalum. The present simple design requires impractically thin foils (≤ 0.25 microns thick) to reach emission temperatures at feasible heater currents.</p> / Thesis / Master of Engineering (MEngr)

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