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dc.contributor.authorSchoenbeck, Lauraen_US
dc.date.accessioned2005-07-28T17:53:19Z
dc.date.available2005-07-28T17:53:19Z
dc.date.issued2005-03-24en_US
dc.identifier.urihttp://hdl.handle.net/1853/6855
dc.description.abstractReservoir-type dispenser hollow cathodes are currently being developed for use on NASAs Prometheus 1 mission. In these cathodes, the reaction between a barium source material and tungsten powder contained in a cavity surrounding a porous tungsten emitter produces barium vapor which is crucial to operation of the cathode. The primary objective of this research was to investigate the reactions between tungsten and a commercial barium source material in a simulated reservoir hollow cath-ode environment. Mixtures of tungsten and a barium calcium aluminate material were sealed inside molybdenum capsules with porous tungsten closures and heated to 1000?1200?and 1300?or 100, 200, and 400 hours. Based on the reaction products, which were identified to be BaAl2O4 and Ba2CaWO6, a reaction was proposed for the barium calcium aluminate material with tungsten. The bottom pellets in the capsules were found to have reacted to a much further extent than the top pellets in all of the samples, possibly due to a temperature gradient or excessive moisture in the base of the capsules. Quantita-tive and semi-quantitative x-ray analysis results did not show a clear trend as to how the concentrations of BaAl2O4 and Ba2CaWO6 vary with time. Most of the barium source materials are hygroscopic, and hydration of the materi-als would substantially reduce the performance of the cathode. Therefore, the environ-mental stability of several barium compounds, 3BaO??2O3 (B3A), 6BaO????2O3 (612), 4BaO????O3 (411), Ba2.9Ca1.1Al2O7 (B4ASSL), and Ba3Sc4O9, were investi-gated in order to evaluate their suitability for use as barium source materials. A micro-balance was used to measure weight gain of the materials as they were exposed to dew points of ??C and 11?t room temperature. The results showed that B3A hydrated more extensively than any of the other materials tested in the low- and intermediate-humidity environments, while the 612, 411, and B4ASSL materials were all reasonably stable in the low-humidity environment. The Ba3Sc4O9 was extremely stable compared to the barium aluminates in the intermediate-humidity conditions.en_US
dc.format.extent5767138 bytes
dc.format.mimetypeapplication/pdf
dc.language.isoen_US
dc.publisherGeorgia Institute of Technologyen_US
dc.subjectReservoir hollow cathodeen_US
dc.subjectBarium source material
dc.subject.lcshSpace vehicles Electric propulsion systemsen_US
dc.subject.lcshTungstenen_US
dc.subject.lcshBarium compoundsen_US
dc.subject.lcshCathodesen_US
dc.subject.lcshNuclear propulsionen_US
dc.titleInvestigation of Reactions between Barium Compounds and Tungsten in a Simulated Reservoir Hollow Cathode Environmenten_US
dc.typeThesisen_US
dc.description.degreeM.S.en_US
dc.contributor.departmentMaterials Science and Engineeringen_US
dc.description.advisorCommittee Chair: Dr. D. Norman Hill; Committee Member: Dr. Joe K. Cochran, Jr.; Committee Member: Dr. Robert F. Speyeren_US


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