Master-Arbeit Univ. St. Gallen, 2006.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1973. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

Thesis (M.S.)--University of Wisconsin--Madison, 1983. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 147-152).

Thesis (M.S.)--University of Wisconsin--Madison, 1984. / Two maps on 2 folded leaves in pocket. Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 70-76).

Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 135-151).

Thesis (Ph. D.)--University of Chicago, 1917. / "Private Edition, Distributed by the University of Chicago Libraries, Chicago, Illinois." "Reprinted from the Astrophysical journal, vol. XLVII, no. 2, March 1918." Includes bibliographical references. Also available on the Internet.

Made available in DSpace on 2014-06-11T19:25:35Z (GMT). No. of bitstreams: 0 Previous issue date: 1997Bitstream added on 2014-06-13T18:53:42Z : No. of bitstreams: 1 mazon_t_me_araiq.pdf: 5981721 bytes, checksum: 910c63ec572ce810427ab47fe2d31f25 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O método de Pechini bem como o uso da adição simultânea de partículas sementes (BaTiO3 ou PbTiO3) e de solução dopante contendo íons Ba2+ e Ti4+ ou Pb2+ e Ti4+ foram usados para preparar o niobato de zinco e chumbo (PZN). Com a finalidade de se estudar a influência do tamanho das partículas sementes na obtenção da fase PZN perovskita estável e na microestrutura da cerâmica, trabalhou-se com dois intervalos de tamanhos das partículas sementes: 1- entre 40 nm < φ < 100 nm, denominadas sementes de menor tamanho (frequência de 1015 partículas por cm3); 2- entre 100 nm< φ < 900 nm, denominadas sementes de maior tamanho (frequência de 1013 partículas por cm3). Os difratogramas de raios X obtidos para as amostras calcinadas a 800 oC ou a 900 oC permitiram identificar a formação das fases perovskita e pirocloro, sendo que a 900 oC predomina a fase perovskita. As amostras preparadas com as sementes de maior tamanho, menor frequência de núcleos cristalinos, apresentaram maior porcentagem de fase pirocloro que as preparadas com as sementes de menor tamanho após a calcinação. Os pós foram compactados isostaticamente e sinterizados entre 950 a 1100 oC. Para a sinterização utilizou-se um sistema fechado contendo atmosfera de pó de PbZnO3 + 5% PbO para controlar a evaporação do chumbo estequiométrico, durante a sinterização. A forma na qual os aditivos foram adicionados ao polímero (se como íons ou como sementes), assim como a frequência de núcleos cristalinos influeciaram no processo de sinterização e na microestrutura desenvolvida. As amostras preparadas com as sementes de maior tamanho exigiram uma temperatura mais elevada para a sinterização e apresentaram uma microestrutura mais heterogênea que as amostras preparadas com as sementes de menor tamanho. A microestrutura dos compactos obtidos a partir de pós contendo 50% dos aditivos na forma... / Pechini method as well as the simultaneous addition of seeds particles (BaTiO3 or PbTiO3) and dopant solutions containing Ba2+ and Ti4+ or Pb2+ and Ti4+ were used to prepare the perovskite phase of lead zinc niobate (PZN). To study the influence of seed particle size in the formation of stable PZN phase and in the ceramic microstructure, two range of seed particle size were considered: a) in the range of 30 to 100 nm, named small seed particles (frequency of 1015 particles/cm3); and b) in the range of 50 to 900 nm, named large seed particles (frequency of 1013 particles/cm3). The perovskite and pyroclore phases were identified for powder calcined at 800 oC and at 900 oC with predominance of perovskite phase for powder calcined at 900 oC. Powders prepared with large seed particles, smaller crystalline nuclei frequency, showed large amount of pyroclore phase after calcining, compared with the powder prepared with small size seeds. Calcined powders were isostaticaly pressed and sintered at temperatures ranging from 900 to 1100 oC. A close system containing powder with PbZnO3 + 5 PbO, to control the lead evaporation from the compacted samples, was used during sintering. Both, the way in which the additives were added to the polymer (seeds or ions) as well as the crystalline nuclei frequency influenced in the sintering process and in the microstructure. Samples prepared with large seeds need higher temperatures for sintering and showed a more heterogeneous microstructure compared with samples prepared with small seed particles. The microstructure of ceramics prepared for powder containing 50% of additives as seed and 50% of additives as ions is more homogeneous. The microstructure of ceramics obtained from powders containing 80% of additives as seeds and 20% as ions showed grains with well-defined crystalline planes. All the sintered samples showed a second phase segregated to the grain boundary...(Complete abstract click electronic access below)

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The instrumentation for digitally driven electrochemical experiments has been developed. Software has been written for experimental control and high speed data aquisition. The digital control methods were successfully used in the study of the electrochemistry of the porous lead electrode (the lead-acid battery negative plate), over an extended temperature range. The effects of a number of commercially pertenent additives have been studied at reduced temperatures. These reaction enhancing materials (expanders) have been studied in detail on both planar and porous lead electrode in sulphuric acid in the range 1M to 5M. Deductions concerning the energetics of the reactions have been made from experimental results. The modes of action of certain expanders are discussed. It was concluded that on the plane lead surface solution phase expander materials modify the mechanism of the lead sulphate electrocrystallisation - the current limiting reaction. This was an effect on the solid state process although a solution Pb2+ process was identified (for the first time) in battery strength acid. Electrode incorporated organic expander materials act by modifying pore geometies and reaction penetration depths. The current transients due to electrocrystallization in porous lead are very complex and require very sophisticated modelling techniques to provide a useful fit.