Thesis (Ph. D.)--University of Wisconsin--Madison. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 167-175).

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Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Aluminum (Al) powder metallurgy (PM) provides a cost effective and environmentally friendly means of creating lightweight, high performance, near net shape components, relative to conventional casting/die casting technology. Unfortunately, the current lack of commercially available Al alloy powder blends has hindered development in this field as a result of the limited scope of mechanical properties available; especially under elevated temperature conditions common to many automotive applications. As such, the objective of this research was to attempt to improve the versatility of current Al PM technology through the incorporation of Fe and Ni transition metal additions into an emerging Al- 4.4Cu-1.5Mg-0.2Sn alloy, as this technique is known to enhance the elevated temperature stability of wrought/cast Al alloys through the formation of stable, Fe/Ni aluminide dispersoids. Initial experimentation consisted of evaluating the feasibility of incorporating Fe and Ni both elementally and pre-alloyed, through a series of tests related to their PM processing behaviour (compressibility, sintering response) and sintered product performance (ambient tensile properties). Results confirmed that pre-alloying of the base Al powder was the most effective means of incorporating Fe and Ni as all such specimens achieved properties similar or slightly superior to the unmodified alloy. Of the pre-alloyed systems considered, that containing 1%Fe+1%Ni displayed the most desirable results in terms of mechanical performance and microstructural homogeneity of the Fe/Ni dispersoid phases present in the sintered product. Bars of the baseline system and that modified with pre-alloyed additions of 1Fe/1Ni were then sintered industrially to gain a preliminary sense of commercial viability and obtain additional specimens for elevated temperature exposure tests. Results confirmed that the sintering response, tensile properties and microstructures were essentially identical in both alloys whether they were sintered in a controlled laboratory setting or an industrial production environment. Furthermore, DSC data indicated that S (Al2CuMg)-type phases were the dominant precipitates formed during heat treatment. The effects of elevated temperature exposure were assessed in the final stage of research. Both alloys were found to exhibit comparable behaviour when exposed to the lowest (120°C) and highest (280°C) temperatures considered. Here, the alloys showed no obvious degradation at 120°C. Conversely, exposure at 280°C prompted a steady decline in yield strength for both alloys with significant precipitate coarsening noted as well. Despite these similarities, differences emerged during isochronal tests at intermediate temperatures. Here, DSC data indicated that the precipitates present in the pre-alloyed material were stable at temperatures up to 160°C while those in the unmodified alloy had begun to overage under the same exposure conditions. These differences were accompanied by increased stability in tensile yield strength for the pre-alloyed material. In all, this study has indicated that the use of Al powder pre-alloyed with Fe/Ni additions is feasible for press-and-sinter PM technology and that the sintered product exhibits improved elevated temperature stability under certain conditions.

Importance of clean, sustainable and renewable energy sources are increasing gradually because of either being environmental friendly or being alternative for fossil fuels. Hydrogen energy system will let the utilization of alternative energy sources. Fuel cells are the most suitable energy conversion devices while passing through the hydrogen economy. The cost of the fuel cell systems need to be reduced in order to achieve commercialization of these systems. One of the most important cost items is platinum which is used as catalyst both in anode and cathode sides of the proton exchange membrane (PEM) fuel cells. Not only is the cost of the platinum, but also the limited reservoir of the platinum is a handicap. Therefore, the utilization of the cheap replacements of platinum catalysts will accelerate the process of commercialization. Because of their highly conjugated structure and high chemical stability metalo phthalocyanines have been encouraging electrocatalytic activity for oxygen reduction. Therefore, electrocatalytic activity for oxygen reduction in fuel cells was studied with some metalo phthalocyanines and some positive effects have been observed. In this study, phthalocyanines of cobalt, iron and nickel were synthesized via phthalic anhydride-urea method and characterized by IR Spectrophotometry, X-Ray Diffractometry and Thermal Gravimetry (TGA). Catalyst materials were prepared by impregnation method such that they contain either 4% cobalt, 4% or 10% iron or 4% nickel phthalocyanines on carbon black (Vulcan XC72) structure. Impregnated catalysts were pyrolyzed at 600oC or 1000oC and cathode electrodes were prepared by these catalysts as well as unpyrolyzed ones by spraying technique. The impregnated catalysts were characterized by scanning electron microscopy (SEM) and pore structures were analyzed by surface area analyzer (by BET and BJH techniques). All of the anode electrodes were prepared by using 20% Pt containing commercial catalyst by the same technique applied for cathode electrodes. A membrane electrode assembly was also prepared by 20% Pt containing commercial catalyst on the cathode electrode. Performance characteristics of the manufactured membrane electrode assemblies were determined by means of a test station, built in Middle East Technical University Chemical Engineering Department, having a 5 cm2 test cell. The highest performance observed with the commercial membrane electrode assembly was 0.40W/cm2 at 0.5 V. Whereas, the power density obtained from the MEA manufactured at the laboratory having 0.4 mg Pt/cm2 loading both on the anode and cathode was 0.18 W/cm2 at 0.5 V. For the phthalocyanine cathodic MEAs, the highest power reached was 0.04W/cm2 which was obtained from the MEA having a loading of 0.28mg Co/cm2 prepared by using the CoPc/C catalyst pyrolyzed at 1000 oC.

The thesis is primarily concerned with the design, construction and preliminary commissioning of a novel polarimeter for full three-dimensional analysis of electron spin polarisation. The polarimeter is described in detail, together with the theoretical basis for its operation. Studies of an amorphous ferromagnetic alloy, Co66Fe4Ni1B14Si15, and its application as a secondary standard are presented. Finally, a design study of a GaAs polarised electron source, capable of providing both longitudinal and transverse polarisations, is detailed.

Made available in DSpace on 2016-12-08T17:19:19Z (GMT). No. of bitstreams: 1 Cleber P Fenili.pdf: 5079728 bytes, checksum: e3ab5832297ac591534e15390527a095 (MD5) Previous issue date: 2013-02-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This work is a study of the behavior of iron and nickel aluminides, since the high energy milling until the consolidation. Particle size and morphology of aluminides after milling and heat treatment were evaluated. A high energy milling with predetermined time and speed along with a defined stoichiometry of elemental powders were thus directed in order to obtain the intermetallic Fe3Al and Ni3Al. By obtaining the intermetallic was studied consolidation processes. The consolidation has great influence on the mechanical and microstructural properties of aluminides, motivating in recent years the study of consolidation as the density x porosity relationship. With the consolidation processes defined, which evaluates the influence of temperature, time, velocity, pressure and atmosphere. The sintering process, sintering and hot forming (S-HP) and hot pressing assisted field (FAHP) were used. The materials obtained after the consolidation processes were evaluated for density, hardness, formation of other phases and oxidation. These properties were evaluated by optical microscopy, scanning electron microscopy, vickers hardness, density, semiquantitative analysis (EDS) and X-ray diffraction. The results showed that the process FAHP is effective in consolidating the iron aluminides and nickel, for resulted in greater densification and therefore a good hardness confirming other studies using similar processes. The other cases in this study had less impressive results when compared to process FAHP, but compared to other references are considered suitable. / Neste trabalho foi realizado um estudo do comportamento dos aluminetos de ferro e níquel, desde a moagem de alta energia até a consolidação. Avaliou-se o tamanho das partículas e morfologia dos aluminetos após a moagem e tratamento térmico. A moagem de alta energia com tempo e velocidade pré determinados juntamente com uma estequiometria dos pós elementares definidos, foram assim direcionados com o intuito de obter os intermetálicos Fe3Al e Ni3Al. Com a obtenção dos intermetálicos estudou-se os processos de consolidação. A consolidação possui grande influência nas propriedades mecânicas e microestruturais dos aluminetos, motivando nos últimos anos o estudo dos processos de consolidação quanto a densidade x porosidade. Com os processos de consolidação definidos, avaliou-se a influência da temperatura, tempo, velocidade, atmosfera e pressão de compactação. Foram utilizados os processos de sinterização, sinterização e conformação a quente (S-HP) e prensagem a quente assistida por campo (FAHP). Os materiais obtidos após os processos de consolidação foram avaliados quanto a densidade, dureza, formação de outras fases e oxidação. Estas propriedades foram avaliadas através das metalografias mediante microscopia óptica, microscopia eletrônica de varredura, microdureza vickers, densidade, análise semiquantitativa (EDS) e difratometria de raios-X. Os resultados mostraram que o processo FAHP é eficaz na consolidação dos aluminetos de ferro e níquel, pois resultou em maior densificação e, por conseguinte uma boa dureza comparando com outros estudos utilizando processos parecidos. Os outros processos deste estudo obtiveram resultados menos expressivos quando comparados ao processo FAHP, porém comparados a outras referências são considerados adequados.

The purpose of this research project was to study the αᵧ phase in Alnico 6. Other phases were studies for comparison. Also the effect of an applied magnetic field on the formation of the αᵧ phase was investigated. Three single crystals of Alnico 6 were heat treated for one hour—one at 1250°C, one at 1000°C, and one at 800°C—and water-quenched. The microstructure of each sample was observed with the optical microscope, and X-ray diffraction patterns were taken to determine the crystal structure of the phases present. Several single crystal samples of Alnico 6 were heat treated at 1000°C and furnace-cooled. Some of the samples were heat treated and furnace-cooled in the presence of an applied magnetic field of about 5000Oe, and the others were heat treated and furnace-cooled without an applied magnetic field. Each set of samples were electrothinned, and the microstructure of the αᵧ and α₁ ₊ α₂ phases was studied using the electron microscope. Electron diffraction patterns and electron micrographs were taken from αᵧ regions and α₁ ₊ α₂ regions of each sample. By a combination of X-ray and electron diffraction, it was determined that the crystal structure of the α, α₁, α₂ and αᵧ phases is body-centered cubic, with a lattice parameter of 2.87 Å. Electron diffraction showed that the crystal structure of the combined α₁ ₊ α₂ phases is ordered body-centered cubic, and that the lattices of these two phases are coherent. Other investigators have found that only the α₁ phase is ordered in Alnico 5 and Alnico 8 and thus is believed be the case in Alnico 6 also. Electron diffraction showed the αᵧ phase to be ordered, with the degree of ordering less than that in the α₁ phase. Some difference was noted between the αᵧ phase formed with a magnetic field and that formed without a magnetic field. The αᵧ formed with a magnetic field showed twinning and some small lattice rotations, while stat formed without a field did not. The reason for this is not known.

Die effiziente Speicherung von elektrischer Energie im elektrochemischen System des Superkondensators wird realisiert durch die Ausrichtung von Elektrolytionen im elektrischen Feld polarisierter, poröser Kohlenstoffelektroden. Der Energieinhalt und die Leistungscharakteristika der elektrostatischen Zwischenspeicherung von Energie bei Lade- und Entladezeiten von wenigen Sekunden bis zu einigen Minuten wird entscheidend durch die Eigenschaften der zur Ladungsspeicherung genutzten Grenzfläche zwischen dem Elektrodenmaterial und dem Elektrolyten bestimmt. Für die Optimierung des Energieinhaltes und der Leistungscharakteristika von Superkondensatoren durch die rationale Modifizierung dieser Grenzfläche konnten entscheidende Trends herausgearbeitet werden. Durch Einbindung eines pseudokapazitiven Eisenoxids in die spezifische Oberfläche des mesoporösen CMK-3 im Redoxverfahren ist die Darstellung einer neuartigen Nanokompositstruktur möglich. Diese weißt eine dreifach höhere spezifische Kapazität im Vergleich zur nicht-modifizierten Kohlenstoffoberfläche unter Beibehaltung der Strombelastbarkeit der Kohlenstoffmatrix auf. Entscheidend für die Weiterentwicklung von Synthesestrategien und die anwendungsorientierte Optimierung für Nanokompositstrukturen ist deren ausführliche Charakterisierung mittels angepasster Verfahren. Die in dieser Arbeit erstmals zur Analyse von porösen CMK-3 basierten Nanokompositstrukturen verwendeten Methoden der Aufnahme eines Tiefenprofils mittels Auger Elektronen Spektroskopie (DP-AES) und der energiegefilterten Transmissionselektronenmikroskopie (EF-TEM) lieferten die Grundlage zur Weiterentwicklung der rationalen, nanoskaligen Grenzflächenfunktionalisierung. In einem weiteren, stark vereinfachten und effektiveren Verfahren der Schmelzimprägnierung der porösen Matrix mit Nitrathydraten, sowie deren anschließendes Kalzinieren zum Übergangsmetall, respektive pseudokapazitiven Übergangsmetalloxid, konnte eine nochmals optimierte Nanokompositstruktur dargestellt werden. Das entwickelte Verfahren wurde für die Einbettung von Nickel/Nickeloxid und Eisen/Eisenoxid in die Oberfläche des mesoporösen CMK-3 eingesetzt. Ein gesteigerter Energieinhalt, wie auch eine deutlich gesteigerte Stabilität der Kapazität bei hohen Strombelastungen für die resultierenden Elektrodenmaterialien konnte eindeutig nachgewiesen werden. Die signifikante Erhöhung der Leistungscharakteristika ist dabei auf die optimale Kontaktierung des Übergangsmetalloxids durch das Übergangsmetall als Leitfähigkeitsadditiv im Sinne einer Kern-Schale Struktur realisiert. Der für das Nanokomposit C-FeO10 berechnete Kapazitätsverlust von < 11 % bei Erhöhung der spezifischen Stromstärke von 1 A/g auf 10 A/g verdeutlicht die beeindruckende Strombelastbarkeit des Materials. In einem weiteren in dieser Arbeit diskutierten Ansatz zur Steigerung des Energieinhaltes eines Superkondensators wurde auf die Verwendung von Ionischen Flüssigkeiten (IL) als Elektrolyt eingegangen. Die gezielte Darstellung eines oberflächenmodifizierten aus Cabiden gewonnen Kohlenstoffmaterials (CDC) unter Beibehaltung der Textur des porösen Systems ermöglichte die Untersuchung des Einflusses der Oberflächencharakteristika des Elektrodenmaterials auf die Strombelastbarkeit des Energiespeichers. Es konnte klar herausgestellt werden, dass für den vielversprechenden IL-Elektrolyten EMIBF4 eine verminderte Polarität, sowie die Abwesenheit azider Protonen an der Oberfläche des Kohlenstoffs deutlich zur Steigerung der Strombelastbarkeit des Speichers beiträgt. Realisiert wurde die Modifizierung der Oberfläche durch deren Chlorierung. Die Einordnung der vielversprechenden Kombinationen aus maßgeschneiderten Elektrodenmaterialien und Elektrolytsystemen wurde anhand der Kenngrößen im Ragone-Diagramm vorgenommen. Die Ergebnisse der Arbeit reihen sich in die derzeit schnell voranschreitende Technologieentwicklung bei Superkondensatoren ein.