Browsing by Subject "Aluminum oxide"
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Item Combustion behavior of nano-composite aluminum iron oxide(Texas Tech University, 2004-05) Plantier, KeithBum rates of nano-scale aluminum (Al) powders mixed with iron oxide (Fe2O3) were measured as a function of Fe2O3 synthesis technique and fuel/oxidizer composition. Three reactant synthesis techniques were examined; two focused on sol-gel processing of nano-scale Fe2O3 particles and the third utilized commercially available nano-scale Fe203 powder. Nano-scale aluminum particles (52.7 nm in diameter) were combined with each oxidizer in various proportions. One goal was to determine the equivalence ratio corresponding to the maximum bum rate. The bum rates of five different nanocomposites of Al/Fe203 were compared. Flame propagation was studied by igniting low density mixtures and taking data photographically with a high-speed camera. Both open and confined burning was examined. Results indicated that the bum rate was a strong function of the stoichiometry of the mixture. An Equivalence ratio of 1.4 provides an optimum bum rate regardless of oxidizer synthesis technique. The magnitude of the bum rate is also a strong function of the oxidizer synthesis technique. Oxidizers processed using the sol-gel technology originally contained impurities which retarded the bum rates. When the same oxidizers were annealed at high temperatures, the new heat-treated oxidizer showed a dramatic improvement, with bum rates on the order of 900 m/s. The results of this work ultimately optimized the sol-gel synthesis process for preparing thermites.Item Design, fabrication and characterization of nonometer-scale variable-geometry MIM tunnel junctions(Texas Tech University, 2004-12) McKinney, Elizabeth A.There is growing interest in a phenomenon known as magnetoresistance in such applications as high-density hard disk drives and magnetic read-heads. The structure used in these applications is a tunnel junction containing ferromagnetic materials and an insulating barrier tunnel oxide. The turmel oxide is typically an Aluminum oxide (AI2O3) film. The growth process for anodic AI2O3 was developed and characterized. Nonmagnetic tunnel junction test structure were designed and fabricated to test the electrical characteristics of the tunnel oxide. Current-voltage plots obtained from devices of different oxide thickness and area were used to determine the tunneling mechanism and to investigate possible fringe effects.Item Evaluation of an activated alumina sorption system for removal of fluoride from water(Texas Tech University, 1983-05) Onuoha, Ukiwo ObasiNot availableItem Synthesis and characterization of nanocomposite alloy anodes for lithium-ion batteries(2012-05) Applestone, Danielle Salina; Manthiram, Arumugam; Goodenough, John; Mullins, Charles; Stevenson, Keith; Meyers, JeremyLithium-ion batteries are most commonly employed as power sources for portable electronic devices. Limited capacity, high cost, and safety problems associated with the commercially used graphite anode materials are hampering the use of lithium-ion batteries in larger-scale applications such as the electric vehicle. Nanocomposite alloys have shown promise as new anode materials because of their better safety due to higher operating potential, increased energy density, low cost, and straightforward synthesis as compared to graphite. The purpose of this dissertation is to investigate and understand the electrochemical properties of several types of nanocomposite alloys and to assess their viability as replacement anode materials for lithium-ion batteries. Tin and antimony are two elements that are active toward lithium. Accordingly, this dissertation is focused on tin-based and antimony-based nanocomposite alloy materials. Tin and antimony each have larger theoretical capacities than commercially available anodes, but the capacity fades dramatically in the first few cycles when metallic tin or antimony is used as the anode in a lithium-ion battery. This capacity fade is largely due to the agglomeration of particles in the anode material and the formation of a barrier layer between the surface of the anode and the electrolyte. In order to suppress agglomeration, the active anode material can be constrained by an inactive matrix of material that makes up the nanocomposite. By controlling the surface of the particles in the nanocomposite via methods such as the addition of additives to the electrolyte, the detrimental effects of the solid-electrolyte interphase layer (SEI) can be minimized, and the capacity of the material can be maintained. Moreover, the nanocomposite alloys described in this dissertation can be used above the voltage where lithium plating occurs, thereby enhancing the safety of lithium-ion batteries. The alloy anodes in this study are synthesized by high-energy mechanical milling and furnace heating. The materials are characterized by X-ray diffraction, scanning and transmission electron microscopies, and X-ray photoelectron spectroscopy. Electrochemical performances are assessed at various temperatures, potential ranges, and charge rates. The lithiation/delithiation reaction mechanisms for these nanocomposite materials are explored with ex-situ X-ray diffraction. Specifically, three different nanocomposite alloy anode materials have been developed: Mo3Sb7-C, Cu2Sb-Al2O3-C, and Cu6Sn5-TiC-C. Mo3Sb7-C has high gravimetric capacity and involves a reaction mechanism whereby crystalline Mo3Sb7 disappears and is reformed during each cycle. Cu2Sb-Al2O3-C with small particles (2 - 10 nm) of Cu2Sb dispersed in the Al2O3-C matrix is made by a single-step ball milling process. It exhibits long cycle life (+ 500 cycles), and the reversibility of the reaction of Cu2Sb-Al2O3-C with lithium is improved when longer milling times are used for synthesis. The reaction mechanism for Cu2Sb-Al2O3-C appears to be dependent upon the size of the crystalline Cu2Sb particles. The coulombic efficiency of Cu2Sb-Al2O3-C is improved through the addition of 2 % vinylethylene carbonate to the electrolyte. With a high tap density of 2.2 g/cm3, Cu6Sn5-TiC-C exhibits high volumetric capacity. The reversibility of the reaction of Cu6Sn5-TiC-C with lithium is improved when the material is cycled above 0.2 V vs. Li/Li+.