UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Functionally Coated Faceted Aluminum Nanocrystals: Aerosol Synthesis and Reactivity(2013) Kaplowitz, Daniel Alan; Zachariah, Michael R; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The demand for large scale manufacture of nanoaluminum for use in propellant applications has motivated research into development of an aerosol production scheme. In addition, the reactive nature of aluminum in the presence of oxygen has inspired investigation into functionally coating bare nanoaluminum prior to exposure to the atmosphere. Faceted aluminum crystals are fabricated in the aerosol phase via thermal pyrolysis of triisobutylaluminum, a low temperature gas-phase synthesis route, and combustion tests of oxygen passivated product in thermite combination show an increase in energy release compared to commercial nanoaluminum. Three different coatings on this bare nanoaluminum are developed: a decoration of Ni/Ni2O3 particles by thermal decomposition of Ni(CO)4, a homogeneous layer of Fe3O4 by thermal decomposition of Fe(CO)5, and a monolayer of perfluoropentanoic acid via bridge bonding between aluminum and carboxylate groups. X-ray photoelectron spectroscopy analysis indicates that the metal oxide coatings have facilitated formation of an expanded aluminum oxide layer during an air bleed, but perfluoropentanoic acid has successfully passivated aluminum. The protection from significant oxide formation for the perfluoropentanoic acid coating is evident in a 16% increase in active fuel content by thermogravimetric analysis compared to the untreated case. Subsequent temperature jump fine wire combustion tests show decreased ignition temperatures for all three coatings. Combustion chamber tests in thermite combinations display poor pressure output for the Ni/Ni2O3 coated case, but reasonable response for the Fe3O4 product. Flame ignition of perfluoropentanoic acid coated product is shown to produce AlF3 by chemical analysis of char, indicating the passivation coating also functions in direct oxidizer delivery.Item Synthesis and Characterization of Low-Valent Aluminum and Gallium Compounds from Aluminum (I) and Gallium (I) Precursors(2011) Mayo, Dennis Hansel; Eichhorn, Bryan W; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this thesis the design, assembly, and operation of a metal halide co- condensation reactor capable of generating metastable solutions of aluminum and gallium monohalides is described. In this reactor, gas-phase molecules are co-condensed with a mixed solvent at 77 K and the resultant metastable solutions are stored at 198 K. Upon warming, these solutions undergo disproportionation reactions to form metalloid cluster compounds. The optimization of multiple reactor settings for monohalide generation is described. The efficacy of the reactor was validated by reproducing the synthesis of large clusters of Ga and Al; namely [Al77(NTMS2)20]2- and [Ga12Br2(GaBrNTMS2)10]2- which were first described by Schnockel et al. In order to better understand the challenges of low-valent aluminum and gallium chemistry a comprehensive literature review is presented. This review describes the synthetic pathways by which low-valent aluminum and gallium compounds are prepared, as well as in-depth discussion of structural and spectroscopic properties of these compounds. Two new low oxidation state Al3 clusters have been prepared by the reaction of lithium phosphides with metastable AlCl*Et2O. Both of these compounds have the general formula Li2[Al3(PR2)6]*2 Et2O (where R = C6H5 or C6H11) and formally contain Al+1.3 ions . These compounds have been characterized by X-ray diffraction and their paramagnetic nature probed by 1H NMR (Evans method) and EPR spectroscopy. The aluminum hydride cluster [Al3H6]2- has been modeled by DFT calculations (6-31G*, Hyperchem) to visualize the molecular orbitals in the [Al3(PR)6]2- clusters. The preparation of three novel aluminum (III) amidinate compounds is described. These compounds (Al(PhC(NiPr)2)3, Al(PhC(NiPr)2)2Cl, and Al(PhC(NCy)2)2Cl) are formed as the result of ligand-exchange and disproportionation processes that occur during the reaction of lithium amidinates with metastable AlCl*Et2O. The synthesis of the gallium dimer Ga2Br4*2 PHCy2 is also described.Item GAS PHASE SYNTHESIS OF ALUMINUM AND CORE-SHELL NICKEL-IRON OXIDE NANOPARTICLES(2009) Pines, Daniel; Zachariah, Michael; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this master's thesis I will address the design of two aluminum and one nickel-iron oxide core-shell nanoparticle reactors, as well as the selection of the chemical precursors' triethylaluminum (TEA), aluminum trichloride, nickel carbonyl, and iron pentacarbonyl. This research provides evidence for the generation of aluminum oxide passivated aluminum nanoparticles from TEA, the failure to completely dissociate aluminum trichloride, and the successful growth of iron oxide (shell) onto nickel (core) nanoparticles. Reactions and synthesis are carried out in gas phase allowing the use of specialized aerosol sampling and characterization techniques. In addition to studying the particle in situ, TEM and EDS measurements are preformed post collection. Motivation for this work is driven by the nanoparticle's enhanced performance when used in explosive and propellants.