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Theses and Dissertations - Department of Metallurgical and Materials Engineering

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Browsing Theses and Dissertations - Department of Metallurgical and Materials Engineering by Author "Bao, Yuping"

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    Fundamental studies on electrochemical production of dendrite-free aluminum and titanium-aluminum alloys
    (University of Alabama Libraries, 2010) Pradhan, Debabrata; Reddy, R. G.; University of Alabama Tuscaloosa
    A novel dendrite-free electrorefining of aluminum scrap was investigated by using AlCl_3 -1-Ethyl-3-methyl-imidazolium chloride (EMIC) ionic liquid electrolyte. Electrodeposition of aluminum were conducted on copper/aluminum cathodes at voltage of 1.5 V, temperatures (50-110ºC), stirring rate (0-120 rpm), molar ratio (MR) of AlCl_3 :EMIC (1.25-2.0) and electrode surface modification (modified/unmodified). The study was focused to investigate the effect of process variables on deposit morphology, cathode current density and their role in production of dendrite-free aluminum. The deposits were characterized using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Modified electrodes and stirring rate (60 rpm) eliminate dendritic deposition by reducing cathode overpotential below critical overpotential (-0.54 V) for dendrite formation. Pure aluminum (>99%) was deposited with current efficiency of 84-99%. Chronoamperometry study was conducted using AlCl_3 -EMIC and AlCl_3 -1-Butyl-3-methyl-imidazolium chloride (BMIC) (MR = 1.65:1) at 90ºC to understand the mechanism of aluminum electrodeposition and find out diffusion parameter of electroactive species Al_2 C_7 ^- . It was concluded that electrodeposition of aluminum is a diffusion controlled instantaneous nucleation process and diffusion coefficient of Al_3 C_7 ^- was found to be 5.2-6.9 × 10-11 m^2 /s and 2.2 × 10-11 m^2 /s for AlCl_3 -EMIC and AlCl_3 -BMIC, respectively. A novel production route of Ti-Al alloys was investigated using AlCl_3 -BMIC-TiCl_4 (MR = 2:1:0.019) and AlCl_3 -BMIC (MR = 2:1) electrolytes at constant voltages of 1.5-3.0 V and temperatures (70-125°C). Ti sheet was used as anode and cathode. Characterization of electrodeposited Ti-Al alloys was carried out using SEM, EDS, XRD and inductively coupled plasma-optical emission spectrometer (ICP-OES). Effect of voltage and temperature on cathode current density, current efficiency, composition and morphology of Ti-Al alloys were determined. The Ti-Al alloys containing about 13-27 atom % Ti were produced using both electrolytes. The current efficiency of AlCl_3 -BMIC was varies between 79-87%. But lower current efficiency (25-38%) was obtained for AlCl_3 -BMIC-TiCl_4 electrolytes due to the formation of TiCl_3 passive layer on the electrodes. To increase the productivity, constant current method (160-210 A/m^2 ) was implemented. This fundamental study on low temperature production of dendrite-free aluminum and Al-Ti alloys is not only efficient but also opens a novel route in aluminum and titanium process metallurgy.
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    On the chemical synthesis of manganese-based high Magneocrystalline anisotropy energy density magnetic nanoparticles
    (University of Alabama Libraries, 2013) Zhang, Lei; Thompson, Gregory B.; Nikles, David E.; University of Alabama Tuscaloosa
    Chemical synthesis routes for two Mn-based high magnetocrystalline anisotropy energy density (K_u) nanoparticles (MnBi nanoparticles and MnAl nanoparticles) and other nanoparticles including BiClO, Bi, Mn, and Al nanoparticles were developed. The MnBi and MnAl nanoparticles have great potential for ultrahigh density magnetic recording applications as well as high energy permanent magnets applications. Bi, Mn, and Al nanoparticles were studied as building blocks of the binary nanoparticle and also because of their own distinctive properties. Bi nanoparticles were synthesized by the reduction of BiCl_3 by 1,2-hexadecanediol. In the presence of moisture, BiClO nanorods were formed. With trioctylphosphine surfactant, faceted Bi nanoparticles with large particle size variation were formed. With oleic acid surfactant, spherical Bi nanoparticles 4.7 nm ± 0.3 nm were synthesized. The reduction with n-butyllithium as a reducing agent resulted in complete reduction of BiCl_3 but large particle size variation. Mn nanoparticles were synthesized with two precursors, MnCl_2 and Mn_2 (CO)_10. The as-synthesized Mn nanoparticles were covered with a layer of low crystallinity MnO due to surface oxidation. Larger particles showed the metallic α-Mn core and low crystallinity MnO shell, while small particles only showed low crystallinity MnO. It was not clear if the smaller particles had an amorphous metal core. Coating the Mn nanoparticles with Au can form a Mn/Au core/shell structure and provided oxidation resistance to the Mn. Al nanoparticles was produced by decomposition of triisobutylaluminum. Binding of the perfluoroundecanoic acid surfactant to the nanoparticle surface was confirmed by FT-IR. MnBi nanoparticles were synthesized in sequential reduction/decomposition method and seed mediated growth method. MnBi nanoparticles with pure Bi nanoparticles were formed in both methods. Magnetic measurements detected ferromagnetic or superparamagnetic phases in the products, indicating the formation of MnBi with small crystallite size. MnAl nanoparticles were synthesized by co-reduction of MnCl_2 and AlCl_3 with strong reducing agent n-butyllithium. The as-synthesized nanoparticles were roughly monodisperse with a size of 4.6 nm ± 0.6 nm. The composition of the co-reduction method products was also in the range of the ferromagnetic τ-phase MnAl, with an average composition of Mn_56 Al_44. However, τ-phase MnAl was not found in the sample both before and after annealing by XRD and magnetic measurement. Evaporation of Al and oxidation of Mn affected the stoichiometry of the nanoparticles and inhibited the formation of τ-phase MnAl.