Browsing by Subject "3DOM"

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    Advances in nanostructured materials via templated sol-gel structure control and self-assembly
    (2015-04) Rudisill, Stephen Gabriel
    This dissertation describes a body of work focused on understanding and improving morphology control of nanoporous structures via their aqueous chemistry. Synthesis of materials was carried out primarily using the Pechini process with metal nitrates and colloidal crystal templates. CeO2 and CeO2-derived compounds were used for a substantial portion of the dissertation as they are useful for thermochemical cycling experiments. Templated CeO2 shows a tenfold improvement over an untemplated material as well as a nanoparticle powder under lab-scale thermochemical cycling experiments.The Pechini process itself was then investigated as a means to obtain greater structural control over colloidal crystal templated materials. The process was demonstrated to involve phase separation, which allowed for the production of microspheres and bicontinuous networks of templated CeO2-based solids. Microspheres produced were between 1-3 µm in size, with polydispersity less than 15%. Further experimentation demonstrated that this phase separation methodology was generalizable to Fe2O3 and Mn3O4, though higher polydispersities were obtained for these materials.The final research project accomplished in this dissertation involves a method to produce ordered collagen fibrils through the incorporation of nanocrystalline cellulose during fibrillogenesis. Results were verified via scanning electron microscopy and a mechanism was proposed based on infrared spectroscopy results indicating a decrease in collagen-collagen hydrogen bonding.
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    Metallis photonic crystals for proposed applications as thermal emission devices.
    (2009-08) Denny, Nicholas Ryan
    Incandescent lighting is highly inefficient. One possible solution is to replace the traditional filament with an ordered photonic crystal filament that will increase the efficiency of the lamp. This work details steps towards the fabrication of such a filament with the fabrication of monolithic three-dimensionally ordered macroporous (3DOM) metallic photonic crystals. The 3DOM metallic materials produced in this work were comprised of W, Mo and alloys of those materials. The 3DOM W materials were produced from the precursors tungsten(VI) chloride, tungsten(V) ethoxide, tungstic acid, peroxotungstic acid, ammonium metatungstate (AMT) and an acetylated peroxotungstic acid (APTA). 3DOM Mo was produced from the precursors ammonium molybdate (AMo) and an acetylated peroxomolybdic acid (APMoA). To fabricate 3DOM W/Mo materials combinations of precursors of AMT and AMo were utilized or a combination of the syntheses APTA and APMoA to create APTA/APMoA was employed. A variety of synthetic conditions were optimized to produce large monolithic pieces of 3DOM W and 3DOM W/Mo with dimensions of up to 1×1×0.3 cm3. These conditions included varying the solvent mixture, precursor concentrations, reduction conditions and precursor infiltration technique. The 3DOM metallic monoliths were tested for thermal stability using both joule heating and radiant heating techniques in N2 atmospheres. Joule heating at 40 W for 15 min destroyed the nanostructure of the material. Radiant heating was employed to study the grain coarsening. At 800 ºC the 3DOM W monolith exhibited grain coarsening and needle formation caused by H2O in the system. Needle formation could be eliminated by rigorous evacuation or by the incorporation of Mo as an alloy. 3DOM W/Mo alloys at 95:5 wt% maintained their nanostructure and relative grain size at 800 ºC but were coarsened at 1000 ºC. At both temperatures the material did not produce needles even in the presence of minute amounts of water. The effect of Mo on the nanostructure was studied by in situ TEM heating to 1000 ºC. In 3DOM W/Mo alloys it is postulated that the Mo has a pinning effect on the dislocations in the structure. These methods provide a route towards fabricating 3DOM metallic photonic crystals for thermal emission.