When 9:00 AM - 11:00 AM Sep 30, 2015
Where 1032 FXB
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Liquid-Feed Flame Spray Pyrolysis Synthesis of Oxide Nanopowders for the Production of Ceramic Composites


Nathan Taylor
Thesis Defense

Richard Laine, advisor

 

Aerosol based particle synthesis methods produce kilotons of single metal oxides annually, but these methods are unable to produce high quality mixed-metal oxides. Liquid-feed flame spray pyrolysis (LF-FSP) offers access to mixed-metal oxide nanopowders through combustion and rapid quenching (< 100 ms) of metalloorganic precursors dissolved in alcohols. Studies on LF-FSP operating parameters revealed flame temperatures in agreement with adiabatic flame temperatures. Flame spray of alcohols with increasing heats of combustion provided longer combustion flames, resulting in increased particle size for studies of TiO2, Al2O3, and Y2O3 nanopowders. Nanopowder phases are independent of flame residence time as combustion time scales are less than those required to reach thermodynamic phases.


In immiscible oxide systems, LF-FSP offers access to novel particle morphologies. LF-FSP synthesis of WO3-TiO2 nanopowders produced TiO2 cores encapsulated in WO3 shells, which are a result of the high vapor pressure of WO3. LF-FSP powders in the CuO-TiO2 system showed a nanocomposite nanoparticle morphology with separate crystallites coexisting within the same particle, as CuO vapor pressure is not high enough to remain as a vapor in the flame.


LF-FSP produces high-quality mixed metal-oxide nanopowders ideal for powder processing. Here we describe two approaches to single phase and composite materials: mixing of single metal oxide nanopowders, and nanopowders having the exact composition. Through these two processing approaches, we investigate the effect of the initial length scale of mixing on phase evolution and final microstructures. For extruded Y3Al5O12 (YAG) tubes made from LF-FSP nanopowders, mixed single metal oxide nanopowders sintered to finer grain sizes (500 ± 30 nm) at lower temperatures than the exact composition nanopowders, which was determined to be a result of significant densification before full transformation to the YAG phase. The same processing scheme was extended to sintering of YAG/α-Al2O3 composites, where mixing of single metal oxide nanopowders (1000 ± 380 nm grain size) again outperformed nanopowders of the exact composition. Finally, a third phase, yttria stabilized zirconia (YSZ), was added to produce YAG/α-Al2O3/YSZ composites. In this system, nanocomposite nanopowders containing all three phases sintered to finer grain sizes (410 ± 170 nm) than mixed single metal oxide powders. In addition, TEM showed the as-produced nanostructured nanoparticles exist as novel three-phase particles. In a separate exercise, single-phase metastable Al2O3 rich spinels with the composition MO•3Al2O3 where M = Mg, Ni, and Co were sintered to produce dense MAl2O4/α-Al2O3 composites. Mixed MAl2O4 + Al2O3 nanopowders sintered to microstructures that had equivalent grain sizes (1000 ± 400 nm) to those from single phase powders. These results suggest particle morphology and initial length scale of phase mixing play a significant role in densification despite final grain sizes orders of magnitude larger than the starting materials.