Jose Azurdia

High-throughput screening of nanoparticle catalysts made by flame spray pyrolysis as hydrocarbon/NO oxidation catalysts.

We describe here the use of liquid-feed flame spray pyrolysis (LF-FSP) to produce high surface area, nonporous, mixed-metal oxide nanopowders that were subsequently subjected to high-throughput screening to assess a set of materials for deNO(x) catalysis and hydrocarbon combustion. We were able to easily screen some 40 LF-FSP produced materials. LF-FSP produces nanopowders that very often consist of kinetic rather than thermodynamic phases. Such materials are difficult to access or are completely inaccessible via traditional catalyst preparation methods. Indeed, our studies identified a set of Ce(1-x)Zr(x)O(2) and Al(2)O(3)-Ce(1-x)Zr(x)O(2) nanopowders that offer surprisingly good activities for both NO(x) reduction and propane/propene oxidation both in high-throughput screening and in continuous flow catalytic studies. All of these catalysts offer activities comparable to traditional Pt/Al(2)O(3) catalysts but without Pt. Thus, although Pt-free, they are quite active for several extremely important emission control reactions, especially considering that these are only first generation materials. Indeed, efforts to dope the active catalysts with Pt actually led to lower catalytic activities. Thus the potential exists to completely change the materials used in emission control devices, especially for high-temperature reactions as these materials have already been exposed to 1500 degrees C; however, much research must be done before this potential is verified.

Systematic synthesis of mixed-metal oxides in NiO–Co3O4, NiO–MoO3, and NiO–CuO systems via liquid-feed flame spray pyrolysis

We report here on the systematic synthesis of three nanopowder series along the NiO–Co3O4, NiO–MoO3, and NiO–CuO tie lines. Sixteen individual samples were produced via liquid-feed flame spray pyrolysis (LF-FSP) and analyzed by SSA, SEM, EDX, FTIR, TGA-DTA, and XRD. The LF-FSP process is a general aerosol combustion synthesis route to a wide range of lightly agglomerated oxide nanopowders. The materials reported here were produced by aerosolizing ethanol solutions of propionate and ammonium molybdate precursors synthesized by reacting the metal nitrate with propionic acid. Particular ratios of the precursors were selected to control the compositions of the samples produced. The powders typically consist of single crystal particles <35 nm in diameter and with specific surface areas (SSAs) of 20–50 m2 g−1. X-Ray powder diffraction (XRD) studies show a gradual change in their patterns from pure NiO to pure MOx (M = Co, Mo, Cu). Most compositions yielded single phase materials but mixed phase materials were also detected. We believe that higher vapor pressures of the ions produced for the transition metals studied resulted in SSAs about a third lower than those measured typically in nanopowders containing NiO. The partial pressure of O2 in LF-FSP affects the formation of particular oxide phases and controls to a certain degree the morphologies of the as-produced materials. We observe in the NiO–MoO3 system preferential growth of certain crystallographic planes in MoO3, due to the relatively high vapor pressure of MoOx species. Unusual particle morphologies seen in the NiO–Co3O4 system are attributed to some phase separation in the as-produced materials. TGA studies combined with diffuse reflectance infrared Fourier transform (DRIFT) spectroscopic studies indicate that both physi- and chemi-sorbed H2O are the principal surface species present in the as-processed nanopowders.

Ultraviolet emission and Fano resonance in doped nano-alumina

Emission properties of Al2O3 nanopowders, synthesized by flame spray pyrolysis with Mg, Cr, and Sc dopants, are investigated, principally in the protein lysing range of 250–290nm (UV-C band). As expected, point defect densities depend on crystal phase and irradiation history and strongly influence emission properties at short wavelengths. Ultraviolet and visible emission intensities of aggregated point defect centers change upon electron beam exposure at high current densities, but ultraviolet emission from point defects is persistently enhanced over a narrow range of Mg-doped Al2O3 compositions slightly off spinel stoichiometry. At 40% Mg concentration, emission intensities at 320nm rise by over an order of magnitude after beam exposure. Quantum efficiency for cathodoluminescence in the 250–300nm range nevertheless remains low. Point defect ionization at high currents shifts the emission of Al2O3 nanopowders to the infrared and is shown to be correlated with a ubiquitous Fano resonance in ionized Cr-vaca...

Roll your own – nano-nanocomposite capacitors

Commercial and liquid-feed flame spray pyrolysis (LF-FSP) processed nano-BaTiO3 with average particle sizes (APSs) of 50 nm were mixed with [glycidylSiMe2OSiO1.5]8 (OG, Q cage epoxy) and diaminodiphenylmethane (DDM) at loadings of 30, 40 and 50 vol% (69, 77 and 83 wt%) to form nano-nanocomposites. We demonstrate processing flexible films at 10–13 μm thicknesses on a variety of substrates but especially 40 μm thick aluminum foil. The octafunctional glycidyl silica cage epoxy resin combines very high flexibility needed for rolling with the potential to impart good-to-excellent breakdown voltages and hence higher energy densities. Nanopowders and cast films with and without nano-BaTiO3 were characterized by FTIR, TGA, SEM, XRD etc. The dielectric constants of the cast films were also characterized providing dielectric constants (loss tangents) of 18 (0.05), 21 (0.06) and 16 (0.11) for 30, 40 and 50 vol% films, respectively at 100 KHz. Only 30 and 40 vol% films were cast on Al foil for processing to wound capacitors as 50 vol% films exhibited excessive porosity resulting from agglomeration induced during curing/coating of the resin. Rolled capacitors were fabricated by simply stacking two strips of nanocomposite cast Al foil and rolling them around a metal rod used as a mandrel. The found energy storage of the capacitors ranged from 80–90 nanofarads (33–37 nF cm−2) whereas that of equivalent biaxially oriented polypropylene (BOPP) capacitors at the same thicknesses would exhibit only 9–12 nanofarads (4–5 nF cm−2) at similar voltages. Current work provides the first example of a rolled BaTiO3/epoxy nanocomposite capacitor with excellent potential for replacing commercially available counterparts. Furthermore, the potential to achieve much higher energy densities through further optimization suggests the possibility of reducing the dimensions of any given capacitor.