Home About us Contact
|
Home About us Contact | ||
|
|
||
Flame Spray Pyrolysis (flame + spray_pyrolysi)
Selected AbstractsFlame-Synthesized Ceria-Supported Copper Dimers for Preferential Oxidation of COADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Richard Kydd Abstract Rapid synthesis of CuCeO2 catalysts by flame spray pyrolysis produces highly active Cu dimer morphologies without the need for additional catalyst pretreatment. The active Cu component is enriched onto the CeO2 surface at concentrations higher than the nominal loading with no evidence of amorphous or crystalline CuO phase. Increasing the Cu content results in a morphological transition from isolated Cu monomers to oxygen-bridged dimers and an associated increase in oxygen vacancy concentration. Dimer-containing CuCeO2 catalysts display high levels of activity and selectivity in the low-temperature preferential oxidation of CO. Experimental measurements and simulations suggest that the geometry of the dimer presents a comparatively ionic CuO bond at the catalyst surface. Further studies indicate that these ionic dimer species promote preferential CO oxidation at lower temperatures than observed for monomeric Cu species. This is the first report to explicitly propose and demonstrate that the structural distortion associated with the formation of Cu dimers directly induces increased bond ionicity at the catalyst surface and that these changes are responsible for improved catalytic activity. [source] Transparent Nanocomposites of Radiopaque, Flame-Made Ta2O5/SiO2 Particles in an Acrylic Matrix,ADVANCED FUNCTIONAL MATERIALS, Issue 5 2005H. Schulz Abstract Mixed Ta2O5 -containing SiO2 particles, 6,14,nm in diameter, with closely controlled refractive index, transparency, and crystallinity are prepared via flame spray pyrolysis (FSP) at production rates of 6.7,100,g,h,1. The effect of precursor solution composition on product filler (particle) size, crystallinity, Ta dispersity, and transparency is studied using nitrogen adsorption, X-ray diffraction, optical microscopy, high-resolution transmission electron microscopy (HRTEM), and diffuse-reflectance infrared Fourier-transform spectroscopy (DRIFTS). Emphasis is placed on the transparency of the composite that is made with Ta2O5/SiO2 filler and dimethylacrylate. Increasing Ta2O5 crystallinity and decreasing Ta dispersity on SiO2 decreases both filler and composite transparencies. Powders with identical specific surface area (SSA), refractive index (RI), and Ta2O5 content (24,wt.-%) show a wide range of composite transparencies, 33,78,%, depending on filler crystallinity and Ta dispersity. Amorphous fillers with a high Ta dispersity and an RI matching that of the polymer matrix lead to the highest composite transparency, 86,%. The composite containing 16.5,wt.-% filler that itself contains 35,wt.-% Ta2O5 has the optimal radiopacity for dental fillings. [source] Pressureless Sintering t -zirconia@,-Al2O3 (54 mol%) Core,Shell Nanopowders at 1120°C Provides Dense t -Zirconia-Toughened ,-Al2O3 NanocompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2010Min Kim Zirconia-toughened alumina (ZTA) is of growing importance in a wide variety of fields exemplified by ZTA prosthetic implants. Unfortunately, ZTA composites are generally difficult to process because of the need to preserve the tetragonal zirconia phase in the final dense ceramic, coincident with the need to fully densify the ,-Al2O3 component. We report here that liquid-feed flame spray pyrolysis of mixtures of metalloorganic precursors of alumina and zirconia at varying compositional ratios provide access in one step to core,shell nanoparticles, wherein the shell is ,-Al2O3 and the core is a perfect single crystal of tetragonal (t -) zirconia. Pressureless sintering studies provided parameters whereby these nanopowder compacts could be sintered to full density (>99%) at temperatures just above 1100°C converting the shell component to ,-Al2O3 but preserving the t -ZrO2 without the need for any dopants. The final average grain sizes of these sintered compacts are ,200 nm. The resulting materials exhibit the expected response to mechanical deformation with the subsequent production of monoclinic ZrO2. These materials appear to offer a low-temperature, low-cost route to fine-grained ZTA with varied Al2O3:t -ZrO2 compositions. [source] Synthesis and Characterization of Mixed-Metal Oxide Nanopowders Along the CoOx,Al2O3 Tie Line Using Liquid-Feed Flame Spray PyrolysisJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2006Jose Azurdia We report here the use of liquid-feed flame spray pyrolysis (LF-FSP) to produce a series of nanopowders along the CoOx,Al2O3 tie line. The 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 alumatrane [Al(OCH2CH2)3N] and a cobalt precursor, made by reacting Co(NO3)2·6H2O crystals with propionic acid. The compositions of the as-produced nanopowders were controlled by selecting the appropriate ratios of the precursors. Nine samples with compositions (CoO)y(Al2O3)1,y, y=0,1 along the CoOx,Al2O3 tie line were prepared and studied. The resulting nanopowders were characterized by X-ray fluorescence, BET, scanning electron microscopy, high-resolution transmission electron micrographs, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and FTIR. The powders typically consist of single-crystal particles <40 nm diameter and specific surface areas (SSAs) of 20,60 m2/g. XRD studies show a gradual change in powder patterns from ,-Al2O3 to Co3O4. The cobalt aluminate spinel phase is observed at stoichiometries (21 and 37 mol%) not seen in published phase diagrams, likely because LF-FSP processing involves a quench of >1000°C in microseconds frequently leading to kinetic rather than thermodynamic products. Likewise, the appearance of Co3O4 rather than CoO as the end member in the tie line is thought to be a consequence of the process conditions. TGA studies combined with diffuse reflectance FTIR spectroscopic studies indicate that both physi- and chemi-sorbed H2O are the principal surface species present in the as-processed nanopowders. The only sample that differs is Co3O4, which has some carbonate species present that are detected and confirmed by a sharp mass loss event at ,250°C. The thermal behavior of the high cobalt content samples differs greatly from the low cobalt content samples. The latter behave like most LF-FSP-derived nanopowders exhibiting typical 1%,4% mass losses over the 1400°C range due mostly to loss of water and some CO2. The high cobalt content samples exhibit a sharp mass loss event that can be attributed to the decomposition of Co3O4 to CoO. [source] | ||||||||||