scholarly journals A Rapid Supercritical Extraction Process for the Production of Silica Aerogels

1996 ◽  
Vol 431 ◽  
Author(s):  
J. F. Poco ◽  
P. R. Coronado ◽  
R. W. Pekala ◽  
L. W. Hrubesh
Keyword(s):  
Lawrence Livermore National Laboratory ◽  
National Laboratory ◽  
Lower Surface ◽  
Extraction Process ◽  
Silica Aerogels ◽  
Supercritical Extraction ◽  
Surface Areas ◽  
Transmission Electron ◽  
Near Net Shape ◽  
Rapid Supercritical Extraction

AbstractSilica aerogels are a special class of porous materials in which both the pore size and interconnected particle size have nanometer dimensions. This structure imparts unique optical, thermal, acoustic, and electrical properties to these materials. Transmission electron microscopy and small angle x-ray scattering show that this nanostructure is sensitive to variations in processing conditions that influence crosslinking chemistry and growth processes prior to gelation. Recently, Lawrence Livermore National Laboratory (LLNL) has demonstrated that a Rapid Supercritical Extraction (RSCE) process can be used to prepare near-net shape silica aerogels in hours rather than days. Preliminary data from RSCE silica aerogels show that they have improved mechanical properties and slightly lower surface areas than their conventionally dried counterparts, while not compromising their optical and thermal performance.

Hydrophobic silica aerogels prepared via rapid supercritical extraction

2009 ◽  
Vol 53 (2) ◽  
pp. 199-207 ◽  
Author(s):  
Ann M. Anderson ◽  
Mary K. Carroll ◽  
Emily C. Green ◽  
Jason T. Melville ◽  
Michael S. Bono
Keyword(s):  
Silica Aerogels ◽  
Supercritical Extraction ◽  
Hydrophobic Silica ◽  
Rapid Supercritical Extraction

Optimization of the rapid supercritical extraction process for aerogels

2002 ◽  
Vol 311 (3) ◽  
pp. 259-272 ◽  
Author(s):  
George W Scherer ◽  
Joachim Gross ◽  
Lawrence W Hrubesh ◽  
Paul R Coronado
Keyword(s):  
Extraction Process ◽  
Supercritical Extraction ◽  
Rapid Supercritical Extraction

scholarly journals Direct Comparison between Modeling and Experiment: an α-Fe Ion Implantation Study

2000 ◽  
Vol 650 ◽  
Author(s):  
Jaime Marian ◽  
Brian D. Wirth ◽  
J. Manuel Perlado ◽  
T. Diaz de la Rubia ◽  
Robin Schäublin ◽  
...  
Keyword(s):  
Kinetic Monte Carlo ◽  
Lawrence Livermore National Laboratory ◽  
National Laboratory ◽  
Positron Annihilation Spectroscopy ◽  
Characterization Methods ◽  
Transmission Electron ◽  
Computational Capability ◽  
The Matrix ◽  
Positron Lifetimes ◽  
Fe Ions

ABSTRACTAdvances in computational capability and modeling techniques, as well as improvements in experimental characterization methods offer the possibility of directly comparing modeling and experiment investigations of irradiation effects in metals. As part of a collaboration among the Instituto de Fusión Nuclear (DENIM), Lawrence Livermore National Laboratory (LLNL) and CIEMAT, single and polycrystalline α-Fe samples have been irradiated with 150 keV Fe- ions to doses up to several dpa. The irradiated microstructure is to be examined with both transmission electron microscopy (TEM) and positron annihilation spectroscopy (PAS). Concurrently, we have modeled the damage accumulation in Fe under these irradiation conditions using a combination of molecular dynamics (MD) and kinetic Monte Carlo (KMC). We aim to make direct comparison between the simulation results and the experiments by simulating TEM images and estimating positron lifetimes for the predicted microstructures. While the identity of the matrix defect features cannot be determined from TEM observations alone, we propose that both large self-interstitial loops, trapped at impurities within the material, and small, spherical nanovoids form.

Synthesis and Characterization of Copper-Nanoparticle-Containing Silica Aerogel Prepared via Rapid Supercritical Extraction for Applications in Three-Way Catalysis

MRS Advances ◽  
2017 ◽  
Vol 2 (57) ◽  
pp. 3485-3490 ◽  
Author(s):  
Ann M. Anderson ◽  
Elizabeth A. Donlon ◽  
Adam A. Forti ◽  
Vinicius P. Silva ◽  
Bradford A. Bruno ◽  
...  
Keyword(s):  
Silica Aerogel ◽  
Silica Aerogels ◽  
Supercritical Extraction ◽  
X Ray Diffraction ◽  
Initial Oxidation ◽  
Catalytically Active ◽  
Show Evidence ◽  
Rapid Supercritical Extraction ◽  
Three Way Catalysis

ABSTRACTCopper-alumina and copper-silica aerogels formed by impregnation of a copper(II) salt into an alumina or silica wet gel before supercritical extraction have been found to contain copper in multiple oxidation states: Cu0, Cu+1 and Cu+2. These aerogels are effective at catalyzing the reduction of NO and the oxidation of HCs and CO under conditions similar to those found in automotive three way catalysts. In this work we have developed a preparation method incorporating Cu0, Cu+1 and Cu+2 nanoparticles directly into silica aerogels. Nanoparticles in the form of (a) Cu0 nanorods (100 nm diameter, 10-20 μm length); (b) Cu+1 nanoparticles (350 nm diameter); and (c) Cu+2 nanoparticles (25-55 nm diameter) were added (0.5-15% by weight) to separate precursor mixtures consisting of tetramethyl orthosilicate, methanol, water and ammonia. These precursor mixtures were then processed using a rapid supercritical extraction (RSCE) method to form aerogels. The resulting aerogels show evidence of nanoparticles dispersed throughout the silica aerogel structure. Addition of Cu+1 and Cu+2 nanoparticles decreases the surface area of the aerogels significantly. X-Ray diffraction shows that regardless of initial oxidation state of the nanoparticles, crystalline Cu0 is detected after RSCE processing to 290 °C. Following heat treatment at 700 °C, crystalline Cu+2 is detected. The copper containing silica aerogels are found to be catalytically active with light-off temperatures (50% conversion) for NO and CO at 400 °C in three-way catalytic applications.

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