| Abstract
| - Low-density, high-surface-area (600−700 m2/g) alumina aerogel monoliths were prepared through the addition of propylene oxide to aqueous or ethanolic solutions of hydrated aluminum salts, AlCl3·6H2O or Al(NO3)3·9H2O, followed by supercritical drying. With this technique, the anion of the Al(III) salt used in the sol−gel reaction had a significant impact on the physical properties of the condensed alumina phase.
- Alumina aerogels were prepared through the addition of propylene oxide to aqueous or ethanolicsolutions of hydrated aluminum salts, AlCl3·6H2O or Al(NO3)3·9H2O, followed by drying with supercriticalCO2. This technique affords low-density (60−130 kg/m3), high-surface-area (600−700 m2/g) aluminaaerogel monoliths without the use of alkoxide precursors. The dried alumina aerogels were characterizedusing elemental analysis, high-resolution transmission electron microscopy, powder X-ray diffraction,solid-state NMR, acoustic measurements, and nitrogen adsorption/desorption analysis. Powder X-raydiffraction and TEM analysis indicated that the aerogel prepared from hydrated AlCl3 in water or ethanolpossessed microstructures containing highly reticulated networks of pseudoboehmite fibers, 2−5 nm indiameter and of varying lengths, whereas the aerogels prepared from hydrated Al(NO3)3 in ethanol wereamorphous with microstructures comprised of interconnected spherical particles with diameters in the5−15 nm range. The difference in microstructure resulted in each type of aerogel displaying distinctphysical and mechanical properties. In particular, the alumina aerogels with the weblike microstructurewere far more mechanically robust than those with the colloidal network, based on acoustic measurements.Both types of alumina aerogels can be transformed to γ-Al2O3 through calcination at 800 °C without asignificant loss in surface area or monolithicity.
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