Iron oxide-based porous solids were prepared by a sol−gel process using Fe(III) salts in various solvents. It was observed that the addition of propylene oxide to Fe(III) solutions resulted in the formation of transparent red-brown monolithic gels. The resulting gels were converted to either xerogels by atmospheric drying or aerogels by supercritical extraction with CO2(l). Some of the dried materials were characterized by nitrogen adsorption and desorption analysis and transmission electron microscopy (TEM). The results of those analyses indicate that the materials have high surface areas (∼300−400 m2/g), pore sizes with mesoporic dimensions (2−23 nm), and a microstructure made up of 5−10 nm diameter clusters of iron(III) oxide. The dependence of both gel formation and its rate was studied by varying the epoxide/Fe(III) ratio, the Fe(III) precursor salt, amount of water (H2O/Fe(III)) present, and the solvent employed. All of these variables were shown to affect the rate of gel formation and provide a convenient control of this parameter. Finally, an investigation of the mechanism of Fe2O3 gel formation was performed. Both pH and nuclear magnetic resonance (NMR) studies suggest that the added epoxide acts as an irreversible proton scavenger that induces the Fe(III) species to undergo hydrolysis and condensation to form an inorganic iron oxide framework. This method can be extended to prepare other transition- and main-group metal oxide materials.

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The fundamental differences between energetic composites and energetic materials made from a monomolecular approach are the energy density attainable and the energy release rates. For the past 4 years, we have been exploiting sol-gel chemistry as a route to process energetic materials on a microstructural scale. At the last ISA conference, we described four specific sol-gel approaches to fabricating energetic materials and presented our early work and results on two methodssolution crystallization and powder addition. Here, we detail our work on a third approach, energetic nanocomposites. Synthesis of thermitic types of energetic nanocomposites are presented using transition and main group metal-oxide skeletons. Results on characterization of structure and performance will also be given.