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.
InfroductionA process for the capacitive deionization (CDI) of water with a stack of carbon aerogel electrodes has been developed by Lawrence Livermore National Laboratory.Aqueous solutions of NaC1 or NaNO3 are passed through a stack of carbon aerogel electrodes, each having a very high specific surface area (400 to 1100 m2/g). After polarization, nonreducibie and nonoxidizable ions are removed from the electrolyte by the imposed electric field and held in electric double layers formed at the surfaces of electrodes, as shown in Fig. la. As desired, the effluent from the cell is purified water. This process is also capable of simultaneously removing a variety of other impurities. For example, dissolved heavy metals and suspended colloids can be removed by electrodeposition and electrophoresis, respectively. CDI has several potential advantages over other more conventional technologies. Unlike ion exchange, no acids, bases, or salt solutions are required for regeneration of the system. Regeneration is accomplished by electrically discharging the cell. Therefore, no secondary waste is generated. In contrast to thermal processes such as evaporation, CDI is much more energy efficient. Since no membranes or high pressure pumps are required, CDI offer operational advantages over electrodialysis and reverse osmosis (RO).
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.
This is a preprint of a paper intended for publication in a journal or proceedings. Since changes may be made before publication, this preprint is made available with the understanding that it will not be cited or reproduced without the permission of the author.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.