John M. Moses

Development and processing of aerogels in a windowed autoclave

Processing of aerogels in a windowed autoclave has shown that the drying process and solvent play important roles in gel quality. Excellent aerogels have been obtained using acetone as the solvent during gel formation, followed by exchange with liquid carbon dioxide with gradient control, and evacuation under supercritical conditions. Observation of the drying process showed that contact between solution discontinuities and the aerogel during the solvent exchange process caused gel deformities. Control of the solvent exchange and elimination of gradient fronts resulted in outstanding aerogel quality. The ability to observe the process in a windowed autoclave allowed this improved understanding of key variables.

Reactivity investigation of mixtures of propane and nitrous oxide

Supercritical and vapor‐phase reactions of oxidizers and fuels under pressure are of commercial interest. Because mixtures of propane and nitrous oxide have the potential to be explosive, a model mixture was studied with the intent of defining safe operating boundaries. This work investigated the nitrous oxide/propane oxidant/fuel system, diluted with the inert solvent carbon dioxide, and a catalyst as an accelerant, to determine the safe operating regions for the oxidation reaction. Using an ARC® calorimeter for the evaluations, variables included initial system density, catalyst, and mixture compositions. Density of the system ranged from 0.05 to 0.62 g/cm3. A number of catalysts were investigated with 10% Pd on carbon being the most active. Strongest reactivity was observed when the mixture was stoichiometric to the complete combustion products of nitrogen, carbon dioxide, and water. Three distinct regions of reactivity were observed: mild reactivity (starting at the sensitivity of the ARC of dT/dt = 0.02 to about 0.1° C/min); strong exothermic reaction (dT/dt ≅ 1° C/min); and flammable and/or explosive (a distinct and substantial jump in dP/dt in <1 s). As a result, a boundary has been proposed for safe mixtures of nitrous oxide, propane, and carbon dioxide, and a basis for determining safe operating compositions for other systems. The computed adiabatic reaction temperature was used to correlate the experimental results to establish the boundary for safe operation.