Wendy Balas

Characterization of Nanothermite Material for Solid-Fuel Microthruster Applications

Nanothermite composites containing metallic fuel and inorganic oxidizer have unique combustion properties that make them potentially useful for microthruster applications. The thrust-generating characteristics of copper oxide/aluminum nanothermites have been investigated. The mixture was tested in various quantities (9―38 mg) by pressing the material over a range of densities. The testing was done in two different types of thrust motors: one with no nozzle and one with a convergent―divergent nozzle. As the packing density was varied, it was found that the material exhibited two distinct impulse characteristics. At low packing pressure, the combustion was in the fast regime, and the resulting thrust forces were ∼75 N with a duration of less than 50 μs full width at half-maximum. At high density, the combustion was relatively slow and the thrust forces were 3―5 N with a duration 1.5―3 ms. In both regimes, the specific impulse generated by the material was 20―25 s. The specific impulse and short thrust duration created by this unique nanothermite material makes it promising for micropropulsion applications, in which space is limited.

Biodegradation of the High Explosive Hexanitrohexaazaiso-wurtzitane (CL-20)

The aerobic biodegradability of the high explosive CL-20 by activated sludge and the white rot fungus Phanerochaete chrysosporium has been investigated. Although activated sludge is not effective in degrading CL-20 directly, it can mineralize the alkaline hydrolysis products. Phanerochaete chrysosporium degrades CL-20 in the presence of supplementary carbon and nitrogen sources. Biodegradation studies were conducted using various nutrient media under diverse conditions. Variables included the CL-20 concentration; levels of carbon (as glycerol) and ammonium sulfate and yeast extract as sources of nitrogen. Cultures that received CL-20 at the time of inoculation transformed CL-20 completely under all nutrient conditions studied. When CL-20 was added to pre-grown cultures, degradation was limited. The extent of mineralization was monitored by the 14CO2 time evolution; up to 51% mineralization was achieved when the fungus was incubated with [14C]-CL-20. The kinetics of CL-20 biodegradation by Phanerochaete chrysosporium follows the logistic kinetic growth model.

Hydrolysis of Hexanitrohexaazaisowurtzitane (CL-20)

The hydrolysis of the α, β, and ϵ polymorphs of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane(CL-20) was investigated in dilute buffered aqueous solutions over a pH range of 4–10 and at 35, 43, 50, 58 and 65°C, with starting concentrations of CL-20 at one half the solubility limit for the respective temperature. In all cases, an overall first-order kinetic behavior was observed. The rate constants, half-lives, activation energies, and Arrhenius pre-exponential factors were determined. The latter was found to vary linearly with pH. Based on these findings, general formulas for the hydrolysis kinetics of the three polymorphs were developed.