Steven Apperson

Generation of fast propagating combustion and shock waves with copper oxide/aluminum nanothermite composites

Nanothermite composites containing metallic fuel and inorganic oxidizer are gaining importance due to their outstanding combustion characteristics. In this paper, the combustion behaviors of copper oxide/aluminum nanothermites are discussed. CuO nanorods were synthesized using the surfactant-templating method, then mixed or self-assembled with Al nanoparticles. This nanoscale mixing resulted in a large interfacial contact area between fuel and oxidizer. As a result, the reaction of the low density nanothermite composite leads to a fast propagating combustion, generating shock waves with Mach numbers up to 3.

Galvanic porous silicon composites for high-velocity nanoenergetics.

Porous silicon (PS) films ∼65-95 μm thick composed of pores with diameters less than 3 nm were fabricated using a galvanic etching approach that does not require an external power supply. A highly reactive, nanoenergetic composite was then created by impregnating the nanoscale pores with the strong oxidizer, sodium perchlorate (NaClO(4)). The combustion propagation velocity of the energetic composite was measured using microfabricated diagnostic devices in conjunction with high-speed optical imaging up to 930000 frames per second. Combustion velocities averaging 3050 m/s were observed for PS films with specific surface areas of ∼840 m(2)/g and porosities of 65-67%.

Silicon-based bridge wire micro-chip initiators for bismuth oxide?aluminum nanothermite

We present a micro-manufacturing process for fabricating silicon-based bridge wire micro-chip initiators with the capacity to liberate joules of chemical energy at the expense of micro joules of input electrical energy. The micro-chip initiators are assembled with an open material reservoir utilizing a novel 47 °C melting point solder alloy bonding procedure and integrated with a bismuth oxide–aluminum nanothermite energetic composite. The electro-thermal conversion efficiency of the initiators is enhanced by the use of a nanoporous silicon bed which impedes thermal coupling between the bridge wire and bulk silicon substrate while maintaining the structural integrity of the device. Electrical behaviors of the ignition elements are investigated to extract minimum input power and energy requirements of 382.4 mW and 26.51 µJ, respectively, both in the absence and presence of an injected bismuth oxide–aluminum nanothermite composition. Programmed combustion of bismuth oxide–aluminum nanothermite housed within these initiators is demonstrated with a success rate of 100% over a 30 to 80 µJ range of firing energies and ignition response times of less than 2 µs are achieved in the high input power operation regime. The micro-initiators reported here are intended for use in miniaturized actuation technologies.

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.

A Novel On-Chip Diagnostic Method to Measure Burn Rates of Energetic Materials

ABSTRACT A novel on-chip diagnostic method has been developed to measure burn rates of energetic materials patterned on a 1 inch × 3 inch glass chip. The method is based on time-varying resistance (TVR) of a sputter-coated thin platinum (Pt) film, in which resistance of the film changes because of the propagation of ignition of the nanoenergetic material over it. The corresponding voltage differential is captured by a high-speed data acquisition system (1.25 × 106 samples/s). We have measured burn rates as high as 504 m/s for thermites of copper oxide (CuO)/aluminum (Al) and 155 m/s for bismuth oxide (Bi2O3)/Al nanoparticles using this method. We have provided an explanation for the change of resistance upon ignition, based on the microstructural characterization and energy dispersive spectroscopy.

On-Chip Initiation and Burn Rate Measurements of Thermite Energetic Reactions

Burn rates of various nano-energetic composites were measured by two techniques; on-chip method and conventional optical method. A comparison is presented to confirm the validity of on-chip method. On-chip initiators were prepared using platinum heater films and nanoenergetic composites. Thin film Pt heaters were fabricated with different dimensions and ignition delay was studied using a nano-energetic composite of CuO nano-rods and Al-nano-particles. The ignition delay as a function of electrical power is presented for the same energetic composite. Heater with smaller surface area is found to be more efficient, which may be due to the lower heat losses.