SBIR-STTR Award

The maximum explosion pressure rate of pressure rise and oxidant consumption will be determined for an air-suspended clouds of a unique fine boron powder less than 10 micrometers in diameter. The unique powder particles are thinly coated by a process developed at AeroChem with magnesium or aluminum to aid in their ignition. The proposed method is based on extensive work at the US Bureau of Mines measuring the explosibility of dust clouds. In Phase I experiments a cloud of particles in air will be ignited inside a closed chamber. A fast-response transducer will be used to obtain the rate of pressure rise and maximum explosion pressure. An oxygen sensor will be used to determine oxidant consumption. Phase I experiments will demonstrate the enhancement of ignition and explosion by magnesium-coated particles relative to otherwise identical uncoated boron particles. The coated particles will be produced on site. Explosion measurements made under identical conditions for the coated and uncoated powders will be correlated against the coating thickness from 1-10X of the particle mass. Phase II work will be comprised of the above and other detailed measurements in a larger scale system on both Mg- and Al-coated particles. The results will be analyzed in mechanistic terms to obtain an understanding of cloud ignition and explosion for the unique coated powders. This proposed program will integrate the particle preparation and evaluation of the new generation of boron particle explosives.

Boron combustion has the potential to provide the highest volumetric enthalpy among currently known fuels. In practice, however, this enthalpy has not yet been realized, due in part to long ignition times of boron particles. The proposed research program will determine the boron ignition mechanism and define the effect of coatings proposed as ignition aids. The ignition time and temperature in air for titanium-coated and fluorinated polymer-coated boron, compared with uncoated boron, will be determined for the first time using electronically heated boron filaments. The coated filaments will be cut into small pieces for single particle combustion measurements. Ignition and combustion times will be compared with this of micron-sized coated and uncoated boron single particles under a subcontract to this program. Complementary experiments will determine the ignition limit, burning rate, maximum explosion pressure, and oxygen consumption of air dispersed uncoated and fluorinated polymer-coated boron powder clouds in a consistent volume bomb. The effect of added aluminum, magnesium, titanium, titanium hydride powders of the uncoated boron explosion parameters will be measured and will provide a consistent picture of the cloud ignition and combustion propagation phenomena. Enhancement characteristics of a wide range of additives will be determined.