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Ordered Packing and Efficient Aerosolization of Anisotropic Particles


OBJECTIVE: Demonstrate a novel system of packing and dissemination for discs or fibers with a major dimension of a few microns and minor dimension of tens of nanometers. DESCRIPTION: Smokes and obscurants play a crucial role in protecting the Warfighter by decreasing the electromagnetic energy available for the function of sensors, seekers, trackers, optical enhancement devices and the human eye. Recent advances in materials science now enable the production of precisely engineered obscurants with nanometer level control over particle size and shape. Numerical modeling predicts that order of magnitude increases over current performance levels are possible if high aspect-ratio conductive particles can be effectively disseminated as an unagglomerated aerosol cloud. One of the fundamental challenges in maximizing the performance of obscurant devices is the method of packing and disseminating high aspect-ratio conductive obscurant particles. In current devices, a pyrotechnic or explosive center burster is used to disseminate a powder contained in a surrounding cylinder. Compacting the obscurant fill powder increases the quantity of powder that can be delivered by the device; however, this compaction process can result in the production of particle agglomerates that are much less effective than individually aerosolized particles. Packing and dissemination cannot be performed in isolation; they are intimately linked. Novel technologies are sought that will allow high fill fraction packing of anisotropic conductive flake or rod particles. When disseminated, the particles should readily separate from each other into a well dispersed aerosol cloud. Effective formulations may require surface modification to the particles, the addition of compounds that increase dispersibility, or an ordered arrangement of particles. Alternative device configurations that create microturbulence (on the order of particle major dimension) during the dissemination process may also be effective in separating particle agglomerates. PHASE I: Demonstrate novel methods of organizing high aspect-ratio obscurant powders into a cylindrical geometry at a high fill fraction (>40%). Demonstrate that the organized powders can be readily dispersed with minimal agglomeration(>40% single particles of original size). Provide samples for testing at ECBC chamber. PHASE II: Demonstrate that particle production and packing techniques can be scaled up to 200-g scale and that performance advantages are retained when aerosolized. If Phase I demonstrated concept with flakes, repeat with microfibers, or vice versa. Provide samples to validate results at ECBC chamber. PHASE III: The techniques developed in this program can be integrated into current and future military obscurant applications. Improved grenades and other munitions are needed to reduce current logistics burden of countermeasures to protect the soldier and his equipment. Improved dissemination techniques can be beneficial for all powdered materials in the metallurgy, ceramic, pharmaceutical and fuel industries. Industrial applications include electronics, fuel cells, batteries and solar energy. REFERENCES: 1. Bohren, C.F.; Huffman, D.R.; Absorption and Scattering of Light by Small Particles; Wiley-Interscience. New York, 1983. 2. Embury, Janon; Maximizing Infrared Extinction Coefficients for Metal Discs, Rods, and Spheres; ECBC-TR-226, Feb 2002, ADA400404 3. Clyens, S.; Johnson, W.; The Dynamic Compaction of Powdered Materials; Materials Science and Engineering, 30, 1977 4. Schwarz, R.B.; Kasiraj, P.; Vreeland T.; Ahrens, T. J.; A Theory for the Shock-Wave Consolidation of Metal Powders; Acta Matall., Vol 32, pp. 1243-1252 5. Gourdin, W.H.; Energy Deposition and Microstuctural Modification in Dynamically Consolidated Metal Powders; J. Appl. Phys. 55 (1), pp. 172-181
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