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Packaging Metal-Coated Fibers for Prolonged Storage and Efficient Dissemination

Description:

TECHNOLOGY AREA(S): Materials 

OBJECTIVE: To develop a low-cost manufacturing process to pack metal-coated fibers to high density and which will allow efficient dissemination. Fibers are theoretically the highest performing particle shape for obscuration, especially in the microwave region of the electromagnetic spectrum. They can also be the most difficult to efficiently pack and to aerosolize. The process to pack fiber will probably, but not necessarily, use an aligned format. Efficient dissemination implies a maximum of single fibers and a minimum of clumps. Phase I will focus on strategies to address issue of less than optimum packing density and dissemination quality, e.g. galvanic corrosion and/or filament to filament adhesion that reduces performance for nickel-coated fibers. Phase II will expand the effort by addressing cold welding in copper-coated fibers. It will also include the ability to demonstrate the usefulness of the concepts by using accelerated storage techniques and performing dissemination trials to show improvements 

DESCRIPTION: Smoke and obscurants play a crucial role in protecting the Warfighter by decreasing the electromagnetic signature that is detectable by various 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 and coating thickness. Numerical modeling and many measured results on metal-coated fibers affirm that more than order of magnitude increases over current performance levels are possible if high aspect-ratio conductive fibers can be effectively disseminated as an un-agglomerated aerosol cloud. Since this is a relatively new area of research for the Army, very little work has been performed so far in this area. One of the difficult issues is the corrosion that results from galvanic reactions in the packing process that degrades the fibers. Another is the particle-to-particle attractive forces that make efficient dissemination of single fibers difficult. 

PHASE I: Describe techniques to minimize mechanisms of filament to filament adhesion, e.g. galvanic corrosion, cold welding, or other means of metallic coating degradation, of nickel-coated fibers during packaging and prolonged storage. Demonstrate with samples an ability to produce packed metal-coated fibers with a bulk density of at least 50% of maximum theoretical bulk density of the nickel-coated fibers, with no degradation, and preferably improvements, in dissemination efficiency. Nickel-coated fibers are available commercially for this effort and should be cut to a length of one centimeter. (5) 100-gm samples shall be provided to ECBC for evaluation PHASE I Option: Describe techniques to minimize cold welding in copper-coated fibers. 

PHASE II: Demonstrate with samples an ability to produce packed copper-coated fibers with a bulk density of at least 50% of maximum theoretical bulk density of the copper-coated fibers with no degradation, and preferably improvements, in dissemination efficiency. Copper-coated graphite fibers are available commercially for this effort and should be cut to a length of one centimeter. (5) 100-gram samples shall be provided to ECBC for evaluation. Demonstrate the processes will improve performance for both nickel- coated and copper-coated fibers through the use of accelerated-aging storage techniques. Demonstrate that the process is scalable by providing 4 1-kg samples of each of the two improved bulk density packaged metal-coated fibers with no loss in performance from that achieved with the small samples. In addition, in Phase II, a design of a manufacturing process to commercialize the concept should be developed. 

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 the current logistics burden of countermeasures to protect the soldier and associated equipment. This technology could have application in other Department of Defense interest areas including high explosives, fuel/air explosives and decontamination. Improved separation techniques can be beneficial for all powdered materials in the metallurgy, ceramic, pharmaceutical and fuel industries. Industrial applications could include electronics, fuel cells/batteries, furnaces and others. 

REFERENCES: 

1. Bohren, C.F.; Huffman, D.R.; Absorption and Scattering of Light by Small Particles; Wiley-Interscience, New York, 1983.

KEYWORDS: Metal-coated Fibers, Prolonged Storage, Microwave, Packing, Aerosolization, Obscuration 

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