The current pyrophoric decoy flare is composed of iron (Fe) coated onto steel foil. The high surface area to mass ratio of the foils makes them flutter after being ejected from the aircraft, taking on the appearance of a moving hot cloud when several decoys are ejected in rapid succession. The current production process relies heavily on the use of hot caustic and toxic leaching solutions to prepare the high surface area, porous, pyrophoric iron metal. These solutions are corrosive and represent both a safety and environmental hazard.
The objective of this SERDP Exploratory Development (SEED) project was to demonstrate use of the "sol-gel" methodology for producing nanostructured energetic materials (i.e., pyrotechnics), while minimizing or eliminating the human health and environmental hazards associated with their current fabrication process. Application of this technique to the manufacture of pyrophoric flares will eliminate the need for caustic and toxic leaching solutions and improve performance of the final products.
New sol-gel methods, recently developed at Lawrence Livermore National Laboratory, can be employed to generate high surface area, porous, Fe (III) oxide-based solids. These materials are synthesized using inorganic Fe (III) salts, propylene oxide, and environmentally benign solvents like water and ethanol. Chemical reduction of such porous solids at low temperatures may allow the preparation of high surface area, porous iron without sintering, the only byproduct being water. Such a material has the potential to be pyrophoric with some utility in pyrophoric decoy flares. The material, prepared by this synthetic route, would not require the use of hot caustic and toxic leaching solutions. In addition, it would not require the incorporation of any hazardous materials or processes that are not already used in the current production.
The results of this project show the reduction of porous, high surface area iron (III) oxide sol-gel materials yields submicron metallic iron powders. Optimum reduction conditions were identified. Taking the characterization into account, there is little doubt that the particle sizes of the powders made by this approach are as or more finely divided than conventional pyrophoric powders. Although the powders produced were not pyrophoric, they were energetic and burned promptly and in a self-sustained manner when ignited with a thermal source. One rationale for the non-pyrophoric behavior of these materials is iron particles with a stable passivation surface. It is possible that the system studied may have suffered from too much water present, which led to gentle passivation and non-pyrophoric materials. In theory, the powders produced can be made pyrophoric through one or more additional processing steps.
Low-temperature reduction of high surface area, porous, sol-gel-derived Fe (III) oxide with molecular hydrogen may result in the formation of porous pyrophoric iron metal, suitable for use in pyrophoric decoy flares. This project demonstrated that processing and preparation with environmentally acceptable media under neutral conditions could potentially replace the current process. The immobilization of pyrophoric iron in a sol-gel-derived metal oxide matrix may also provide some advantages concerning the dispersion, burn, and spectral characteristics of the decoy flare. (SEED Project Completed - 2003)