Perchlorates are high-energy oxidizers that have good thermal and chemical stability and are used in a wide range of military applications including rocket propellants and pyrotechnics. When used in ammunition incendiary systems, compositions containing potassium perchlorate and metal fuels are formulated to produce both an incandescent flash and smoke to mark an impact point or act as ignition sources for flammable liquids. In some munitions the compositions are used to initiate an explosive train.
Potassium perchlorate has a high solubility in water which results in very low retardation in aquifers. Consequently, any groundwater plumes can be extensive and pose severe remediation problems. Potassium perchlorate can be released into the environment as a result of spillages during manufacture, demilitarization, or when ammunition fails to function correctly. The presence of potassium perchlorate in drinking water is a cause for concern as all perchlorates are recognized as a potential hazard to human health. In particular, their ingestion is known to inhibit iodide uptake by the thyroid gland.
The primary objective of this project was to prepare and assess environmentally benign, perchlorate-free pyrotechnic formulations based on novel oxidizers and fuels. These new formulations need to meet safety and performance criteria, including toxicity, stability, sensitivity, ignitability, hygroscopicity, light output, and burning time. A secondary objective was to reduce the occurrence of bush fires on training ranges. This project focused on eliminating perchlorate soil, surface water, and groundwater contamination from training, testing, production, and disposal of incendiary munitions.
Ingredients for use in perchlorate-free pyrotechnic formulations were identified and evaluated to ensure that they were more environmentally benign than the materials they would replace. The fuels selected were magnesium/aluminum alloy, magnesium, aluminum, and boron. All of these compounds showed high persistence but low values for bioaccumulation, toxicity and ecotoxicology and were therefore suitable for the formulation studies. The oxidants considered were potassium dinitramide, barium, potassium, sodium and strontium nitrates, barium, calcium, potassium, sodium and strontium sulfates, copper, iron, molybdenum and tungsten oxides, and these generally showed high persistence. The binders selected were hexafluoroproplyene vinylidene fluoride polymer, polyglycidyl nitrate (polyGlyN), poly(3-methyl-3-nitratomethyloxetane (PolyNIMMO), glycidyl azide polymer (GAP), polyvinyl chloride (PVC), and calcium resinate.
Researchers conducted laboratory scale formulation and manufacture of pyrotechnic compositions. Over 350 formulations containing magnesium/aluminum alloy, magnesium, or aluminum as the fuel were prepared for pyrotechnic and thermal studies. Most of the formulation studies concentrated on the magnesium/aluminum alloy compositions to reduce the number of changes in the formulation so that the physical properties including flow and bulk density are minimized. These compositions are also likely to be more readily ignitable by impact on a target than those containing magnesium or aluminum as the fuel.
A series of gun firing and aging studies were completed on formulations containing sodium and potassium nitrate and selected binders. A significantly lower rate of aging was observed for the compositions based on sodium nitrate, and the aging was further reduced by the addition of a binder particularly calcium resinate.
A further gun firing trial confirmed that the formulations containing magnesium/aluminum alloy sodium nitrate and either 2% or 4% calcium resinate gave a performance that matched that of the control compositions containing potassium perchlorate in terms of flash size and duration. When subjected to longer term aging at 50°C and 65% RH, the composition containing 4% calcium resinate was found to have the lower heat flow. Ignition differential scanning calorimetry showed that the ignition temperature for this formulation was also lower and a hazard assessment confirmed that this formulation had acceptable safety characteristics. Pyrotechnic formulations developed under this project are being demonstrated in ESTCP in Project WP-201110.
The primary benefit of this effort is to provide information on manufacturing new perchlorate-free pyrotechnic formulations for incendiary munitions, which are more environmentally benign than the present perchlorate-containing formulations. A subsidiary outcome includes reductions in the occurrence of bush fires on training ranges.