State-of-the-art signaling devices (e.g., the MK25 round, Hydra 70 warhead) explosively disseminate a slow-burning material, such as red phosphorous (RP), to produce white smoke upon combustion and reaction with the moisture in the atmosphere. This type of burning smoke generator forms colloidal phosphorous pentoxide, which is quickly hydrolyzed by moisture to become phosphoric acid droplets that are the actual visible constituents of the smoke. The generation of white smoke is used for screening and marking targets. Despite being a mature and reliable technology, the current production process for the markers involves the use of volatile organic compounds (VOC) and hazardous air pollutants (HAP), which are usually quite flammable, electrostatic discharge (ESD) sensitive, and harmful and/or toxic if inhaled or ingested. Elimination of these solvents from the process would diminish the attendant safety and environmental hazards.
The objective of this project was to develop castable or pourable, chemically-cured RP formulations with sufficiently high binder content to eliminate the need for solvent processing aids, while concurrently mitigating ESD sensitivity. This was achieved while still maintaining the burn characteristics or white smoke-cloud formation produced by traditional RP formulations.
Commercial energetic binders that are low-viscosity for casting/pouring, self-deflagrating to assist RP burning, chemically-cured to tailor RP fragment size, and reasonably conductive to dissipate electrostatic energy and enhance insensitivity were applied. Self-deflagrating energetic binders do not inhibit the burning of RP. The explosive dissemination of the RP smoke ignites the binder along with the RP. Since the burn characteristics of the energetic binder are self-sustaining, the RP continues to produce white smoke. Achievement of the optimum cloud size and duration is a function of explosive charge weight, explosive brisance, and structural integrity of the RP composition. Variations of these parameters were performed iteratively. The best performing RP smoke compositions were evaluated in prototype target makers. Dimensions of the marker cloud, cloud duration, and cloud density were measured using standard visible light transmission techniques which employ a monochromatic visible light source.
Castable, solvent-free, red phosphorus compositions employing energetic binder systems have been demonstrated for the following two applications: explosivelydisseminated target markers and long-burning marine location markers. The new formulations show improved safety characteristics. RP content, energy content, and burn rates of the formulations can be tailored through addition of gas generants or co-oxidizers or through modification of the energetic binder. Such tailorability provides latitude for optimization to the specific application of interest. This project was completed in FY 2002.
This project offers improvements in both safety and environmental impact for the production of target markers utilizing explosively-disseminated red phosphorous. VOCs and HAPs can be eliminated completely from the production process with the resulting marker formulations meeting or exceeding current performance requirements.