Currently, solid rocket motor propellants used by the Department of Defense contain toxic/hazardous materials. Some propellants contain lead as a ballistic modifier, which becomes an exhaust product during combustion. Other propellants contain ammonium percholorate, which produces hydrochloric acid (HCl) during combustion. Hazardous solvents must also be used to process oxidizers.
The goals of this project include (1) develop lead-free extrudable and castable propellant for minimum smoke systems, (2) develop complete and clean HCl-free combustion of propellant, and (3) develop solventless methods for processing energetic oxidizers.
Navy extrudable PNC/BTTN and castable formulations of ammonium dinitramide (ADN)/CL-20 propellants are being developed. Combinations of CL-20 and ADN oxidizers are being tested for combustion properties and performance along with their chemical and physical properties. Army testing has developed formulations with alternatives to lead, including bismuth salicylate and bismuth citrate. Both provide equal or superior performance over lead-based formulations.
Ultrafine aluminum (UFAL)/ADN propellant compositions using low-solid content and energetic plasticizers to provide highly efficient and clean burning propellants while meeting performance requirements are being evaluated as an alternative to formulations containing ammonium perchlorate. UFAL is being characterized to determine particle size distribution, particle shape, and surface area. Propellant compositions are being optimized and evaluated.
A liquified gas antisolvent process is being developed and tested. This method produces comminuted oxidizers in a size, shape, and purity suitable for propellant manufacture without the use of traditional solvents.
The U.S. Army Aviation and Missile Command has developed a lead free minimum smoke propellant that utilizes bismuth compounds as a ballistic catalyst. The Naval Surface Warfare Center at Indian Head (NSWC-IH) has developed a PNC/BTTN lead free formulation. This technology is now ready to transition to full scale-up.
Formulations using ADN and ADN/CL-20 have been developed at the Navy Air Warfare Center, China Lake. These propellants have 15 percent higher calculated performance than conventional propellants. The combustion products are basically benign gases with no HCl. This technology, along with the UFAL formulations, is a promising candidate for transition to other Navy programs. At the Air Force Research Lab (AFRL), Edwards AFB, HCl free propellant using UFAL technology with low concentrations of Ultra Fine Ammonium Perchlorate offers a promising formulation consistent with requirements for Air Force booster programs. This technology is now ready to transition to demonstration testing. AFRL has also worked to transition the Polyhedral Oligomeric Silsesquioxanes nanotechnology, which was developed for inhibitor systems to private industry, and plans to continue development of this technology with NSWC-IH.
The liquefied carbon dioxide anti-solvent capability for processing oxidizers was transitioned from lab scale by the Army to bench scale and is now feasible for use. This project was completed in FY 2000.
Alternative propellant formulations will provide a solution for eliminating lead and HCl emissions, while the development of solventless methods for processing energetic oxidizers will minimize solvent usage and disposal.