The objective of this project was to validate that a Lead-Free Electric Primer (LFEP) based on a nano energetic composite could be used to replace the conventional M52A3B1 primer for medium caliber ammunition while meeting MIL-DTL-1394G requirements. The primary performance objective was meeting the all-up round action time (AUR-AT) requirement of less than 4.0 ms at ambient and low-temperature (-65°F). The program was to optimize a small scale LFEP composition based on AUR-ATs, develop a scalable process for LFEP synthesis, demonstrate the scaled-up LFEP met Department of Defense (DoD) AUR-ATs, automate the LFEP loading and pressing steps, demonstrate LFEP reliability in a Gatling Gun firing of 505 rounds, and transition the technology to the DoD and industry.
At the beginning of this project, a number of obstacles arose including the need to re-formulate the LFEP composition. Three of the five components used in the previous SERDP project WP-1331, Al(50nm), BTATZ, and Kel-F, had to be replaced with commercially available material. The ability to develop and characterize new Energetic Nano Composites (ENCs) was mainly performed at Universities and Department of Energy (DOE) National Laboratories where ENCs were tested using pressure cells and burn tubes. Therefore changing the ENC composition, finding a new gas additive, and suitable binder for the LFEP was a daunting task.
To address this need, Naval Air Warfare Center Weapons Division (NAWCWD) developed a new laboratory tool that enabled the rapid optimization of ENCs and LFEP compositions, called the Al Pan Dent Test. This test helped identify a wide range of other useful ENCs that could be used to make LFEP composites, igniters, and pyrotechnics. The Al/MoO3 ENC turned out to be one of the poorer performing composites in the Al Pan Dent Test. However, a LFEP composition using this ENC was developed, 66% Al(80nm)/MoO3, 30% AN, 2% Kel-F, 2% C, that met DoD requirements. The synthesis process was simplified to eliminate most hazardous steps, but the dry addition of carbon to the Al/MoO3/AN/Kel-F was essential. The carbon is only needed for electric ignition systems, but for percussion systems the Al/MoO3/AN/Kel-F is suitable candidate. This standard composition when prepared and consolidated correctly gave typical AUR-ATs of 3.05 + 0.08 ms at ambient and 3.12 + 0.08 ms at -65 °F. Good AUR-ATs were obtained for compositions with AN in the weight percent range of 25 to 38%. The Al(80nm)/MoO3(45nm) molar ratio of 2.63 to 2.69 was found to produce the lowest AUR-ATs at both ambient and low-temperatures. To ensure starting material quality and LFEP reliability, a list of recommended characterizations was developed for each of the starting materials.
A significant advancement was made in the area of nanoenergetic composites. Prior to this program, ENCs were generally made on a 1-2 g scale by sonication. A scalable process was developed to prepare ENCs and the scaled-up materials appear to be superior to the small scale sonicated materials. Many 100g batches have been prepared and characterized. Over 2 Kg of ENC have been prepared and tested using the scale-up method developed in this program for DTRA applications. The labor cost of preparing ENCs has been drastically reduced, but starting material costs are still an issue. Multi-kilogram batches could be easily made in an industrial setting.
A scaled-up 100g batch of the LFEP composite was successfully prepared in the laboratory and had an average AUR-AT of 3.21 ms. However, the final step of carbon addition to the Al/MoO3/AN/Kel-F powder failed in the scale-up facility. Poor mixing led to a very heterogeneous composite due to a design flaw in the mixing apparatus. The flaw can be easily fixed and the redesign was tested in the laboratory, but has yet to be demonstrated on the 100g scale. The final dry addition of carbon is achievable in an industrial environment on a multi-kilogram scale. The LFEP was successfully scaled-up in the laboratory but not at the scale-up facility.
A powder loading system in combination with the 5x5 multi-die set have been demonstrated using the LFEP. The powder loading system was used to fill one primer cup at a time, but an automated system could be developed to reduce labor costs. The multi-die set configuration may also reduce labor cost by combining the cutting of the seal paper and pressing in one step and by pressing 25 primers at once. Although the powder loading system and multi-die set was demonstrated with LFEP material, the AUR-ATs averaged almost 4 ms. Additional testing is needed to identify critical parameters and lower the AUR-ATs to acceptable limits. The powder loading system and multi-die pressing system have been tested, but not validated.
A working LFEP material has been developed, validated on a small scale, scaled-up, and a viable primer loading system tested that could be transitioned to the industry. Due to funding issue and capability realignment issues, the final testing was not performed under ESTCP funding. Funding was secured from the Navy Environmental Sustainability Development to Integration (NESDI) Program for primer loading and pressing and support was obtained from PMA-242 to pay for the firing and data collection. A 200g batch of LFEP was prepared, 40 20 mm rounds built-up and Mann Barrel gun firing produced acceptable AUR-ATs averaging 3.21 ms. A total of 505 primers were loaded into primer cups in September 2012 (after 4 month of storage in hexane), 505 20 mm rounds built at Picatinny Arsenal in May 2012 (after five plus months of primer cup storage at Picatinny Arsenal) and fired in September 2012. The rounds failed to meet the 3.5 ms AUR-AT. The data set has not been received at this point, but is expected by November 2012 from PMA-242. Normally, the preparation of the LFEP material is followed by the primer loading and pressing, and then the 20 mm rounds are built-up. This entire process usually is performed within five working days. Due to lack of funding and loss of capabilities issue because of Base Re-alignment and Closure, the process took close to 10 months. The primer material was made and stored in hexane in a polyethylene bottle for four months before the 505 primers were made. They were shipped to Picatinny Arsenal where the primers sat for over five months before round build-up. The LFEP aged during the storage in hexane or while the unprotected primers awaited build-up at Picatinny Arsenal. The PMA-242 transition of this technology will not occur due to final testing failure.