Observations on aluminum reactions in the cylinder test using low-temperature insensitive explosive formulations

The reaction of particulate aluminum metal in detonation products is a complex, multivariable process involving the chemistry of the parent explosive and binder system as well as the particle size and amount of aluminum in the formulation. This chemistry dictates both the availability of oxidizing species available for aluminum combustion as well as reaction zone temperature and length and the conditions in the following flow. Most formulations investigated that are designed to burn aluminum very quickly to provide enhanced metal-pushing ability, sometimes called combined effects explosives, are usually formulated with high-power nitramines such as RDX, HMX and CL-20, but little investigation has been performed on lower-energy insensitive formulations. To this end, formulations have been produced using TATB, DAAF and NTO as the principle crystalline explosive ingredient. In CYLEX testing, TATB formulated with Al and the binder KelF-800 (PBX 9502-Al), showed no indication of aluminum reaction when H-2 aluminum (~3.5 µm diameter) was used. However, interestingly, when 80 nm aluminum was used, roughly 25-50% aluminum participation was observed via cylinder wall velocity records, which is a distinct divergence from aluminum particle size effects observed in nitramine formulations. Formulations with isotopically substituted TATB-d6 were also evaluated, however failed to detonate in the same CYLEX configuration, indicating a relationship in the kinetic isotope effect in failure diameter in addition to the previously observed decrease in detonation velocity. As a comparison to the TATB formulations DAAF and NTO were selected as additional insensitive explosive ingredients of study with either similar calculated detonation temperatures or oxygen balance (O.B.); TATB = 2483. 9 K, O.B. -55.8, DAAF; 3055.9 K O.B. = -52.8%, NTO; 2319.1 K, O.B. = -24.6%.