Characterizing Oxidizer Chemistry in Metallic Additives for Polymer-Bound Explosives

The energy density of plastic-bonded explosives (PBX) like octogen (HMX) can be increased by adding aluminum powders. However, when shocked, aluminum powders react more slowly than HMX as they need to mix and react with extrinsic oxidizers. Aluminum reduces the detonation pressure but enhances the subsequent blast. Arrested reactive milling (ARM) is a promising method to produce more powerful PBX by fabricating composite aluminum microparticles containing finely dispersed nanometric oxidizer. ARM involves several process variables, such as milling time, ball-to-powder mass ratio, etc., so optimizing composites is accomplished with high-throughput tabletop shock testing of multiple batches. We use laser-launched 4 km/s flyer plates to shock tiny HMX-based PBX samples with chosen composites and measure thermal emission spectral radiance, which gives the energy release rate and the temperature. Superior additives produce longer-lived nanosecond hot spots, hotter than HMX (~4300K) and improved deflagration characteristics. Here, we answer the question, can a thermodynamically inferior composition (Al/CuO) that has been optimized outperform a thermodynamically superior but unoptimized composition (Al/MoO3 with 5 wt.% KNO3). The answer is yes. The PBX with optimized Al/CuO had higher emissive power and temperatures. This result confirms the need for high-throughput shock testing to produce the most powerful aluminized additives.