More Powerful Detonations with Aluminum

Aluminum powders with appropriate oxidizers can increase the total energy released from organic explosives such as HMX, but they typically react in microseconds or even milliseconds, which is not fast enough (a few to tens of nanoseconds) to increase the detonation pressure and velocity. Here we studied individual Al/CuO fuel/oxidizer composite microparticles produced by arrested reactive ball milling (ARM). Single polymer-bonded particles were subjected to 30 GPa shock compression and a nanosecond optical pyrometer measured time-dependent temperatures from the thermal emission. Two types of Al microparticles with embedded oxidizer nanoparticles, termed well-mixed and poorly-mixed, were produced by milling with different ball-to-powder ratios. Electron microscopy analysis of sectioned microparticles showed that the oxidizer nanoparticles were on average about four times smaller in size in the well-mixed particles. Surprisingly, the poorly-mixed particles were much more reactive and produced higher temperatures, on the order of 5000K within several nanoseconds. The greater reactivity of Al microparticles with larger CuO nanoparticle oxidizers was attributed to the generation of larger hot spots inside the microparticles which led to more efficient reaction growth. The high temperatures produced from Al combustion on such short time scales indicates ARM methods might be capable of producing microparticle additives that can boost detonation pressures.