Detonation of ultrafine explosives

Detonation of PETN and HMX with a particle size of about 1 $\mu$m was investigated by an electromagnetic method. At an initial density of 0.9–1.2 g/cm$^3$, the von Neumann spike was weak or not observed at all. This indicates a fast reaction, whose time is outside the experimental resolution (about 5 ns). Electrical conductivity measurements provided only a rather rough upper-bound estimate of the reaction time (less than tens of nanoseconds). Density measurements using synchrotron radiation showed that the initiation of PETN with an air shock wave led to almost instantaneous detonation initiation, without any acceleration region. In general, the results of the study confirm the acceleration of the chemical reaction in ultrafine explosives.