Observations of shock-induced chemistry with subnanosecond resolution

We report observations of the effects of shock-induced chemical reactions that build to a steady detonation in an energetic material. The chemical reactions in certain materials initiate and build quickly, such that traditional characterization techniques for energetics cannot provide the spatial fidelity necessary to resolve the onset and build-up of reactions. In this work, physical vapor deposition was used to create films of an energetic material with precisely controlled thicknesses to investigate the growth to detonation resulting from shock-induced chemical reactions with microscale spatial resolution. Finite duration shocks were supplied from a well-defined electrically-driven flyer. The velocity of the transmitted shock was measured by photonic Doppler velocimetry with subnanosecond resolution. Initiation experiments were performed on deposited hexanitrostilbene samples ranging from 30 to 150 μm thickness to observe the emergent effects of chemical energy release. The resulting output interface velocity was observed to increase from that predicted for an unreacted shock to that of a chemically supported detonation within 100 μm. A build-up to detonation has not previously been quantified in such a short distance.