The Dlott group is interested in studying materials that respond to shock waves by undergoing chemical transformations and understanding the underlying mechanisms that govern these reactions. Shock waves are nearly discontinuous changes in material speed, pressure, density and temperature that move through a substance. To comprehend the magnitude of a shock wave, keep in mind that the loudest sound waves in air increase the pressure by 0.005 atm where shock waves typically generate over 10,000 atm changes in pressure. We produce shock waves using the impact of laser-driven flyer-plates that move at speeds of upwards of 4.5 km/s (mach 13). Flyer motions and shock induced phenomenon are monitored using a home built photonic Doppler velocimeter and chemistry is probed using high speed spectroscopic methods.

Using shock waves allows us to examine materials in conditions where reactions can occur that are unobtainable in ambient conditions. Our focus is on examining both energetic materials and shock wave energy dissipating (SWED) compounds. Energetic materials such as explosives and thermites (solid state metal/metal oxide systems) have been studied extensively for their potential use in weapons systems, but the more intrinsic process that underlie their shock reactivity is poorly understood. This is because the size of large scale of typical experiments obscures intrinsic reaction rates. Our group studies samples of micron thicknesses which allow us to probe these fundamental processes and develop mechanisms for reaction. We are currently examining several systems including ball milled nano thermites, multi-layer nano thermties, and propellants prepared by collaborators.

 

Figure 1: Left: A typical flyer history tracked using our photonic Doppler velocimeter. Right: Our system can launch different thickness flyers, which produce shock durations from 5-20 ns, over a range of speeds.

 

Our second project is motivated by shock wave related injuries that account for 20% of the casualties sustained by USA troops in battle. This is a problem because our armors are capable of stopping a bullet or fragment of shrapnel, but not the shock that is generated by the impact. The Dlott group is exploring a new paradigm of SWED that uses molecular level volume collapse driven by chemical transformations in compounds in order to reduce the energy of a shock wave. This project will examine the material mechanisms that are most effective in SWED in order to create more effective materials that can be used to protect soldiers on the battlefield.

 

Figure 2: Time dependent emissions from thermite single particles for varying impact velocities

 

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