Shock compression dynamics under a microscope

Dlott, Dana D.

doi:10.1063/1.4971456

Cited by 14 publications

(3 citation statements)

References 30 publications

(50 reference statements)

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“…The experimental concept is depicted in Figure . Our shock compression microscope , uses a pulsed laser with a spatially homogeneous beam to launch flyer plates, ,, 0.5 mm diameter, 25 μm thick disks from Al-1100 foils, at velocities from 0.5 to 4.5 km/s. The impact produces shocks in the liquid that remain planar for about 250 μm, roughly equivalent to a 40 ns run time .…”

Section: Methodsmentioning

confidence: 99%

“…Liquid nitromethane (NM) has for decades served as a model system for shock wave ignition and the shock-to-detonation transition in condensed-phase explosives. , In NM, the shock-to-detonation transition is a reactive flow in a nominally homogeneous fluid. It is “nominally” homogeneous because the shocked liquid produces gas and a carbon-rich solid condensate , often called “soot”.…”

Section: Introductionmentioning

confidence: 99%

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Ethylenediamine Catalyzes Nitromethane Shock-to-Detonation in Two Distinct Ways

2021

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Adding amines to liquid nitromethane (NM) is known to lower the threshold for the shock-to-detonation transition because amines catalyze proton transfer reactions that are the initial steps in the energy release process. We studied NM with 1 wt % ethylenediamine (NM/EDA) with 4 ns input shocks using time and space resolved diagnostics: photon Doppler velocimetry (PDV), optical pyrometry, and nanosecond video imaging. The 4 ns shocks are fast enough to time-resolve the reaction kinetics and the shock-to-detonation transition. We find that it is possible to shock ignite the NM/EDA without producing a detonation, so there is more to amine sensitization of the shock-to-detonation process than simply lowering the barrier to initial reactions. We find that although 1 wt % EDA has little effect on the ambient properties of NM, it dramatically alters the Hugoniot. The shock speed in NM/EDA is reduced, indicating that shocked NM/EDA is significantly more compressible than NM. Higher compressibility is associated with greater adiabatic heating, so EDA both lowers the barrier to proton transfer reactions and increases shock energy absorption. To explain the enhanced compressibility, we propose that shocking NM/EDA produces a reactive flow that has a much higher ionic strength than in NM. The sudden transformation from a molecular liquid to an ionic liquid with stronger intermolecular interactions is responsible for enhanced compressibility and shock heating.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Ethylenediamine Catalyzes Nitromethane Shock-to-Detonation in Two Distinct Ways

2021

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“…The input shocks were about 4 ns in duration, which produced a calculated pressure of 19 GPa in the PU polymer and 25 GPa in the explosive crystal (Supporting Information (SI), Section I). The shock compression microscope with a high-speed camera and optical pyrometer is depicted in Figure b and has been described in detail elsewhere. ,− A photon Doppler velocimeter (PDV) was used to measure the flyer plate velocity, and the entire sample manifold is held under rough vacuum (100 mTorr). , A spatial filter at an auxiliary focus was used to select the region of interest for viewing by the camera or pyrometer. The spatial filter was also used to exclude light artifacts, including triboluminescence, resulting from flyer launching. , …”

Section: Methodsmentioning

confidence: 99%

Observing Hot Spot Formation in Individual Explosive Crystals Under Shock Compression

et al. 2020

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The formation of hot spots in dynamically compressed, plastic-bonded explosives is known to be the primary mechanism by which these materials ignite and initiate, but hot spots are small, fleeting, and hard to observe. Using a microscope equipped with laser-launched, miniflyer plates, we have studied hot spots in small grains of cyclotetramethylene-tetranitramine (HMX) embedded in a polyurethane binder, shocked to about 20 GPa. A nanosecond video with 4 μm spatial resolution is used to observe hot spot formation and growth, while nanosecond optical pyrometry measured temperature. Using individual ∼200 μm nominally single crystals of HMX (HMX-SC), we observed hot spots forming preferentially on corners or edges. These hot spots are about 4000 K. When there are multiple hot spots, the flame propagated along crystal edges, and the crystal is mostly combusted after about 300 ns. Using polycrystalline grains (HMX-PC), 6000 K hot spots are created near internal defects or crystal junctions. However, the thermal mass of the material at 6000 K is quite small, so after those hot spots cool down, the HMX combustion is similar to the single crystals. Comparing a HMX-based polymer-bonded explosive (PBX) to the individual polymer-bonded HMX-SC and HMX-PC grains shows that the myriad hot spots in the PBX are hotter than HMX-SC and colder than HMX-PC, but they persist for a longer time in PBX than in the individual grains.

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Shock Compression Spectroscopy Under a Microscope

Dlott

2019

31st International Symposium on Shock Waves 1

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Shock compression dynamics under a microscope

Cited by 14 publications

References 30 publications

Ethylenediamine Catalyzes Nitromethane Shock-to-Detonation in Two Distinct Ways

Ethylenediamine Catalyzes Nitromethane Shock-to-Detonation in Two Distinct Ways

Observing Hot Spot Formation in Individual Explosive Crystals Under Shock Compression

Shock Compression Spectroscopy Under a Microscope

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