Reactive solids under shock compression

Shaw, William L

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https://hdl.handle.net/2142/95261 Copy

Description

Title

Reactive solids under shock compression

Author(s)

Shaw, William L

Issue Date

2016-08-17

Director of Research (if dissertation) or Advisor (if thesis)

Dlott, Dana D.

Doctoral Committee Chair(s)

Dlott, Dana D.

Committee Member(s)

• Glumac, Nick
• Hirata, So
• Jain, Prashant

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Flyer Plate
• Shock Wave

Abstract

In this dissertation chemically reactive solids, such as thermites and energy absorbing molecular materials, under shock compression are explored. To drive shock waves into target materials, an apparatus to launch and monitor laser-driven flyer-plates was developed. This was coupled to a home built photonic Doppler velocimeter (PDV) which tracks the motion of flyer plates and embedded gauges. This system was characterized using PDV to determine the range of impact velocities and shock wave durations that aluminum or copper flyers can impart into materials. Ultrafast stroboscopic imaging was used to determine the planarity and size of flyer plates at the time of material impact. By combining spectroscopic methods with PDV data and other observations of the launch and impact processes, we have proposed a new launch mechanism for these flyers that differs from previous ideas in the literature. Through coupling the laser-driven flyer-plate apparatus with ultrafast spectroscopic detectors such as a streak camera and photomultiplier tubes, the emission from impacted target materials was used to monitor reaction progress and postulate mechanochemical mechanisms in novel target materials. The thermite systems of interest are Al∙Teflon nanocomposite films, ball milled 8Al∙MoO3 and Zr∙CuO multi-layer nano-thermites. Target emissions from these systems were tracked with nanosecond time resolution using a wavelength integrating photomultiplier tube and wavelength resolved streak camera. Al∙Teflon experiments explore the mechanism for reactivity in this structurally relevant material. Through our tests we have determined that decompression of the aluminum nanoparticles, after shock compression, drives the fracturing of the aluminum oxide shell and initiates a self-sustained reaction. Tests on 8Al∙MoO3 explore the method for shock ignition in these reactive materials and demonstrated significant differences in the reaction processes depending on the mechanism used to initiate the reaction. This we postulate is due to disparate heating rates when CO2 laser ignition is compared with shock or spark induced ignition. We have also investigated shock reactivity in Zr∙CuO reactive nanolaminates. These experiments observed an impact velocity dependent threshold behavior for chemistry to occur and impact-to-reaction time delays that correspond with oxygen diffusion through the material. Using the laser-driven flyer-plates, a technique for detecting the attenuation of shock waves by mechanically-driven chemical reactions has been developed. The attenuating sample was spread on an ultrathin Au mirror deposited onto a glass window having a known Hugoniot. As shock energy exited the sample and passed through the mirror, into the glass, the PDV monitored the velocity profile of the ultrathin mirror. Through the window Hugoniot, the velocity profile could be quantitatively converted into a shock energy flux or fluence. The flux gave the temporal profile of the shock front, and showed how the shock front was reshaped by passing through the dissipative medium. The fluence, the time-integrated flux, showed how much shock energy was transmitted through the sample. Samples consisted of microgram quantities of carefully engineered organic compounds selected for their potential to undergo negative-volume chemistry. Post mortem analytical methods were used to confirm that shock dissipation was associated with shock-induced chemical reactions. The two systems of interest here are tetrathiofulvalene/chloranil cocrystals and ZIF-8, a zinc imidizolate metal organic framework.

Graduation Semester

2016-12

Type of Resource

text

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http://hdl.handle.net/2142/95261

Copyright and License Information

Copyright 2016 William Shaw

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