Instrumentation To Enable Novel Real-Time Vibrational Spectroscopy Of Shocked Materials
Abstract
We are requesting instrumentation that will enable a dramatic advance in our ability to monitor the physical and chemical evolution of complex materials under dynamic shock loading. We recently constructed a novel experimental system in which a short-duration laser pulse is used to generate a shock wave and subsequent laser pulses and a multi-frame camera are used to record multiple images that display shock propagation through target samples and the sample responses to shock loading. The video images reveal macroscopic physical and chemical decomposition in samples including RDX energetic crystals and silica glass. However, the images do not show the microscopic processes that lead to macroscopic decomposition. The requested instrumentation will provide direct and incisive microscopic insight by allowing us to record the lattice and molecular vibrational spectra of samples at selected times following shock loading. The crystal lattice vibrational frequencies will reveal shock-induced phase transitions into new crystalline forms, while the molecular vibrational frequencies will reveal shock-induced chemical reactions and the identities of reaction intermediates and products. In energetic organic crystals such as RDX and other common explosives, the lattice vibrational frequencies will reveal time-dependent structural phase transitions into new crystalline forms which are believed to occur and which may precede chemical decomposition. The molecular vibrational frequencies will reveal time-dependent chemical decomposition products including the initial bond breakage events and subsequent chemical evolution. The insights gained will guide the development of energetic materials with superior properties, especially reduced shock sensitivity. In the case of silica and other glasses, the spectra will reveal time-dependent structural change from amorphous to ordered crystalline structures that have characteristic lattice vibrational frequencies. An understanding of shockinduced dynamic structural responses will guide the design of superior protective materials for shock mitigation. New laser equipment and delay stages are requested to enable us to generate wavelength-tunable femtosecond and picosecond-duration pulses that will drive and record coherent lattice and molecular vibrations at specified times following shock loading. The femtosecond stimulated Raman scattering (FSRS) vibrational spectra can be recorded in a single laser shot, so even though the shocked sample region is ultimately destroyed, the measurement can still be conducted. The microscopic, mechanistic insights that are provided, complementary to the macroscopic observations that we now carry out, will provide a detailed understanding of complex material responses to dynamic shock loading.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 10, 2018
- Source ID
- N000141812378
Entities
People
- Keith A. Nelson
Organizations
- Massachusetts Institute of Technology
- Office of Naval Research
- United States Navy