Dynamic Structural and Chemical Responses of Energetic Solids
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Dynamic Structural and Chemical Responses of Energetic Solids Haoyan Wei and Choong-Shik Yoo Department of Chemistry and Institute for Shock Physics, Washington State University, Pullman, WA 99164, U.S.A.
ABSTRACT Understanding the dynamic responses of energetic materials is central to evaluating the energetic and chemical performance as well as development of novel energetic solids. These include thermal, mechanical and chemical processes in a relevant temporal (ns-to-s) and spatial (atomistic-to-micro) scales. In this paper, we describe our recent developments of time-resolved characterization techniques capable of probing real-time structural and chemical evolutions across single event, metal combustions and intermetallic reactions. The methods utilize highspeed microphotography, spectro-pyrometry, and synchrotron x-ray powder diffraction and determine in-situ the particle sizes, temperatures and structures in s time resolution. These timeresolved data provide insights into the fragmentation dynamics, thermal history, phase transitions, reaction mechanisms, and chemical kinetics governing these exothermic metal combustions and intermetallic reactions.
INTRODUCTION Understanding the dynamic response of solids under extreme conditions of pressure, temperature and strain rate is a fundamental scientific quest and a basic research need in materials science. Specifically, obtaining the atomistic/molecular level description of structural and chemical changes of solids under rapid heating and/or compression over a large temporal, spatial and energy range is critical to understanding the dynamics and mechanisms of mechanical deformation and fractures, thermal and mass diffusions, structural phase transitions, and chemical reactions. Coupled with reaction quenching, ex-situ static characterization techniques, such as electron microscopy, energy- or wavelength- dispersive spectroscopy and calorimetry, have been a popular approach to study the microstructural and chemical changes at different combustion stages.1,2 Additionally, slow kinetic x-ray diffraction with time-resolution of only millseconds is utilized to investigate the structural changes in the reaction.3 Although these techniques are well suitable in understanding initial/final states and slow reactions at later stages, they are inadequate in revealing the fast dynamic changes, especially at the critical initial stage, because of the inability to freeze the reaction by quenching or to capture the transient steps by slow kinetic techniques. Therefore, in-situ dynamic characterization capability is essential in order to develop new energetic materials and better engineer existing materials. However, obtaining such realtime dynamic information in energetic solids across single-event exothermic processes such as combustions, deflagration, and detonation is a daunting challenge and requires time-resolved structural and chemical probes in micro- and nano-second time frames. Because of the very short acquisition time for each time stamp, the signal-to-noise ratio is
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