Bulletin of the American Physical Society
19th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 60, Number 8
Sunday–Friday, June 14–19, 2015; Tampa, Florida
Session D2: Energetic and Reactive Materials I: Reactive Materials I |
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Chair: Scott Stewart, University of Illinois at Urbana-Champaign, Christopher Molek, Air Force Research Laboratory, Eglin Room: Grand F |
Monday, June 15, 2015 2:00PM - 2:15PM |
D2.00001: Shock induced crystallization of amorphous Nickel powders Mathew Cherukara, Alejandro Strachan Recent experimental work has shown the efficacy of amorphous Ni/crystalline Al composites as energetic materials, with flame velocities twice that of a comparable crystalline Ni/crystalline Al system. Of further interest is the recrystallization mechanisms in the pure amorphous Ni powders, both thermally induced and mechanically induced. We present large-scale molecular dynamics simulations of shock-induced recrystallization in loosely packed amorphous Nickel powders. We study the time dependent nucleation and growth processes by holding the shocked samples at the induced pressures and temperatures for extended periods following the passage of the shock (up to 6 ns). We find that the nanostructure of the recrystallized Ni and time scales of recrystallization are dependent on the piston velocity. At low piston velocities, nucleation events are rare, leading to long incubation times and a relatively coarse nanostructure. At higher piston velocities, local variations in temperature due to jetting phenomena and void collapse, give rise to multiple nucleation events on time scales comparable to the passage of the shock wave, leading to the formation of a fine-grained nanostructure. Interestingly, we observe that the nucleation and growth process occurs in two steps, with the first nuclei crystallizing into the BCC structure, before evolving over time into the expected FCC structure. [Preview Abstract] |
Monday, June 15, 2015 2:15PM - 2:30PM |
D2.00002: Laser Interferometry Measurements of Cold-Sprayed Copper Thermite Shocked to 30 GPa Christopher Neel, David Lacina Plate impact experiments were conducted on a cold-sprayed Al-CuO thermite at peak stresses varying between 5-30 GPa to determine the Hugoniot and characterize any shock induced energetic reaction. Photon Doppler Velocimetry (PDV) measurements were used to obtain particle velocity histories and shock speed information for both the shock loading and unloading behavior of the material. Low stress experiments (\textless 20GPa) exhibited a linearly increasing shock speed with increasing particle velocity. However, an obvious change in slope (i.e. a ``kink'') is present in the Hugoniot at stresses above $\sim$ 20 GPa which follow a linear increase up to the highest stresses attained in this work. The change in Hugoniot curve suggests a volume-increasing reaction occurs in this shocked Al-CuO thermite near 20 GPa, but an analysis of the measured particle velocity histories does not support this assertion. To better characterize any shock-induced thermite reactions, emission spectroscopy measurements were obtained at stresses above and below 20 GPa. [Preview Abstract] |
Monday, June 15, 2015 2:30PM - 3:00PM |
D2.00003: Exploring Rapid Initiation of Intermixing, Phase Formation, and Combustion in Reactive Materials Invited Speaker: Timothy Weihs Reactive materials are being developed and commercialized for a variety of applications ranging from local heat sources for bonding to controlled burning for chemical time delays to dispersed heat sources for bioagent and target defeat. In all cases the reactive materials are fabricated into an unstable state from which large amounts of energy can be released. This is true for materials that enable formation reactions, reduction-oxidation reactions, and simple combustion reactions. In this presentation we consider a number of the factors that control the initiation of reactions as well as the rate of heat release in the full reaction. The initiation of formation and reduction-oxidation reactions will be explored following pulses of thermal, electrical and mechanical energy, and the impact of reactant chemistry and microstructure on ignition will be identified. In the final part of the presentation we will review the impact of chemistry and geometry on the combustion of reactive foils and particles in air. Results from novel in situ studies will be presented, along with numerical simulations and direct measurements of reaction temperatures, propagation rates, and heat production. [Preview Abstract] |
Monday, June 15, 2015 3:00PM - 3:15PM |
D2.00004: High Energy Density Nitrogen-Rich Extended Solids Dane Tomasino, Minseob Kim, Choong-Shik Yoo The application of thermo-mechanical energy (by high pressures and temperatures) comparable to chemical bond energies in solids can contribute to this concept in unique ways, as it often converts simple molecular solids into novel three-dimensional network structures in high energy density states. A good example is \textit{cg}-N that was initially predicted to be stable at high pressures and later discovered by laser-heating experiments$^{\, }$above 110 GPa and 2000 K. In this talk, we will describe our recent finding of yet-another form singly bonded polymeric nitrogen, synthesized in the stability field higher than that of cg-N. This new phase is characterized by its singly bonded, layered polymeric (LP) structure similar to the predicted \textit{Pba2} and two colossal Raman bands, arising from two groups of highly polarized nitrogen atoms. The present result also provides a new constraint for the nitrogen phase diagram, highlighting an unusual symmetry lowering \textit{3D cg}- to \textit{2D} LP-N transition and thereby the enhanced electrostatic contribution to the stabilization of this densely packed LP-N. [Preview Abstract] |
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