Bulletin of the American Physical Society
20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017; St. Louis, Missouri
Session L7: Phase Transitions IV |
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Chair: David Jones, Los Alamos National Laboratory Room: Regency Ballroom F |
Tuesday, July 11, 2017 3:45PM - 4:00PM |
L7.00001: Phase transitions in shocked porous quartz M. C. Akin, R. S. Crum, J. Lind, D. C. Pagan, M. A. Homel, R. C. Hurley, E. B. Herbold The presence of porosity in granular media provides the means to probe regions of the phase diagram that do not coincide with the principal Hugoniot. In particular, the potential for increased heating is likely to lead to observable changes in phase boundaries. 55{\%} dense quartz and forsterite were prepared by tap filling. These samples were shock compressed using the two stage light gas gun at DCS-APS to examine the impact of the increased porosity on the phase boundary. Here we discuss the observed changes to phase in quartz and forsterite compared to the fully dense materials, the effects of porosity upon compaction and phase transitions, and the implications for constructing the phase diagram.\\ \\Funding Acknowledgement: This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Work was supported by LLNL’s LDRD program under grant 16-ERD-010. The Dynamic Compression Sector (35) is supported by Department of Energy / National Nuclear Security Administration under Award Number DE-NA0002442. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. [Preview Abstract] |
Tuesday, July 11, 2017 4:00PM - 4:15PM |
L7.00002: Shock Induced Phase Changes in Forsterite and Iron Silicide M. Newman, P. Asimow, R.G. Kraus, R. Smith, F. Coppari, J.H. Eggert, J. Wicks, S. Tracy, T. Duffy The equation of state of magnesium silicates and iron alloys at the pressures and temperatures near the melt curve is important for understanding the thermal evolution and interior structure of rocky planets. Here, we present a series of laser driven shock experiments on single crystal Mg$_{\mathrm{2}}$SiO$_{\mathrm{4}}$ and textured polycrystalline iron silicide (Fe-15Si), conducted at LLE. In situ x-ray diffraction measurements were used to probe the melting transition and investigate the potential decomposition of forsterite into solid MgO and silica rich liquid and Fe-15Si in to silicon rich B2 and iron rich hcp structures. This work examines kinetic effects of chemical decomposition due to the short time scale of laser-shock experiments. Preliminary results demonstrate solid-solid and solid-liquid phase transitions on both the forsterite and Fe-15Si Hugoniots. For Fe-15Si, we observe a texture preserving martensitic transformation of D03 Fe-15Si into an hcp structure and melting at 318 GPa. For forsterite, we observe diffraction consistent with B1 MgO and melting at 215 GPa. [Preview Abstract] |
Tuesday, July 11, 2017 4:15PM - 4:45PM |
L7.00003: In situ observation of high-pressure phase transition in silicon carbide under shock loading using ultrafast x-ray diffraction Invited Speaker: Sally June Tracy SiC is an important high-strength ceramic material used for a range of technological applications, including lightweight impact shielding and abrasives. SiC is also relevant to geology and planetary science. It may be a host of reduced carbon in the Earth's interior and also occurs in meteorites and impact sites. SiC has also been put forward as a possible major constituent in the proposed class of extra-solar planets known as carbon planets. Previous studies have used wave profile measurements to identify a phase transition under shock loading near 1 Mbar, but lattice-level structural information was not obtained. Here we present the behavior of silicon carbide under shock loading as investigated through a series of time-resolved pump-probe x-ray diffraction measurements up to 200 GPa. Our experiments were conducted at the Materials in Extreme Conditions beamline of the Linac Coherent Light Source. \textit{In situ} x-ray diffraction data on shock-compressed SiC was collected using a free electron laser source combined with a pulsed high-energy laser. These measurements allow for the determination of time-dependent atomic arrangements, demonstrating that the wurtzite phase of SiC transforms directly to the B1 structure. Our measurements also reveal details of the material texture evolution under shock loading and release. [Preview Abstract] |
Tuesday, July 11, 2017 4:45PM - 5:00PM |
L7.00004: Dynamic XRD, Shock and Static Compression of CaF$_{\mathrm{\mathbf{2}}}$ Patricia Kalita, Paul Specht, Seth Root, Nicholas Sinclair, Adam Schuman, Melanie White, Andrew Cornelius, Jesse Smith, Stanislav Sinogeikin The high-pressure behavior of CaF$_{\mathrm{2}}$ is probed with x-ray diffraction (XRD) combined with both dynamic compression, using a two-stage light gas gun, and static compression, using diamond anvil cells. We use XRD to follow the unfolding of a shock-driven, fluorite to cotunnite phase transition, on the timescale of nanoseconds. The dynamic behavior of CaF$_{\mathrm{2}}$ under shock loading is contrasted with that under static compression. This work leverages experimental capabilities at the Advanced Photon Source: dynamic XRD and shock experiments at the Dynamic Compression Sector, as well as XRD and static compression in diamond anvil cell at the High-Pressure Collaborative Access Team. These experiments and cross-platform comparisons [1], open the door to an unprecedented understanding of equations of state and phase transitions at the microstructural level and at different time scales and will ultimately improve our capability to simulate the behavior of materials at extreme conditions. [1] S. Root \textit{et al}., Shock Compression Response of Calcium Fluoride. This Conference. \textit{Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.} [Preview Abstract] |
Tuesday, July 11, 2017 5:00PM - 5:15PM |
L7.00005: Shock Compression of Highly Oriented Pyrolytic Graphite: Role of Microstructure on the Phase Transformation Travis Volz, Y. M. Gupta Past experiments on shock-compressed highly oriented pyrolytic graphite (HOPG) have shown that HOPG samples with different orientational orders respond differently above and below the \textasciitilde 20 GPa phase transition. The objectives of the present study are to examine and compare the high pressure response of the ZYH-grade HOPG and ZYB-grade HOPG above the phase change stress, to determine the structure of the high pressure phase for the two types of HOPG samples, and to understand the role of the orientational order on the phase change mechanisms in shocked HOPG. Three types of plane shock wave~experiments, utilizing time-resolved measurements, are being conducted to address these objectives. Transmission experiments to measure the propagating wave profiles, front-surface impact experiments to accurately characterize the peak shocked state and to determine the longitudinal sound speeds in the peak state, and XRD measurements to determine the microstructure of shocked ZYB and ZYH-grade HOPG samples above the transition. All three types of experiments have provided good initial data and analysis of the experimental results is currently underway. Our initial findings suggest that~the shock response of the two HOPG grades, above the phase change stress, is more similar than previously reported. Further experiments and detailed analyses are underway. [Preview Abstract] |
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