Bulletin of the American Physical Society
21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 64, Number 8
Sunday–Friday, June 16–21, 2019; Portland, Oregon
Session N6: GPS: Earth and planetary materials |
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Chair: Marius Millot, Lawrence Livermore National Laboratory (LLNL) Room: Broadway III/IV |
Wednesday, June 19, 2019 9:15AM - 9:30AM |
N6.00001: Shock velocity, sound speed, and Hugoniot temperature in silicate liquids to 100 GPa Paul Asimow, Jinping Hu, Olivia Pardo, Chang Su, Xiaojuan Ma Modeling planetary interiors and magma oceans requires the liquid properties expressed by a thermodynamically complete equation of state (EoS), relating pressure, volume, temperature, and internal energy. Shock compression offers techniques that can, in concert, yield data needed to calibrate a complete liquid EoS. The Hugoniot is not sufficient; it must be coupled with shock temperature and bulk sound speed. We studied two silicate liquids, diopside-anorthite eutectic (preheated above glass transition) and soda-lime glass. A matching pair of light gas gun shots at each pressure use thick and thin flyer plates; the Caltech six-channel pyrometer is the diagnostic. A thick flyer launches a supported shock through the sample, yielding shock temperature and shock velocity. A thin flyer produces a rarefaction wave that overtakes the shock, yielding bulk sound speed and a replicate temperature. The shock and rarefaction velocities of Mo flyers and drivers are known. Temperature data confirm heat capacities larger than ambient pressure values or classical limits. Sound speeds confirm increasing Gr\"{u}neisen parameter upon compression, consistent with previously finite difference comparison of parallel Hugoniots. More experiments will test the Mie-Gr\"{u}neisen approximation for these liquids. [Preview Abstract] |
Wednesday, June 19, 2019 9:30AM - 9:45AM |
N6.00002: Secondary Hugoniot of MgO Linda Crandall, Margaret Huff, Greg Tabak, Zaire Sprowal, J. Ryan Rygg, Danae Polsin, Mohamed Zaghoo, Gilbert Collins, Dayne Fratanduono, Ray Smith, John Eggert, Damien Hicks Magnesium oxide (MgO), or periclase, is a one of the most common constituents of Earth's mantle, as well as the cores of exoplanets. MgO also serves as a pressure standard in ramp-compression experiments because of its very stable B1 (ambient MgO solid) phase and high melting temperature. Exploring the secondary Hugoniot of materials allows us to study the phase diagram at lower temperatures than can be reached with singly shocked experiments. We present measurements of doubly shocked MgO to map the melt curve out further in pressure space. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856, the University of Rochester, and the New York State Energy Research and Development Authority. [Preview Abstract] |
Wednesday, June 19, 2019 9:45AM - 10:15AM |
N6.00003: Direct shock compression of pre-synthesized high-pressure silicates: Implication for internal structure of super-Earth Invited Speaker: Yingwei Fei Accurate measurements of the equation of state of silicate to terapascal pressure range are essential for modeling the silicate mantle of super-Earths. Using the Sandia Z-machine, my collaborators and I have performed direct shockwave loading of pre-synthesized MgSiO$_{\mathrm{3}}$-bridgmanite up to a shock velocity of 24 km/s. The large dense MgSiO$_{\mathrm{3}}$-bridgmanite samples were synthesized in the multi-anvil press using 1-inch sintered-diamond cubes, and then prepared for Z-shots. In this presentation I will describe the experimental procedure and present the Hugoniot data up to 1.2 TPa, and compare the new Z experiment data to the DFT-MD calculations. Finally, I will discuss the implications for interior structure of the observed super-Earths. [Preview Abstract] |
Wednesday, June 19, 2019 10:15AM - 10:30AM |
N6.00004: Sound Velocities in Shock-Synthesized Stishovite to 72 GPa Eleanor J. Berryman, J. Michael Winey, Yogendra M. Gupta, Thomas S. Duffy Stishovite (rutile-type SiO$_{\mathrm{2}})$ is expected to occur in the Earth's lower mantle and is an archetype for lower-mantle silicates. Constraints on the stishovite sound speed at relevant pressure and temperature conditions are necessary for understanding its thermoelastic behavior at deep Earth conditions and for interpreting seismic data. In situ X-ray diffraction measurements have shown that stishovite forms in fused silica shock-compressed above 34 GPa [Tracy, et al., PRL (2018)]. Here, we report shock-wave profiles and sound-speed measurements in fused silica shock-compressed to 44 - 72 GPa. Plate-impact experiments were conducted using a two-stage light-gas gun in both transmission (Al or Cu impacting fused silica) and front-surface-impact (fused silica impacting LiF) geometry. Laser interferometry was used to measure particle velocity profiles. The shock and particle velocities determined from the transmission-shock wave profiles are consistent with previous experiments. Longitudinal sound speeds were determined from the release wave velocities in the front-surface-impact experiments. The results will be compared to previous experimental and theoretical sound velocities for stishovite and evidence for melting on the fused silica Hugoniot will be assessed. [Preview Abstract] |
Wednesday, June 19, 2019 10:30AM - 10:45AM |
N6.00005: Shockless compression of hydrated silicate glasses Jean-Paul Davis, Alisha N. Clark, Steven D. Jacobsen, J. Matthew Lane, Kyle R. Cochrane, Joshua P. Townsend, Adam R. Sarafian Recent work suggests that Earth's mantle transition zone (MTZ, 410-660 km, 12-28 GPa) may store significant amounts of water. Low seismic velocities observed at the upper and lower boundaries of the MTZ may reflect the production of hydrous silicate melts from dehydration reactions during mantle convection. Quantifying this connection will require experimental data on the physical properties and equations of state for both hydrous and anhydrous silicate melts at relevant pressures to help understand melt fraction and volatiles content. Measurements on solid amorphous silicate glasses can provide insight to the behavior of molten silicates because both states exhibit anomalous behavior thought to arise from similar mechanisms. We performed quasi-isentropic compression experiments using Sandia's Thor small pulser on MgSiO$_{3}$ and NaSiO$_{3}$ glasses, both hydrous ($\sim$1.5 wt\%) and anhydrous ($\sim$0.05 wt\%), to as high as 30 GPa longitudinal stress. Analysis of velocimetry data from these experiments gives compressibility along a thermodynamic path closer to a planetary adiabat than the isothermal path probed by static experiments. We investigate the effect of composition on anomalous compressibility and densification, comparing to models and computations. [Preview Abstract] |
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