Bulletin of the American Physical Society
18th Biennial Intl. Conference of the APS Topical Group on Shock Compression of Condensed Matter held in conjunction with the 24th Biennial Intl. Conference of the Intl. Association for the Advancement of High Pressure Science and Technology (AIRAPT)
Volume 58, Number 7
Sunday–Friday, July 7–12, 2013; Seattle, Washington
Session H5: GP1: Geophysics II |
Hide Abstracts |
Chair: Natalia Dubrovinskaia, University of Bayreuth Room: Cascade I |
Tuesday, July 9, 2013 9:15AM - 9:30AM |
H5.00001: Analytic multiphase equation of state for MgO O. Heuze, D.C. Swift, N.D. Drummond, R.G. Kraus, G.J. Ackland MgO is an important prototype and end-member constituent for the mantle of rocky planets. Planetary structures and the response to impacts depend on the equation of state (EOS), notably including any phase transitions. MgO adopts the B1 crystal structure under ambient conditions, and has been predicted to change to B2 under compression. There are large variations in theoretical predictions of this transition and of the conditions for shock melting; experimental observations are inconsistent or unclear. We have previously constructed equilibrium B1-B2 EOS for MgO, in tabular form, using ab initio electronic structure calculations based on density functional theory and the quasiharmonic approximation for lattice vibrations. Here, we use our new formalism for thermodynamically-complete Mie-Grueneisen EOS to construct an analytic, multiphase EOS for MgO. We also constructed an approximate liquid EOS as a perturbation of the B1. We investigated the effect of phase change kinetics, including an asymptotic case in which the Maxwell construction is omitted. The principal shock Hugoniot calculated using kinetics appears to agree closely with pressure-temperature states measured for a decaying shock, corresponding to the B1-B2 region of the EOS. [Preview Abstract] |
Tuesday, July 9, 2013 9:30AM - 9:45AM |
H5.00002: Elastic Anisotropy and Auxetic Behavior in Minerals Thomas Duffy The elastic properties of minerals are of fundamental importance for understanding thermodynamic and mechanical behavior as well as for interpretation of seismic data. In recent years, there has been renewed interest in novel aspects of single-crystal elastic behavior. A database of single-crystal elastic properties of minerals and related phases has been constructed in order to evaluate auxetic behavior among minerals at ambient conditions and at high P and T. Partially auxetic behavior (directions with negative Poisson's ratios) is common among minerals, especially among the quartz, rutile, calcite, spinel, and sphalerite structures. Auxetic behavior is most common in the cubic and trigonal systems and correlates strongly with the elastic anisotropy as measured by the universal anisotropy index. MgO provides a striking example of P-T tuning of auxeticity and anisotropy. The larger variation in elastic anisotropy of MgO from ambient P and 3000 K to ambient T and 250 GPa samples nearly the entire range of extrema in Poisson's ratio of cubic crystals. MgO is strongly auxetic along [110] at high temperatures. [Preview Abstract] |
Tuesday, July 9, 2013 9:45AM - 10:00AM |
H5.00003: MgO melting curve constraints from shock temperature and rarefaction overtake measurements in samples preheated to 2300 K O.V. Fat'yanov, P.D. Asimow In a continuous effort to determine experimentally the melting curve of MgO at 100-200 GPa, we extended our target preheating capability to 2300 K. The limit was primarily caused by intense sublimation of pure MgO in vacuum above $\sim$2050 K. Completely redesigned Mo capsules holding $\sim$20 mm long MgO crystals with controlled thermal gradients were impacted by thin Ta flyers launched at 6.5 to 7.5 km/s on the Caltech two-stage light-gas gun. Radiative shock temperatures and rarefaction overtake times were measured simultaneously by a 6-channel pyrometer with 3 ns time resolution, over 440-750 nm spectral range. All our experiments showed smooth pressure dependence of MgO sound speed consistent with the solid phase at 204-239 GPa. Observed temperatures are $\sim$1000 K lower than those predicted by the solid phase model, but the plot of measured shock temperature versus pressure exhibits a pattern typical of shock melting at the highest pressure investigated. This may suggest that the Hugoniot of MgO preheated to 2300 K crosses its melting line at 220-240 GPa. Sound speed data indistinguishable from the solid phase model do not exclude the possibility of melting there. [Preview Abstract] |
Tuesday, July 9, 2013 10:00AM - 10:15AM |
H5.00004: Ramp compression of magnesium oxide to 234 GPa Jue Wang, Raymond F. Smith, Federica Coppari, Jon H. Eggert, Thomas R. Boehly, Gilbert W. Collins, Thomas S. Duffy Periclase, MgO, is of fundamental importance for geophysics as the end-member of the ferropericlase, (Mg,Fe)O, solid solution. It is also of interest for understanding the interiors of extrasolar planets. In this work, we report a study of MgO using laser-based ramp compression. Ramp wave loading can be used to obtain equation-of-state data in the region of thermodynamic space lying between the principal isentrope and Hugoniot. Ramp compression experiments were performed using the Omega laser at LLE of the University of Rochester. A series of three steps were lithographically etched into a single-crystal MgO wafer that was then polished to the requisite thickness. A planar compressive wave was launched into the sample with high-powered ramp-shaped laser pulse. The free surface velocities of different sample thicknesses were measured using a line-imaging VISAR. The velocity profiles were integrated to obtain the stress-density response using a Lagrangian analysis technique. Our experiments reached a maximum pressure of 234 GPa, and the measured equation of state is consistent with previous shock and static studies. [Preview Abstract] |
Tuesday, July 9, 2013 10:15AM - 10:45AM |
H5.00005: Transport properties of the Earth's core Invited Speaker: Dario Alfe I will report on the thermal and electrical conductivities of iron and two liquid silicon-oxygen-iron mixtures (Fe$_{0.82}$Si$_{0.10}$O$_{0.08}$ and Fe$_{0.79}$Si$_{0.08}$O$_{0.13}$), representative of the composition of the Earth's outer core at the relevant pressure-temperature conditions, obtained from density functional theory calculations with the Kubo-Greenwood formulation. We find thermal conductivities $k$ =100 (160) W m$^{-1}$ K$^{-1}$, and electrical conductivities $\sigma = 1.1 (1.3) \times 10^6 \Omega^{-1}$ m$^{-1}$ at the top (bottom) of the outer core. These values are between 2 and 3 times higher than previous estimates, and have important implications for our understanding of the Earth's thermal history and the functioning of the Earth's magnetic field, including rapid cooling rate for the whole core or high level of radiogenic elements in the core. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700