Bulletin of the American Physical Society
16th APS Topical Conference on Shock Compression of Condensed Matter
Volume 54, Number 8
Sunday–Friday, June 28–July 3 2009; Nashville, Tennessee
Session C5: GS-1: Rocks and Minerals |
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Chair: Sarah Stewart, Harvard University Room: Magnolia Ballroom |
Monday, June 29, 2009 11:00AM - 11:15AM |
C5.00001: On the Relationship between HEL and Grain Size in Geological Materials C.H. Braithwaite, D.J. Chapman, J.E. Field, W.G. Proud Through the use of laterally mounted stress gauges the HELs of various geological materials have been measured. These materials, kimberlite, basalt, siltstone, quartz/feldspathic gneiss and amphibolite show a range of HEL values, from 1.3 GPa to 5 GPa. The value of the HEL appears to be influenced strongly by the grain size of the material, whereas, for example, it would appear to be independent of both the elastic properties and the measured Hugoniot. The current experimental data has been supplemented with relevant literature data. [Preview Abstract] |
Monday, June 29, 2009 11:15AM - 11:30AM |
C5.00002: Effect of Crystalline Anisotropy on Shock Propagation in Sapphire G.I. Kanel, W.J. Nellis, A.S. Savinykh, S.V. Razorenov, A.M. Rajendran The shock-wave response of sapphire of seven orientations ($c$, $d$ , $r$, $n$, $s$, $g$, $m)$ which correspond to the angles between the load direction and the $c$-axis varying from 0 to 90 degrees was investigated with the goal to find optimal conditions of its use as a window material. In the experiments at shock stresses in a range from 16 GPa up to 85 GPa the VISAR particle velocity histories were recorded using LiF windows. In most cases measured waveforms are noisy as a result of heterogeneity of deformation. The measured HEL values depend on peak shock stress and direction of shock compression. Highest HEL values reaching 24 GPa have been recorded at shock loading along c-axis and perpendicularly to it ($c$- and $m$-directions) whereas shock compression along the $s$-direction is accompanied with smallest heterogeneity of the deformation and smallest rise time in plastic shock wave. Results of experiments with varying transversal stresses admit to conclude that inelastic deformation of sapphire begins in ductile mode and leads to fracture and fragmentation as a result of interaction of shear bands or twins. [Preview Abstract] |
Monday, June 29, 2009 11:30AM - 11:45AM |
C5.00003: Isothermal equation of state for MgO derived from shock Hugoniot data and its implication on pressure scale Ke Jin, Qiang Wu, Xinzhu Li, Lingcang Cai, Fuqian Jing The isothermal bulk modulus, its first pressure derivative and the specific volume at zero pressure and temperature for MgO were derived directly from the experimental shock Hugoniot data with a simple method. Based on the derived parameters and Vinet equation of state, the isothermal equations of state for MgO were calculated to the relative volume change of 0.55 and high temperatures, which have excellent agreements with the available quasi-hydrostatic measurements in diamond-anvil-cell experiment. Comparison of the calculated results with the previous theoretical investigations also has been performed. The crosscheck on independent data and the excellent agreements with experimental data confirm that the present isothermal equations of state for MgO can be used as high-pressure scale for future static DAC experiments. [Preview Abstract] |
Monday, June 29, 2009 11:45AM - 12:00PM |
C5.00004: Shock temperatures of preheated MgO O.V. Fat'yanov, P.D. Asimow, T.J. Ahrens Shock temperature measurements via optical pyrometry are being conducted along $<$100$>$ single-crystal MgO preheated before compression to 1923 K. Planar shocks were generated by impacting hot Mo(driver plate)-MgO targets with Mo flyers launched by the Caltech two-stage light-gas gun up to 6.5 km/s. At this velocity, calculated Hugoniot pressure in MgO is 172 GPa and the 4-channel brightness temperature is 5700 K. Extrapolating previous Hugoniot EOS centered at 298 K to present preheated states predict Hugoniot temperature of 6800 K for the solid. The $\sim $1000 K temperature deficit suggests MgO melting above 155 GPa and 5200 K. This is consistent with the relatively flat melting curve extrapolated from diamond anvil cell results (Zerr {\&} Boehler) and some molecular dynamics (MD) studies (Strachan et al) but not with the steeper melting curves from most MD studies (Cohen {\&} Weitz, Belonoshko). Features of preheated shock temperature experiments, pyrometer calibration and multichannel radiance data processing are discussed. [Preview Abstract] |
Monday, June 29, 2009 12:00PM - 12:15PM |
C5.00005: Ultra High-Pressure Equation of State and Melting of MgSiO$_{3}$ Dylan Spaulding, Raymond Jeanloz New laser-driven shock experiments, using both single-crystal and glass starting materials, extend equation of state measurements on MgSiO$_{3}$ to 4.5 Mbar and 15,000 K. Simultaneous collection of temporally and spatially resolved velocimetry, pyrometry and reflectivity data document shock-induced melting at pressures above 275GPa, with an apparent increase in optical reflectivity ($>$20{\%}) and density (several percent). These observations indicate transformation to a metallic state upon melting, implying that the distinction between silicate and metallic constituents are blurred at Earth's core-mantle boundary. This was particularly the case at the high temperatures and pressures present after the late-stage giant impact that formed the Moon. [Preview Abstract] |
Monday, June 29, 2009 12:15PM - 12:30PM |
C5.00006: Advances in Shock Compression of Mantle Minerals and Implications Thomas Ahrens, Jed Mosenfelder, Paul Asimow Synthesis and consolidation of polycrystalline, 3 mm diameter, shock wave targets of the high-pressure mantle polymorphs Mg$_{2}$SiO$_{4}$ wadsleyite and MgSiO$_{3}$ perovskite was carried out in multi-anvil high-pressure modules at Caltech and Bayreuth, respectively. Hugoniot equation of state measurements on these samples, together with data on lower-density isochemical materials, constrain the thermal equations of state and melting temperatures of the simplified lower mantle assemblages MgSiO$_{3 }$(perovskite and post-perovskite) and MgSiO$_{3}$(perovskite) + MgO. Evaluation of V($\partial $P/$\partial $E)$_{v}$ for the high-pressure melts of both compositions yield Gr\"{u}neisen parameters that \textbf{\textit{increase}} by about a factor of three upon two-fold compression. This result predicts a large temperature increase with depth along a model lower mantle magma ocean adiabat, and is consistent with the deep residual magma ocean model of Labrosse et al. (2007). Possibly, the high density, partially molten layer at the base of the mantle discovered by seismology is a very thin, highly enriched (K,U,Th and Xe) remnant of an ancient magma ocean. [Preview Abstract] |
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