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 O4: Phase Transitions II: Metals I |
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Chair: Nenad Velisavljevic, Los Alamos National Laboratory, John Carpenter, Sandia National Laboratories Room: Grand H |
Wednesday, June 17, 2015 9:15AM - 9:30AM |
O4.00001: In Situ X-ray diffraction of Mo on a light gas gun Minta Akin, Brian Maddox, Neil Holmes We report on recent results using a newly developed x-ray diffraction system on a two stage light gas gun.~~Using slightly focusing polycapillary x-ray optics we are able to significantly reduce the background noise, improving diffraction~lines, while keeping the x-ray source over 1 meter away and away from possible shrapnel sources. Using this system we obtained diffraction patterns for molybdenum and tin, and will discuss these results. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Wednesday, June 17, 2015 9:30AM - 9:45AM |
O4.00002: X-ray diffraction of solid tin to 1.2 TPa Amy Lazicki, Ryan Rygg, Federica Coppari, Ray Smith, Dayne Fratanduono, Dave Braun, Richard Kraus, Damian Swift, Gilbert Collins, Jon Eggert We present x-ray diffraction studies of solid crystal structure at the highest stress state where such measurements have ever been performed. Using laser-driven ramp compression methods coupled with angle-resolved powder x-ray diffraction at the Omega laser facility, we explore the phase diagram of tin below the melting curve between 0.1 and 1.2 terapascals (TPa). We demonstrate that, at dynamic-compression rates on the order of 10$^7$ s$^{-1}$, tin transforms from the ambient tetragonal beta-Sn phase to the stable high pressure body-centered cubic (bcc) phase with densities consistent with static-compression measurements. Above 0.16 TPa our experiments identify a new feature in the phase diagram: a crystal structure clearly inconsistent with the hexagonal-close-packed (hcp) phase identified at these conditions by ambient-temperature static-compression measurements and by zero-kelvin density functional theory structure predictions. Our results suggest that the bcc phase is stabilized relative to hcp at high temperature, analogous to the heavier group IV metal Pb and numerous other elemental metals, and retains this phase during ramp compression to 1.2 TPa. [Preview Abstract] |
Wednesday, June 17, 2015 9:45AM - 10:00AM |
O4.00003: Melting Curves of Tin, Iron, and Tantalum from In-Situ X-Ray Diffraction Richard Kraus, Federica Coppari, Dayne Fratanduono, Amy Lazicki, Damian Swift, Jon Eggert, Gilbert Collins The melting curve represents a tremendous rheological transition, from a material with strength to one without. This transition is critical to the evolution of the Earth, as the latent heat from solidification of Earth's inner core helps to drive the magneto-dynamo in the liquid outer-core. The sound velocity along the Hugoniot has been used as a diagnostic of melting, however, the interpretation of the data has sometimes come into question and diamond anvil cells are limited in pressure and temperature. Here we present melting and re-solidification experiments at the Omega and Omega EP laser facilities. We use in-situ x-ray diffraction as a diagnostic of melting along the principal Hugoniots of iron and tantalum. We also present data on the re-crystallization of tin on the nanosecond timescale after re-compression from the Hugoniot state. We use signal from both solid diffraction and diffuse scattering from the liquid to constrain melting and solidification. We are able to show that melting and solidification can occur on nanosecond timescales and that these techniques can be used to determine the equilibrium ultra-high pressure melting curves of a wide range of materials. [Preview Abstract] |
Wednesday, June 17, 2015 10:00AM - 10:15AM |
O4.00004: Dynamic reflectance of tin shocked from its beta to BCT phase Gerald Stevens, Brandon La Lone, Lynn Veeser, Dale Turley Shock-induced phase transitions have historically been inferred by features in loading/unloading velocity wave profiles, which arise due to volume or sound speed differences between phases. In 2010, we used a flash-lamp illuminated multi-band reflectometer to demonstrate that iron, tin, cerium, and gallium have measureable reflectance changes at phase boundaries. We have improved upon our prior technique, utilizing an integrating sphere with an internal xenon flash lamp to illuminate a shocked metal beneath a LiF window. The new reflectance system is insensitive to motion, tilt, or curvature and measures the absolute (not relative) reflectance within five bands centered at 500, 700, 850, 1300, and 1550 nm. We have made dynamic reflectance measurements of tin samples shocked to pressures above and below the beta-bct phase transition using either high explosives or a gas gun. Below the transition, the visible reflectance decreases with pressure. At and above the transition, the visible reflectance increases to values higher than the ambient values. Reflectance can therefore be used to locate the beta-bct phase transition boundary for tin, independent of the velocity wave profile. [Preview Abstract] |
Wednesday, June 17, 2015 10:15AM - 10:30AM |
O4.00005: Modeling dynamic beta-gamma polymorphic transition in Tin Camille Chauvin, Frank Montheillet, Jacques Petit Solid-solid phase transitions in metals have been studied by shock waves techniques for many decades. Recent experiments have investigated the transition during isentropic compression experiments and shock-wave compression and have highlighted the strong influence of the loading rate on the transition. Complementary data obtained with velocity and temperature measurements around the polymorphic transition beta-gamma of Tin on gas gun experiments have displayed the importance of the kinetics of the transition. But, even though this phenomenon is known, modeling the kinetic remains complex and based on empirical formulations. A multiphase EOS is available in our 1D Lagrangian code Unidim. We propose to present the influence of various kinetic laws (either empirical or involving nucleation and growth mechanisms) and their parameters (Gibbs free energy, temperature, pressure) on the transformation rate. We compare experimental and calculated velocities and temperature profiles and we underline the effects of the empirical parameters of these models. [Preview Abstract] |
Wednesday, June 17, 2015 10:30AM - 10:45AM |
O4.00006: Phase transition of tin under ramp compression Tao Chong, Jianheng Zhao, Zhiping Tang, Fuli Tan In this paper, the phase transition experiments of tin were done under magnetically driven quasi-isentropic compression technology on the facility CQ-4,which is capable to deliver a current of peak of 4 MA within rise time of 470 $\sim$ 600ns. As shown in Figure 1, the loading pressure P produced by large pulsed current J interaction with the self-inducing magnetic field B acts on the surfaces of electrodes of electrode panels. Simulation of one dimensional dynamic process with MEOS (multiphase~equation of state) phase transition model is done. The simulation input is a stress loading history boundary of surfaces of electrode panels, and the stress is calculated by the plate/window interface velocity. Since the plate/window interface velocity doesn't have the information of the rarefaction wave reflection between the sample and window, the process can only simulate the loading stage now. [Preview Abstract] |
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