Bulletin of the American Physical Society
15th APS Topical Conference on Shock Compression of Condensed Matter
Volume 52, Number 8
Sunday–Friday, June 24–29, 2007; Kohala Coast, Hawaii
Session L3: Phase Transitions II |
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Chair: Dennis Hayes, Sandia National Laboratories Room: Fairmont Orchid Hotel Plaza I |
Wednesday, June 27, 2007 8:00AM - 8:15AM |
L3.00001: Effect of Pulse Duration on Polytetrafluoroethylene Shocked Above the Crystalline Phase II--III Transition Eric N. Brown, George T. Gray III, Philip J. Rae, Carl P. Trujillo, Neil K. Bourne We present an experimental study of crystalline structure evolution of polytetrafluoroethylene (PTFE) due to pressure-induced phase transitions in a semi-crystalline polymer using soft-recovery, shock-loading techniques coupled with mechanical and chemical post-shock analysis. Gas-launched, plate impact experiments have been performed on pedigreed PTFE 7C, mounted in momentum-trapped, shock assemblies, with impact pressures above and below the phase II to phase III crystalline transition. Below the phase transition only subtle changes were observed in the crystallinity, microstructure, and mechanical response of PTFE. Shock loading of PTFE 7C above the phase II--III transition was seen to cause both an increase in crystallinity from 38{\%} to $\sim $53{\%} (by Differential Scanning Calorimetry, DSC) and a finer crystalline microstructure, and changed the yield and flow stress behavior. We particularly focus on the effect of pulse duration on the microstructure evolution. [Preview Abstract] |
Wednesday, June 27, 2007 8:15AM - 8:30AM |
L3.00002: Phase transformation kinetics - equilibrium and metastable conditions Marina Bastea, S. Bastea, J. Reaugh, D. Reisman The kinetics of first order phase transformations has been a topic of great experimental and theoretical interest. The development of new high pressure techniques has brought new perspectives on this problem and new insights on long-standing scientific puzzles e.g. the formation of natural diamond and the freezing of water. Dynamic compression experiments afford the study of equilibrium and non-equilibrium processes occuring on very short time-scales - $10^{-12}$ to $10^{-6}$ s, which are otherwise difficult to investigate with most traditional static high pressure techniques. I will discuss results on the freezing of water and diamond formation along quasi-adiabatic high pressure paths. For water the emphasys will be on dynamic features resembling Van der Waals loops while for carbon I will present results on diamond formation from different initial condition states. Both systems exhibit a large metastability range. A comparison with near-equilibrium phase transformations in other materials will also be included. This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48. [Preview Abstract] |
Wednesday, June 27, 2007 8:30AM - 8:45AM |
L3.00003: Kinetics of Phase Transition Under Tailored Dynamic Compression Jeffrey H. Nguyen, Daniel Orlikowski, J. Reed Patterson, L. Peter Martin, Neil C. Holmes High Pressure-High Temperature phase boundaries are typically mapped out in static compression experiments where the kinetics of these phase transitions are not fully explored. Dynamic compression experiments, on the other hand, are traditionally limited to the principal Hugoniot or the principal quasi-isentrope. Recent advances of the functionally graded density impactor now allow us to explore the phase diagram of materials in previously inaccessible regions of the PVT phase diagram and at strain rates comparable to the time-scales of many phase transitions in metals and molecular liquids. We present here experiments exploring liquid-solid and solid-solid transitions on principal and ``hot'' quasi-isentropes. Our principal focus will be on the liquid-solid transition in water, but we will also discuss other solid-solid transitions in metals as appropriate. These phase transitions have been characterized with changes in both the particle velocity and optical properties. The kinetics of the water-ice transition will be discussed in terms of changes in the optical properties in addition to the time evolution of the ice volume fraction during the transition. This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. [Preview Abstract] |
Wednesday, June 27, 2007 8:45AM - 9:00AM |
L3.00004: Experimental and computational investigation of the shock melting properties of diamond Marcus Knudson, Michael Desjarlais, Raymond Lemke The shock melting of diamond has gained interest of late due to its possible use as an ablator material in inertial confinement fusion capsules. Recently, experiments utilizing the flyer plate capability at the Sandia Z accelerator were performed to determine the Hugoniot and the shock melting properties of polycrystalline diamond. Composite aluminum/copper flyer plates were used to shock load diamond samples to pressures ranging from 5 to 14 Mbar. Multiple samples and fast diagnostics provided Hugoniot measurements with roughly 1 percent accuracy in density. Furthermore, measurements of the release behavior may provide direct indication of the extent of the coexistence region on the Hugoniot. These high precision Hugoniot and release measurements at multi-Mbar pressures allow for high fidelity comparisons with recent quantum molecular dynamics calculations, and provide insight into the shock melting of diamond. [Preview Abstract] |
Wednesday, June 27, 2007 9:00AM - 9:30AM |
L3.00005: Dynamic compression of diamond across the melt transition Invited Speaker: The past two years have seen dramatic improvements in dynamic compression experiments on diamond using laser-induced compression methods. We will present an overview of our current experimental understanding of the phase-diagram and equation of state of high pressure carbon. We have carried out: (i) measurements the shock Hugoniot up to 3600 GPa; and, (ii) measurements of the shock front temperature along the Hugoniot that show a clear slope discontinuity when the Hugoniot enters the solid-liquid coexistence region providing the first direct observation of the pressure-temperature locus along the melt curve between 850-1100 GPa. Comparison with recent quantum molecular dynamics calculations shows better agreement than with previous models. In addition, we have observed a rate-dependent elastic limit ranging between 60 and 200 GPa. From these experiments we have been able to extract a wide variety of thermodynamic quantities, including the latent heat of fusion, the volume discontinuity at melt and the specific heat at very high pressures. In collaboration with J.H. Eggert, D.K. Bradley, A.A. Correa, E.F. Schwegler, D.G. Hicks, R.F. Smith, R.S. McWilliams, and G.W. Collins of LLNL; T.R. Boehly and J.E. Miller of the University of Rochester. [Preview Abstract] |
Wednesday, June 27, 2007 9:30AM - 10:00AM |
L3.00006: Mulitphase equation of state of Carbon from first principles simulations and applications to shock wave experiments and design Invited Speaker: Hydrodynamic and finite element simulations are of primary importance in the current point design of the ignition capsules for fusion at the National Ignition Facility. In particular, nano-structured diamond has been proposed as an ablator material. The reliability of the hydrodynamic results depends critically on the equation of state tables used as input. Ab initio molecular dynamics and electronic structure calculation had become one of the most useful tools to investigate properties of materials. In this talk we present a concrete example showing how ab initio results can be expressed in a way that is useful for hydrodynamics calculations, particularly we show how to build a analytic equation of state for Carbon that involves solid (diamond, BC8) and liquid phases. Strength properties --important to the interpretation of shock wave experiments-- can be added to the model using the same theoretical framework. \newline \newline In collaboration with Lorin Benedict and Eric Schwegler, Lawrence Livermore National Laboratory. [Preview Abstract] |
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