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 E2: PS-1: Phase Transitions |
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Chair: Cindy Bolme, Los Alamos National Laboratory Room: Hermitage AB |
Monday, June 29, 2009 3:30PM - 3:45PM |
E2.00001: Implementation of a complex multi-phase equation of state for cerium and its correlation with experiment Frank J. Cherne, Brian J. Jensen, Vyacheslav M. Elkin The complexity of cerium combined with its interesting material properties makes it a desirable material to dynamically examine. Characteristics such as the softening of the material before the phase change, low pressure solid-solid phase change, predicted low pressure melt boundary, and the solid-solid critical point add an additional puzzle to the construction of an equation of state for the material. Currently, we are incorporating a feedback loop between a theoretical understanding of the material and an experimental understanding. We have performed a number of experiments using front surface impact (cerium impacting a plated window) and normal geometry (i.e. known material impacting cerium-windowed and unwindowed). The front surface impact experiments show that there is a rarefactions shock upon release. The release states appear to occur at different magnitudes, thus allowing us to plot out the $\gamma$-$\alpha$ phase boundary. The dynamic melt boundary will also be discussed. Support for this work was done under US DOE contract DE-AC52-06NA25396. [Preview Abstract] |
Monday, June 29, 2009 3:45PM - 4:00PM |
E2.00002: Measurement of the Temperature Dependence of the $\beta $ -- $\gamma $ Transition Pressure in Tin Using Dynamic Isentropic Compression J.L. Wise, J.-P. Davis, D.H. Dolan, C.A. Hall, D.B. Hayes Electromagnetically driven stress-wave tests employing a new sample preheating capability were conducted in Sandia's Dynamic Integrated Compression Experimental (DICE) Facility to measure the temperature dependence of the $\beta $ -- $\gamma $ solid/solid structural transition pressure in tin samples subjected to ICE (Isentropic Compression Experiment) loading conditions. For several initial temperatures ranging from 20 to 200 C, velocity interferometer (VISAR) diagnostics provided time-resolved measurements of the sample free-surface motion. These measurements exhibited the distinct two-wave structure expected as a consequence of the phase transition. The ICE wave-profile data have been analyzed to determine discrete points along the $\beta $ -- $\gamma $ phase boundary on the basis of wavecode simulations incorporating a multiphase material model for tin. The observed transition pressure decreased as the initial sample temperature was increased, consistent with the equilibrium phase diagram of tin. [Preview Abstract] |
Monday, June 29, 2009 4:00PM - 4:30PM |
E2.00003: Shock Wave Experiments to Examine the Multiphase Properties of Metals Invited Speaker: There is a scientific need to obtain new data to constrain and refine next generation multi-phase equation-of-state (EOS) for metals. Experiments are needed to locate phase boundaries, determine transition kinetic times, and to obtain EOS and Hugoniot data for relevant phases. The objectives of the current work were: (1) to examine the orientation dependence of the transition kinetics and stress for single crystal iron, and (2) to examine the multiphase properties for cerium including the dynamic melt boundary and the low-pressure solid-solid phase through the critical point. These objectives were addressed by performing plate impact experiments that used multiple experimental configurations including front-surface impact experiments to directly measure transition kinetics, preheat experiments to map out phase boundaries, and complex loading methods to obtain off-Hugoniot data. Data obtained on single crystal iron illustrate an orientation dependence of the transition stress as well as transition times that are dependent on the impact stress spanning values from picoseconds to hundreds of nanoseconds. Data obtained for cerium metal provide information on the melt boundary along with other phase boundaries such as the low-pressure solid-solid boundary. Details of the experimental methods and recent experimental results for both iron and cerium will be presented. [Preview Abstract] |
Monday, June 29, 2009 4:30PM - 4:45PM |
E2.00004: Influence of Impurities on the Solid-Solid Phase Transitions in Zirconium P.A. Rigg, C.W. Greeff, G.T. Gray, III, M.D. Knudson In an effort to better understand the influence of impurities on the solid-solid phase transitions in Group IVb metals, experiments have been carried out in zirconium using plate impact and isentropic loading techniques. Samples with three levels of impurities were shock-loaded using both gas and powder-driven guns and isentropically loaded using magnetic drive (Sandia's Z-Machine) to determine the properties and characteristics of both the $\alpha-\omega$ and $\omega-\beta$ transitions. In addition to the transmission type experiments that were performed in the past, front surface impact experiments --- where the sample is impacted directly onto a LiF window --- were performed to obtain direct Hugoniot measurements in both the $\omega$ and $\beta$ phases. Comparisons of all data obtained to calculations using our current Equation of State will be presented. [Preview Abstract] |
Monday, June 29, 2009 4:45PM - 5:00PM |
E2.00005: Sub-microsecond graphite-diamond transformation at normal and elevated temperatures Andrey S. Savinykh, Gennady I. Kanel, Sergey V. Razorenov, Galina S. Bezruchko, Konstantin V. Khishchenko The graphite-diamond transformation was studied under conditions of shock compression at initial temperatures 293~K and 750~K. The samples of two kinds of pressed natural graphite contained 5{\%} or 27{\%} of rhombohedral phase and had the three-dimensional order degree parameters 0.85 and 08, respectively. In the experiments, the VISAR particle velocity histories were recorded at the interface between a graphite sample and a LiF window. Results of measurements at normal and elevated temperatures were analyzed using wide-range equations of state of graphite, LiF and aluminum. It has been shown by calibrating experiments the LiF correction of the VISAR velocity-per-fringe constant does not noticeably changes with heating in this temperature range. In this way it has been found the transition pressure decreases with heating in this temperature range from 18.9 to 16.9 GPa and from 20.3 to 18.3 GPa for graphites with 5{\%} and 27{\%} of rhombohedral phase, respectively. [Preview Abstract] |
Monday, June 29, 2009 5:00PM - 5:15PM |
E2.00006: Kinetic effects in the deformation of High-Pressure Low-Temperature States Raymond Smith Recent experiments have demonstrated the production and propagation of high stress ramp-waves that result in quasi-isentropic compression of condensed materials. We have discovered that for materials at high pressures kinetic effects play a pivotal role in determining the pressure onset of plastic flow and the transformation pressure for structural phase transitions. These time-dependent effects seem to be universal to all materials we have studied. However, the compression rate at which kinetic effects dominate is found to be very material dependent. We will present recent results on Bi, Fe and Si taken on the Janus and Omega laser facilities. In addition, we also describe recent results using a new two-dimensional velocimeter to study deformation mechanisms in materials under ramp compression. [Preview Abstract] |
Monday, June 29, 2009 5:15PM - 5:30PM |
E2.00007: Influence of structure and orientation of graphite on its polymorphic transformation under shock compression Galina S. Bezruchko, Gennady I. Kanel, Sergey V. Razorenov, Andrey S. Savinykh, Vladimir V. Milyavskiy, Konstantin V. Khishchenko Measurements of the transition pressure and rate under shock compression of different graphites at different sample orientations have been carried out with the goal to verify possible mechanisms of the graphite-diamond transformation. The materials tested were highly ordered synthetic graphite plates and samples prepared by pressing of powders of highly ordered pure graphite and several kinds of natural graphite. In experiments the VISAR wave profiles were measured using the LiF windows in the transformation pressure region. It has been found the shock direction significantly affects the detected pressure of the transformation and its rate. Results of the measurements show that means shifts in basal planes complicate high-rate graphite--diamond transformation. The effect is more pronounced in more ordered graphite. It was found also the transformation pressure increases and the transformation rate decreases as the degree of three-dimensional ordering of graphite decreases. Content of rhombohedral phase (up to 30{\%}) does not much influence on the transformation parameters. [Preview Abstract] |
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