Bulletin of the American Physical Society
2005 14th APS Topical Conference on Shock Compression of Condensed Matter
Sunday–Friday, July 31–August 5 2005; Baltimore, MD
Session D6: Phase Transitions II |
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Chair: Brian Jensen, Los Alamos National Laboratory Room: Hyatt Regency Chesapeake A/B |
Monday, August 1, 2005 1:30PM - 1:45PM |
D6.00001: X-ray diffraction measurements to observe the B1 to B2 phase transformation in KCl shocked along [111] Stefan J. Turneaure, Y.M. Gupta Plate impact experiments were performed on KCl shocked along [111] to peak stresses exceeding the B1 to B2 phase transformation stress. The spacing between lattice planes normal to the shock direction was monitored using x-ray diffraction measurements. VISAR measurements at the rear of the target showed that the x-rays were pulsed while the KCl was in a nearly constant stress state. In the peak stress state, two diffraction peaks were observed. One peak was consistent with the 200 peak of a cubic B2 unit cell, while the second peak, at a slightly higher Bragg angle, was not consistent with peaks from cubic unit cells of either phase. A possible origin for the higher Bragg angle peak will be discussed. Previously, it had been found that the two phases are related such that B1[100]//B2[110] when the KCl is shocked along the [100] direction [1]. The orientational relationship found in the present experiments, B1[111]//B2[100], suggests that the atomic transformation pathway depends on the loading direction. Work Supported by DOE. [1] T. d'Almeida and Y. M. Gupta, Phys. Rev. Lett. \textbf{85}, 330 (2000). [Preview Abstract] |
Monday, August 1, 2005 1:45PM - 2:00PM |
D6.00002: Phase transition of MnF$_2$ by shock compression up to 33 GPa Teruhisa Hongo, Nobuaki Kawai, Kazutaka Nakamura, Ken-ichi Kondo, Toshiyuki Atou, Kunio Yubuta, Keiji Kusaba, Masae Kikuchi Shock-induced phase transition of MnF$_2$ with the rutile structure was investigated using gun method in the pressure range between 3 and 33 GPa. Recovered samples were examined using X-ray diffraction method and transmission electron microscope (TEM) observation. The $\alpha$-PbO$_2$-type phase was observed in the recovered samples, and its yield had a maximum at about 10 GPa. Lamella patterns consisting of the rutile-phase and the $\alpha$-PbO$_2$-type phase intergrowth texture were observed in the TEM images of the sample shock-loaded to 9 GPa. The crystallographic relationship between both phases can be expressed as (001){\scriptsize $\alpha$-PbO$_2$} $\|$ (-101) {\scriptsize rutile} and [110]{\scriptsize $\alpha$-PbO$_2$} $\|$ [111]{\scriptsize rutile} by TEM observation. This directional relationship is different from that of TiO$_2$ previously reported, suggesting that possibility of a new mechanism for the phase transition from the rutile-type to the $\alpha$-PbO$_2$-type through fluorite-related structure under high pressure. [Preview Abstract] |
Monday, August 1, 2005 2:00PM - 2:15PM |
D6.00003: Technique for Detection of Phase Transitions in Materials L.C. Chhabildas, W.D. Reinhart, T.J. Vogler When materials undergo polymorphic phase transitions, it is generally accompanied by a volume change. Systems such as iron, exhibit large volume changes and the phase transitions has been observed under shock loading conditions both in shock-velocity vs. particle-velocity measurements and also in time-resolved particle-velocity measurements. However, these techniques are not sufficiently sensitive if the phase change is accompanied by only a small volume change. In this study, we will report measurements of the loading profiles in the form of particle-velocity histories for both silicon-carbide and sapphire, under shock loading and also under re-shock loading to the same stress in multiple steps. These results will demonstrate the value of this technique for detecting phase transformations in materials with relatively small volume changes and will put a maximum bound on the volume change accompanying the phase change. *Sandia is a mulitprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy National Nuclear Security Administration under contract DE-AC04-94AL8500 [Preview Abstract] |
Monday, August 1, 2005 2:15PM - 2:30PM |
D6.00004: Dynamically driven phase transformations in damaged composite materials JeeYeon Plohr, Brad Clements, Frank Addessio A model developed for heterogeneous materials undergoing dynamically driven phase transitions in its constituents has been extended to allow for complex material micro-structures and the evolution of damage. In this work, damage is described by interfacial debonding and micro-crack growth. We have applied the analysis to silicon carbide-titanium (SiC-Ti) unidirectional metal matrix composites. In these composites, Ti can undergo a low pressure and temperature solid-solid phase transition. With these extensions we have carried out simulations to study the complex interplay between loading rates, micro-structure, damage, and the thermo-mechanical response of the system as it undergoes a solid-solid phase transformation. [Preview Abstract] |
Monday, August 1, 2005 2:30PM - 2:45PM |
D6.00005: Nonmonotonic conductivity change of C60 fullerene crystals under dynamic compression up to 300 kbar Vladimir V. Avdonin, V.I. Postnov, D.V. Shakhray, K.L. Kagan, A.F. Shestakov, V.E. Fortov, V.V. Kveder, R.K. Nikolaev, N.S. Sidorov, Y.A. Ossipyan In the present work the conductivity of fullerene C$_{60}$ crystals has been measured under smooth shock wave quasi-isentropic loading conditions up to 30 GPa at initial temperature T=293 K. Not monotone behavior of conductivity has been revealed under compression of crystal with pressure increasing: -at first conductivity grows by many orders then it falls very fast. Conductivity increasing is explained by decreasing of bandgap of C$_{60}$ under compression whereas conductivity decreasing can be explained on the assumption that the energy barrier of polymerization of C$_{60}$ reduces with pressure increasing approximately in the same measure as band-gap energy. Research is financially supported by the Russian foundation for basic research, the grant N 03-02-16322, the grant of the President of Russia NS 1938.2003.2, and program of basic researches of the Russian Academy of Science ``Thermophysics and mechanics of processes at high energy densities.'' [Preview Abstract] |
Monday, August 1, 2005 2:45PM - 3:00PM |
D6.00006: Hugoniot of C$_{60}$ fullerite: new results Vladimir Milyavskiy, Alexander Utkin, Andrey Zhuk, Vladislav Yakushev, Vladimir Fortov Recently, we have experimentally studied shock compressibility of C$_{60}$ fullerite and sound velocity in shock-compressed fullerite at the pressure range up to $\sim$50 GPa [1]. In this work we present the results of new shock experiments executed with C$_{60}$ fullerite in the same pressure range. On the base of new experimental results, we have made some correction of our concept [1] of the processes occurring in C$_{60}$ fullerite at shock compression. In particular, the anomalous behavior of the rear surface velocity profiles was detected at pressure $\sim $9 GPa [1]. Additional experiments have shown that this anomalous behavior was caused by jump of the sound velocity in C$_{60}$ because of formation of more hard carbon phase. We assume that it is a polymerized C$_{60}$ phase. In the pressure region 9-25 GPa, destruction of this phase and formation of a graphite-like carbon occurs. With further growth of shock pressure, phase transition of the graphite-like carbon to a diamond-like phase is observed with a transition onset pressure $\sim $25 GPa. If shock pressures higher than $\sim $33 GPa, Hugoniot of C$_{60}$ is determined by the thermodynamic properties of the diamond-like phase. [1] V.V. Milyavskiy, A.V. Utkin, E.B. Zaretsky, A.Z. Zhuk, V.V. Yakushev, V.E. Fortov. AIP CP 706 (2004) 667. [Preview Abstract] |
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