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 C4: Phase Transitions I |
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Chair: Marina Bastea, Lawrence Livermore National Laboratory Room: Fairmont Orchid Hotel Plaza II |
Monday, June 25, 2007 1:45PM - 2:15PM |
C4.00001: Ab initio studies of electronic and structural transitions in low-Z liquids under extreme conditions Invited Speaker: The liquids of group I elements (H, Li, Na, and K) are studied using first principles theory. It will be shown that they undergo electronic and structural transitions analogous to that observed in their solids, but commencing at much lower pressure in the presence of disorder. These changes result in exotic melting behavior and in molten phases with unusual properties. The theoretical predictions will be compared with experimental data and ways for further experimental verification of the theoretical results will be suggested. [Preview Abstract] |
Monday, June 25, 2007 2:15PM - 2:30PM |
C4.00002: Phase separation in H2O:N2 mixtures and implications for detonation. Laurence Fried, Amitesh Maiti, Richard Gee, Sorin Bastea A class II atomistic force field with Lennard-Jones 6-9 nonbond interactions is used to investigate equations of state (EOS) for important high explosive detonation products N2 and H2O in the temperature range 700-2500 K and pressure range 0.1-10 GPa. A standard 6th order parameter-mixing scheme is then employed to study a 2:1 (molar) H2O:N2 mixture, to investigate in particular the possibility of phase-separation under detonation conditions. The simulations demonstrate several important results, including: (i) the accuracy of computed EOS for both N2 and H2O over the entire range of temperature and pressure considered; (ii) accurate mixing-demixing phase boundary as compared to experimental data; and (iii) the departure of mixing free energy from that predicted by ideal mixing law. The importance of supercritical phase separation during detonation will be discussed. The work was performed under the auspices of the U.S. Department of Energy by the University of California Lawrence Livermore National Laboratory under Contract W-7405-Eng-48. [Preview Abstract] |
Monday, June 25, 2007 2:30PM - 2:45PM |
C4.00003: Shock Crystal Growth of Water in Dynamic-DAC. Choong-Shik Yoo, William Evans, Geun-woo Lee While diamond anvil cells (DACs) and gas-guns are capable of generating high pressures to 300-400 GPa, the precise and tunable control of de/compression rates has been a formidable challenge to both static and dynamic high-pressure research. Furthermore, the pressure-induced polymerization, amorphorization, and diffusion controlled crystal growth occur at an intermediate time scale (micro-to-millisecond) of conventional shock and static experiments, for which no compression technology is readily available for \textit{in-situ} studies. To address this situation, we have recently developed \textit{dynamic}-DAC ($d$-DAC) capable of precise controlling of pressure and compression rates at high static pressures. Coupling with time-resolved synchrotron x-ray, optical microscopy, and laser spectroscopy, $d-$DAC enables one to measure time-resolved structural evolutions of a sample across melting and other phase transitions. In this paper, following the brief description of dynamic-DAC, we will present our recent observations in $d$-DAC including shock crystal growth of ice VI dendrites and ice VII metastably grown from the stability field of ice VI. [Preview Abstract] |
Monday, June 25, 2007 2:45PM - 3:00PM |
C4.00004: Shock Induced Melting Behavior of Eutectic Systems Chris Adams Under equilibrium conditions, melting in multi-phase alloy systems is accompanied by short-range diffusion at inter-phase boundaries. The degree to which diffusion contributes to shock induced melting in simple eutectic systems is still an open question. While there exists a considerable body of previous work on shock induced melting in single phase systems, there has been much less work performed on multiphase systems. We will present the results of a series of gas-gun recovery experiments performed over a range of shock loading conditions, illustrating our observations of shock induced deformation and melting behavior in cast and thermo-mechanically processed Ag-Cu simple eutectic samples. Assessments of the shock wave profiles, shock states achieved, and sound speeds at pressure will be discussed in conjunction with pre-and post-shot microstrucural characterization of thermo-mechanically processed pre-shot and recovered materials. [Preview Abstract] |
Monday, June 25, 2007 3:00PM - 3:15PM |
C4.00005: TEM observation of disproportionation of mullite and sillimanaite under shock compression Toshiyuki Atou, Nobuaki Kawai, Kazutaka G. Kakamura, Ken-ichi Kondo, Masae Kikuchi, Shun Ito, Kunio Yubuta The aluminum silicates, mullite and sillimanite are fundamental raw minerals for the refractory industry and ceramics. Shock compression curves of these materials indicate phase transitions above about 30 GPa. Large volume decrease accompanied with the phase transitions have been attributed to disproportionation to alumina and silica. However, detailed behavior of the disproportionation has not been well understood yet. Using transmission electron microscopy, we confirmed very fine (less than 10nm) $\gamma $-alumina in mullite specimen shock-loaded to 65 GPa. In sillimanite specimen shock-loaded to 54 GPa, $\gamma $-alumina was also observed, but the particle sizes were much larger (10-20 nm) than those in mullite specimen, suggesting that the disproportionation in sillimanite specimen occurred at lower shock pressure than in mullite specimen. Furthermore, characteristic nano texture observed in mullite specimen could not found in sillimanite specimen, which might be caused by difference in crystal structures between mullite and sillimanite. [Preview Abstract] |
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