Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session Q4: Physics and Chemistry at High Pressure: Static and Low Rate Studies |
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Chair: Choong-Shik Yoo, Washington State University Room: Renaissance Ballroom C |
Wednesday, June 29, 2011 4:00PM - 4:15PM |
Q4.00001: Bonding evolution towards phase transitions for nitrogen-rich high energy density solids under high pressure Anguang Hu, Fan Zhang The evolution of chemical bonds towards phase transitions under high pressure can be a complex process and may happen over widely different pressures, depending on both bond strengths and structures. This often results in the formation of unexpected intermediate states and leads to difficulties on accurate predictions of phase transitions and experimental syntheses. To understand bonding evolution towards phase transitions under high pressure, first-principles simulations have been conducted for experimentally established phase transitions. The results reveal that the bonding evolution from a parent phase under high pressure is characterized by electron delocalization towards the direction of neighboring molecules. This process manifests itself by decreasing inter-molecular bond lengths while simultaneously stretching intra-molecular bond lengths. The dynamics of the electron delocalization leads to a volume collapse and the formation of a new phase which basically satisfies Lewis structures. On this basis, new nitrogen-rich high energy density solids, C$_{3}$N$_{12}$, C$_{6}$N$_{16}$, N$_{4}$H$_{4}$ and N$_{2}$H$_{2}$, are predicted together with their equations of state, pressure-enthalpy phase diagrams and metastability, as well as their molecular crystal precursors and high-pressure phase transition paths for experimental syntheses. [Preview Abstract] |
Wednesday, June 29, 2011 4:15PM - 4:30PM |
Q4.00002: Pressure-induced Polymerization in Substituted Acetylenes Raja Chellappa, Dana Dattelbaum, Stephen Sheffield, David Robbins A fundamental understanding of shock-induced chemical reactions in organics is still lacking and there are limited studies devoted to determining reaction mechanisms, evolution of bonding, and effect of functional group substitutions. The fast timescale of reactions occurring during shock compression create significant experimental challenges (diagnostics) to fully quantify the mechanisms involved. Static compression provides a complementary route to investigate the equilibrium phase space and metastable intermediates during high pressure chemistry, although at a much slower timescale. In this study, we present our results from our ongoing high pressure \textit{in situ} synchrotron x-ray diffraction and vibrational spectroscopy experiments on substituted acetylenes: tert-butyl acetylene [TBA: (CH$_{3})_{3}$-C$\equiv $CH] and ethynyl trimethylsilane [ETMS: (CH$_{3})_{3}$-Si$\equiv $CH]. We observed that the onset pressure of chemical reactions (at room temperature) in these compounds is significantly higher in static compression (TBA: 11 GPa and ETMS: 26 GPa) when compared to shock input pressures (TBA: 6.1 GPa and ETMS: 6.6 GPa). The products were polymeric in nature, recovered to ambient conditions with little degradation and fully characterized using spectroscopy, calorimetry, and other techniques to identify reaction mechanisms. [Preview Abstract] |
Wednesday, June 29, 2011 4:30PM - 5:00PM |
Q4.00003: Static High Pressure Studies Under Non-Hydrostatic/Non-Equilibrium Conditions Invited Speaker: This presentation will discuss new developments aimed at measuring phase diagrams and strength under intentionally non-equilibrium, non-hydrostatic conditions. Though static high-pressure studies using diamond anvil cells (DACs) have traditionally sought to achieve ideal conditions (hydrostatic equilibrium), non-ideal configurations permit the measurement of important material properties. At one extreme, samples with no pressure medium have been used to evaluate the strength of materials under load. We find that using various pressure media that are nominally quasi-hydrostatic, though differing in the degree of hydrostaticity, can nonetheless induce wide variations in phase transition pressures. Finally, a dynamic DAC has been used to study phase transitions and metastability of materials over a range of compression rates. Examples of these topics and future directions will be discussed. This work performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344. Portions of this work were performed at HPCAT (Sector 16), Advanced Photon Source (APS), Argonne National Laboratory. HPCAT is supported by CIW, CDAC, UNLV and LLNL through funding from~DOE-NNSA, DOE-BES and NSF. APS is supported by DOE-BES, under Contract No. DE-AC02-06CH11357. [Preview Abstract] |
Wednesday, June 29, 2011 5:00PM - 5:15PM |
Q4.00004: High Pressure X-ray Spectroscopy at HP-CAT Yuming Xiao, Paul Chow, Eric Rod, Curtis Kenny-Benson, Arun Bommannavar, Guoyin Shen The high-pressure experimental end-station 16-IDD (HP-CAT) at the Advanced Photon Source at Argonne National Laboratory employs a number of spectroscopy techniques to measure properties of materials in diamond anvil cells. We will give an overview of the techniques that we use including: nuclear forward scattering, nuclear resonant Inelastic scattering, X-ray Raman, X-ray emission (resonant and non-resonant), and as well as measurements of electronic excitations, absorption and fluorescence at high pressure. For some of these measurements, we also take diffraction patterns to assess the structure of the sample at the same time spectroscopy measurements are taken. We will briefly discuss the instrumentation and scientific highlights of these techniques. [Preview Abstract] |
Wednesday, June 29, 2011 5:15PM - 5:30PM |
Q4.00005: Supporting facilities for synchrotron high-pressure high/low temperature research at HPCAT, APS Stanislav Sinogeikin, Eric Rod, Guoyin Shen High Pressure Collaborative Access Team (HPCAT) is dedicated to advancing cutting-edge, high-pressure science and technology using synchrotron radiation at Sector 16 of the Advanced Photon Source (APS) of Argonne National Laboratory. Recently a number of supporting facilities have been developed and implemented to expand the P-T range of the experimental conditions, increase efficiency and productivity of the beamlines, and improve the quality of experimental data. We have developed instrumentation for remote and automatic pressure control in diamond anvil cells (DACs) during synchrotron experiments. These include mechanical (gearboxes) and pneumatic (double-diaphragm membrane) devises for controlling pressure in virtually any type of DAC at a variety pressure and temperature conditions - from cryogenic to laser heating experiments. We have expanded our cryogenic facilities by designing and implementing a number of compact cryostats for different synchrotron techniques and a variety of standard and novel DACs. All these devices can be easily integrated with our new portable online optical systems for pressure measurements and in-situ Raman characterization. These and other developments will be presented and discussed during the meeting. [Preview Abstract] |
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