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 S5: Phase Transitions V |
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Chair: Joel Kress, Los Alamos National Laboratory Room: Hyatt Regency Constellation F |
Thursday, August 4, 2005 9:30AM - 10:00AM |
S5.00001: Metastability in solid--liquid transitions: the limit of superheating and supercooling Invited Speaker: The inherent free energy barrier to the first-order phase transition may give rise to metastable melting and crystallization, i.e., superheating and supercooling. The limit of superheating and supercooling, a subject of scientific significance, is directly relevant to ultrafast dynamic experiments and molecular dynamics simulations. In the absence of satisfactory first-principles theories for solid--liquid transition and its metastability, we have established the systematics for the maximum superheating and supercooling at a given isobaric heating or cooling rate based on nucleation theory and supercooling experiments. The systematics have been demonstrated to be consistent with molecular dynamics simulations, Landau models and shock wave experiments. The applications of the systematics include, but are not limited to, the interpretation of dynamic experiments and development of the hysteresis method for determining the equilibrium melting temperature and the solid--liquid interfacial energy from superheating or supercooling. In light of superheating and supercooling, we also discuss the effects of defects and heating/cooling rates, the equivalence of temperature and pressure, and the Lindemann melting law. [Preview Abstract] |
Thursday, August 4, 2005 10:00AM - 10:15AM |
S5.00002: Theoretical melt curves of Al, Cu, Ta and Pb Shailesh Mehta The melt curves of Al, Cu, Ta and Pb are computed using simple but physically meaningful models of the solid and liquid phases in conjunction with a minimal amount of experimental data. The thermal ionic contribution to the Helmholtz free energy of the solid phase is modelled using a mean field approximation. The cold curve is obtained by iteratively determining the parameters of common analytic expressions for this quantity so that key properties of the solid are reproduced at RTP. The free energy of the ions in the liquid phase is evaluated using a modified CRIS model. By correcting the liquid free energy to reproduce experimental measurements of various melt quantities at atmospheric pressure, it is found that the melt curve remains in reasonable agreement with experiment and more advanced theoretical calculations to high pressure. [Preview Abstract] |
Thursday, August 4, 2005 10:15AM - 10:30AM |
S5.00003: Directional-dependence in shock-induced melting of fcc metals Ramon Ravelo, Brad Holian, Timothy Germann, Peter Lomdahl We report on simulations of shock-induced melting in fcc single crystals as function of shock direction. The solid-liquid Hugoniot of Al, Cu and Lennard-Jones crystals was generated for shock waves propagating along the (100),(111) and (110) crystallographic directions utilizing large-scale non-equilibirum molecular dynamics (NEMD) simulations as well as a new equilibrium molecular dynamics method for following the dynamical evolution of condensed matter subjected to shock waves\footnote{R. Ravelo, B.L. Holian, T.C. Germann and P.S. Lomdahl, Phys Rev B, 70, 014103 (2004).}. In these three systems, it is found that the shear stresses at the shock-front dominate the melting process. As a function of orientation, melting occurs at lower pressures (temperatures) for (110) shocks and at higher pressures (temperatures) for (100) shocks. The magnitude of the shear stress at the melting pressure correlates with the orientations:(100):(111):(110), with (100) shocks exhibiting the smallest value and (110) shocks the largest. [Preview Abstract] |
Thursday, August 4, 2005 10:30AM - 10:45AM |
S5.00004: Atomistic Simulations of Shock-Induced Melting in Iron Single Crystals K. Kadau, T.C. Germann, P.S. Lomdahl, B.L. Holian We report on non-equilibrium and Hugoniostat atomistic simulations of shock-induced melting in iron single crystals. The large-scale simulations show that the melting pressure varies by less than 10 GPa with the crystallographic shock direction. This is in contrast to a large dependence of more than 50 GPa in copper single crystal simulations. We discuss the different behavior of iron and copper and compare our theoretical results to experimental data. Acknowledgments: This work has been supported by the U.S. Department of Energy under contract no. W-7405-ENG-36 by the Advanced Simulation and Computing Program (ASC). [Preview Abstract] |
Thursday, August 4, 2005 10:45AM - 11:00AM |
S5.00005: Simulation of Shock Fronts J. Matthew D. Lane, Michael P. Marder We study the deformation and transitions at the shock front using a moving window technique. We demonstrate the technique using model systems, and apply it to realistic material potentials to efficiently study the shock melting of tin. [Preview Abstract] |
Thursday, August 4, 2005 11:00AM - 11:15AM |
S5.00006: A pressure-induced phase-transition from liquid to solid in Water Daniel Orlikowski, Jeffrey H. Nguyen, Neil C. Holmes In connection with recent isentropic experiments on water where a functionally graded impactor in a light-gas gun is used to systematically probe the high-pressure meltline for water, hydrodynamic simulations of water undergoing a pressure-induced phase transition into its ice phase are presented. From a well defined set of initial conditions, the liquid system is isentropically compressed into its solid phase, thus a mitigating first-order phase transitions occurs during which the energy of the system increases. Specifically, the simulations use a tabular, single-phase equation of state (EOS) for each phase. We use a thermodynamic mixing scheme of single-phase equations of state to treat mixed phase regions. In this scheme a time constant is related to the phase transition rate which incorporates the underlying effects of kinetics. The simulation models in one dimension the entire experimental setup, accounting for the wave interactions throughout the impactor and target. The calculated results are directly compared with particle velocity records from the experiment. [Preview Abstract] |
Thursday, August 4, 2005 11:15AM - 11:30AM |
S5.00007: Modelling Of Shock Waves with Multiple Phase Transitions in Condensed Materials Marc Missionnier, Olivier Heuze When a shock wave crosses a solid material and submit it to solid/solid or solid liquid phase transition, related phenomena occur: shock splitting , and the corresponding released shocked wave after reflection. Modelling of these phenomena raises physical and numerical issues. After shock loading, such materials can reach different kinds of states: \begin{itemize} \item single phase states, \item binary phase states, in the case of solid/solid or solid/liquid mixtures \item triple points, where binary zones intersect, for instance solid A/solid B, solid A/liquid, and solid B/liquid. \end{itemize} The thermodynamic path can be studied and easily understood in the (V,E) or (V,S) planes. In the case of 3-phases-tin ($\beta $ , $\gamma $ , and liquid) submitted to shock waves, seven states can occur: $\beta $ , $\gamma $, liquid , $\beta -\gamma $, $\beta $-liquid, $\gamma $-liquid, and $\beta -\gamma $-liquid. After studying the thermodynamic properties with a complete 3 phase Equation of State, we show the existence of these seven states in a hydrodynamic modelling. [Preview Abstract] |
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