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 U3: Phase Transitions IV |
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Chair: Jean-Paul Davis, Sandia National Laboratories Room: Fairmont Orchid Hotel Plaza I |
Friday, June 29, 2007 8:00AM - 8:15AM |
U3.00001: Response of silicon to shock wave compression along [100] and [111] orientations Stefan J. Turneaure, Y.M. Gupta Silicon is a high strength, brittle solid that undergoes multiple compression induced phase transformations. To complement x-ray diffraction measurements to examine inelastic deformation and phase transformations in shocked Si, we have examined the continuum response of silicon under shock compression. Transmitted wave profiles were measured at Si/LiF interfaces using a velocity interferometer. Peak stresses ranged between 11 and 22 GPa. The measured HELs were 9.2 GPa and 7.7 GPa for [100] and [111] orientations, respectively. Following the phase transformation, which occurred at about 13.5GPa, the volume compression was roughly 23{\%} for peak stresses ranging from 15 to 22 GPa. This volume compression is consistent with a completed phase transformation and is much larger than previously reported volume compressions [1,2]. Work supported by DOE. [1] W. H. Gust and E. B. Royce, J. Appl. Phys. \textbf{42}, 1897 (1971). [2] T. Goto et al., Jap. J. Appl. Phys. \textbf{21}, L369 (1982). [Preview Abstract] |
Friday, June 29, 2007 8:15AM - 8:30AM |
U3.00002: Dynamic response of pure titanium up to 1300 K. Eugene Zaretsky Dynamic response (yield and spall strengths) of pure polycrystalline Ti (Alfa Aesar, 99.99{\%} Ti) was studied in a series of planar impact experiments with initial sample temperature ranged from 300 to 1300 K. In the separate series of experiments the temperature dependence of the longitudinal speed of sound in Ti was measured on the base of the reverberation of the stress pulse generated in the 3-mm Ti sample by 1-mm aluminum impactor. In all the experiments the velocity of the sample free surface was continuously monitored by VISAR. It was found that in spite of a softening preceding the HCP-BCC transformation in titanium (1155 K) the HCP phase still maintains some substantial, HEL(1145 K) = 0.4 GPa, strength. Just above the transition temperature the strength experiences more that two-fold increase: HEL(1170 K) = 0.94 GPa. The spall strength of BCC titanium at this temperature is of about 2 GPa, and close to that of HCP titanium at 1145 K, 2.3 GPa. Possible variation of the strength mechanisms caused by the temperature increase and the phase transition are discussed. [Preview Abstract] |
Friday, June 29, 2007 8:30AM - 8:45AM |
U3.00003: Structural and Chemical Changes in Pyrene Crystals under Static High Pressures Baozhou Sun, Zbigniew Dreger, Yogendra Gupta To gain insight into the response of molecular crystals to high pressures, pyrene crystals were examined in diamond-anvil cell experiments using Raman and FTIR spectroscopy. Three distinct Raman spectra were observed around 0.5 GPa, depending on the type of pressure transmitting medium. It was demonstrated that pyrene I: (i) transforms to pyrene II, in water and mineral oil, (ii) transforms to pyrene III, in argon and nitrogen and (iii) remains in the same phase, in solid media. These changes are discussed in terms of nonhydrostaticity of pressure transmitting media and intercalation of medium and sample. Irreversible chemical changes were observed upon compressing pyrene above 25 and 40 GPa. Recovered product was examined using FTIR spectroscopy indicating gradual transformation to an amorphous hydrogenated carbon structure. Work supported by DOE and ONR. [Preview Abstract] |
Friday, June 29, 2007 8:45AM - 9:00AM |
U3.00004: Initial Temperature Effects on the Dielectric Properties of PZT 95/5 During Shock Compression Robert Setchell, Stephen Montgomery, David Cox, Mark Anderson A strong electric field is generated when the shock-induced depoling current from a normally poled PZT 95/5 sample is passed through a large resistive load. The portion of total depoling current that is retained on the sample electrodes to account for capacitance is governed by the dynamic dielectric properties of both unshocked and shocked PZT 95/5. Early studies used measured load currents from single samples to assess models for dielectric response. More recent studies used shock-driven circuits in which multiple PZT 95/5 elements were displaced both parallel and perpendicular to the shock motion. This allowed both load and charging currents to be measured for individual elements that are subjected to shock compression and release at different times. In the present study, these techniques have been utilized to examine dielectric properties in PZT 95/5 samples at initial temperatures from -50 to 70 \r{ }C. Measured currents show large temperature effects on dielectric properties, and different models for dielectric response have been examined for simulating these results. [Preview Abstract] |
Friday, June 29, 2007 9:00AM - 9:15AM |
U3.00005: Study of near critical point states of tantalum and lithium by pulse heating under launching. Vladimir Ternovoit, Dmitry Nikolaev, Sergey Kvitov, Alexey Pyalling, Vladimir Fortov The near critical point states of the liquid-vapor phase transition of tantalum and lithium were investigated. The heating of tantalum foil samples in 1-D geometry was carried out by multiple-shocked He from back side of the tantalum foil and heating of lithium - by shocked He from the front side under dynamically created isobaric conditions. The temperature of sample was measured by fast 6-channel optical pyrometer. The pressure was obtained from measured shock velocity in He using stepped transparent window. Two sets of experiments with various history of heating were carried out, allowed to evaluate the critical point location of the studied metals in P-T plane. [Preview Abstract] |
Friday, June 29, 2007 9:15AM - 9:30AM |
U3.00006: Simulation of phase transitions and material decomposition in ultrashort laser--metal interaction Mikhail Povarnitsyn, Pavel Levashov, Konstantin Khishchenko A numerical hydrodynamic study of femtosecond laser irradiation (800~nm, 100~fs, 10$^{12}$--5$\times$10$^{13}$~W/cm$^2$) of metal targets (Al, Au, Cu) is presented. A detailed analysis of laser induced phase transitions, melting wave propagation and material decomposition is performed using a thermodynamically complete two-temperature equation of state with separate stable and metastable phase states and phase boundaries. Material evaporation from the target surface and fast melting wave propagation into the bulk are observed. Investigation of the phase trajectories of different target layers shows the presence of the metastable states in rarefaction wave. The lifetime of the metastable liquid state is estimated by means of the theory of homogeneous nucleation. Mechanical fragmentation of the target material at high strain rates is controlled with the help of Grady criterion. As a result, several ablation mechanisms are observed. A major fraction of the ablated material, however, is found to originate from the metastable liquid region, which is decomposed either \textit{thermally} in the vicinity of the critical point into a liquid--gas mixture, or \textit{mechanically} at high strain rate and negative pressure into liquid droplets and chunks. The calculation results explain available experimental findings. [Preview Abstract] |
Friday, June 29, 2007 9:30AM - 9:45AM |
U3.00007: Study of Phase Transitions in Cerium by Pressure Gauge PVDF Mikhail Zhernokletov, Vladimir Simakov, Valery Borissenok, Viacheslav Bragunets, Vasily Volgin, Frank Cherne, Marvin Zocher This paper examines phase transitions in cerium during shock compression using PVDF gauges. A two-wave structure was observed with loading pressures of 4GPa~- 12GPa. The wave structure consists of leading isentropic compression wave followed by a shock wave. This wave structure was formed as a result of the isomorphic ($\gamma -\alpha )$ phase transition. The wave profiles exhibited no peculiarities resulting from the polymorphic transition ($\alpha -\varepsilon )$ as predicted by Elkin et. al [\textit{Proceedings of the International Conference VII Khariton Readings, }Sarov 2005, p. 116]. [Preview Abstract] |
Friday, June 29, 2007 9:45AM - 10:00AM |
U3.00008: Measurement of sound velocities and shear strength of cerium under shock compression Alexei Kovalev, Mikhail Zhernokletov, Vladimir Komissarov, Mikhail Novikov Sound velocity in shock-compressed cerium was measured in the pressure range of 35$\div$140GPa by the rarefaction overtake technique with use of the indicator liquids carbogal and tetrachloromethane. The samples were loaded by generators of planar shock waves based on use of powerful HE. Luminescence of the liquid indicators was recorded by optical gauges based on photodiode FD256. In the pressure range of 13$\div$35GPa, sound velocity was measured in cerium samples by the method of counter release with use of manganin-based piezoresistive gauges. Initial density of cerium samples was 6.75g/cub.cm. Basing on the measured values of longitudinal and volume sound velocities, Poisson's ratio and shear strength of cerium were determined, boundaries of melting at shock adiabat were revealed. Experimental data were compared to calculation results. [Preview Abstract] |
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