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 C6: Phase Transitions I |
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Chair: Daniel Orlikowski, Lawrence Livermore National Laboratory Room: Hyatt Regency Chesapeake A/B |
Monday, August 1, 2005 11:00AM - 11:15AM |
C6.00001: Shock and Recovery of Polytetrafluoroethylene Above and Below the Phase II To Phase III Transition Eric N. Brown, Philip J. Rae, Carl P. Trujillo, Dana M. Dattelbaum, George T. Gray III, Neil K. Bourne Polytetrafluoroethylene (PTFE) is semi-crystalline in nature with its linear chains forming complicated temperature and pressure dependent phases. Due to its desirable mechanical properties applications of PTFE include structures designed for dynamic largescale plasticity excursions. Experimental studies on pressure-induced phase transitions using shock-loading techniques and the resulting changes in crystalline structure are presented. Disks of pedigreed PTFE 7C have been shock loaded in momentum trapped assemblies using a 80~mm gas launcher. Challenges in momentum trapping and soft recovery arising from the low yield stress of PTFE (9 MPa at room temperature) are discussed. Experiments were performed with impact pressures from 0.4 to 0.85 GPa to investigate the material response above and below the phase II to phase III crystalline transition. Changes in crystalline structure of the recovered materials were quantified using dynamic scanning calorimetry (DSC) and density. [Preview Abstract] |
Monday, August 1, 2005 11:15AM - 11:30AM |
C6.00002: Dynamic Response of PBX-9501 through the HMX Beta-Delta Phase Transition Brad Clements, Eric Mas, JeeYeon Plohr, Axinte Ionita, Frank Addessio The Gibbs free energy of the beta and delta phases of HMX are constructed from zero pressure heat capacity data, specific volume measurements, numerical simulations, and diamond anvil cell experiments. The free energies are then provided as input into our dynamic phase transition model developed for heterogeneous materials undergoing dynamically driven phase. This model, which uses the Method of Cells analysis to treat the HMX- polymer binder composite, is used to study dynamically loaded PBX-9501 as the HMX transforms from the beta to the delta phase. [Preview Abstract] |
Monday, August 1, 2005 11:30AM - 11:45AM |
C6.00003: The amorphization and disproportionation of Mullite (3Al$_{2}$O$_{3}$ 2SiO$_{2})$ under shock compression Nobuaki Kawai, Kazutaka Nakamura, Ken-ichi Kondo, Toshiyuki Atou, Shun Ito, Kunio Yubuta, Masae Kikuchi Shock-recovery experiments have been performed on mullite (3Al$_{2}$O$_{3}$ 2SiO$_{2})$ polycrystals in the pressure range up to 65 GPa. The recovered samples have been examined by using XRD method and TEM observation. In the samples shocked at 40 and 49 GPa, an amorphization of mullite occurs. Mullite nanocrystals ($<$10 nm) are dispersed in an amorphous phase. The direction of crystal axis of these nanocrystals seems to be preserved to that of the starting sample, indicating that the relatively large starting mullite crystal ($\sim $10 $\mu $m) break into nanocrystals accompanied with the amorphization. In contrast, at 65 GPa, the mullite decomposes into amorphous SiO$_{2}$ and $\gamma $-Al$_{2}$O$_{3}$. Very fine $\gamma $-Al$_{2}$O$_{3}$ particles less than 10 nm are observed in the matrix of the amorphous SiO$_{2}$. The electron diffraction reveals that the $\gamma $-Al$_{2}$O$_{3}$ crystals are randomly oriented, suggesting that a rapid disproportionation reaction of mullite have been induced. [Preview Abstract] |
Monday, August 1, 2005 11:45AM - 12:00PM |
C6.00004: Transverse Shock Wave Depolarization of the Pb(Zr$_{52}$Ti$_{48}$)O$_{3}$ Polycrystalline Piezoelectric Energy-Carrying Element Of A Compact Pulsed Power Generator Jason Baird, Sergey Shkuratov, Larry Altgilbers, Allen Stults, Evgueni Talantsev, Henry Temkin, Yaroslav Tkach The results are presented on experimental investigations of the depolarization of a poled lead zirconate titanate Pb(Zr$_{52}$Ti$_{48})$O$_{3}$ polycrystalline energy-carrying piezoelectric ceramic element within a compact ferroelectric generator (FEG) by an explosive shock wave traveling across the polarization vector \textbf{\textit{P}}$_{0}$. We show that shock wave compression of the energy-carrying ferroelectric element causes a phase transition in the ferroelectric material that results in almost complete depolarization of the sample. The electric charge stored in the ferroelectrics, due to their remnant polarization, is released within a short time interval and can be transformed into pulsed power. Detailed experimental results are presented for shock wave depolarization of Pb(Zr$_{52}$Ti$_{48})$O$_{3}$ energy-carrying elements of different shapes and sizes. [Preview Abstract] |
Monday, August 1, 2005 12:00PM - 12:15PM |
C6.00005: Shock Wave Compression of Nd$_{2}${Fe}$_{14}$B Hard Ferromagnets: The Pressure-Induced Magnetic Phase Transition Sergey Shkuratov, Jason Baird, Larry Altgilbers, Allen Stults, Evgueni Talantsev, Henrik Temkin, Yaroslav Tkach Recently, we developed a series of autonomous pulsed power sources that utilize the electromagnetic energy stored in hard ferri- and ferromagnetic materials. We present the results of experimental investigations of the demagnetization of Nd$_{2}$Fe$_{14}$B high-energy hard ferromagnets by explosive shock waves traveling across and along the magnetization vector \textbf{\textit{M}}. We show that shock wave compression of Nd$_{2}$Fe$_{14}$B ferromagnets causes a phase transition in the ferromagnetic material that results in almost complete demagnetization of the samples. Due to this phase transition the magnetostatic energy stored in Nd$_{2}$Fe$_{14}$B ferromagnets is released within a short time interval and can be transformed into pulsed power. Detailed experimental results are presented for both longitudinal and transverse shock wave demagnetization of Nd$_{2}$Fe$_{14}$B hard ferromagnets of different shapes and sizes. [Preview Abstract] |
Monday, August 1, 2005 12:15PM - 12:30PM |
C6.00006: Dielectric Properties of PZT 95/5 During Shock Compression Under High Electric Fields Robert Setchell, Stephen Montgomery, David Cox, Mark Anderson Shock-induced depoling of the ferroelectric ceramic PZT 95/5 is utilized in pulsed power devices. High electric fields are generated within a ceramic element when the depoling current is passed through a large load resistor. Under these conditions, a portion of the depoling current is retained on the element electrodes to account for capacitance. This effect is governed by the dielectric properties of both unshocked and shocked PZT 95/5 as the field develops during shock transit. Previous studies proposed either constant or relatively simple relaxing behavior for dielectric properties on either side of the shock front. However, interpreting these experimental results is complicated by possible field effects on depoling kinetics. Recent studies have used different experimental configurations to better isolate the dielectric behavior. Multiple PZT 95/5 elements are displaced in the direction of shock motion to allow for sequential charging of unshocked and shocked samples. These experiments show a complex dielectric behavior for which a simple relaxation model is inadequate. [Preview Abstract] |
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