Bulletin of the American Physical Society
16th APS Topical Conference on Shock Compression of Condensed Matter
Volume 54, Number 8
Sunday–Friday, June 28–July 3 2009; Nashville, Tennessee
Session Z1: DC-7: Shock Chemistry Using Lasers |
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Chair: Von Whitley, Los Alamos National Laboratory Room: Magnolia Ballroom |
Friday, July 3, 2009 10:30AM - 11:00AM |
Z1.00001: Unraveling Shock-Induced Chemistry Using Ultrafast Lasers Invited Speaker: The exquisite time synchronicity between shock and diagnostics needed to unravel chemical events occurring in picoseconds has been achieved using a shaped ultrafast laser pulse to both drive the shocks and interrogate the sample via a multiplicity of optical diagnostics. The shaped laser drive pulse can produce well-controlled shock states of sub-ns duration with sub-10 ps risetimes, sufficient for investigation of fast reactions or phase transformations in a thin layer with picosecond time resolution. The shock state is characterized using ultrafast dynamic ellipsometry (UDE) in either planar or Gaussian spatial geometries, the latter allowing measurements of the equation of state of materials at a range of stresses in a single laser pulse. Time-resolved processes in materials are being interrogated using UDE, ultrafast infrared absorption, ultrafast UV/visible absorption, and femtosecond coherent Raman spectroscopies. Using these tools we showed that chemistry in an energetic thin film starts only after an induction time of a few tens of ps, an observation that allows differentiation between proposed shock-induced reaction mechanisms. These tools are presently being applied to a variety of energetic and reactive sample systems, from nitromethane and carbon disulfide, to micro-engineered interfaces in tunable energetic mixtures. [Preview Abstract] |
Friday, July 3, 2009 11:00AM - 11:15AM |
Z1.00002: Laser-driven shock-induced reaction in nitromethane and carbon disulfide Cindy Bolme, Daniel Eakins, Shawn McGrane, David Moore, David Funk The experimental measurement technique of ultrafast dynamic ellipsometry (UDE) measures material motion and changes in optical properties of samples under laser driven shock loading, allowing the picosecond probing of material dynamics in a single shot. Nitromethane and carbon disulfide were investigated with UDE, and both liquids showed evidence of chemical reaction in the first 200 ps after the arrival of the shock wave. The material motion and optical properties data that indicate reaction will be presented. [Preview Abstract] |
Friday, July 3, 2009 11:15AM - 11:30AM |
Z1.00003: Laser-Ignition of Laser-Shock Dispersed Metal Particles James Lightstone, Joel Carney Understanding the ignition and combustion of metal particles loaded in an explosive under the extreme conditions encountered in detonations is important for maximizing the energy output in blast applications. Of particular interest is the effect of particle velocity on ignition and sustained combustion. Published laboratory experiments are typically limited to velocities in the range 5 to 10 m/s. These are significantly lower than velocities achieved in detonating explosives which can reach 500 m/s to 1 km/s. The work presented in the paper describes a new technique to examine the ignition and combustion properties of particles travelling at high velocity in an oxidizing atmosphere. The technique utilizes two short (10 ns) IR laser pulses. The first launches the particles at velocities reaching 250 m/s as determined by high-speed digital shadowgraphy. The second, fired after a delay period, heats a section of the resulting particle cloud to ignition. Ignition and combustion is monitored using photodiodes, pyrometry, and time-resolved spectroscopy. Data acquired for particle sizes ranging from 1 to 100 microns and velocities ranging from 100 to 250 m/s will be presented. [Preview Abstract] |
Friday, July 3, 2009 11:30AM - 11:45AM |
Z1.00004: Ultrafast vibrational spectroscopy of shock compression with molecular resolution: energetic material simulants Dana Dlott, Aaron Lozano, Alexei A. Lagutchev This project focuses on understanding the properties of molecules immediately behind a shock front using a femtosecond laser to generate a shock wave in a molecular monolayer. In previous work we used nonlinear coherent vibrational spectroscopy to study long chain alkane molecules with a 4 GPa shock. The long-chain molecules have little strength along the long axis, and we found they quickly created \textit{gauche} defects by rotation around carbon-carbon bonds. We have greatly improved the sensitivity of our laser apparatus. We have also developed the ability to study ``heat shocks'' where large amounts of heat flow ballistically rather than diffusively from a metal surface into the monolayer. We look at energetic molecule simulants, which are monolayers having either nitro or nitramine functionalities. This material is based on work supported by the US Army Research Office under award number UNLV 08-655K-A-00 and the Air Force Office of Scientific Research under award number FA9550-06-1-0235. Aaron Lozano acknowledges the Stewardship Sciences Academic Alliance Program from the Carnegie-DOE Alliance Center under grant number DOE CIW 4-3253-13. [Preview Abstract] |
Friday, July 3, 2009 11:45AM - 12:00PM |
Z1.00005: Femtosecond laser-driven shock synthesis of high-pressure phases of silicon Masashi Tsujino, Tomokazu Sano, Akio Hirose, Norimasa Ozaki, Ryosuke Kodama, Osami Sakata, Masayuki Okoshi, Narumi Inoue High-pressure phases of silicon: SiII, SiXI, and SiV phases, which have never remained after pressure release with conventional compression methods, are synthesized using the femtosecond laser-driven shock wave. A femtosecond laser pulse is focused and irradiated on the single crystal silicon surface in air at the room temperature. We analyze the crystalline structures of the silicon with x-ray diffraction methods using synchrotron x-ray of SPring-8. Grazing incidence x-ray diffraction measurements show the evidence that SiII, SiXI, and SiV phases exist in the atmospheric pressure. Transmission x-ray diffraction measurements using micro x-ray for the cross section of the laser irradiated spot suggested the existence of SiVIII phase and that the particle size of the phase is around 180 nm. Many defects are observed and it is suggested that large residual stress is loaded to SiI: diamond structure with transmission electron microscopy. [Preview Abstract] |
Friday, July 3, 2009 12:00PM - 12:15PM |
Z1.00006: Laser Shock Compression Induced Reaction and Spalling of Reactive Ni-Al Laminate Composites Chung-Ting Wei, Brian Maddox, Timothy Weihs, Vitali Nesterenko, Marc Meyers Reactive laminates produced by rolling layers of Ni and Al (bilayer thicknesses of 8.3 and 48$\mu$m) were subjected to extreme laser loading. Laser energy was varied between $\sim$8.3 x 103J/cm2 (estimated initial pressure~140GPa) and $\sim$3.33 x 104J/cm2 ($\sim$350GPa) with two initial durations: 3 and 8ns. Hydrodynamic calculations (HYADES) were used to predict propagation of shockwave in laminates. SEM and EDS were carried out to study the damage, failure modes, reaction propagation and spall. The 8.3$\mu$m bilayer thickness laminate exhibited localized interfacial reaction at 3.33 x 104J/cm2 laser energy; the reaction products were identified as NiAl and Al rich intermetallic compounds. The reactionfront forming intermetallic compounds propagated about 50$\mu$m into the sample with thinner bi-layer thickness (8.3$\mu$m). Estimated cooling rate was 5.7 x 105 K/s. The estimated highest temperature was about 1470K. Increase in the duration of laser shock wave induces increased reaction, which occurs also in the thicker bilayer laminate samples (48$\mu$m bi-layer thickness). The laser shock methodology is well suited to investigate the threshold conditions for dynamic mechanical reaction initiation. [Preview Abstract] |
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