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 C2: Detonations and Shock-Induced Chemistry II |
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Chair: Alex Tappan, Sandia National Laboratories Room: Grand Ballroom IV-VI |
Monday, June 27, 2011 11:00AM - 11:30AM |
C2.00001: Benchtop Energetics Progress Invited Speaker: We have constructed an apparatus for investigating the reactive chemical dynamics of mg-scale energetic materials samples. We seek to advance the understanding of the reaction kinetics of energetic materials, and of the chemical influences on energetic materials sensitivity. We employ direct laser irradiation, and indirect laser-driven shock, techniques to initiate thin-film explosive samples contained in a high-vacuum chamber. Expansion of the reacting flow into vacuum quenches the chemistry and preserves reaction intermediates for interrogation \textit{via} time-of-flight mass spectrometry (TOFMS). By rastering the sample coupon through the fixed laser beam focus, we generate hundreds of repetitive energetic events in a few minutes. A detonation wave passing through an organic explosive, such as pentaerythritol tetranitrate (PETN, C$_{5}$H$_{4}$N$_{4}$O$_{12})$, is remarkably efficient in converting the solid explosive into final thermodynamically-stable gaseous products ($e.g.$ N$_{2}$, CO$_{2}$, H$_{2}$O{\ldots}). Termination of a detonation at an explosive-to-vacuum interface produces an expanding pulse of hyperthermal molecular species, with leading-edge velocities $\sim $ 10 km/s. In contrast, deflagration (subsonic combustion) of PETN in vacuum produces mostly reaction intermediates, such as NO and NO$_{2}$, with much slower molecular velocities; consistent with expansion-quenched thermal decomposition of PETN. We propose to exploit these differences in product chemical identities and molecular species velocities to provide a chemically-based diagnostic for distinguishing between detonation and deflagration events. In this talk we also report recent progress towards the quantitative detection of hyperthermal neutral species produced by direct laser ablation of aluminum metal and of organic energetic materials, as a step towards demonstrating the ability to discriminate slow reaction intermediates from fast thermodynamically-stable final products. [Preview Abstract] |
Monday, June 27, 2011 11:30AM - 11:45AM |
C2.00002: A hydrocode study of explosive shock ignition George Butler, Yasuyuki Horie This paper discusses the results of hydrocode simulations of shock-induced ignition of PBXN-109, Octol, and PETN, using the History Variable Reactive Burn model in the CTH hydrocode. The simulations began with small-scale sympathetic detonation experiments, from which normalized values of pressure and time were derived and used to define an upper bound for ignition. This upper bound corresponds to the well established Pop-plot data for supported detonation, $i.e.$ detonations in which a constant shock pressure is applied to an explosive until full detonation is achieved. Subsequently, one-dimensional flyer-plate simulations were conducted where the response of constant-amplitude, limited-duration shock pulses into semi-infinite explosive samples was examined. These simulations confirmed not only the existence of an upper bound for ignition as expected, but also showed ignition by ``lower level'' shocks, in which full detonation is reached at a time longer than the input shock duration. These lower-level shocks can be used to define a distinct minimal ignition threshold, below which shock pulses do not result in detonation. Numerical experiments using these bounds offer a new framework for interpreting explosive initiation data. [Preview Abstract] |
Monday, June 27, 2011 11:45AM - 12:00PM |
C2.00003: Effects of Electric Fields on the Chemical Reaction Rates of Detonating Solid Explosives Craig Tarver The presence of a strong electric field has been demonstrated to effect the shock initiation and detonation wave propagation of solid high explosives. Several mechanisms have been proposed to explain the observed increased shock sensitivity, increased detonation velocity, and decreased failure diameter of certain explosives. One chemical mechanism is thought to be the excitation of some of the explosive molecules to higher energy electronic states, which rapidly decay to the ground electronic state while vibrationally exciting the molecules. This process increases the overall reaction rate of the explosive and produces a shorter duration reaction zone. The shorter reaction time results in a more rapid transition to detonation, a decreased failure diameter, and an increased detonation velocity for a specific charge diameter. This work was performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344. [Preview Abstract] |
Monday, June 27, 2011 12:00PM - 12:15PM |
C2.00004: Numerical simulation of detonation propagation in PETN at arbitrary initial density by simple model Shiro Kubota, Tei Saburi, Yuji Ogata, Kunihito Nagayama Since the detonation velocity and pressure are dependent to the initial density of high explosive, the parameters of the equation of state (EOS) is dependent to the initial density. In general, the parameter set for each initial density has to be obtained to compute detonation phenomena. For simulation of arbitrary initial densities cases, we try to construct new simulation procedure which only employs the information of theoretical maximum density (TMD). The well known linear relationship between detonation velocity and initial density for high explosive has been employed for this study. Two types of simulation were carried out. The Gruneisen parameter as function of specific volume was calculated by solving the ordinary differential equation, and was employed as unified form EOS to simulate detonation phenomena. To obtain the information of the EOS for arbitrary initial density, the simulation of another type was executed. The calculation field is filled with the particle for TMD and the air, and the density of the high explosive is adjusted. It is investigated whether the velocity of detonation for an arbitrary density can be reproduced only by information on TMD. [Preview Abstract] |
Monday, June 27, 2011 12:15PM - 12:30PM |
C2.00005: Benchtop Energetics: Detection of hyperthermal species Emily Fossum, Christopher Molek, William Lewis, Mario Fajardo We present an apparatus designed for investigating reacting small-scale energetic materials. In the test setup, sub-mg explosive samples are initiated under vacuum, where the expansion effectively quenches the reaction, preserving the intermediates for mass spectrometric analysis. It is known that the expansion of a detonation wave into vacuum produces hyperthermal molecular species, with leading-edge velocities in excess of $\sim $10 km/s. An important step, therefore, is to demonstrate our ability to detect such fast species and distinguish them from slow species resulting from deflagration. The time between the initiation and the arrival of species at the detection region provides a metric for determining molecular velocity; however, the instrumental sensitivity is influenced by the velocity of incoming species, and thus a thorough investigation of the sensitivity and limits of the instrumentation is essential. Laser-ablated aluminum provides simple source of fast atoms; we compare experimental results with SIMION calculations, to determine a velocity-dependent ``instrument transfer function.'' We also present mass spectra of energetic materials subjected to direct-laser-irradiation; products ranged in velocity from 2 km/s to $>$ 10 km/s, depending on initiation conditions. These results provide steps toward a chemically-based diagnostic for distinguishing between detonation and deflagration events. [Preview Abstract] |
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