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 K5: DC-1: Chemistry of Energetics and Reactive Metals |
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Chair: Shawn McGrane, Los Alamos National Laboratory Room: Cheekwood GH |
Tuesday, June 30, 2009 1:30PM - 1:45PM |
K5.00001: Radiation-induced Precursors in Crystalline Energetic Composites I. Plaksin, L. Rodrigues, S. Plaksin, J. Campos, R. Mendes, J. Ribeiro, J. Gois We present new experimental evidence that demonstrates the origination of precursors of the major reaction front at SDT in PBXs, based on the results of wedge tests of the HMX/Epoxy 77/23 (wt. {\%}) and HMX/Water composites. The precursors were spatially resolved in the modified wedge tests performed with the Multi-Channel Optical Analyzer -- MCOA by means of the simultaneous registration of the reaction radiance transmitting through the explosive bulk at the SDT and the stress field, which is induced by the reaction zone in the optical monitor. Experimental evidence, obtained at a wide variation of the HMX particle sizes (1.64 $\mu$m $<$ d50 $<$ 960 $\mu$m), point to the fact that the precursor is arisen as a result of the radiation heating due to the photon absorption, as the reaction radiation is scattered within the bulk of the crystalline explosive material. Within the precursor layer, thickness of which depends on both, temperature localization and radiation intensity in the major DRZ as well as on optical and kinetic properties (the photon absorption and further reactivity of the explosive particles), the explosive particles undergo thermal expansion, phase transformation and partial decomposition. Such a mechanism implies that the photo-excitation and energy localization due to radiation of the shock front play a crucial role in starting decomposition process. [Preview Abstract] |
Tuesday, June 30, 2009 1:45PM - 2:00PM |
K5.00002: Time-Resolved Temperature Measurements of Shock Initiation in Heterogeneous Exothermic Mixtures Francois-Xavier Jette, Sam Goroshin, Andrew Higgins, David Frost, Julian Lee Because the onset of reaction in shock-initiated exothermic powder compositions is difficult to observe, few dynamic measurements that could provide information about the initiation delay or the reaction mechanism have been reported. A method has been developed to experimentally measure the delay between the time of shock arrival and the time when most of the reactions have taken place using embedded thermocouples. The powder mixtures used in the tests were Ni-Al, Mn-S, Ti-Si, Ti-C and Ti-B. The test samples were placed in planar recovery ampoules containing thermocouples and a strong shock was delivered via the detonation of an explosive charge. A sharp temperature rise was measured, providing a reliable measurement of the time at which an exothermic reaction had occurred in the bulk mixture. The delay time before the temperature rise provided an upper bound of the initiation delay time, as well as information regarding the reaction mechanism. The results for all mixtures tested showed that bulk temperature starts to rise 10's of milliseconds after the mixture was shocked, which indicates that most of the reaction did not take place on the microsecond timescale. [Preview Abstract] |
Tuesday, June 30, 2009 2:00PM - 2:15PM |
K5.00003: In-situ measurement of shock-induced reactive flow in a series of related hydrocarbons S.A. Sheffield, D.M. Dattelbaum, D.B. Stahl Understanding of the chemistry that occurs under extreme, high-pressure, high-temperature shock environments poses both a significant scientific challenge, due to the difficulty of direct experimental observations, and an opportunity for discovery of new materials and bonding constructs. The combined high pressure, high temperature conditions induced by shock loading results in prompt reactions that may include dynamic bond breaking, dimerization and polymerization, and dissociation to small molecules. Detonating high explosives represent a case where the exothermicity of the chemical reactions drives a steady reactive flow field. Understanding of the evolution of different reaction pathways as a function of shock input remains a significant challenge, due to both the very short shock timescales, and difficulty in measurement of reaction intermediates and products. We have used \textit{in-situ} electromagnetic gauges to measure mechanical variables (such as multiple shock waveforms) that result from the chemistry occurring in the shock. This allows us to gain some understanding of the nature of the input conditions necessary to start the reaction. Among the materials studied are benzene, toluene, phenyl acetylene, benzonitrile. This work has led to a systematic study of shock-induced chemistry as a function of chemical structure. [Preview Abstract] |
Tuesday, June 30, 2009 2:15PM - 2:30PM |
K5.00004: The Effect of Charge Reactive Metal Cases on Air Blast Fan Zhang, William Wilson Experiments were conducted in a 23~m$^{3}$ closed chamber using explosive encased in a cylindrical reactive metal case to study the effect on air blast from the case fragments. Parameters varied included explosive material, case material, case/explosive mass ratio and charge internal diameter, which ranged from 7.62 to 12.7~cm. The pressure histories measured on the chamber wall showed a double-shock front structure with an accelerating precursor shock followed by the primary shock, suggesting the early-time reaction of small case fragments. During the early reflections on the chamber wall, the pressure rise achieves a factor of 1.6 versus the steel-cased and a factor of 1.2-1.4 versus the bare charges, indicating combustion of a large amount of small case particles generated by secondary fragmentation. The analysis of explosion pressures and recovered fragments and solid products showed that the burnt case mass increases with detonation pressure and case/explosion mass ratio over a test range from 0.29 to 1.75 in a quadratic function. The influences of charge diameter and various reactive metal cases on the burnt case mass are further investigated. [Preview Abstract] |
Tuesday, June 30, 2009 2:30PM - 2:45PM |
K5.00005: Effect of Particle Morphology on Critical Conditions for Shock-Initiated Reactions in Titanium-Silicon Powder Mixtures David Frost, Francois Jette, Samuel Goroshin, Andrew Higgins, Julian Lee The effect of titanium particle morphology on the shock sensitivity of titanium-silicon powder mixtures has been investigated experimentally. The powder mixtures were tested in a planar recovery capsule, with the shock loading produced by a high explosive Tetryl booster charge placed on top of the capsule and a PMMA attenuator. Reactions were not observed for stoichiometric mixtures of large (75 -- 106 $\mu $m), spherical Ti particles with fine ($<$ 44 $\mu $m) Si particles for incident peak shock pressures of up to 23 GPa, estimated with LS-DYNA. In contrast, mixtures with fine ($<$ 45 $\mu $m) spherical Ti particles or irregularly-shaped fine ($<$ 20 $\mu $m) Ti particles had critical shock pressures for reaction initiation of 7$\pm $3 GPa and 5$\pm $2 GPa, respectively. Microscopy and spectroscopy were used to identify the degree of intermixing between the particles for shock loading just below the reaction threshold. For the largest spherical Ti particles, little particle intermixing was evident. However, differential thermal analysis carried out demonstrated that even for the large Ti particles, shock loading of the samples generated microstructural effects which lowered the temperature for the onset of exothermic reaction of the shocked sample by about 80$^{\circ}$C. [Preview Abstract] |
Tuesday, June 30, 2009 2:45PM - 3:00PM |
K5.00006: Experimental study on shock-induced doping of titania photocatalysts Xiang Gao, Jianjun Liu, Pengwan Chen Titania is a most effective photo-functional material and is widely used. But since the band gap of titania is large (Eg=3.2 eV), it is only active in the ultraviolet region, which accouts only 3{\%}-5{\%} of the overall solar intensity. Therefore, it is very important to enhance the visible light activity of the titania photocatalyst. In this study, the nitrogen-doping of titania photocatalysts were induced by shock waves, which were generated through detonation-driven flyer impact. The samples were shocked at different flyer impact velocities and recovered successfully. Two nitrogen resources containing hexamethylene tetramine(HMT) and dicyandiamide were considered. The phase composition, light absorption spectra and N doping status of the recovered samples under different shock conditions were characterized. The absorption edge of the N-doped titania photocatalysts by shock wave was extended to 450nm corresponding to visible light region. The photocatalytic degradation to rhodamine B of the samples doped with dicyandiamide increased with the increase of the flyer velocity due to the higher N doping concentration and wider response to visible light. [Preview Abstract] |
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