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 L1: EM-8: Energetic Material Properties |
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Chair: William Cooper, Air Force Research Laboratory Room: Tennessee Ballroom C |
Tuesday, June 30, 2009 3:30PM - 3:45PM |
L1.00001: Thermal Ignition of Detonable Hydrogen Peroxide Compositions Jonathan Zucker, Timothy Foley, Peter Dickson Hydrogen peroxide can be mixed with a variety of fuels to produce detonable compositions. These compositions can be thermally unstable and their behavior can be difficult to predict. Furthermore, the addition of some acids to the mixture could increase its sensitivity. Presented here are the outcome of cookoff experiments performed on hydrogen peroxide and fuels compositions, as well as acid-sensitized mixtures. [Preview Abstract] |
Tuesday, June 30, 2009 3:45PM - 4:00PM |
L1.00002: Comparison of Mechanical and Thermal Ignition Characteristics for Reactivity Enhanced Ni/Al Powders Robert Reeves, Jeremiah White, Steven Son, Alexander Mukasyan Efforts have recently been made to understand the ignition mechanism of gasless reactive systems. It has been known that processes such as high-energy ball milling can enhance reactivity through extensive plastic deformation and introduction of crystal defects in the material. Reducing the particle size of the constituent materials to nano-scales also enhances reactivity. However, the effect of such reactivity enhancing processes on ignition mechanisms is not well known. Mixtures of micron size Ni/Al powders, nano-scale Ni/Al powders, and ball milled Ni/Al powders are studied. Differential thermal analysis (DTA) was used to study thermal ignition properties. Ignition by mechanical stimulus was studied by impacting samples with a projectile from a gas gun. DTA showed the ball-milled materials reacted at a temperature below the melting point of Al However these materials could not be ignited through mechanical means. The nano-mixtures reacted at higher temperature than the ball-milled in the DTA, but were readily ignited through mechanical stimulation. This indicates reactivity enhancement affects the thermal and mechanical ignition mechanisms in different ways. [Preview Abstract] |
Tuesday, June 30, 2009 4:00PM - 4:15PM |
L1.00003: Effect of Aluminum Particle Surface Area and Morphology on the Combustion Properties of KClO$_4$/Al Compositions Stanley Caulder, Joseph Mackey, John Wilkinson Compositions of KClO$_4$/Al are used in military applications as well as the pyrotechnics industry. The reaction rate as well as the ease of initiation depends on metal particle surface area as well as particle morphology. This factor is especially important for metal fuels having a melting point higher than the melting point of the oxidizer component in the energetic composition. Aluminum powder and turnings of various particle sizes were combined with KClO$_4$ to form an energetic composition. The explosives mixtures were combusted in a rapid scanning calorimeter device (RSD). dP/dt and dT/dt results were measured and heats of reaction were calculated. The effect of Al particle surface area and particle morphology on the combustion properties of KClO$_4$/Al is discussed. [Preview Abstract] |
Tuesday, June 30, 2009 4:15PM - 4:30PM |
L1.00004: Impact Initiation of Pressed Al-based intermetallic Forming Powder Mixtures Siwei Du, Naresh Thadhani Aluminum-based intermetallic forming powder mixtures (Ni-Al, Ta-Al, Nb-Al, Mo-Al and W-Al) were uniaxially pressed into 80{\%} dense pellets, to study the impact initiation of reactions. The pressed pellets mounted in front of a projectile were impacted onto a steel anvil using a 7.62 mm gas gun, under a 50 millitorr vacuum. Projectiles made of copper, aluminum or poly carbonate and varying impact velocity (up to 500 m/s) provided different levels of stress, strain, and kinetic energy. The IMACON 200 framing camera was used to observe the transient deformation states and reaction ignition characteristics. AUTODYN 2D was used to simulate the densification and deformation process, and correlate with that observed by high-speed imaging. It is found that the continued straining following densification of the powder compact by the kinetic energy of the projectile, and the resulting stress are both contributing to the initiation of the intermetallic reaction. In this presentation the characteristics of impact initiated reactions in the various intermetallic systems will be presented. [Preview Abstract] |
Tuesday, June 30, 2009 4:30PM - 4:45PM |
L1.00005: Physical and chemical properties of the new energetic material Si-PETN You Lin, Aaron Landerville, Ivan Oleynik, Carter White A new energetic material Si-PETN, having a structure similar to that of PETN, has recently been synthesized (T.M. Klap\"{o}tke, \textit{et al.}, J. Am. Chem. Soc. 129, 6908 (2007)) and shown to exhibit extreme sensitivity that has precluded investigation of its physical and chemical properties by experiment. Although it is highly unlikely that Si-PETN will be used as munition due to its high sensitivity, it could provide valuable information about the nature of sensitivity in energetic materials. Due to its inherent instability, the equation of state (EOS) for Si-PETN is currently unknown. First-principles van-der-Waals density functional theory was used to obtain the EOS for Si-PETN under hydrostatic compression and anisotropic EOS under uniaxial compressions. Both the EOS and shear stresses were compared to those of PETN. We also investigated the hypervelocity chemistry of initiation reactions in Si-PETN using first-principles reactive molecular dynamics. The bimolecular collisions that should occur behind the shockwave front of shocked Si-PETN were simulated as a function of both collision velocity and orientation. The sensitivity properties of Si-PETN were quantified by determining the threshold collision velocities of reaction initiation for each orientation and compared to those of PETN. [Preview Abstract] |
Tuesday, June 30, 2009 4:45PM - 5:00PM |
L1.00006: Explanation of the Colossal Sensitivity of Silicon Pentaerythritol Tetranitrate (Si-PETN) Wei-Guang Liu, Sergey Zybin, Siddharth Dasgupta, William Goddard III A new extremely sensitive silicon-based explosive was recently synthesized in Germany by the nitration of tetrakis(hydroxymethyl)-silane, Si(CH$_{2}$OH)$_{4}$, with nitric acid. This sila-pentaerythritol tetranitrate (Si-PETN), Si(CH$_{2}$ONO$_{2})_{4 }$(tetrakis(nitratomethyl)-silane) has a molecular structure nearly identical to its carbon analog - PentaErythritol TetraNitrate (PETN), C(CH$_{2}$ONO$_{2})_{4}$ - with the central carbon atom replaced by silicon. Unexpectedly, SiPETN shows dramatically increased sensitivity, exploding with just a touch of a spatula, making it extremely dangerous and difficult to study. We have performed DFT calculations on paths of unimolecular decomposition and identified a novel central carbon-oxygen (or silicon-oxygen) rearrangement which shows a dramatic difference that may explain the colossal sensitivity. In particular, this reaction in SiPETN has significantly lower barrier and far more exothermic, which leads to a large net energy release at very early stages of Si-PETN decomposition facilitating a fast temperature increase and expansion of the reaction zone. [Preview Abstract] |
Tuesday, June 30, 2009 5:00PM - 5:15PM |
L1.00007: Brazilian disc testing of a UK PBX through the glass transition temperature David Williamson, Stuart Palmer, William Proud, Rebecca Govier Previous research at the Cavendish Laboratory has shown a change in failure mechanism from that of intergranular to transgranular when PBX Brazilian disc specimens are tested below the glass transition condition of their binder system. The current study builds on this early work, illustrating how the strengths of the samples change as a function of temperature. The increase in strength at low temperatures is identified with the stiffening of the polymer binder as the glass transition condition is approached. [Preview Abstract] |
Tuesday, June 30, 2009 5:15PM - 5:30PM |
L1.00008: First-principles studies of hydrostatic and uniaxial compression of a new energetic material -- an energetic nitrate ester Michael Conroy, Aaron Landerville, Ivan Oleynik, Carter White Density functional theory calculations with an empirical vdW correction were performed on a new energetic material (EM), a nitrate ester, that was recently synthesized by Chavez \textit{et al}. [Angew. Chem. Int. Ed. \textbf{47}, 8307 (2008)]. This EM was shown to have physical properties superior to another nitrate ester, PETN. The equilibrium structure was calculated by vdW-DFT in excellent agreement with experiment (to within about 0.1{\%} of the equilibrium volume of the unit cell). From the hydrostatic-compression simulation, the isothermal EOS and bulk modulus were predicted prior to any known experimental results. In addition, uniaxial compressions were simulated in the $<$100$>$, $<$010$>$, $<$001$>$, $<$110$>$, $<$101$>$, $<$011$>$, and $<$111$>$ directions to examine the anisotropic quality of the constitutive relationships. The calculated physical properties of the nitrate ester at extreme conditions are compared with other important energetic materials. [Preview Abstract] |
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