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 Q1: Energetic Materials V |
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Chair: William Holt, Naval Surface Warfare Center, Dahlgren Room: Hyatt Regency Constellation B |
Wednesday, August 3, 2005 9:30AM - 9:45AM |
Q1.00001: The Role of Binders in Controlling the Explosiveness of HMX/HTPB Compositions Malcolm Cook, Peter Haskins, Christopher Stennett, Richard Briggs There is a clear difference in cook-off vulnerability between compositions such as LX-14 (pressed 95{\%} HMX-5{\%} binder), which yield violent responses, and Rowanex 1100 (cast 88{\%} HMX-12{\%} binder), which yields relatively mild responses. These two classes of composition differ primarily in three features: the binder quantity, the bulk moduli of the binders, and the manufacturing method. An experimental study was conducted in an attempt to determine which of these features, under cook-off conditions, is the most important in governing explosiveness. Here we describe a series of small-scale cook-off experiments in which pressed compositions of 88{\%}, 91{\%}, 95{\%} and 96{\%} HMX, mixed with cured, cross-linked HTPB, were studied. The experiments used a novel glass-windowed test vehicle, instrumented internally with thermocouples. A trend of increasing event violence with increasing proportion of HMX was found, although in none of the experiments was a detonation recorded. The results from these experiments are discussed with reference to the binder characteristics and manufacturing method used. [Preview Abstract] |
Wednesday, August 3, 2005 9:45AM - 10:00AM |
Q1.00002: Collapse of Hollow Cylinders of PTFE and Its Mixtures with Metal Particles Using Hopkinson Bar Jing Cai, Vitali F. Nesterenko Hopkinson bar based thick walled cylinder (TWC) method was developed to collapse hollow cylinders made from Teflon and its mixtures with Al or Sn particles of different sizes (2 and 95 microns for Al and 44 microns for Sn particles). Different media (water, suspension of alumina particles in water, glycerol) in different geometry were investigated to ensure collapse of hollow cylinders under single pressure pulse achievable in Hopkinson bar. Only mixture of Teflon and small aluminium particles (2 micron) demonstrated the evidence of decomposition/reaction localized along shear bands in the form of dark residue. Raman spectrum of this residue demonstrated two peaks which were absent in Raman spectrum of C2F4 monomer typical for the degradation of PTFE. This phenomenon was not detected under collapse of cylinders made from pure Teflon or from mixture of Teflon and large aluminium particles or in mixture of Teflon and Sn particles. This work was supported by ONR (N00014-02-1-0491). [Preview Abstract] |
Wednesday, August 3, 2005 10:00AM - 10:30AM |
Q1.00003: Reaction of Fluoropolymer-Metal Mixtures on Impact Invited Speaker: |
Wednesday, August 3, 2005 10:30AM - 10:45AM |
Q1.00004: Impact Initiation of Rods of Pressed Polytetrafluoroethylene (PTFE) and Aluminum Powders Willis Mock, Jr., William H. Holt A gas gun has been used to investigate the shock initiation of rods consisting of a mixture of 74 wt {\%} PTFE (28 $\mu $m particle size) and 26 wt {\%} aluminum (5 $\mu $m particle size) powders. The 7.6 mm diameter by 51 mm long rods were fabricated from material that had been pressed and sintered to a full density of 2.27 gm/cm$^{ 3}$. The rods were sabot-launched into 4340 steel anvils at impact velocities ranging from 104 to 777 m/s. This corresponds to calculated impact stresses of 3.3 to 48 kbar. The experiments were carried out in a 50-100 mtorr vacuum. A framing camera was used to observe the time sequence of events. These include changes in rod shape, fracture, and the initiation and evolution of the reaction phenomena. Observation of first visible light after impact was taken as the initiation time. Initiation of the reaction occurred at discrete locations in the rod material. At low velocity, no initiation occurred. Above an initiation threshold, the initiation time dropped abruptly from 56 $\mu $s just above threshold to 4 $\mu $s at the highest impact velocity. Two experiments were performed for pure PTFE material for comparison with the PTFE/Al rods. The pure PTFE showed more extensive radial flow without obvious brittle fracture. For the 784 m/s impact experiment, small points of light were observed on the edge of the mushroomed portion of the rod about 20 $\mu $s after impact, suggesting the onset of chemical reaction. [Preview Abstract] |
Wednesday, August 3, 2005 10:45AM - 11:00AM |
Q1.00005: Thermal behaviour of Fe2O3/Al thermite mixtures in air and vacuum environments Luisa Duraes, Regina Santos, Antonio Correia, Jose Campos, Antonio Portugal The thermal behaviour of Fe2O3/Al thermite mixtures, when heated in air and vacuum, is studied. Individual reactants and three mixtures - stoichiometric and over aluminized - are tested, by Simultaneous Thermal Analysis (STA) and heating microscopy with a heating rate of 10 C/min. The end temperatures were 1500 C and 1400 C, respectively. The STA results show that the presence of O2, from environmental air, or from residual air in vacuum experiments, determines the occurring reactions. The Al oxidation by this oxygen is extensive making the thermite reaction with Fe2O3 unviable. There is evidence of significant conversion of the Fe2O3 into Fe3O4, near the end temperature, which support the previous conclusion. Therefore, the STA curves for the three mixtures are similar and all display features of the individual reactants curves. The heating microscopy images confirm the STA conclusions, with one exception: the thermal explosion of the Al sample close to 550 C. The absence of this phenomenon in STA results is explained by the limited amount of material used in each sample. [Preview Abstract] |
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