We report a time-of-flight mass spectroscopic study of the chemical reaction zone in base-sensitized detonating liquid nitromethane (NM--CH3NO2). Mass spectra of the reaction zone region are presented for cases where the CH3NO2, 13CH3NO2, and CD3NO2 forms of NM were detonated. In experiments in which detonation was made to occur, the detonation process was initiated by a slapper detonator system. The NM explosives were confined in steel, and the charge geometry was chosen such that the detonations were traveling steadily by the time the detonation wave reached the end of the charge. Various nondetonation control experiments were also performed and are described. Two-dimensional numerical fluid-dynamic computations that mimic the experimental system were performed in order to help in the interpretation. We estimate that, for the base-sensitized NM explosive used, the steady two-dimensional chemical-reaction zone is ca. 50 μm in spatial extent and has a time duration of ca. 7 ns. The most important result obtained is that the new chemical species that are observed in the reaction zone are the result of condensation reactions where two or more NM molecules combine to form molecules more massive than NM or produce molecules in which numerous nitrogen atoms are present. A brief review of earlier work on this problem is presented to aid readers in understanding the new results.
Articles you may be interested inShock initiation of the tri-amino-tri-nitro-benzene based explosive PBX 9502 cooled to −55 ° C The channel effect: Coupling of the detonation and the precursor shock wave by precompression of the explosive We have completed a series of ambient temperature ͑23±2°C͒ shock initiation experiments on four lots ͑batches͒ of the insensitive high explosive PBX 9502. PBX 9502 consists by weight of 95% dry-aminated tri-amino-tri-nitro-benzene ͑TATB͒ and 5% of the plastic binder Kel-F 800, a 3 / 1 copolymer of chloro-trifluoro-ethylene and vinylidene-fluoride. Two of the four lots were manufactured using the "virgin" process. Both of these lots had few fine TATB particles. One virgin lot was stored the majority of its life ͑Ͼ15 yr͒ as a molding powder and pressed as a 240 mm diameter by 130 mm thick cylinder. The other virgin lot was stored the majority of its life as a hollow hemispherical pressing. Two lots were manufactured using the "recycle" process and had many fine TATB particles. One recycled lot was stored the majority of its life as a molding powder, while the other was stored as a pressed charge. Shock initiation experiments were performed using precisely characterized planar shocks generated by impacting an explosive sample with a projectile accelerated in a two-stage gas gun. The evolution of the shock into a detonation was measured using 10 or 11 embedded electromagnetic particle velocity gauges and three "shock tracker" gauges. Results include the following: ͑1͒ high quality particle velocity wave forms which should be useful for calibrating reactive burn models, ͑2͒ no difference in the sustained shock initiation response between lots regardless of material processing or storage history, ͑3͒ responses for all lots equivalent to those measured by Dick et al. ͓J. Appl. Phys. 63, 4881 ͑1988͔͒, additional Hugoniot and Pop-plot data for PBX 9502, and ͑5͒ the short shock response which, when compared to the sustained shock response, shows no extension in the run distance unless the rarefaction overtakes the shock front prior to the distance it would have run towards a detonation as a sustained shock.
Detonation fronts in solid high explosives have been examined through measurements of particle velocity histories resulting from the interaction of a detonation wave with a thin metal foil backed by a water window. Using a high time resolution velocity-interferometer system, experiments were conducted on three explosives—a TATB (1,3,5-triamino-trinitrobenzene)-based explosive called PBX-9502, TNT (2,4,6-Trinitrotoluene), and CP (2-{5-cyanotetrazolato} pentaamminecobalt {III} perchlorate). In all cases, detonation-front rise times were found to be less than the 300 ps resolution of the interferometer system. The thermodynamic state in the front of the detonation wave was estimated to be near the unreacted state determined from an extrapolation of low-pressure unreacted Hugoniot data for both TNT and PBX-9502 explosives. Computer calculations based on an ignition and growth model of a Zeldovich–von Neumann–Doering (ZND) detonation wave show good agreement with the measurements. By using the unreacted Hugoniot and a JWL equation of state for the reaction products, we estimated the initial reaction rate in the high explosive after the detonation wave front interacted with the foil to be 40 μs−1 for CP, 60 μs−1 for TNT, and 80 μs−1 for PBX-9502. The shape of the profiles indicates the reaction rate decreases as reaction proceeds.
An optically recording velocity interferometer system, called ORVIS, has been developed to measure particle velocity histories in shock wave experiments on condensed matter. The interferometer fringe motion is recorded with a high speed electronic streak camera, rather than with photomultiplier tubes and oscilloscopes as in previous interferometry systems. With this approach, the particle velocity of a witness foil in a detonation wave experiment was measured with 300-ps time resolution. We believe that 20-ps time resolution can be achieved with this technique which would represent an improvement of two orders of magnitude over previous measurement techniques.
The pressure-temperature (P-T) phase diagram of ammonium nitrate (AN) [NH(4)NO(3)] has been determined using synchrotron x-ray diffraction (XRD) and Raman spectroscopy measurements. Phase boundaries were established by characterizing phase transitions to the high temperature polymorphs during multiple P-T measurements using both XRD and Raman spectroscopy measurements. At room temperature, the ambient pressure orthorhombic (Pmmn) AN-IV phase was stable up to 45 GPa and no phase transitions were observed. AN-IV phase was also observed to be stable in a large P-T phase space. The phase boundaries are steep with a small phase stability regime for high temperature phases. A P-V-T equation of state based on a high temperature Birch-Murnaghan formalism was obtained by simultaneously fitting the P-V isotherms at 298, 325, 446, and 467 K, thermal expansion data at 1 bar, and volumes from P-T ramping experiments. Anomalous thermal expansion behavior of AN was observed at high pressure with a modest negative thermal expansion in the 3-11 GPa range for temperatures up to 467 K. The role of vibrational anharmonicity in this anomalous thermal expansion behavior has been established using high P-T Raman spectroscopy.
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