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    • Hahma et al tested certain thermobaric explosives and descri

    2018-11-01

    Hahma et al. tested certain thermobaric explosives and described their TNT-equivalents [76]. Thermobaric charges with four different liquid fuels and several powder fuels were prepared and fired and their TNT equivalences in the open field were determined. The test results have showed that the shock wave component of thermobaric explosion mostly originated from cp-690550 processes. The fuel component was deemed critical for the generation of a thermobaric explosion. Throughout the tests, only IPN (iso-propyl nitrate) demonstrated some advantageous properties and a reliable ignition of the fuel and metal powder components in all proportions tested. IPN was also found to be the only fuel able to create effective, aerobic explosions even with excessive amounts of metal powder producing enormous overpressure pulses. The powder fuel seemed to be critical for the ignition delay in the aerobic stage. The activated aluminum showed the most promising properties followed by Elektron (92:7:1 Mg-Al-Zn alloy), phosphorus and boron. Note that metal combustion rate is a critical parameter in generating high pressure levels in the aerobic stage. According to Pahl and Kaneshige the temperature of the particles in thermobaric explosives is a parameter of importance in determining when and to what extent aluminum particles participate in the expanding detonation products cloud [77]. In this paper, an experimental technique using 2-color pyrometry was used to measure the temperature and its spatial variation. The details of the diagnostic technique was presented along with the light intensity and estimated temperature data obtained from tests of certain aluminized-explosives [77]. The article by Trzciński and Maiz reviews the available literature on thermobaric explosives and enhanced-blast explosives (high-destructive explosives) [8]. These types of explosives are defined, and their common features and differences are shown. The review discussed the data excerpted from the literature based on various tests (including small scale tests, larger scale tests, blast ability tests, underground tests, closed chamber tests, sensitivity tests, cylinder tests, particle size tests, etc.). Klahn et al. investigated spectroscopically the afterburn reactions during explosions of enhanced blast explosives in a detonation chamber and in free field experiments [78]. Via concatenation of the spectra of three different spectrometers, a wide spectral range is accessible for investigation. Hence, it fits to the thermal continuum as well as to the water emission bands of the spectra to estimate the combustion temperature and water vapor content which could be improved. Then, different charges can be characterized by the obtained combustion temperature and the reaction course. Years long experience has indicated that metal-based reactive composites have great potential as energetic materials due to their high energy densities and potential uses as enhanced-blast materials. However, these materials can be difficult to ignite with typical particle size ranges. Although mechanical activation of reactive powders increases their ignition sensitivity, it is not yet entirely understood how the role of refinement of microstructure due to the duration of mechanical activation influences the impact ignition and combustion behavior of these materials. Mason et al. studied impact ignition and combustion behavior of mechanically-compacted activated Ni/Al reactive powder in one of their work on microstructure refinement by using a modified assay shear impact experiment [79]. They obtained some properties such as the impact ignition threshold, combustion velocity and ignition delay time, as a function of milling period. It was found that the mechanical impact ignition threshold decreases from an impact energy of greater than 500 J to an impact energy of ca. 50 J as the dry milling time increases. It was observed that during the mechanical activation process the largest jump in the sensitivity was between the dry milling period of 25% of the critical reaction milling time (tcr) (4.25 min) and 50% tcr (8.5 min), corresponding to the time at which nanolaminate structures begin to form. The differential scanning calorimetry analysis have indicated that this jump in the sensitivity to thermal and mechanical impact was dictated by the formation of nanolaminate structures, which reduce the temperature needed to begin the dissolution of nickel into aluminum. It was shown that a milling time (of 50%–75% critical reaction milling time) may be near optimal when taking into account both the increased ignition sensitivity of mechanically-activated Ni/Al and potential loss in reaction energy for longer milling times applied. In the same range for all milling times considered which were less than the critical reaction milling time, some ignition delays were observed due to the formation of hotspots ranging from 1.2 to 6.5 ms. During the investigation the combustion velocities were found to be ranged from 20 to 23 cm/s for thermally-ignited samples and from 25 to 31 cm/s for impacted samples at an impact energy of 200–250 J [79].