To obtain reaction zone parameters for several high explosives, experimental measurements of the detonation wave profiles in HMX-, RDX- and PETN-based explosives were performed using photon Doppler velocimetry (PDV). Planar detonations were produced by impacting the explosive with a sapphire flyer in a gas gun. Particle velocity wave profiles were measured at the explosive/window interface. LiF windows with very thin vapor-deposited aluminum mirrors were used for experiments. All measurements show a distinct end to the reaction zone, indicating a Chapman-Jouguet (CJ) point. For HMX-based explosives, the presented measurements show that the fast reaction time is approximately 10±2 ns, whereas for RDX- and PETN-based explosives, the values are 14±3 ns and 7±2 ns, respectively. The reaction times or reaction zone lengths obtained in the present study are smaller than previously reported data but much closer to the estimated values in theory. Additionally, the velocity at the Von Neumann (VN) spike was analyzed using the “beat cycles” method, and the pressure at the VN spike was obtained.
In order to obtain the chemical reaction zone of HMX based JOB-9003 explosive, experimental measurements on the detonation wave profile of solid explosives using photon Doppler velocimetry (PDV) have been performed. Planar detonations were produced by impacting the explosive with sapphire flyer launched from a powder gun. Particle velocity wave profiles were measured at the explosive/window interface. LiF windows with very thin vapor deposited aluminum mirrors were used in the experiments. The time resolution of PDV is about 1 ns, and the velocity uncertainty is less than 2%. The measurements show distinct end to the reaction zone indicating a CJ point in JOB-9003. The results show that the reaction time of JOB-9003 is (11±2) ns, and the corresponding reaction length is (0.075±0.014) mm. The CJ pressure is (35.6±0.9) GPa, and the pressure at Von-Neumann spike is (47.9±1.2) GPa.
Aluminized explosives exhibit excellent performance because the oxidation of aluminum (Al) powders enhances the pressure and temperature of detonation products. However, the equation of state (EOS) of detonation products has not been understood well. In the present study, we conducted long-time tests (approximately 1 ms) of a metal rod driven by detonation products of RDX, RDX/LiF, and RDX/Al. In addition, we used laser velocimetry (PDV) to measure the freesurface velocity of the rod. Thermochemical code DLCHEQ was successfully applied to the hydrodynamic program SSS to perform the rod-driven test, and a novel method was established to study the EOS of detonation products from the perspective of composition. The reliability of DLCEHQ was validated by a small deviation (<10%) between the experimental rod free-surface velocity of RDX and the calculated results; the deviation was considerably less than that from the results obtained using the JWL EOS and ideal-gas EOS. The endothermic process and the reaction of Al powders (Al+H2O+NO+CO2→CO+H2+N2+Al2O3) were analyzed by calculating the rod free-surface velocity of RDX/LiF and RDX/Al, respectively. The results of the present study demonstrated that the thermodynamic state of Al powders has notable influence on the EOS of aluminized detonation products, and the findings were compared with those of previous studies. First, the temperature equilibrium between Al powders and CHNO products is not always achieved, and the disequilibrium is more obvious when the reaction of Al powders is stronger. Second, the reaction rate of Al powders depends on pressure and Al content. Finally, the endothermic process of Al powders has a high contribution to the decrease in the work ability of RDX/Al instead of the gasconsumption mechanism of the Al reaction. More than half of the reaction heat of Al powders is used to heat itself, whereas the gas consumption during the reaction is negligible.
Metal particle size and environment will affect the reaction properties of aluminized polytetrafluoroethylene (Al/PTFE) reactive material. This study experimentally investigated the reaction properties of Al/PTFE with different Al particle sizes through time-resolved self-emitting imaging and emission spectroscopy under nanosecond laser ablation in air and an inert argon environment. The results show that the laser ablation causes a continuous combustion characteristic and a long energy release time in Al/PTFE. Furthermore, the reaction properties of Al/PTFE are closely related to the particle size of Al powder. The emission intensities and durations increase as Al particle size decreases, but it no longer conforms to this rule when Al particle size decreases to nanometers. This inconsistency may be due to the oxidation of Al powder and agglomeration of nano-Al powder. The experiments in different gas environments proved that the reactivity of Al/PTFE in the inert gas environment is not as good as that in air because of the lack of the oxidation reaction between Al and oxygen from the air.
Natural aluminum particles have the core–shell structure. The structure response refers to the mechanical behavior of the aluminum particle structure caused by external influences. The dynamic behavior of the structural response of aluminum core–shell particles before combustion is of great importance for the aluminum powder burning mechanism and its applications. In this paper, an aluminum particle combustion experiment in a detonation environment is conducted and analyzed; the breakage factors of aluminum particles shell in detonation environment are analyzed. The experiment results show that the aluminum particle burns in a gaseous state and condenses into a sub-micron particle cluster. The calculation and simulation demonstrate that the rupture of aluminum particle shell in the detonation environment is mainly caused by the impact of the detonation wave. The detonation wave impacts the aluminum particles, resulting in shell cracking, and due to the shrinkage-expansion of the aluminum core and stripping of the detonation product, the cracked shell is fractured and peeled with the aluminum reacting with the detonation product.
Abstract To characterize the effect of the particle size on the combustion time of aluminum (Al) in aluminized explosives, a series of cylinder tests was performed with RDX and Al compositions (median size of 2, 10, and 47 μm). Similar compositions were also prepared with RDX and lithium fluoride (LiF). The expanding velocities of the cylinders were measured using photonic Doppler velocimetry (PDV). The results show that the Al reaction delay is less than 3 μs, and the majority of the Al reaction is less than 25 μs. Among the RDX/Al formulas with 0 %, 15 %, and 30 % weight percent of Al, the formula with 15 % Al has the best metal acceleration ability. The effects of the particle size on the cylinder test are surprisingly negligible over the range of 2–47 μm, which implies that the Al particle combustion in the detonation product does not obey the classical d 1 law. Finally, a novel Al combustion model in the detonation product was proposed based on the experimental result and theoretical analysis. The model suggests that the Al particle breakup plays an important role in the post‐detonation combustion of Al.
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