Lin et al investigated the explosion characteristics of nano

Lin et al. investigated the explosion characteristics of nano-aluminum powders with particle sizes of 35, 75, and 100 nm in a 20-liter spherical explosion chamber [64]. The results have indicated that the maximum explosion pressure and the maximum rate of pressure rise mainly depend on the dust concentration. For dust concentrations below 1000 g/m3, the maximum explosion pressure increases gradually to a maximum value with increasing the dust concentration, whereas after the dust concentration increases above 1250 g/m3, the maximum explosion pressure starts to decrease. The trends of the maximum rate of pressure rise follow the same pattern with increasing dust concentration. They found the lower explosion concentration limits of nano-aluminum powders with sizes of 35, 75, and 100 nm as to be 5, 10, and 10 g/m3, respectively, whereas the lower explosion concentration limit of ordinary aluminum powders is about 50 g/m3. The investigation has revealed that: The review article on diazoxide Supplier aluminized explosives by Vadhe et al. considers the thermobaric PBX compositions [65]. Thermobaric (TB) compositions are most suitable to modern warfare threats. Indian researchers (the Naval Surface Warfare Center Indian Head Division (NSWC IHD) and the Talley Defense Systems (TDS)) developed some solid thermobaric compositions containing a moderate-to high aluminum content for lightweight shoulder-launched penetrating or anti-cave warhead for the M72 LAW system [66]. Various compositions which they developed with PBXIH-135 as the baseline composition are summarized below (Table 1). The composition, PBXIH-135 (HMX/Al/Poly urethane) present in Table 1, is one of the best examples categorized under thermobaric warhead systems. Thus, these insensitive munitions can be used effectively against bunkers, hard surfaces, tunnels and caves. It is worth mentioning that supersonic missiles and bombfill of the “General Purpose” category (500 and 2000 pound) demand insensitive munitions. Hall and Knowlton [67] reported some thermobaric compositions based on wax, HTPB, or GAP as a binder. The challenge of their study was to determine comparative thermobaric characteristics for some chosen compositions in confined tests. They observed the highest impulse and average peak pressure for GAP based compositions. Ti/HTPB based compositions have been found to be superior to the corresponding aluminum-based compositions in terms of the average peak pressure and impulse. The abovementioned researchers also studied compositions containing GAP in combination with propriety energetic plasticizers and achieved the average impulse up to 975 kPa.msec. Hall and Knowlton [67] also reported gelled thermobaric compositions incorporating 60–70% Mg/Al/Ti/Zr as a fuel with 20–30% energetic liquid nitromethane (NM) and isopropyl nitrate (IPN). The NM-based compositions exhibited a higher impulse, as compared to IPN-based compositions. Also AN/AP/HMX composites were incorporated as oxidizer/energetic components. The researchers found some compatibility for all the combinations. The best results were obtained with the 30/30/40 NM/Al/HMX combination in terms of the average peak pressure (0.5 MPa) and average impulse (802 kPa.msec) [67]. The thermobaric weapons are employed to produce pressure and heat effects instead of armor penetrating or fragmentation damage effects [5]. These weapons as mentioned before are particularly effective in enclosed spaces such as tunnels, buildings, and field fortifications [1,68]. Their reactivity requires aluminum (or other reactive metals) to be employed inexplosive ordnance in the form of fine powder (added to explosives) to enhance their blast effect [65,69]. Generally, the main affection of the large aluminum mass fraction improves spatial mixing of components in explosives with oxidizing gases in the detonation products, thus resulting in the release of more efficient afterburning energy. However, the effect of aluminum in thermobaric explosives has been well identified; the high ignition temperature of aluminum is a key step in its application in TBXs. It is known that the reaction of aluminum and oxygen is affected by various factors such as the dispersion of aluminum particles, the scale of the aluminum particles or the coated/uncoated particles. Investigations have focused to improve the whole impact of TBXs. Hence, the search for additional materials which can release high enthalpy like aluminum [11] is a promising strategy to improve the energy of TBXs. Mechanistically, the reaction of a thermobaric explosive is divided into three stages and the parameter σ is introduced to explain the differences of the three stages. Because the combustion and detonation of TBXs do not only rely on chemistry, but also are affected by a lot of other parameters such as the charge mass, charge geometry, etc., there are various thermobaric models introduced into the literature to simulate the propagation of the detonation products with the surrounding environment. Xing et al. in their paper emphasize the basic theory of the reaction mechanism of TBXs. Concentrating on the relative details on the explosion of TBXs with aluminum, the parameter, σ, for TBXs was defined as [5]where Cp is the heat capacity at constant pressure, ΔH is the heat changing term when the reaction proceeds, β is the thermal expansion coefficient and V is the volume of the system. According to the theory on flow in a reactive medium [70], parameter σ reflects the rate of transformation of chemical bond energy to molecular and bulk translation energy. Note that the parameter σ is introduced to estimate the detonation occurrence. By this method, the first stage is a detonation process in contrast to the last stage. This is in coincidence to the experimental phenomenon that the third stage of the process is afterburning. Actually, the mixture is heated up by the detonation process and the afterburning process becomes intense when the detonation processes finish. However, one should keep in mind that the confined environment is as important as the ignition temperature factor in the explosion of TBXs.