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    • On the other hand Zimmermann studied transition

    2018-11-15

    On the other hand, Zimmermann studied transition metal carbonyl complexes as blast enhancers and boosters for hollow charge explosives in order to improve burning [34]. The carbonyls tested consist of Cr(CO)6, Mo(CO)6, W(CO)6, Fe(CO)5, Fe2(CO)9, and Fe3(CO)12[34].
    Mechanism of action Fuel-air explosives (also called thermobaric explosives/weapons) with organic fuels have been known since the 1960s. Such composites have a high negative Gibbs free lysophospholipid receptor of reaction, but exhibit only a moderate detonation pressure [35,36]. However, due to an enhanced impulse, the blast effect of such explosives is much higher than that of ordinary high explosives. In fuel-air explosives atmospheric oxygen is used as an additional oxidizer for the explosives. Therefore metal fuels having high negative Gibbs free energy per mole of consumed oxygen (e.g. Al) are also used as additives in thermobaric explosives. When a warhead detonates, for instance inside the hull of a ship, in the first-hand the ship hull experiences a shock loading and then a quasi-static pressure develops. The latter is considered a determining factor for the structural damage. Optimal performance is achieved when the quasi-static pressure is sufficiently high to destroy the dividing walls present between the compartments of the ship structure. Afterburning may subsequently occur by reactions with oxygen in the available air in the neighboring compartments [30,37,38]. A proviso for this event is that the Al content and particle size will not reduce the effects of fragments in a significant way. In open air, the afterburning becomes far from complete due to the rapid expansion, thus cooling of the fireball ensues. When the reaction products expand and mix turbulently with the air, the temperature of the gases decreases rapidly, thus leading to incomplete combustion process. Therefore, small metal particles are to be preferred because they burn faster. Trzcinski et al. studied blast waves and found that the maximum impulse occurred at an aluminum content of around 30%. The peak value was reported as approximately 15% higher than that of pure RDX [39]. Furthermore, they asserted that the overpressure peak of the incident wave was comparable to or lower (by 5 to 17%) than that of RDX. The conclusion was that in general the blast performance was only slightly increased. However, it has been shown that for a gelled based metal-enhanced fuel-air explosive (metal content of approximately 60%), air blast surpasses the energy density of conventional propylene oxide fuel-air type explosives. TNT equivalents of about 500% have been observed [30]. Note that enhanced-blast weapons are primarily designed and effective to demolish bunkers, caves and enclosed structures (see Reference [40] for a review of thermobaric weapons). However, for semi-confined explosions, the conclusion is not so obvious. It is conceivable that walls will be blown out before aluminum will be appreciably mixed with air and oxidized. Then, the energy of explosion depends on the available air oxygen to an extent which is related to the oxygen deficiency. The addition of about 40% aluminum to high explosives like RDX or HMX leads to a significant enhancement of the calorimetric heat of explosion (also called energy of explosion or energy of detonation) [39]. This enhancement is typically around 40%, which is substantially lower than predicted from the theoretical calculations. Furthermore, a set of explosions has been performed in a closed chamber having different atmospheres in order to estimate the degree of afterburning of the detonation products in confined or semi-confined chambers. It has been found that the quasi-static pressures in closed compartments are much lower than the thermodynamically calculated values, but may be around 20% higher than of pure RDX when 45% Aluminum is added. The pressure is indeed much higher than the pressure calculated by the assumption of inert aluminum. This result indicates that it reacts with oxygen from the air in the chamber as well as with RDX decomposition products [39]. It has been found that the quasi-static pressure in a chamber filled with air is higher than the case if the chamber is filled with nitrogen or argon. The analyses of the chamber residues after detonation (0.15 m3 chamber, 200 gram explosive) have revealed that only in air, alumina constitutes the residues entirely. This means that the aluminum that has not reacted in the detonation/combustion wave is fully oxidized in expanding and re-shocked RDX products, meanwhile consuming oxygen from air [36].