Explosives, initiation reactivity

Since 1967, the International Colloquia on the Dynamics of Explosions and Reactive Systems (ICDERS) were organized in addition to the Combustion Symposia. ICDERS was initiated by a group of visionary combustion scientists (Numa Manson, Antoni K. Oppenheim, and Rem Soloukhin). They considered the subject of these colloquia to be important to the future of combustion technology and control of global environmental emission. 

Aspects in the Shock Initiation of Fuel Droplets", Third International Colloquium on Gasdynamics of Explosions and Reactive Systems, Astronautics Acta 17, 693—702(1972) 12) Staff, The Detroit News, Sect F, p 2F (12 Oct 1972) 13) C.A. Robinson Jr,... 

Self-reactive substances are those which can initiate exothermic decomposition without reacting with oxygen in the air, causing rapid gas generation and deflagration leading to combustion or explosion. Self-reactive substances are occasionally called unstable substances because many of them experience thermal decomposition at a relatively low temperature. Recently the term "self-reactive substance" has been used as an official term both in Japan and abroad. 

Knystautas, R., Guirao, C.M., Lee, J.H.S., Sulmistras, A. "Measurements of Cell Size in Hydrocarbon-Air Mixtures and Predictions of Critical Tube Diameter Initiation Energy and Detonability Limits", 9th Int. Colloq. on Dynamics of Explosions and Reactive Systems (1983). 

Sensitivity of high energy materials (EMs) is primarily due to the chemical character of the materials this means it is possible to use the term initiation reactivity of EMs in this case. However, the means of transfer of the initiation impulse to the reaction centre of the EM molecule or the molecule of the most reactive component of the explosive mixture is also of great importance. Therefore, according to Dlott a complex solution to the problem of initiation must involve the areas of continuum mechanics, chemistry and quantum mechanics (quantum chemistry) (1). The main interest has been focused on studies of shock and impact sensitivities of EMs. In the last 16 years the preferred tools for the solution of these sensitivities have involved quantum chemistry [1-5]. The appUcation of chemistry to these problems is relatively reluctant and mostly without any broader contexts. Nevertheless, the approach of physical organic chemistry has been apphed not only to studies of impact and shock reactivity [6,7], but also sensitivity to electric spark [6,8], and in part to thermal reactivity of EMs [7] as well. This survey presents development trends of studies of initiation reactivity of EMs over the last nine years with emphasis on the contribution of physical organic chemistry to these studies. Research results presented at conferences and seminars are quoted here only as the exception. 

In the past nine years, two review articles have been published about laser ignition and initiation [40,41]. hi this section, facts are presented that are connected with studies of initiation reactivity of explosives. 

Up-Pumping [1,74]. As already mentioned in Sect. 3.1, the author consulted a number of specialists in advance about his ideas. However, in this way he introduced into his model the ideas of primary fragmentation of EMs under extreme conditions. Nevertheless, he enriched the theory of initiation of explosive transformations of EMs by introducing significant ideas about transfer of initiation impulse to molecules in the crystal lattice of these materials. Experimental verification of this model is absent to date. In Dlott s opinion [1,74] the initiation by impact is a particular case of initiation by mechanical impulses (Low Velocity Initiation). Also [105] (Sect. 3.3.4) clearly documents the difference between the initiations by impact and by shock, though the authors do not call attention to this fact. Both the cited facts agree with study results of initiation reactivity of polynitro compounds by means of physical organic chemistry (Sects. 4.7 and 4.11), where the initiation by impact is treated separately from the set of initiations by shock, electric spark and heat. 

Numerical modeling using reactive hydrodynamic codes have given us increased understanding of the effect of heterogeneities or density discontinuities on explosive initiation. 

The penetration velocities of projectiles interacting with explosives initiated by the projectile have been found to be much lower than the penetration velocities of inerts of the same density. Studies of projectile penetration dynamics in inert and reactive targets have been performed using the Eulerian reactive hydrodynamic code 2DE described in Appendix C. 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials No reaction Stability During Transport Stable Neutralizing Agents for Acids and Caustics Not pertinent Polymerization Heat may cause an explosive polymerization. Strong ultraviolet light can also initiate polymerization Inhibitor of Polymerization Hydroquinone and its methyl ether, in presence of air. ... 

Chain reactions begin with the initiation of a reactive intermediate that propagates the chain and concludes with termination when radicals combine. Branching chain reactions can be explosively fast. 

The chain length, i.e. number of RH —> RC1 conversions per Cl produced by photolysis, is wlO6 for CH4, and the reaction can be explosive in sunlight. Chlorination can also be initiated thermolytically, but considerably elevated temperatures are required to effect Cl2 — 2C1, and the rate of chlorination of C2H6 in the dark at 120° is virtually indetectable. It becomes extremely rapid on the introduction of traces of PbEt4, however, as this decomposes to yield ethyl radicals, Et, at this temperature, and these can act as initiators Et- + Cl—Cl —> Et—Cl + Cl. Chlorination of simple alkanes such as these is seldom useful for the preparation of mono-chloro derivatives, as this first product readily undergoes further attack by the highly reactive chlorine, and complex product mixtures are often obtained. 

In a review of incidents involving explosive reactivity of liquid chlorine with various organic auxiliary materials, two involved hydrocarbons. A polypropylene filter element fabricated with zinc oxide filler reacted explosively, rupturing the steel case previously tested to over 300 bar. Zinc chloride derived from the oxide may have initiated the runaway reaction. Hydrocarbon-based diaphragm pump oils or metal-drawing waxes were violently or explosively reactive [8], A violent explosion in a wax chlorination plant may have involved unplanned contact of liquid chlorine with wax or chlorinated wax residues in a steel trap. Corrosion products in the trap may have catalysed the runaway reaction, but hydrogen (also liberated by corrosion in the trap) may also have been involved [9],... 

In some reactions involving gases, the rate of reaction estimated by the simple collision theory in terms of the usually infened species is much lower than observed. Examples of these reactions are the oxidation of H2 and of hydrocarbons, and the formation of HC1 and of HBr. These are examples of chain reactions in which very reactive species (chain carriers) are initially produced, either thermally (i.e., by collision) or photochemically (by absorption of incident radiation), and regenerated by subsequent steps, so that reaction can occur in chain-fashion relatively rapidly. In extreme cases these become explosions, but not all chain reactions are so rapid as to be termed explosions. The chain... 

Under the simulation conditions, the HMX was found to exist in a highly reactive dense fluid. Important differences exist between the dense fluid (supercritical) phase and the solid phase, which is stable at standard conditions. One difference is that the dense fluid phase cannot accommodate long-lived voids, bubbles, or other static defects, whereas voids, bubbles, and defects are known to be important in initiating the chemistry of solid explosives.107 On the contrary, numerous fluctuations in the local environment occur within a time scale of tens of femtoseconds (fs) in the dense fluid phase. The fast reactivity of the dense fluid phase and the short spatial coherence length make it well suited for molecular dynamics study with a finite system for a limited period of time chemical reactions occurred within 50 fs under the simulation conditions. Stable molecular species such as H20, N2, C02, and CO were formed in less than 1 ps. 

Safety of Reactive Chemicals and Pyrotechnics (Yoshida et al. 1995). Addresses both the hazardous properties of reactive chemicals and appropriate handling methods. Describes several test methods and the evaluation of fire and explosion hazards of reactive substances, including the impact of initiating events such as earthquakes. 

An NFPA instability rating of 4 means that materials in themselves are readily capable of detonation or explosive decomposition or explosive reaction at normal temperatures and pressures (13 of 131 PSM-listed chemicals have an NFPA 4 reactivity). A rating of 3 means that materials in themselves are capable of detonation or explosive decomposition or explosive reaction, but require a strong initiating source or must be heated under confinement before initiation (25 of 131 PSM-listed chemicals have an NFPA 3 reactivity). 

In consideration of external effects, it is essential to emphasize that under some conditions the thermal induction period could persist for a very long period of time, even hours. This condition arises when the vessel walls are thermally insulated. In this case, even with a very low initial temperature, the heat of the corresponding slow reaction remains in the system and gradually self-heats the reactive components until ignition (explosion) takes place. If the vessel is not insulated and heat is transferred to the external atmosphere, equilibrium is rapidly reached between the heat release and heat loss, so thermal explosion is not likely. This point will be refined in Section C.2.a. 

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