Explosion stimuli

As we have seen in the previous chapter, energetic materials are often initiated using thermal processes. However, the explosion stimuli could also come from mechanical or electrostatic sources. Therefore, it is important to know the exact sensitivities for explosive compounds. The important values that have to be determined are ... 

Explosive Stimulus Transfer. Under a program to develop a technique to compute probability of detonation transfer between a donor and an acceptor, experiments were performed to measure the effects of seven variables. These included two donor parameters fragment slack energy and five acceptor parameters confinement, closure thickness, explosive material, explosive particle size and closure material... 

The effect on detonation transfer of the parameters shown in Fig Ex22 were reviewed for the donor and acceptor expls RDX, HNS-1 (2,4,6,2/,4/,6/-Hexanitrostilbene of 3 microns particle size) HNS-11 (Same as HNS-1, except of 200-300 microns particle size), DATB (1,3-Diamino-2,4,6-trinitrobenzene), and TATB (1,3,5-Triamino-2,4,6-trinitrobenzene) with a wide cross-section of sensitivities. Eash of these parameters has been individually qualified and explained on both the theoretical level and the impact on practical hardware design. The experimental study is described in Ref 2 Refs 1) M.L.Schimmel, "Quantitative Understanding of Explosive Stimulus Transfer... 

QUEST), McDonnell Douglas Corp Summary Report-Tasks 1 thru 6, MDC AID21, St.Louis, Missouri (June 1971) 2)L.J.Bement, "Quantitative Understanding of Explosive Stimulus... 

Another favored test for the past few years has been a form of gap testing, usually cards, whereby the explosive stimulus necessary to initiate the material to detonation is determined. Again, as for impact testing, the results are presented in terms of inches or numbers of cards which attenuate the donor shock wave to non-initiation. The results are much more valuable if expressed in terms of the minimum initiation pressure necessary to initiate the system since a quantitative assessment... 

These catastrophic accidents showed that ammonium nitrate even diluted by another ammonium salt, is an explosive capable of detonating under a sufficiently powerful explosive stimulus [33]. 

Many compounds explode when triggered by a suitable stimulus however, most are either too sensitive or fail to meet cost and production-scale standards, requirements for safety in transportation, and storage stability. Propellants and explosives in large-scale use are based mosdy on a relatively small number of well-proven iagredients. Propellants and explosives for military systems are manufactured ia the United States primarily ia government owned plants where they are also loaded iato munitions. Composite propellants for large rockets are produced mainly by private iadustry, as are small arms propellants for sporting weapons. 

Explosives are commonly categorized as primary, secondary, or high explosives. Primary or initiator explosives are the most sensitive to heat, friction, impact, shock, and electrostatic energy. These have been studied in considerable detail because of the almost unique capabiUty, even when present in small quantities, to rapidly transform a low energy stimulus into a high intensity shock wave. 

Historically, the outbreak of the first World War provided a stimulus for the industrial preparation of large amounts of synthetic phenol, which was needed as a raw material to manufacture the explosive picric acid (2,4,6-trinitrophenol). Today, more than 2 million tons of phenol is manufactured each year in the United States for use in such products as Bakelite resin and adhesives for binding plywood. 

Davies, J. A. et al., J. Chem. Soc., Dalton Trans., 1980, 2246-2249 Extremely sensitive to thermal and mechanical shock, occasionally detonating spontaneously without external stimulus, it should only be prepared and used in solution. The solid is an extreme hazard, and the acetone-solvated complex is also explosive. 

Mixtures with nitrobenzene were formerly used as liquid high explosives, with addition of carbon disulfide to lower the freezing point, but high sensitivity to mechanical stimulus was disadvantageous [1], Dining the recovery of acids from nitration of toluene, mixtures of the oxide with nitrotoluene or dinitrotoluene may... 

Dissolution of a zinc-ruthenium alloy in hydrochloric acid leaves an explosive residue of finely divided ruthenium [1], More probably this is the hydride, which may decompose on slight stimulus, the evolved hydrogen probably igniting because of the catalytic activity of the metal. Ruthenium prepared from its compounds by borohydride reduction is especially dangerous in this respect [2],... 

Basics of Free-Field Blast Waves. The most severe types of energy releases which can occur in toxic chemical and explosives facilities are explosions of high explosive materials. When such materials are initiated by some stimulus, they may burn, deflagrate or detonate. Detonation is by far the most severe of these three chemical reactions, so it is usually assumed to occur in accident situations, unless one can prove otherwise quite conclusively. 

Primary explosives are sensitive to modest stimuli such as heat, spark, or friction application of the correct stimulus will lead to a detonation. The primary explosives used in detonators are typically extremely sensitive but not particularly powerful common examples are mercury fulminate, lead azide, and lead styphnate. In principle, the heavy metals present in most primary explosives should be a good cue for detection however, there are primary explosives that do not contain such elements. 

Note These compounds readily undergo explosive decomposition when sufficient ignition stimulus is applied. shock stimulus is frequently needed to activate the nonionic organic molecules (e.g., TNT) these compounds will frequently merely burn if a flame is applied. 

Andrej Ma ek, "Sensitivity of Explosives , ChemRevs 62, 41-63(1962). "The sensitivity of an explosive can be defined as the minimum amount of energy that must be imparted to the explosive, within limited time and space, to initiate explosive decomposition (p 60). This definition can serve as a basis of quantitative fundamental treatments provided the imparted energy is thermal and provided its initial distribution in time and space is known. If the energy is not supplied directly as heat, but by mechanical means (such as a shock), there is the additional requirement of quantitative assessment of conversion of the stimulus into heat (p60)... 

The unified approach adopted by Ma ek assumed that all initiations are ultimately thermal. More precisely every initiating stimulus (shock, impact, electric discharge, friction, etc) serves to heat up the explosive or a portion thereof, initially at a temperature T to an elevated temperature T. It is assumed that T and the length of time t the explosive is exposed to T are the two variables sufficient to account for initiation. The 3rd factor influencing the reaction rate, density p, is important in gaseous combustions and explosions where it varies considerably with temperature and pressure in homogeneous solids and liquids it is nearly constant... 

Explosion Spectra of Metals. Anderson was the first to use the "explosion method of exciting spectral lines of a metal. He studied the flash of light emitted when a thin wire of a metal to be studied was exploded by an oscillatory discharge from a condenser charged to several diousand volts. As the atoms of the metal are subjected to a powerful stimulus vety abruptly, the conditions of excitation are vety much different from those prevailing in an arc of the same metal carrying a low current. Several investigators have developed this techr... 

The reaction of the two systems to an ignition stimulus is markedly dissimilar the cohesive material presents a combustible surface wherein the rate of regression is controlled by thermal diffusivity into the propellant the non-cohesive system offers flame paths of convection into the explosive bulk, which if ignited produce gases to fracture the ma-... 

Tests made on explosives for "sensitivity by impact or friction, although in reality only ignition tests, should correlate well with the hazard of detonating the material. On the other hand, the same tests on a cohesive solid propellant would indicate only its ignitability under that particular stimulus and would not correlate prior experience in the explosives industry. 

Also, a common hazard in the handling of explosives is for them to be subjected to the effects of a blow which is, to some extent, at a glancing angle. This corresponds neither to pure impact nor to pure friction. Also, it is difficult to devise a test which delivers only the friction stimulus without impacting the sample and indirectly heating it by contact with a sliding component in the apparatus. 

Explosives can therefore be classified by the ease with which they can be ignited and subsequently exploded. Primary explosives are readily ignited or detonated by a small mechanical or electrical stimulus. Secondary explosives are not so easily initiated they require a high velocity shockwave generally produced from the detonation of a primary explosive. Propellants are generally initiated by a flame, and they do not detonate, only deflagrate. 

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