Explosions initiators

T. J. Tucker, "Explosive Initiators," ia Behavior and Etilic tion of Explosives in Engineering Design, 12th Annual Symposium, University of New Mexico, Albuquerque, 1972. 

The fact that hot spots are required for explosive initiation can be seen by calculating for the bulk temperature, say 350 K, and the anticipated hot-spot temperature, say 700 K. We take typical values of Arrhenius constants for secondary explosives QjCp 2500 K, //c = 25,(X)0 K, and V = 10 s V Hence... 

That some enhancement of local temperature is required for explosive initiation on the time scale of shock-wave compression is obvious. Micromechanical considerations are important in establishing detailed cause-effect relationships. Johnson [51] gives an analysis of how thermal conduction and pressure variation also contribute to thermal explosion times. 

By the development of hot spots by friction. This is shown particularly by the effect of added materials of a gritty nature. For initiation to occur, the melting point of the grit must be above a limiting temperature dependent on the explosive. Initiation is favoured by a low thermal conductivity and also by a high hardness value. 

Gelatine explosives, initiated by commercial detonators, will normally fire at the low velocity of detonation initially, although this may well build up quite quickly into the high velocity. For some applications a high velocity of detonation is essential. This can be ensured by the addition of barium sulphate, or other material with density exceeding 2-8, in a fine form. Such additives have the property of ensuring rapid transition to the high velocity of detonation. This is, for example, of particular importance when the explosive is to be fired under a hydrostatic head, as in submarine work. 

Disposal of 2 1 of the solvent into a rusted iron sewer caused an explosion. Initiation of the solvent-air mixture by rust was suspected [1], A hot gauze falling from a tripod into a laboratory sink containing some carbon disulfide initiated two explosions [2], It is a very hazardous solvent because of its extreme volatility and flammability. The vapour or liquid has been known to ignite on contact with steam pipes, particularly if rusted [3], When a winchester of the solvent fell off a high shelf and broke behind a rusted steel cupboard, ignition occurred [4],... 

Extremely shock-sensitive and violently explosive initiation has been caused by prolonged freezing at —196°C, or by sawing a stopcock off a metal trap containing trace amounts [1], It may be stored safely at — 80°C [2], Detonative explosion during trap-to-trap distillation of purified material is noted [3],... 

Mixtures of ethylene and carbon tetrachloride can be initiated to explode at temperatures betwen 25 and 105°C and pressures of 30-80 bar, causing a six-fold pressure increase. At 100°C and 61 bar, explosion initiated in the gas phase propagated into the liquid phase. Increase of halocarbon cone, in the gas phase decreased the limiting decomposition pressure. 

The azide is very explosive, even when moist. Loosening the solid from filter paper caused frictional initiation. Explosion initiated by impact is very violent, and spontaneous explosion has also been recorded [1], It is also an exceptionally powerful initiator [2]. Detonation of the azide when dry has been confirmed [3], Good crystals are considerably more sensitive to shock, friction and electric discharge than is powder [4],... 

Mixtures of sodium nitrite and various cyanides [1] explode on heating, including potassium cyanide [2], potassium hexacyanoferrate(III), sodium pentacyanonitro-sylferrate(II) [3], potassium hexacyanoferrate(II) [4], or mercury(II) cyanide [5], Such mixtures have been proposed as explosives, initiable by heat or a detonator [5],... 

Explosive, initiated by shock, friction, pressure or temperatures over 30°C [1], It may also detonate spontaneously at ambient temperature [2],... 

A thermal explosion is the third type of chemical explosion. In this case, no reaction front is present, and it is therefore called a homogenous explosion. Initially, the material has a uniform temperature distribution. If the temperature in the bulk material is sufficiently high so that the rate of heat generation from the reaction exceeds the heat removal, then self-heating begins. The bulk temperature will increase at an increasing rate, and local hot spots may develop as the thermal runaway proceeds. The runaway reaction can lead to overpressurization and possible explosive rupture of the vessel. 

Catalytic forms of copper, mercury and silver acetylides, supported on alumina, carbon or silica and used for polymerisation of alkanes, are relatively stable [3], In contact with acetylene, silver and mercury salts will also give explosive acetylides, the mercury derivatives being complex [4], Many of the metal acetylides react violently with oxidants. Impact sensitivities of the dry copper derivatives of acetylene, buten-3-yne and l,3-hexadien-5-yne were determined as 2.4, 2.4 and 4.0 kg m, respectively. The copper derivative of a polyacetylene mixture generated by low-temperature polymerisation of acetylene detonated under 1.2 kg m impact. Sensitivities were much lower for the moist compounds [5], Explosive copper and silver derivatives give non-explosive complexes with trimethyl-, tributyl- or triphenyl-phosphine [6], Formation of silver acetylide on silver-containing solders needs higher acetylene and ammonia concentrations than for formation of copper acetylide. Acetylides are always formed on brass and copper or on silver-containing solders in an atmosphere of acetylene derived from calcium carbide (and which contains traces of phosphine). Silver acetylide is a more efficient explosion initiator than copper acetylide [7],... 

The 2nd method is by far more sensitive, and extremely high temps can be achieved in gas pockets trapped in this manner [See also Birth and Growth of Explosion, etc in Vol 2 of Encycl, p B127-L and in this Volume under Detonation (and Explosion), Initiation (Birth), Growth Spread and Propagation in Explosive Substances]... 

Its definition is given, together with definition of detonation head, at the end of the item entitled "Detonation (and Explosion) Initiation of Explosives and Shock Processes"... 

In solid explosive initially at atmospheric pressure pQ (which is negligible in comparison with pj), one obtains after substituting Eqs (1), (2) (5) in (6), the following ... 

Primary Explosives, Initiating Efficiency of. See under Initiating Efficiency of Primary Explosives, etc in Vol 1, p XVIII... 

See at the end of description of Detonation (and Explosion), Initiation (Birth) and Pro-. pagation (Growth or Spread) in Explosive Substances... 

Some unconfined high expls can also be ignited to deflagration especially if they are in a molten condition (such as TNT), or spread in a thin layer (such as MF or Diazodinitrophenol). In many cases deflagration develops into detonation [See also Detonation (and Explosion), Initiation of] Refs 1) F.P. Bowden, "The Initiation of Explosion and Its Growth to Detonation , PrRoySoc 204A, 20 ff (1950) la) A.F. Belyaev, ZhPraktKhim 23, 432 ff (1950). 

J- Wenograd, "A Photographic Study of Explosion Initiated by Impact , pp 10-23 in the 3rdONRSympDeton (I960)... 

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