Dead pressing

Lead azide is not readily dead-pressed, ie, pressed to a point where it can no longer be initiated. However, this condition is somewhat dependent on the output of the mixture used to ignite the lead azide and the degree of confinement of the system. Because lead azide is a nonconductor, it may be mixed with flaked graphite to form a conductive mix for use in low energy electric detonators. A number of different types of lead azide have been prepared to improve its handling characteristics and performance and to decrease sensitivity. In addition to the dextrinated lead azide commonly used in the United States, service lead azide, which contains a minimum of 97% lead azide and no protective colloid, is used in the United Kingdom. Other varieties include colloidal lead azide (3—4 pm), poly(vinyl alcohol)-coated lead azide, and British RE) 1333 and RE) 1343 lead azide which is precipitated in the presence of carboxymethyl cellulose (88—92). 

Some initiating expls (such as MF, DADNPh, TATNB, etc) stop detonating from thermal impulse but can be ignited. This phenomenon, known as dead-pressing , was... 

Detonation, Dead Pressing in. See Dead-Pressed Explosives" in Vol 3 of Encyfcl, p D20... 

Other evidence indicates that the pre-compression need have no dynamic character, to cause quenching of the detonation. All that is required is the achievement of an initial density above a critical value. In general, this critical value depends on the charge dimensions the smaller the charge, the lower the critical density. For some explosives this density may be lower than the TMD at atmospheric pressure for instance, MF 8t LA,under certain conditions, will not support a high-velocity detonation at densities near crystal (See "Dead-Pressed Explosives in Vol 3 of Encycl, p D20)... 

HMTD is an explosive of the initiating type it is more powerful and brisant than MF, rather being comparable to LA and Cyanuric Triazide. It does not become dead-pressed even at pressures of 11000 psi (an advantage over MF)... 

See Dead-Pressed Explosives in Vol 3, p D20-L. Ficheroulle Kovache claim that this salt is not useful as an explosive primer (Ref 4)... 

Hypercompression of Explosives. See Vol 3, p D20-R under Dead-Pressed Explosives... 

Initiation by Flame. Various aspects of this process were described under Burning and Combustion, Vol 2, pp B343-346 Dead-Pressed Explosives, Vol 3, p D20 Ignition in this Vol Thermal Explosion in a future Vol... 

Tetracene exists as colorless or pale yel ndls mp decomp ca 142° and explodes at 160° in 5 secs (vs 190° for MF) explodes in a flame w/o much noise but producing much bk smoke apparent a only 0.45, but yields a pellet of d 1.05 when compressed at 3000 psi. It is practically insol in w, ale, eth, acet, benz, CC14 and ethylene dichloride sol in dilute nitric acid decompd by boiling w with formation of 2N2 per mole can easily be dead-pressed (Ref 10)... 

Under a pressure greater than 1660 kg/cm2 mercury fulminate becomes dead pressed i.e. takes fire with difficulty and burns without detonation. 

It is characteristic of lead azide that even under a pressure as high as 2000 kg/cm2 it cannot be dead pressed . This is a great advantage. In practice a pressure of 500-600 kg/cm2 is used. 

The specific gravity of trinitrotriazidobenzene is 1.8054. Under a pressure of 3000 kg/cm2 it gives a density of 1.751 and under 5000 kg/cm2 the density achieved is 1.7526. A pressure higher than 300 kg/cm2 may make it dead pressed . 0.02 g of the substance compressed under the pressure of 300 kg/cm2 detonates trinitrotoluene, and 0.01 g detonates tetryl. It is therefore one of the most vigorous initiators. 

Clark confirmed that dinitrodiazophenol does not become dead pressed even under a pressure of 9140 kg/cm2 which is a great advantage in an initiating material. Smoleriski and Plucinski quote the following figures which are characteristic of its... 

Thus, at a pressure of 200 kg/cm2 the substance nears the condition of being dead pressed . In spite of the fact that burning under this condition passes to detonation with difficulty, when greatly compressed the material maintains its ability to be detonated by a cap. Thus, 0.4 g of tetrazene, pressed under a pressure of 200 kg/cm2, develops its maximum power, i.e. 21.1 g of sand crushed, when initiated with 0.4 g of mercury fulminate. The difficulty in passing from burning to detonation makes tetrazene unsuitable for detonators and its application is thus limited to... 

Its specific gravity is 1.57, but its apparent density only 0.66. A density of 0.91 can be obtained under a pressure of 170 kg/cm2. It is not liable to become dead pressed even under a pressure of 730 kg/cm2. 

On the other hand, the certainty of deton by initiation decreased with an increase in d of the AN that is, the salt tended to become dead pressed (See also studies by Parisot, Ref 67)... 

Properties of TATNB. When ignited in the open, it burns rapidly with a dazzling blue flame. When dead pressed(ca 3000kg/cm2), it either burns when ignited or puffs weakly(Ret 6a). When con-fined(even slightly, as in detonators) it expl when heated in a flame. A violent deton takes place when TATNB, compressed in a metal tube, is heated... 

Dead-Cooling (Tot-kiihlung in Ger). When a MF cap was cooled in liq air or liq oxygen, the expl lost its prop to initiate, just as if it were dead-pressed (qv)... 

Dead-Pressed Explosives. Some expls, such as MF, LSt, TATNB, Tetracene or N4S4, lose their sensitivity to detonation (become insensitive) to flame, hot wire, spark or fuse if they are previously subjected to very high pressures, such as 25000-30000psi (Muraour, Ref 3 gives for MF 700kg/cm 2). These expls are then said to be dead-pressed (surcomprimee, in Fr). 

Accdg to Muraour et al (Refs 3 5), MF or LSt will, under these conditions ignite on the surface. If, however, a small amt of other initiating expl, such as pressed LA, will be brought in contact with dead-pressed MF or LSt and LA detonated, then MF or LSt will detonate also. Muraour has shown that contrary to prevalent opinion the brisance of dead-pressed MF or LSt increases with the degree of compression. The phenomenon... 

Muraour et al (Ref 3) think that the reason for MF not to detonate when ignited is that it burns on the surface only and the hot gases cannot penetrate inside the mass of expl, while in the case of not highly compressed material, they easily penetrate inside the mass, thus causing the deton. If this theory is accepted, then it would be understandable why LA cannot be dead-pressed. This is because when it is touched with a hot wire, it detonates without previous combustion. Diazodinitrophenol, Ag azide, Hg Azide, Ag Fulminate also cannot be dead-pressed... 

Muraour Wohlgemuth (Ref 2) have shown that if dead-pressed MF is preheated to 120-130° and then touched with a hot wire, it will detonate without previous combustion. This means that MF behaves in this case like L A. Direct deton of dead-pressed MF takes place either at atm pressure or in vacuo Refs l)Anon, Army Ordn 3, 58 (1922) CA 16, 3395 (1922) (Dead-pressed expls) 2)H. Muraour J. .Wohlgemuth, Chim Ind (Paris)... 

Muraour (Addnl Ref D, p 895), who also investigated this problem, stated that the "densite limite exists only for expl mixts and not for definite chem compds, such as PA, TNT, Tetryl, etc. He also stated that "densite7 limite must not be confused with the density at which an expl, such as MF, is "dead-pressed ... 

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