Secondary explosives detonation

Explosive substances can also be detonated if they are subjected to a high velocity shockwave this method is often used for the initiation of secondary explosives. Detonation of a primary explosive will produce a... 

Available evidence indicates that secondary explosives in detonators are initiated by shock waves. This evidence consists of streak traces showing an accelerating shock front passing from the azide to the secondary explosive, and flash X-ray studies show the secondary explosive detonating at the interface between the lead azide and the secondary. Since the theory of shock waves at interfaces has been adequately treated in other texts [27,32,39], only the major aspects will be presented. 

Detonating explosives are primary or secondary. Primary explosives detonate by flame,... 

High explosives which detonate to produce shock waves. Materials which are easily detonated by mechanical or electrical stimuli are termed primary explosives . Those requiring an impinging shock wave to initiate them are secondary explosives . 

Detonator. A metal tube containing a primary explosive used for initiating a secondary explosive. 

Secondary explosive. Alternative name for high explosive indicating that the explosive does not burn to detonation but is detonated by suitable devices. 

Primary explosives differ from secondary explosives in that they undergo a rapid transition from burning to detonation and have the ability to transmit the detonation to less sensitive (but more powerful) secondary explosives. Primary explosives have high degrees of sensitivity to initiation through shock, friction, electric spark, or high temperature, and explode whether confined or unconfined. Some widely used primary explosives include lead azide, silver azide, tetrazene, lead styphnate, mercury fulminate, and diazodinitrophenol. Nuclear weapon applications normally limit the use of primary explosives to lead azide and lead styphnate. 

Lead azide (PbN6) is a colorless to white crystalline explosive. It is widely used in detonators because of its high capacity for initiating secondary explosives to detonation. However, since lead azide is not particularly susceptible to initiation by impact, it is not used alone in initiator components. It is used in combination with lead styphnate and aluminum for military detonators, and is used often in a mixture with tetrazene. It is compatible with most explosives and priming mixture ingredients. Contact with copper must be avoided because it leads to formation of extremely sensitive copper azide. 

Secondary explosives (also known as high explosives) are different from primary explosives in that they cannot be detonated readily by heat or shock and are generally more powerful. Secondary explosives can be initiated to detonation only by a shock produced by the explosion of a primary explosive. Widely used secondary explosives include trinitrotoluene (TNT), tetryl, picric acid, nitrocellulose, nitroglycerine, nitroguanidine, cyclotrimethylenetrinitramine (RDX), cyclotetramethylenetetranit-... 

Pentaerythritol tetranitrate (PETN) is a colorless crystalline solid that is very sensitive to initiation by a primary explosive. It is a powerful secondary explosive that has a great shattering effect. It is used in commercial blasting caps, detonation cords, and boosters. PETN is not used in its pure form because it is too sensitive to friction and impact. It is usually mixed with plasticized nitrocellulose or with synthetic rubbers to form PBXs. The most common form of explosive composition containing PETN is Pentolite, a mixture of 20 to 50% PETN and TNT. PETN can be incorporated into gelatinous industrial explosives. The military has in most cases replaced PETN with RDX because RDX is more thermally stable and has a longer shelf life. PETN is insoluble in water, sparingly soluble in alcohol, ether, and benzene, and soluble in acetone and methyl acetate. 

Explosives are classed as primary or secondary. Typically, a small quantity of a primary explosive would be used in a detonator (known colloquially as a cap ), whereas larger quantities of secondary explosives are used in the booster and the main charge of a device. This collection of explosives is known as an explosive train in which a signal (mechanical, thermal, or electrical) from the control system is converted first into a small explosive shock from the detonator, which in turn initiates a more powerful explosion in the booster, which amplifies the shock into the main charge. 

It should be noted that there are modem detonators that are designed to function without primary explosives. These usually rely on an electrically generated shock to produce detonation in a small charge of a specially prepared and sensitive charge of a secondary explosive. 

The requirement for an explosive train, that is, a primary explosive to initiate the secondary explosive, is a safety feature. In the past, people wishing to illegally use explosives usually had to steal the detonators (e.g., Timothy McVey). Consequently, the effective control of access to detonators has been widely regarded as a key pubhc safety measure by many governments and law enforcement agencies. However, recently, triacetone triperoxide (TATP) has been used as the primary explosive (e.g., Richard Reid s shoe bomb) and TATP is readily, although hazardously, synthesized from acetone, hydrogen peroxide, and acid. 

Returning to the subject of detonability , it may be noted, that it has been found difficult to induce detonation without simultaneous application of high pressures and temperatures in both secondary explosives and propellants. There is, of course, considerable heating in a shock compression. For the growth of detonation under marginal circumstances, however, the essential macro-... 

To achieve high-order detonation in secondary explosives, it has always been necessary to allow much longer delays in order to let the low-order process initially started "jump to high order [Compare with Detonation (and Explosionjby Influence] Note 2 In a review of 23 papers on initiation, ignition, and growth of reaction presented at the 4thONRSympDeton bv G.P. 

M.A. Cook etal, TrFaradSoc 56, 1028-38(1960 Promotion of shock initiation of detonation by metallic surfaces) 36a) Andreev Belyaev (i960), 265-68 (Starting impulse and mechanism of initiation) 268-70 (Initiation by heat) 270-73 (Initiation by flame) 273-86 (Initiation by shock or friction) 287-89 (Initiation of expln in projectiles on hitting a target) 36b) J. Favier C. Fauquignon, MP 42, 65-81(1960) (Initiation of expls. and transmission of detonation) 37) D.B. Moore J.C. Rice, Detonation of Secondary Explosives by Lead Azide , SRI (Stanford Research Institute), Poulter Laboratories, Technical Report 004-60(1960) 37a) S.J. Jacobs, AmRocket-... 

This distinction is more in kind than in degree. Small quantities of primary or initiating explosives usually detonate when exposed to flames or high temperatures whiie secondary explosives usually burn or deflagrate under these conditions. However under slightly altered conditions primary explosives can be made to deflagrate and secondary explosives can be made to detonate. Examples of primary explosives are Lead Azide, Mercury Fulminate, DDNP, etc Examples of secondary explosives are PETN, RDX, HMX, Tetryl, TNT, as single HE compns and Comp B, Comp C, PBX 9404, Dynamite ANFO (Ammonium Nitrate/Fuel Oil) as HE mixtures... 

Secondary explosives will burn without detonating if unconfined or lightly confined. Some secondary explosives, such as PETN, are difficult to ignite and propagate burning only at slightly elevated ambient pressures... 

Initiation by Primers (and Boosters) is the standard method of initiating secondary explosives. Thus hot wires (or other means) are used to initiate the primer charge (Lead Azide, Mercuric Fulminate etc) explosive whose detonation then initiates the main charge of PETN,... 

A major difference between primary and secondary explosives arises from the fact that primary explosives are initiated to detonate by burning whereas secondary explosives are initiated to detonate by shock waves. Therefore, the most important property of a primary explosive is its ability to undergo a fast deflagration-to-detonation transition (DDT). Thus, fast DDT is the strength of primary explosives as well as their weakness. All other parameters being equal, the faster the DDT, the better the primary explosive. At the same time,... 

Implosion method Explosives are also used in nuclear weapons to generate the implosion required to bring the two halves of the radioactive device together. The implosion is achieved with the help of secondary explosives which surround the material and rapidly compress the mass to a supercritical state on their detonation. This encompasses two major assemblies (i) com-... 

On the other hand, Dudek et al. found that the impact sensitivity (h50% ) of e CL-20 28 cm is comparable to that of [5-HMX (h50% = 30 cm) [124]. Agrawal et al. have not only given impact sensitivity of CL-20 but also the mechanism of initiation on impact leading to its detonation. This is in line with the mechanism of initiation by hot spot formation on impact followed by detonation similar to other secondary explosives [125]. 

The manufacturing process of BX4 was found to be more favorable than that of BX3. The detonation pressure and test of their ability to initiate a secondary explosive have shown that BX4 is the most powerful of these formulations and therefore, it is considered the most promising booster formulation. Another attribute of BX4 is that it could be converted into a blast formulation by the addition of aluminum powder and this modified formulation may find application as a main-charge blast formulation. 

The burning of the mixture may end with an explosion (detonation) if its composition is suitable. The explosion of the gas mixture is accompanied by a bright flame. This secondary flame is elliptical and visible for a great distance. The dimensions of the flame and the intensity of the flash depend to a great extent on the calibre of the gun e.g. a shot from a 30 cm naval gun gives a secondary flame up to 50 m long, visible for a distance of 50 km. 

Primary explosives differ considerably in their sensitivity to heat and in the amount of heat they produce on detonation. The heat and shock on detonation can vary but is comparable to that for secondary explosives. Their detonation velocities are in the range of 3500-5500 ms-1. 

Some secondary explosives are so stable that rifle bullets can be fired through them or they can be set on fire without detonating. The more stable explosives which detonate at very high velocities exert a much... 

---