Explosions of lead azide

Slow decomposition of lead azide takes place under the influence of ultra-violet irradiation, as demonstrated by the investigations of Garner and Maggs [84] and Tompkins etal. [22, 85], but if the irradiation is very intense, explosion may occur, as was shown by Berchtold and Eggert [86] and Meerkamper [87]. In another paper Eggert [88] reported that the light intensity required to cause the explosion of lead azide is 2.0 J/cm2 when the electrical energy of the flash is 240 J, and the half-life of the flash 0.8 msec. 

Spontaneous explosions of lead azide also take place during crystallization from saturated solution in ammonium acetate. A detailed study of this phenomenon has been made by Taylor and A. T. Thomas [105]. When the concentration of the solutions and the temperature and conditions of cooling were carefully controlled, they were able to predict the time at which spontaneous explosions occur. E.g. ... 

INITATION OF EXPLOSION OF LEAD AZIDE PELLETS BY IMPACT... 

Groocock [16] made an experimental and theoretical study of the thermal explosion of lead azide but found no crystal size effect. However, he used batches of l0,000 crystals in vacuum so it was a different experiment from that of Bowden and Singh. The critical temperature for a batch of crystals will be reached when any one crystal reaches critical conditions, and this will be influenced by the heat transfer from neighboring crystals. Unfortunately, neither Bowden and Singh nor Groocock specify their vacuum conditions, although one can infer that Groocock s work was at lower pressures his analysis also assumes... 

Research on the spontaneous explosion of lead azide was recently reviewed by Fox et al. [123], who discuss the main three hypotheses which have been suggested to explain the phenomenon. These involve (1) the release of stored energy sufficient to cause explosion [124], (2) reactive chemical products or intermediates formed in the solution from which the lead azide is growing [122,125], and (3) spark initiation caused by discharge between growing crystals [121] ... 

Mechanical treatment alone may be sufficient to induce significant decomposition such processes are termed mechanochemical or tribo-chemical reactions and the topic has been reviewed [385,386]. In some brittle crystalline solids, for example sodium and lead azides [387], fracture can result in some chemical change of the substance. An extreme case of such behaviour is detonation by impact [232,388]. Fox [389] has provided evidence of a fracture initiation mechanism in the explosions of lead and thallium azide crystals, rather than the participation of a liquid or gas phase intermediate. The processes occurring in solids during the action of powerful shock waves have been reviewed by Dremin and Breusov [390]. 

An explosion occurred during blending and screening operations on a mixture of lead azide and 0.5% of calcium stearate. If free stearic acid were present as impurity in the calcium salt, free hydrogen azide may have been involved. 

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. 

Performance tests consisted of loading DBX-1 as a transfer charge in U.S. Army M55 stab detonators. Standard M55 detonators consist of three separate explosive layers, pressed sequentially into a metal detonator cup as shown in Figure 6. The first layer is 15 mg of the stab initiation mix (NOL-130) it is a combination of lead azide, lead styphnate, barium nitrate, antimony sulfide, and tetrazene [l-(5-tetrazolyl)-3-guanyltetra-zene hydrate], pressed at 70,000 psi. The second layer is 51 mg of transfer charge, lead azide, pressed at 10,000 psi. Lastly, the third layer is 19 mg of output charge, RDX, pressed at 15,000 psi. 

In general, C-nitro compounds are more stable than /V-nitro compounds because of the higher bonding energies in the former type. Evidence is offered [1] that decomposition and explosion of many nitro-derivatives proceeds through the aci-form, and that sensitivity corresponds to the proportion of that present. In terms of this work, sensitisation by very small proportions of soluble organic bases is most important this is not limited to nitroalkanes. TNT can apparently be brought to the sensitivity of lead azide by this means. For a physicist s view of this sensitisation,... 

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... 

The erstwhile Explosives Research and Development Laboratory (ERDL), now High Energy Materials Research Laboratory (HEMRL), Pune, had undertaken a study on primary explosives with a view to synthesizing a series of new explosives, which are safer, powerful and free from the drawbacks of lead azide and MF. As a result of these sustained efforts, HEMRL has successfully synthesized and developed a new and safer initiatory explosive called basic lead azide (BLA). 

The earlier opinion that the / -form is the more sensitive to impact appears to be incorrect. This problem will be discussed more fully in the section on the explosive properties of lead azide. 

As shown by the investigations of a number of authors, irradiation of lead azide (and other azides) with a-particles, X-rays and y-rays does not cause explosion (Ha issinsky and Walden [89] Gunther, Lepin and Andreyev [90]). However, it produces a slow decomposition of lead azide, according to Kaufman [91]. 

According to various authors, the ignition temperature of lead azide ranges from 327 to 360°C. When a test sample is dropped onto a metal plate instant explosion ensues if the temperature of the plate is 380°C or higher. The ignition temperature of lead azide is the highest ignition temperature of an explosive ever to have been observed. 

Rogers and Harrison [103] tried to determine the conditions governing this phenomenon, i.e. the explosion during the growth of /Mead azide. Their experiments, which are illustrated diagrammatically in Fig. 46, were carried out in a test-tube. Three solutions were carefully introduced so that they did not mix. The bottom layer consisted of 20% lead nitrate (2 cm3). The middle layer was 20% sodium nitrate (1 cm3). The top layer was 10% sodium azide (2 cm3). Crystals of lead azide formed in the sodium nitrate layer after ihr. They appeared to start from the walls and spread inwards. A major explosion generally occurred in the system after the crystals had been growing for 6-12 hr. A series of very small explosions accompanied by clicks sometimes preceded the major explosion. 

Taylor and Thomas have shown that spontaneous explosions are not associated with the large crystals of lead azide that are formed they filtered off-large crystals ca. 30 min before the predicted time of explosion and at the predicted time the mother liquor exploded while the filtered lead azide crystals remained intact. 

According to Kaufman [91] spontaneous explosion can also take place during the growth of a-lead azide crystals, e.g. when a supersaturated solution of lead azide in ammonium acetate is seeded with crystals of the a-form. Spontaneous explosions have also been observed with mercuric azide and in some cases with cadmium azide. 

According to Sudo [96] spontaneous explosion can occur during the formation of lead azide from sodium azide and lead acetate, when the concentration of reacting solutions is high (10% or more). 

Yuill [81] investigated the sensitiveness of lead azide to impact at room temperature and at — 190°C. He found that 10-15% more energy is required for the initiation of explosion by impact at a low temperature than that at room temperature (Table 31). 

Other data concerning the initiating properties of lead azide, as compared with the other primary explosives, are given in Table 32. 

Fig. 49. Diagram of the design and operation of a reactor for the manufacture of lead azide and other primary explosives (tetrazene, lead styphnate and lead picrate).

From the magnesium styphnate solution so prepared, 86.4 1. of liquid was decanted, leaving the lower layer in which the sediment was collected. This solution was heated to 60°C, while stirring, and 22.71. of 34% solution of lead nitrate, s.g. 1.274 (31°Be) was then poured into it during a period of 20-30 min, while stirring continued and the temperature was maintained at 60°C. When the solutions were mixed, the contents of the reactor were cooled as quickly as possible to 25°C when this temperature has been reached the stirrer was stopped and the precipitated sediment of lead styphnate was allowed to settle. The liquid from above the sediment Was then decanted, and the latter was first washed out of the reactor by a stream of water, and transferred onto a cloth filter, where it was washed again as is the custom with other primary explosives. From the above mentioned amounts of raw material about 8 kg of lead azide was obtained. 

Aluminium detonators with lead azide and other explosives were used in the mining industry for some time, e.g. a No. 8 detonator, contained 1 g of tetryl and 0.3 g of a mixture of lead azide and lead styphnate. These were more powerful than those with a fulminate-tetryl charge, but the use of detonators with aluminium sheathing was soon forbidden in coal-mines due to the danger created by the burning of the aluminium. 

To determine the sensitiveness to detonation of mining explosive in some countries (including Poland) special standard detonators have recently been introduced, containing 0.05, 0.1,0.t5, 0.20 g etc. of silver azide. The stronger contains 0.60 g of silver azide or an equivalent quantity of lead azide. 

Curtius added lead acetate to a solution of sodium or ammonium azide resulting in the formation of lead azide. In 1893, the Prussian Government carried out an investigation into using lead azide as an explosive in detonators, when a fatal accident occurred and stopped all experimental work in this area. No further work was carried out on lead azide until 1907 when Wohler suggested that lead azide could replace mercury fulminate as a detonator. The manufacture of lead azide for military and commercial primary explosives did not commence until 1920 because of the hazardous nature of the pure crystalline material. 

Study of the Explosive Characteristics of Lead Azide Prepared Commercially 2)Wm.H.Rinkenbach, USP 1,914, 530(1933) "Method of Producing Noncrystalline Explosive Azide 3)W.E.Garner A.S.Gomm, JCS 1931, 2123 34 (Thermal de-compn and deton of LA crysts) 4)F.D. 

Miles, JCS 1931 2532-42 (Formation and characterization of crysts of LA and some other initiating expls) 5)K.S.Warren, PATR 1152 (1942), "Study of the Action of Lead Azide on Copper 6)J.Fleischer J.B. Burtle, USP 2,421,778 (1947) "Initiating Explosives 7)Wm.H.Rinkenbach A.J. Clear, PATR Rev 1(1950), "Standard Laboratory Procedures for Sensitivity, Brisance and Stability of Explosives 8)U.S.Military Specification MIL-L-3055, Amend 1(1952) (Requirements and tests for dextrinated lead azide) 9)J-Bernstein, GLR 51-HI-2332, Pic Arsn (1952) "Hygroscopicity of Dextrinated Lead Azide 10)J.W.Lavitt, PATR 1957 (1953), "An Improved Microscopic Method for the Determination of the Crystal Size Distribution of 2-Micron RDX" 11)F.P. Bowden K.Singh, Nature 172, 378(1953) (Size effects in the initiation and growth of explosives) 12)J.W.C.Taylor, A.T.Thomas... 

---