Lead azide, decomposition

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]. 

Lead azide, Pb(N,)2, is used as a detonator, i i) What volume of nitrogen at STP (1 atm, 0°Ci does 1.5, of It id azide produce when it decomposes into lead metal and nitrogen gas (b) Would 1.5 g of mercury(ll) azide, Hg(N which is also used as a detonator, produce a larger or smallei volume, given that its decomposition products i c elemental mercury and nitrogen gas (c) Metal azides in general are potent explosives. Why ... 

The endothermic nitride is susceptible to explosive decomposition on friction, shock or heating above 100°C [1], Explosion is violent if initiated by a detonator [2], Sensitivity toward heat and shock increases with purity. Preparative precautions have been detailed [3], and further improvements in safety procedures and handling described [4], An improved plasma pyrolysis procedure to produce poly (sulfur nitride) films has been described [5], Light crushing of a small sample of impure material (m.p. below 160°C, supposedly of relatively low sensitivity) prior to purification by sublimation led to a violent explosion [6] and a restatement of the need [4] for adequate precautions. Explosive sensitivity tests have shown it to be more sensitive to impact and friction than is lead azide, used in detonators. Spark-sensitivity is, however, relatively low [7],... 

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,... 

Initiation, Spontaneous. This is really a misnomer. What it refers to is the self-heating of an explosive as a result of autocatalytic decomposition eventually leading to a thermal explosion. Spontaneous initiation may also occur during crystal growth eg in Lead Azide see Detonation (and Explosion), Spontaneous in Vol 4, pp D561-563... 

S. Kleinberg F.P. Stein, Effect of Particle-Size Distribution on the Thermal Decomposition of a-Lead Azide , JPhysChem 77, No 7, 870— 875 (1973) 13) Director, Explosives Re-... 

Lead azide [Pb(N3)2] (LA) is a salt of hydrazoic acid (N3H, highly poisonous) and is prepared by reacting solutions of sodium azide and lead acetate or nitrate. This exists in two forms the a form (orthorhombic and stable) and P form (monoclinic) which has a tendency to revert back to the a form. The P form is much more sensitive. The two forms differ in their rate of decomposition when heated. Crystalline LA is stored in dry conditions because it becomes more sensitive when... 

Service lead azide (SLA) SLA is prepared by double decomposition of lead acetate and sodium azide in the presence of sodium carbonate and acetic acid. 

Thermal decomposition of pure explosives such as primary explosives lead azide, lead styphnate, mercury fulminate etc. [35], monomethylamine nitrate [36] and explosive mixtures RDX + HMX mixtures [37]. 

Lead azide is insoluble in an aqueous solution of ammonia. Acetic acid causes its decomposition but it is soluble in water and concentrated solutions of sodium nitrate, sodium acetate or ammonium acetate. There are fairly big differences of solubility, depending on temperature. 

Lead azide, like hydrazoic acid, is liable to undergo oxidation and reduction reactions. It is partially decomposed by atmospheric oxygen to form free hydrazoic acid, nitrogen and ammonia. This reaction is promoted by the presence of carbon dioxide in the air. When boiled in water, lead azide undergoes slow decomposition with the evolution of hydrazoic acid. 

When exposed to light lead azide soon turns yellow on the irradiated side. The layer of changed substance protects the deeper layers from further decomposition and thus irradiation does not entail changes in the explosive properties of the substance. However, as Wohler and Krupko [80] have shown, if the lead azide is subjected to stirring during irradiation, decomposition may proceed too far. 

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. 

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]. 

Bowden and Singh [94] and later Bowden and McAuslan [95] using the electron microscope, observed that on heating at a temperature above 120°C the separate crystals of lead azide (like those of cadmium or silver azides), break down into fine particles, approximately 10 5 cm in dia. and decomposition reaction takes place chiefly on the newly-formed surfaces. This makes it evident that the thermal decomposition of azides cannot be regarded as a surface reaction or a process occurring within large crystals only the whole mass is involved, due to crystal breakdown. 

According to Garner and Gomm [37] the activation energy of the thermal decomposition of lead azide is 38.0 kcal/mole, assuming that the reaction can be expressed by an equation of the form p=kt. 

Primary explosives (also known as primary high explosives) differ from secondary explosives in that they undergo a very rapid transition from burning to detonation and have the ability to transmit the detonation to less sensitive explosives. Primary explosives will detonate when they are subjected to heat or shock. On detonation the molecules in the explosive dissociate and produce a tremendous amount of heat and/or shock. This will in turn initiate a second, more stable explosive. For these reasons, they are used in initiating devices. The reaction scheme for the decomposition of the primary explosive lead azide is given in Reaction 2.2. 

Fig 2 The Effect of Slow Neutron Irradiation on the Subsequent Thermal Decomposition of Lead Azide (Ref 28)... 

Gomm, The Thermal Decomposition and Detonation of Lead Azide Crystals , JCS 2123-34 (1931) 7) W, Roginski, FhysZSow 1,656... 

Muraour, Effect of Electron Impact Upon Lead Azide and Silver Acetylide-Theoretical Observations Upon the Thermal Decomposition of Explosives , Chim Ind 30, 39- 40 (1933)... 

Groocock, The Effect of High Energy X-rays and Pile Irradiation in the Thermal Decomposition and Thermal Explosion of a-Lead Azide , ProcRoySoc A246, 225-32 (1958) 60) J.K. 

Decomposition of Irradiated a-Lead Azide , BNL-6632, Brookhaven Natl Lab, Upton (1963) 112) J.G. Horton, Exploration of Solid Propellant Characteristics under Simulated Space Conditions , Proc 1963 Mtg Inst of Environmental Sciences (1963), 177—84 113) G. 

D.J. Moore, Thermal Decomposition of Barium Azide , Nature 203, 860—61 (1964) 132) J. Roth, Initiation of Lead Azide by High Intensity Light , JChemPhys 41, 1929—36 (1964) 133) G. Odian et al, Radiation-... 

The military explosive HMX. Violent decomposition occurred at 279°C [1]. HMX has several crystalline forms, only one of which is safe , another being as sensitive as lead azide [2]. 

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