1 Lead Azide

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 

The introduction of LA into commercial detonators resulted in an unacceptably high level of explosions during manufacture and use and hence its use was discontinued until it could be prepared in less sensitive form. A number of methods have been used to prepare LA in a less sensitive form. The main control of properties is by synthesis rather than by any other approach. Lead azide compositions RD 1343 (improved CMC co-precipitated LA), RD 1352 (improved dextrinated LA) and Service lead azide (SLA) illustrate some modified LAs which are used depending on the requirements. Different processes developed for the modification of LA may be summarized as follows  

In this process, LA crystals grow around the lead carbonate nucleus and as a result, formation of larger and sharp needle-shaped crystals is prevented, making it comparatively less sensitive than pure LA. SLA is still sensitive to friction and sometimes causes accidents. However, it is used in the absence of any other alternative. 

The product obtained has lower bulk density than SLA. The use of sodium amylose offers some advantages over both Na-CMC and dextrine [6]. 

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Property Mercury fiihninate Lead azide Silver azide Normal lead styphnate DDNP Tetrazene... 

Only relatively few compounds can act as primary explosives and still meet the restrictive military and industrial requirements for reflabiUty, ease of manufacture, low cost, compatibiUty, and long-term storage stabiUty under adverse environmental conditions. Most initiator explosives are dense, metaHoorganic compounds. In the United States, the most commonly used explosives for detonators include lead azide, PETN, and HMX. 2,4,6-Triamino-l,3,5-triuitrobenzene (TATB) is also used in electric detonators specially designed for use where stabiUty at elevated temperatures is essential. 

Lead Azide. The azides belong to a class of very few useflil explosive compounds that do not contain oxygen. Lead azide is the primary explosive used in military detonators in the United States, and has been intensively studied (see also Lead compounds). However, lead azide is being phased out as an ignition compound in commercial detonators by substances such as diazodinitrophenol (DDNP) or PETN-based mixtures because of health concerns over the lead content in the fumes and the explosion risks and environmental impact of the manufacturing process. 

Lead azide tends to hydrolyze at high humidities or in the presence of materials evolving moisture. The hydrazoic acid formed reacts with copper and its alloys to produce the sensitive cupric azide [14215-30-6] Cu(N2)2- Appropriate protection must be provided by hermetic sealing and the use of noncopper or coated-copper metal. 

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). 

Ma.nufa.cture. Lead azide is typically made from sodium azide [26628-22-8] in small (eg, 5 kg) batches buffered by the reaction solutions of lead nitrate or lead acetate ... 

D. E. Seeger, and R. H. Stresau, "Lead Azide Precipitated with Polyvlayl Alcohol," ia 2nd ONR Symposium on Detonation, Office of Naval Research, Washiagton, D.C., 1955, p. 92. 

Lead azide, Pb(N3)2, is used as a detonator in car airbags. The impact of a collision causes PMN to be converted into an enormous amount of gas that fills the airbag. A125°C, a saturated solution of lead azide is prepared by dissolving 25 mg in water to make 100.0 mL of solution. What is Kv for lead azide ... 

The reaction of Lead Azide (LA) with Cu (see Table) deserves special comment, Although this reaction is relatively slow, even in the presence of w, some forms of Cu Azide are so sensitive that they create a serious hazard even in minute quantities, particularly when in contact with LA. For this reason, AJ and stainless steel containers are now used exclusively. PicArsn requires that all new fuze designs contain no Cu or Cu alloys, with the possible exception of the electrical system. Even here, the Cu must be coated for protection against the formation of hydrazoic acid. Another prohibition involves the use of Pb thiocyante in contact with A1 (Refs 4, 5 6)... 

Kaye, An Electron Microscope Method for the Determination of the Particle Size Distribution and Particle Shape of Colloidal and Ball-Milled Lead Azide , PATR 2133 (1955) 25a) A.T. 

The work of Avrami et al on the impact sensy of Lead Azide-water (LA-w) mixts contg various expls and drying agents, conducted with the standard PicArsn impact test app, is of interest. 

A.R. Garabrant, J.F. Coburn L. Avrami, Moderation of the Sensitivity of Certain Lead Azide/RDX Mixtures , Third International Conference on Rocket Projectile Guidance/... 

H. Jackson, Impact Sensitivity of Lead Azide in Various Solid and Liquid Media ,... 

Not detonated by 0.35g of Lead Azide and 0.2g of Tetryl, or by 0.5g of Mercury Fulminate 6 minutes Good... 

CAHN RG ELECTROBALANCE/SEDIMENTATION ACCESSORY. This app produces a continuous, visible chart record of the sediment weight collected on the balance pan. It has been evaluated for measuring particle size distributions of the primary expls Lead Styphnate, Lead Azide, Tetracene by Hutchinson (Ref 41). 

It is difficult to obtain accurate particle size analyses of primary expls because (1) consideration and acceptance of necessary safety precautions make the usually tedious job of particle size analysis even more tedious, and (2) many primary expls used in production contain particles which are non-spherical in shape and are in the subsieve size range. Dry screening Lead Azide, for instance, is hazardous and must be done remotely. Furthermore, static charges... 

Four samples of Lead Styphnate were analyzed by dispersing in acet and were found to have average diameters of 15.9 y with a standard deviation of 0.4p. The reproducibility for Tetracene, with average diameter of 35 y, was 2y. Methanol was found to be a satisfactory dispersant for Lead Azide with average particle diameter of 12y... 

In general terms, PETN can be characterized as a sensitive , brisant, and powerful high expl. Explosive sensitivity is a rather nebulous quantity, but there can be no doubt that PETN is a much more sensitive material than TNT, but rather less sensitive than Lead Azide. In particular, PETN requires very little priming i charge (less than 1 mg LA) to initiate its detonation. This is the characteristic that makes PETN so widely used in blasting cap base charges, in detonating cord and in boosters... 

It is significant, however, that in most, and probably all, relative rankings of the impact sensitivities of solid expls (see Vol 7, I42-R), PETN ranks as the most sensitive secondary expl (primary expls, such as Lead Azides, Mercuric Fulminate, etc, are more sensitive)... 

A.C. Forsythe, Photodecomposition of a Lead Azide in the Solid State , JPhysChem 71... 

Stengach, The Dielectric Strength of Pressed Lead Azide , ZhPriklMekhiTekhFiziki 1 (1972),... 

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