Improved lead azide

Improved lead azide (Co-precipitated Na-CMC) For this form of LA, precipitation is carried out using sodium carboxy methyl cellulose (Na-CMC). 

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). 

Many other methods of making lead azide in a safe form have been described, but the only one to have found commercial importance consists of replacing the dextrine by a small proportion of gelatine. When properly made this form of lead azide is as safe to handle as the dextrinated form and has improved sensitiveness to flame. It can therefore be used by itself in electric and delay detonators, but not in plain detonators as it is not ignited with certainty by safety fuse. 

Lead styphnate is a poor initiating explosive which when dry is very sensitive to friction and impact, to electrostatic discharge, and to flame. Its main use is as an additive to lead azide to improve flame sensitiveness (see p. 101). When pressed to a density of 2-6 g ml-1 it has a velocity of detonation of4900 m s l. 

Although the requirement for flame sensitiveness is the main consideration for initiating explosives for plain detonators, others are important in manufacture. The explosive must be capable of compression into a coherent mass and at the same time leave the equipment free from adhesions. Lead azide can be somewhat deficient in cohesion, and to improve this a small proportion of tetryl is sometimes added to the... 

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],... 

Accdg to Gorst (Ref 71, pp 15—16, it was proposed in Russia to use LA (Lead Azide) in lieu of MF (Mercuric Fulminate) in compound detonators with Tetryl and later with Ten (PETN). Much work on improvement of LA detonators was done by Col A.A. Solonina. 

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 ... 

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... 

It is as efficient as fulminate only if it is externally initiated. It is used in detonators either initiated by another primary explosive and functioning as an intermediate booster or mixed with another primary explosive to increase the sensitivity of the latter to flame or heat. A recent patent62 recommends the use of a mixture of tetracene and lead azide in explosive rivets. Tetracene is used in primer caps where as little as 2 °/o in the composition results in an improved uniformity of percussion sensitivity. 

Illinois, "Lead Azide Laboratory Manual , Revised in 1953 by B.C.Carlson (Lab procedures used in the manuf.of Na and Pb azides and a brief description of manufg process developed by the Du Pont Co) 10)S.G. Landsman J.M.Rosen, "Improved Method for the Assay of Lead Azide", Navord Rept 4191(1955) lOJ.VfeStdl et al, Chem Prumysl 6, 50-2(1956) CA 50, 14229(1956) (Chelatometric detn of Pb in LA) 12)Y. Mizushima 8t S.Nagayama, JlndExplosives Soc Japan 17, 113-15(1956) CA 50, 16557... 

Before Raap, Gaponik et al. [37] improved the synthesis reported by Stolle et al. [38]. By reacting thiosemicarbazide with lead oxide and sodium azide in a CO2 atmosphere, a carbodiimide intermediate is formed and reacts in situ with HN3 to lead to 1,5-DAT (Fig. 10). Unfortunately, this reaction leads to large amounts of lead azide as the side-product, which makes this synthesis problematic for an industrial scale. 

Lead azide is used in many applications accompanied by other substances that compensate for its drawbacks, particularly its low sensitivity to flame and stab. The most common additive in detonators is lead styphnate which improves the inflammability of resulting mixture. A typical composition of this binary mixture is 30 % LS and 70 % LA. It is sometimes presented that lead st3q)hnate can serve as a protective layer against access of water and carbon dioxide to LA surface [3, 4]. However, lead styphnate increases the level of acidity and accelerates the rate of hydrolysis of LA in presence of moisture [35, 49]. Regardless of this fact a combination of LA/LS is still used in detonators. 

A method of preparing a reduced sensitivity SA introduced in USA is called the Costain process after Thomas Costain who improved the original procedure for RD 1336 developed in England in the ERDE laboratories shortly after World War 11 [96]. In the Costain process, aqueous solutions of silver nitrate and sodium azide are added to the dilute aqueous ammonia (or an aqueous solution of sodium azide is added to an aqueous solution of silver nitrate and ammonia). The reaction mixture is then heated and part of the ammonia is distilled from the solution. When the first silver azide precipitate appears, a small amount of acid (e.g., acetic acid) is added to induce crystal seeding and results in profuse nucleation ( shock crystallization ). The distillation of ammonia then continues and the precipitation of silver azide is total. Costain reported several improvements for his product, first of all bulk density 1.4 g cm [96]. Hirlinger and Bichay later reported a further improvement leading to a product with density 1.6 g cm [97] (vs. 1.0 g cm for original ERDE silver azide). Further, concentration and addition parameters are not as critical as for the ERDE process [96]. Not much has been published about the Costain process but some details have been published in [98]. 

The lead salt of 5,5 -azotetrazol is a powerful primary explosive that can be used as an initiator either alone or in a mixture. Its flame sensitivity is higher than that of lead azide and therefore PbAzTZ can be used in a mixture with lead azide to improve its flammability [90]. 

---