Service lead azide

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). 

Different types of initiatory explosives essentially developed for military applications have also been used for commercial detonators and cap compositions. Service lead azide (SLA) has been extensively used as an initiatory explosive for detonators. However, it has the limitation that hydrazoic acid forms on ageing and ultimately forms sensitive copper azide with copper tube-based detonators (responsible for many unfortunate accidents all over the globe) therefore SLA has been replaced by a new and safe initiatory explosive known as basic lead azide (BLA). 

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 ... 

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. 

Density of AN based expls can be controlled by the addn of vermiculite) K) R.L. Wagner et al, "Investigation of British Service Lead Azide , EDS (Explosives Development Section) Rept 457248, PicArsn, Dover, N.J. 

RDX, etc) are too sensitive to be used per se and must be desensitized. For example LA may be desensitized by coating its crysts either with dextrin (See Dextrinated Lead Azide in Vol 1, pp A 46 to A548) or with PVAlc (polyvinyl alcohol) (See Vol 1, p A558-R). It can also be desensitized by controlling the size and shape of its crysts [See Service Lead Azide (Brit) in Vol 1, p A557-R], or by pptg it in colloidal form (See Vol 1, p A558-L)... 

T.R. Phillips, The Effect of High Energy X-Rays on the Thermal Detonation of Service Lead Azide , ARDE Rpt (B) 7/56 (1956) 43) A. 

D.E.Seeger,PicArsn EDS Rept No 57(1959), "Investigation of British Service Lead Azide. 23)R.L.Wagner, K.G.Sheffield ... 

A) Dextrinated Lead Azide (abbrd as DLA), known also as Type / LA (US). Its prepn and props are described under Lead Azide 6) Service Lead Azide (abbrd as SLA)... 

The picture of the product by this interesting method is given in Fig. 81 (b. c). For comparison British Service lead azide (a) is also given. 

There are phlegmatized lead azides which in the physical appearance is entirely different from tlie aggregates which are typical of most processes. Instead of being opaque granules, they are equant transparent crystals (Figure 10). The first of these, called Service lead azide, is made by the near-simultaneous... 

Figure 10. British Service lead azide, 170X. (Photo courtesy of ERDE, Waltham Abbey, England.)...

The first cousin of British Service lead azide is the crystal form precipitated in the presence of polyvinyl alcohol PVA lead azide. At the present time, little (if any) PVA lead azide is produced in the United States, although it is believed... 

One process, developed by the Bofors-Liab Company in Sweden leads to the precipitation of 3-lead azide in a pure form. The precipitate is washed and allowed to stand in water overnight, where it recrystallizes to the a form. The product is claimed to be veiy pure but with a density less than that of Service lead azide. 

The iron from the capsule experiments was brittle and fell apart when rubbed. In this investigation iron azide (ferric or ferrous azide) and hydrazine could not be detected, contrary to the work of Franklin [51] and Curtius and Risson [52]. Polyethylene becomes brittle, opaque, and porous when exposed to hydrazoic acid, and hydrazoic acid diffused through 0.008 in polyethylene bags within 90 days. Blay and Dunstan [53] reported little azide interaction with polyethylene, but noted a marked drop in azide value when Service lead azide was in contact with various rubbers, plastics, and other synthetic packaging materials. A reduction in azide content as high as 70% was shown (Figure 4). This was attributed to the slow release of carbon dioxide from the test material, followed by further hydrolysis of the lead azide. 

Figure 4, Compatibility of Service lead azide at 60°C, 95% relative humidity, 4-week test.

Service lead azide/10% beta lead azide 11.91 0.081... 

Service lead azide/10% gamma lead azide 10.31 0.149... 

Copp et al. believed that percussion sensitiveness (with the ball and disk apparatus) was very complex and involved, in addition to the formation of hot spots through friction, a tribochemical reaction in which there was a more direct transfer of mechanical energy to activation energy than was the case when the mechanical energy is first converted to heat. An example of this is shown with experiments using nickel and tin disks to confine Service lead azide in which the surfaces of the low melting point lessened the grit sensitivity but enhanced the impact sensitivity. 

Table XIII illustrates the role surfaces play in determining friction sensitivity. The effect of emergy-papered surfaces is very apparent with Service lead azide, dextrinated lead azide, and lead styphnate.

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