Lead Azide Explosive Properties

One of the reasons stimulating the search for new primary explosives today is the need to replace toxic lead azide with some environmentally benign alternative (other reasons are described in Chap. 1). A suitable replacement needs to have many of lead azide s properties within relatively narrow ranges. It would therefore be desirable to have the ability to influence the properties of the resulting substance by slightly modifying its structure. This goal is not achievable with metal salts alone but seems to be realistic with metal complexes or coordination compounds or, as recommended by lUPAC, coordination entities [1]. 

The material is impact-sensitive when dry and is supplied and stored damp with ethanol. It is used as a saturated solution and it is important to prevent total evaporation, or the slow growth of large crystals which may become dried and shock-sensitive. Lead drains must not be used, to avoid formation of the detonator, lead azide. Exposure to acid conditions may generate explosive hydrazoic acid [1], It has been stated that barium azide is relatively insensitive to impact but highly sensitive to friction [2], Strontium, and particularly calcium azides show much more marked explosive properties than barium azide. The explosive properties appear to be closely associated with the method of formation of the azide [3], Factors which affect the sensitivity of the azide include surface area, solvent used and ageing. Presence of barium metal, sodium or iron ions as impurities increases the sensitivity [4], Though not an endothermic compound (AH°f —22.17 kJ/mol, 0.1 kj/g), it may thermally decompose to barium nitride, rather than to the elements, when a considerable exotherm is produced (98.74 kJ/mol, 0.45 kJ/g of azide) [5]. 

The isolated solid is a very shock- and friction-sensitive explosive [1], but the preparation and safe handling of dilute solutions in solvents other than ether have been described [2], The need to use appropriate techniques and precautions when using iodine azide as a reagent is stressed [3], The purer the more explosive explosive properties are characterised (lead-block test, etc.) in a footnote to [4],... 

Lead azide explodes on heating at 350°C or on percussion. Its detonation velocity is 5.1 km/sec (Meyer, E. 1989. Chemistry of Hazardous Materials, 2nreaction with carbon disulfide and forms shock-sensitive copper and zinc azides when mixed with the solutions of copper and zinc salts (Patnaik, P. 1999. A Comprehensive Guide to the Hazardous Properties of Chemical Substances, ed. New York John Wdey). 

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 ... 

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. 

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. 

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

The explosive properties of sodium, calcium, strontium and barium azides have been investigated at the Chemisch-Technische Reichsanstalt [135]. These azides differ markedly from lead, silver and cupric azides in that they show none of the properties of primary explosives. All three may be ignited by a spark, a glowing wire or the flame of blackpowder. Calcium azide bums most rapidly and has distinctly marked explosive properties. Larger quantities of it may explode when ignited in a closed tin, while strontium and barium merely bum violently. Calcium azide detonates under the influence of a detonating cap. The sodium azide does not decompose in these conditions. The other azides show weak decomposition under the influence of a standard (No. 3) detonator. Their most important properties are tabulated below. 

Explosive Properties A548 Destruction (Disposal or Killing) of Lead Azide A550... 

Properties of Ag-salts of 1-(iV-nitramino)-, 2-(Wnitramino)-, 5-(W-nitramino)tetrazole, and l-methyl-5-(fV-nitramino)-tetrazole have been examined. The initiation power of these salts was estimated from minimal blasting charge in RDX. Silver salts of l-(W-nitramino)- and 2-(iV-nitramino)tetrazole have a DDT (deflagration-to-detonation transition) period shorter than the salts of 5-(W-nitramino)tetrazole and l-methyl-5-(W-nitramino)tetrazole. The salt of 2-(fV-nitramino)te-trazole is a more powerful initiative explosive than lead azide <2006MI39>. 

While the environmental impact of cadmium azide in deep oil deposits is relatively low, the long-term use of Pb(N3)2 and lead styphnate in military training grounds has resulted in considerable lead contamination (see Ch. 1.2.3, see Fig. 1.17). On demand lead azide (ODLA) is available from the reaction of lead acetate and sodium azide. The recently introduced iron and copper complexes of the type [Cat]2 [Mn(NT)4(H20)2] ([Cat]+ = NH4, Na+ M = Fe, Cu NT = 5-nitrotetra-zolate) as green primary explosives [3] are relatively easily obtained and show similar initiator properties as those of lead azide (Tab. 2.2). 

Tab. 2.2 Properties of lead azide (LA) and lead styphnate (LS) in comparison to new green primary explosives.

Eschbach patented priming compositions made by mixing lead azide with lead trinitroresorcinate. Marshall investigated the explosive properties of hexanitrodiphenylamme. 

Properties Claimed not to give rise to a supersensitive explosive in contact with copper, such as is the case with lead azide. 

Caution The well-documented explosive properties of lead azide demand appropriate safety precautions, including the use of remote controlled equipment and adequate shielding. The lead azide is destroyed by dissolution in 50% aq NaOH. 

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