Lead azide properties

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

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]. 

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 ... 

Surve, R.N. (1992) Ph.D. Thesis entitled, Studies on The Preparation and Properties of Basic Lead Azides, University of Poona. 

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 initiating properties of dinitrodiazophenol were investigated by Clark [15] and Smoleriski and Pluciriski [13]. According to Clark the initiating power of the substance is approximately twice as great as that of mercury fulminate, but a little less than that of lead azide. 

There are some indications that silver perchlorate has initiating properties since in some unexplained cases, the large crystals detonate on slight friction in a way similar to the detonation of crystals of lead azide or silver azide (Hein [127]). 

Lead azide can exist in two allotropic forms the more stable a-form which is orthorhombic, and the /1-form which is monoclinic. The a-form is prepared by rapidly stirring a solution of sodium azide with a solution of lead acetate or lead nitrate, whereas the /1-form is prepared by slow diffusion of sodium azide in lead nitrate solutions. The /1-form has a tendency to revert to the a-form when its crystals are added to a solution containing either the a-form crystals or a lead salt. If the /1-form crystals are left at a temperature of 160 °C they will also convert to the a-form. Some of the properties of lead azide are presented in Table 2.3. 

Various Types of Lead Azide Comparison of Some Properties)... 

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>. 

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