Aluminium lead styphnate

Detonators containing lead azide are loaded into aluminium capsules. Lead azide may be used alone or in conjunction with lead styphnate or tetrazene, the use of which facilitates ignition of azide. The layer of azide may also be covered... 

Aluminium detonators with lead azide and other explosives were used in the mining industry for some time, e.g. a No. 8 detonator, contained 1 g of tetryl and 0.3 g of a mixture of lead azide and lead styphnate. These were more powerful than those with a fulminate-tetryl charge, but the use of detonators with aluminium sheathing was soon forbidden in coal-mines due to the danger created by the burning of the aluminium. 

Lead azide has a good shelf life in dry conditions, but is unstable in the presence of moisture, oxidizing agents and ammonia. It is less sensitive to impact than mercury fulminate, but is more sensitive to friction. Lead azide is widely used in detonators because of its high capacity for initiating other secondary explosives to detonation. On a weight basis, it is superior to mercury fulminate in this role. However, since lead azide is not particularly susceptible to initiation by impact it is not used alone in initiator components. Instead, it is used with lead styphnate and aluminium (ASA mixtures) for military detonators, in a mixture with tetrazene, and in a composite arrangement topped with a more sensitive composition. 

Lead styphnate is a weak primary explosive because of its high metal content (44.5%) and therefore is not used in the filling of detonators. It is used in ignition caps, and in the ASA (i.e. lead azide, lead styphnate and aluminium) mixtures for detonators. Some of its properties are shown in Table 2.4. 

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