R. Meyer J. Köhler A. Homburg Explosives

195 Lead Azide
energy of formation: +397.5 cal/kg = +1663.3 kJ/kg
enthalpy of formation: +391.4 cal/kg = +1637.7 kJ/kg
oxygen balance: –5.5%
nitrogen content: 28.85%
volume of explosion gases: 231 l/kg
explosion heat: 391 kcal/kg = 1638 kJ/kg
density: 4.8 g/cm3 lead block test: 110 cm3 /10 g
detonation velocity, confined:
4500 m/s = 14800ft/s at r = 3.8 g/cm3 5300 m/s = 17400ft/s at r = 4.6 g/cm3 deflagration point: 320–360 °C = 600–680 °F
impact sensitivity:
pure product: 0.25–0.4 kp m = 2.5– 4 N m
dextrinated: 0.3–0.65 kp m = 3–6.5 N m
friction sensitivity:
at 0.01–1 kp = 0.1–1 N pistil load explosion
Lead azide is insoluble in water, is resistant to heat and moisture, and
is not too hygroscopic. It is prepared by reacting aqueous solutions of
sodium azide and lead nitrate with each other. During the preparation,
the formation of large crystals must be avoided, since the breakup of
the crystalline needles may produce an explosion. Accordingly, technical
grade product is mostly manufactured which contains 92–96%
Pb(N3)2, and is precipitated in the presence of dextrin, polyvinyl alcohol,
or other substances which interfere with crystal growth. Lead
azide is employed as an initiating explosive in blasting caps. When
used as a primary charge, it is effective in smaller quantities than
mercury fulminate, has a higher triggering rate, and, unlike mercury
fulminate, cannot be dead-pressed by even relatively low pressures. In
order to improve its flammability, an easily flammable additive, such as
lead trinitroresorcinate, is added. Lead azide is decomposed by atmospheric
CO2, with evolution of hydrazoic acid.
Lead azide detonators for use in coal mining have copper capsules;
for all other blastings, aluminum caps are used.
Specifications
net content (by determination
as PbCrO4): not less than 91.5 %
moisture: not more than 0.3 %
mechanical impurities: none
water solubles: not more than 1 %
lead content: at least 68 %
copper: none
reaction: neutral, no acid
bulk density: at least 1.1 g/cm 3
deflagration point: not below 300 °C = 572 °F