The Sensitivity of Initiator Explosives to Mechanical Impact

Abstract

An original ball-drop impact apparatus has bee11 consiructed and used to test the sensitivities of dextrin lead azide and mercury fulminate to mechanical Impact. Ball masses artd heights were both varied. Both the net kinetic energy and the change of nlomentuIn gave contin~~ous functions with the percentage of detonations. Con~parisons of the absolute values of the net kinetic energy and the change of momentum with another reported in the literature suggest that momentum is the more important factor in determining the probability of detonation. Values for the momenturn a t 50% detonatior~s for lead azide and mercury fulminate are 4.6 X 10' and 2.6 X lo4 c.g.s. units, respectively, with an area of contact of about 0.08 cm.? The corresponding times of impact were found to be ahout 2.2 X lo-' and 1.9 X 10-"ec.The question of whether the probability of the detonation of an initiator explosive is chiefly determined by the kinetic energy or the momentum of the impacting mass is of theoretical interest in interpreting the process of detonation by impact (8). In their earlier work, Taylor and Weale (9) suggest that kinetic energy is the important factor, although in 1938 (10) they introduce experiments and calculations based on momentum. Taylor and Weale do not mention the rebound of the steel balls used in their impact tests, although the measurement of rebound was introduced decades ago (referred to in Ref. 11). Powell, Skelly, and Ubbelohde (8) measured the momenta and kinetic energies of impact for mercury fulminate and lead styphnate. In their calculations, they assumed without measurement a definite value for the coefficient of restitution of the impacting mass. In the present work, some measurements of the net kinetic energy, change of momentum (hereinafter called impulse), and time of impact for the initiator explosives mercury fulminate and lead azide are reported. The time measurements allowed estimations to be made of the forces involved and these were found to be comparable with those found by Taylor and Weale (10) by an entirely independent method. EXPERIMENTAL MaterialsDextrin lead azide was prepared from sodium azide which had been recrystallized from a water-acetone mixture. Separate 50 ml. aqueous solutions containing 4 gm. sodium azide and 10.2 gm. lead nitrate C.P. were simultaneously added from burettes (delivery time-134 sec.) into 250 ml. of 0.5% aqueous solution of dextrin. Microscopic examination showed that the crystals of lead azide were of the same form as those prepared by Lowndes (6).

Properties and Promise of Catenated Nitrogen Systems As High-Energy-Density Materials

“…In practice, a thickener such as dextrin is used to create a less sensitive, more reproducible sample. Such samples of lead azide are still sensitive to shock (∼0.7 J), friction (0.26 N), and electrostatic discharge (32 mJ). As is normally the case with primary explosives, lead azide has a low VoD of about 4500 m/s .…”

Proliferation and Use of Improvised Explosive Devices in West Africa

“…Time-operated IEDs are IEDs designed to operate following a predetermined time delay. These time delays can be implemented by mechanical, chemical, electrical, or pyrotechnical processes (Hollies et al, 1953).…”