The sensitiveness of explosives - The effect of compression on the sensitiveness of initiators

Abstract

The sensitiveness of the following initiators has been compared when used loose, and when compressed up to 2300 kg./cm. Crystalline Service azide (crystals 75 X 10-4 cm.). Powdered Service azide (fragments 1 to 25 x 10~4 cm.). Dextrinated lead azide. Mercury fulminate. Sensitiveness to heat was measured by determining the induction period at various temperatures, and also by evaluating threshold temperatures below which no detonation was observed for various masses of initiators. Tests were also made to see how far the action of flame, and of percussion, could be correlated with the action of heat on these initiators. Compression reduces the induction period in all cases, but the values of E and B (see text) are differently affected in the case of different initiators. Compression also lowers the threshold temperature below which a given mass of initiator will not detonate. Thus in all cases sensitiveness to heat is increased by compression. On the other hand, compression lessens the sensitiveness of mercury fulminate to flash and percussion, corresponding with the well-known phenomenon of ‘dead-pressing’. If anything, compression increases the sensitiveness of lead azide to flash and percussion. A new detonation mechanism has been observed for both service and dextrinated lead azides. The experimental results throw further light on the build-up of the detonation wave in explosives. When the volume of explosive ‘primarily’ involved in the sensitiveness phenomenon is small, as is usually the case for initiators, the mechanism of build-up differs from the ‘self-heating’ mechanism which may overtake it with larger volumes of explosive. A simple explanation is suggested for the ‘dead-pressing’ of explosives, which is to be expected when ‘self-heating’ is the mechanism controlling the build-up of detonation.