Thin Flyer Impact Initiation Threshold Comparison of HNS-IV, CL-20, CL-20/HMX Co-Crystal in Slapper Detonator

Abstract

Slapper detonator consists of exploding metal foil, thin polyimide flyer, spacer (barrel) and high density explosive pellet. When high electrical energy applied in short duration, the metal foil explodes, to accelerate thin polyimide flyer to a velocity of 2-3 km/s. The impact of flyer on explosive pellet leads to prompt initiation by shock-to-detonation phenomenon. HNS-IV explosive is widely used in this application as it is highly insensitive and thermally stable with small critical diameter. However, the HNS-IV explosive has limitations of batch-to-batch variation, low velocity of detonation (VoD) (~7200 m/s) and low CJ pressure (20 GPa). Recently, CL-20 explosive has emerged as one of the potential high energy material for application in slapper detonator. CL-20 has high VoD (~9400 m/s) and CJ pressure (~48.2 GPa) and can be used in miniaturization of futuristic explosive devices. In this research work, HNS-IV, CL-20 and CL-20/HMX co-crystals were processed using novel technique of nozzle based solvent-antisolvent method. The processed explosives were characterized for particle size, shape and morphology. Experimental prototypes of slapper detonators were fabricated with same configuration of flyer, barrel diameter and exploding foil dimensions to evaluate and compare the performance. The threshold trials were carried out using Bruceton test. Comparative results of explosive characterization and threshold initiation voltage of the three explosives is presented. The particle size of all the three explosives is in the range of 0.5 to 9 μm and the threshold initiation voltages for HNSIV, CL-20 and CL-20/HMX co-crystals are in the range of 1.75 kV, 0.9 kV and 1.5 kV respectively with standard deviation of ±0.1 kV. It is observed that CL-20 has lowest threshold initiation voltage; however, it is more impact and friction sensitive. The sensitivity properties of CL-20 can be tailored by making co-crystals with HMX. This enables to get insensitive and more powerful slapper initiators with advantage of miniaturization, as CL- 20/HMX co-crystal has sensitivity and thermal properties near to HMX and better than CL- 20.