Observations on Detonation Growth of Lead Azide at Microscale

Abstract

Lead azide (LA) is a commonly used primary explosive, the detonation growth of which is difficult to study because it is so sensitive and usually has a small charge size in applications. We used photon Doppler velocimetry (PDV) and calibrated polyvinylidene fluoride (PVDF) gauges to reveal the detonation growth in LA, which was pressed in the confinements with controlled heights. The particle-velocity profiles, output pressure, unsteady detonation velocity, reaction time, and reaction-zone width were obtained and analyzed. Three phases of detonation propagation of LA microcharges are discussed. The volume reactions occur at the beginning of detonation in LA microcharges without forming complete shock profiles. Then the shock front is fast with a slow chemistry reaction zone, which is compressed continuously between the height of 0.8 mm and 2.5 mm. Finally, the steady detonation is built at a height of 2.5 mm. The stable detonation velocity and CJ pressure are 4726 ± 8 m/s and 17.12 ± 0.22 GPa. Additionally, the stable reaction zone time and width are 44 ± 7 ns and 148 ± 11 μm. The detailed detonation process has not previously been quantified in such a small geometry.

Design of a Microflyer Driven by a Microsized Charge Combined with an Initiation Criterion

“…The influencing factors of lead azide are the diameter, height, density, and constraint conditions of the charge. In the MEMS detonation system, the diameter of the primary explosive is at the level of 1 mm [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ], so the simulation range of the diameter should be about 1 mm; in [ 17 , 18 ], the output performance of lead azide with a charge height of 0.6 mm~3 mm was verified, so the charge height in the simulation was also set in this range. The common density of lead azide is more than 3 g·cm −3 , and the crystal density is slightly larger than 4 g·cm −3 , so the density range in the simulation was set to 2 g·cm −3 ~4 g·cm −3 .…”

“…In Section 2.3.1 , it was introduced that the diameter of the lead azide was at the 1 mm level, so the diameter of the lead azide in this experiment was submillimeter (0.9 mm); when the pressing pressure was 188 MPa, the corresponding theoretical density of 3.83 g·cm −3 was used as the charge density of the lead azide [ 19 ], which was also close to that used in the literature [ 17 , 18 ]. According to the preliminary simulation results, the flyer had a relatively high speed when the charge height was 1.2 mm, the thickness of the titanium flyer was 0.1 mm, and the aperture of the stainless steel acceleration chamber was 0.6 mm.…”

“…The azide-type primary explosive has a short detonation distance and certain power, and it is often used as the primary charge in a detonator. The output performance of microsized lead azide was proved [ 17 , 18 ], and the pressing characteristics of microsized lead azide was studied [ 19 ]. Copper azide and silver azide are relatively sensitive, while the sensitivity of lead azide is relatively low, making it the most widely used primary explosive at present.…”

Study on microcharge design and output performance test

“…Among them, microcharge is the energy source of MEMS pyrotechnics. The performance of microcharge directly determines the performance of MEMS pyrotechnics [2][3][7][8]. The characteristic size of microcharge of MEMS pyrotechnics is generally tens of microns to 1mm, which is lower than the critical size of stable fire transmission and explosion transmission of conventional fireworks, and typical non-ideal characteristics are presented in micro-size detonation [9].…”

“…The study of charging method shows that the precision pressing technology is only suitable for charging above millimeter scale. Although in-situ self-assembly, vacuum charging and other forming technologies can obtain sub-millimeter size charge, the molding density is low (65% TMD) and the explosion capacity is poor [7][8][9]. Common charging processes are no longer suitable for MEMS pyrotechnic charging.…”