Influence of exothermic chemical reactions on laser-induced shock waves

Abstract

Differences in the excitation of non-energetic and energetic residues with a 900 mJ, 6 ns laser pulse (1064 nm) have been investigated. Emission from the laser-induced plasma of energetic materials (e.g. triaminotrinitrobenzene [TATB], cyclotrimethylene trinitramine [RDX], and hexanitrohexaazaisowurtzitane [CL-20]) is significantly reduced compared to non-energetic materials (e.g. sugar, melamine, and l-glutamine). Expansion of the resulting laser-induced shock wave into the air above the sample surface was imaged on a microsecond timescale with a high-speed camera recording multiple frames from each laser shot; the excitation of energetic materials produces larger heat-affected zones in the surrounding atmosphere (facilitating deflagration of particles ejected from the sample surface), results in the formation of additional shock fronts, and generates faster external shock front velocities (>750 m s(-1)) compared to non-energetic materials (550-600 m s(-1)). Non-explosive materials that undergo exothermic chemical reactions in air at high temperatures such as ammonium nitrate and magnesium sulfate produce shock velocities which exceed those of the inert materials but are less than those generated by the exothermic reactions of explosive materials (650-700 m s(-1)). The most powerful explosives produced the highest shock velocities. A comparison to several existing shock models demonstrated that no single model describes the shock propagation for both non-energetic and energetic materials. The influence of the exothermic chemical reactions initiated by the pulsed laser on the velocity of the laser-induced shock waves has thus been demonstrated for the first time.

Improving the Explosive Performance of Aluminum Nanoparticles with Aluminum Iodate Hexahydrate (AIH)

“…The brightness and contrast of some of the later frames have been adjusted to improve visualization of the shock wave, and the top of the images have been cropped. The metal additives produce brighter plasmas as a result of the extensive aluminum-related emission features while energetic materials such as TNT produce less intense plasmas, as previously observed 2,6 . The reduced plasma emission from the TNT-AIH composites (compared to TNT with the other Al-containing additives) is indicative of increased energy release; the reduced emission is likely a result of the formation of exothermic reaction products which do not emit in the visible wavelength region (unlike neutral or ionic Al).

Figure 5Snapshots from videos of laser excited ( a ) micron-sized Al, ( b ) Al 2 O 3 , ( c ) Al/I 2 O 5 , ( d ) AIH6, ( e ) AIH15, and ( f ) TNT.

Figure 6Snapshots from videos of laser excited ( a ) TNT + Al, ( b ) TNT + Al 2 O 3 , ( c ) TNT + Al/I 2 O 5 , ( d ) TNT + AIH6, and ( e ) TNT + AIH15.

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“…The LASEM experimental setup has been described previously 2,3 . Briefly, a 6-ns pulsed Nd:YAG laser (Quantel Brilliant b, 1064 nm, 900 mJ) is focused just below the sample surface with a 10 cm lens.…”

“…Exothermic reactions were subsequently shown to increase the laser-induced shock wave velocity and/or the laser-induced deflagration reaction following pulsed laser excitation of energetic materials 2 . The strong correlation between the measured laser-induced shock velocities produced by laser ablation of energetic materials and the reported detonation velocities from large-scale detonation tests provides a laboratory-scale method for estimating the fast (i.e., microsecond-timescale) energy release from milligram quantities of energetic materials 3 .…”

Experimental Study of the Transient Response of Bunsen Flame to Nanosecond Pulsed Discharges

“…At that time, the measured velocities of the shock waves are above 700 m/s in the flames with different equivalence ratio. The values are consistent to that in the investigation of laser induced plasmas on non-energetic and energetic materials by Gottfried [23] in which the excitation of energetic materials generates faster external shock front velocities ([750 m/s -1 ) compared to non-energetic materials (550-600 m/s -1 ) while the shock front velocities of non-explosive materials is about 650-700 m/s -1 . In the investigation, it had been proved that the thermal energy in energetic materials was caused by both the energy transferred from the laser and the subsequent exothermic chemical reactions of the ablated species.…”

Machine learning to analyze images of shocked materials for precise and accurate measurements

“…5,10,13,14 The combination of ultrafast imaging methods that capture spatially varying material responses with advanced image processing algorithms that reliably define the different regions under observation can further our understanding of complex shock-induced responses. 5,10,13,[15][16][17][18][19][20][21] In the field of shock physics, many images are manually segmented to extract material features from images. Most image analysis uses Fourier filtering, which suppresses high-frequency noise, but also diminishes the high-frequency features inherent to shock waves.…”