Dany - 12-8-2013 at 15:16
metastable materials like explosive substance can be made to explode via several mechanisms. The most common one is shock wave generated by exploding
an adjacent charge or impact of high velocity projectile. other mean include friction, thermal pulse etc...However, light source as initiator for
energetic material remain one of the most exotic method for future detonator applications. It is believed that the actual trigger of decomposition and
subsequent detonation is thermal in nature. Although light is the actual source of energy this energy must be coupled to explosive molecule in the
form of "heat". In fact all mechanism mentioned above (impact, friction...) are believed to degrade to thermal energy in explosive before any
decomposition is detected. 2 interesting paper dealing with optical initiation of explosive should be mentioned here. In fact, the authors in the two
studies uses clever means to push explosive materials to explode/decompose under light pulse. The first paper entitled "Light-induced detonant
materials- charge-transfer complexes of tetrathiafulvalene (TTF) with hexanitrostilbene (HNS) and tetraazidoquinone (TAZQ) an and their associated
C-H-O hydrogen-bonded networks". In this study the goal was to use coherent laser energy in the near infrared region (1060 nm wavelength) as a light
source for ignition, which are favorable when compared to ultraviolet laser. Immediately a problem arise which lies in the explosive system. most
explosive materials absorb energy in the UV-visible region and thus infrared irradiation cannot be absorbed by this material.To overcome this problem
the authors uses the concept of charge transfer complexes. When a poor electron donating explosive material like HNS or TAZQ react with a good
electron donor organic compound like TTF a charge complexes forms which absorb light energy in the infrared region and thus enable the absorption of
laser energy. The result shows that the mentioned energetic materials forms a 1:1 complex with TTF and initiation test demonstrate that laser light is
able to induce deflagration in a TTF-TAZQ small column.
The second paper which in my opinion is more promising is simpler than the concept of laser initiation. The team from the Lawrence Livermore National
Laboratory uses an ordinary flash bulb as light source. The secret for initiation of the explosive material is the presence of Single- Walled
Nanotube (SWCTs). All what is required is a small quantity of SWCTs that is able to absorb light from flash bulbe, transform it to heat and by mean
of the high thermal conductivity of SWCTs the heat is concentrated on the explosive material in contact with these nanotubes . The explosive used in
this study is K-6 (a powerful explosive based on dinitrourea explosophoric moeity, K-6 is as dense as HMX but it is slightly more powerful). The test
is actually a cylinder expansion test where the SWCTs lies on the top of the cylinder. In this configuration explosive can be detonated and detonation
velocity can be measured. The result were successful. The K-6 deflagrate and then detonate which is visible from the witness plate (a clear hole in
it) and from the stable detonation speed recorded during the test.
The 2 papers (actually a full paper and a communication) are interesting to read, important conclusion can be drawn from these studies so to improve
the concept of optical initiation in future exotic initiating system.
Dany.
Attachment: Flash Ignition and Initiation of Explosives-Nanotubes Mixture.pdf (330kB)
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Attachment: Light-induced detonant materials- charge-transfer complexes.pdf (231kB)
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[Edited on 12-8-2013 by Dany]
franklyn - 12-8-2013 at 18:43
Prompt Detonation of Secondary Explosives by Laser
www.osti.gov/bridge/purl.cover.jsp?purl=/67499-reSQ0B/webviewable/67499.pdf
Laser Ignition of Explosives, Pyrotechnics & Propellants
www.dtic.mil/dtic/tr/fulltext/u2/a299465.pdf
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Dany - 12-8-2013 at 23:56
Thanks Franklyn for the extra references.
Dany.