Shock Initiation of Nano-Al + Teflon: Time-Resolved Emission Studies

Abstract

Laser-launched flyer plates were used to impact-initiate reactive materials consisting of Al nanoparticles (50 nm) and Teflon microparticles (3 μm). The initiation process was probed with time- and wavelength-resolved emission spectroscopy. Teflon particle and Teflon foil samples without Al fuel were also studied. During ∼15 ns duration shocks produced by 50 μm thick flyers, Teflon was heated to a greater extent than Al. Al/Teflon underwent explosive chemical reactions lasting ∼500 ns at an impact velocity threshold of 1.0 ± 0.1 km/s. The Teflon samples emitted a continuum spectrum attributed to triboluminescence. C2 emission (Swan bands) from the powder Teflon could be detected at impact velocities of 0.7 km/s, after a few microseconds, presumably from gases trapped between the decomposing sample and the observation window, indicating that Teflon can be at least partially decomposed to carbon and fluorine. During the 15 ns shock, the Al/Teflon had almost the same emission temporal and spectral profile and absolute emission intensity as Teflon alone. At the end of the shock, the Al/Teflon exploded twice in succession, creating intense emission bursts much stronger than those from Teflon alone. Each of the two explosions had an abrupt onset of ∼10 ns, and each lasted 100–200 ns. The first explosion was associated with the arrival of the compressive release wave and the second, whose emission burst was ∼1/3 as intense as the first, with the arrival of shear release waves from the flyer plate edges. For Al/Teflon to react, the Al fuel nanospheres must be released from their passivating oxide shells. The abrupt onset of the two explosions led us to propose a mechanism where tensile stresses resulting from compressive and shear waves cause the Al shells to crack open, allowing hot Teflon to react with Al. A limited number of studies using 25 μm thick flyers, which produced 8 ns shocks, show that the pressure threshold for initiation was about twice as large as with 15 ns shocks.

Design and fabrication of energetic superlattice like-PTFE/Al with superior performance and application in functional micro-initiator

“…The fuel of choice is Al because of its high relative heat. Moreover, Al and PTFE have an ultrahigh energy density of 21 kJ/cm 3 [27,29]. Second, the reaction of PTFE and Al exhibits a potential gas release because of the low boiling point of reaction product (AlF 3 ) and carbon which would react with oxygen to form oxycarbide in the atmospheric conditions, which is beneficial for the release of energy, combustion rate and many applications [30,31].…”

Laser-driven flyer plates for shock compression science: Launch and target impact probed by photon Doppler velocimetry

“…[1][2][3][4][5][6][7] Recently, our group described a "simplified" system for laser-launched flyer plates that was developed for shock wave spectroscopy of materials under well-characterized shock conditions. 6 The term "simplified" was applied because the system used a commercial one-box launch laser and a flyer launch assembly with minimal complexity, so that 100 or more shock experiments could be accomplished in one day.…”

Shock compression dynamics under a microscope

“…We have studied several different types of RM using our laser flyer plate apparatus, including nano-Al + Teflon [27] and Al + MoO 3 [28]. Our latest study of the emission from shocked RM uses as an example the Al + CuO nanothermite reaction.…”