Time-Resolved Emission Spectroscopy Of Electrically Heated Energetic Ni/Al Laminates
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Time-Resolved Emission Spectroscopy Of Electrically Heated Energetic Ni/Al Laminates Christopher J. Morris1, Paul Wilkins2, Chadd May2, Timothy P Weihs3 1
U.S. Army Research Laboratory, 2800 Powder Mill, Rd, Adelphi, MD, 20783, USA
3
Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, USA
3
Johns Hopkins University, 3400 North Charles Street, Baltimore, MD, 21218, USA
ABSTRACT The nickel-aluminum (Ni/Al) intermetallic system is useful for a variety of reactive material applications, and reaction characteristics are well studied at the normal self-heating rates of 103– 106 K/s. Recent experiments at 1011–1012 K/s have measured the kinetic energy of material ejected from the reaction zone, indicating additional kinetic energy from the reactive system despite high heating rates. In order to better probe reaction phenomena at these time scales, and determine the presence of expected elements and their temperatures, we report on emission spectroscopy of electrically heated, patterned Ni/Al bridge wires, time resolved over 350 ns through the use of a streak camera. Unlike previous studies where emission was dominated by Ar and N from residual gasses in the vacuum test chamber, here we report on experiments with encapsulated laminates allowing better quantification of Al and Ni emission. We were able to identify all major spectral lines from the dominant elements present in the films, and found the multilayered Ni/Al laminates to exhibit a brighter and longer duration emission than either Al or Ni control samples. We also found the measured electrical energy absorption of the Ni/Al laminates to follow that of the Al samples up to 150 ns following the onset of emission, indicating that the exothermic mixing of vapor phase Ni and Al was the most likely source for the higher emission intensity. These results will be important for new, energetically enhanced, high efficiency bridge wire applications, where shock initiation of subsequent energetic reactions may be accomplished with less electrical energy than is currently required. INTRODUCTION Many groups have studied reactive nickel-aluminum (Ni/Al) laminates for a variety of applications [1], including the initiation of subsequent reactions, thermal batteries [2], and localized heating for welding and joining [3-5]. The reaction of a Ni/Al laminate is typically driven by heat diffusion along and between the reactive layers, leading to self-heating rates of 103–106 K/s and reaction front velocities as high as 10 m/s [1]. We have studied these laminates at the much higher heating rates of 1011–1012 K/s, induced electrically through joule heating [6]. By evaluating the kinetic energy of a conformal coated polymer layer which was ejected from the surface of the Ni/Al laminate, we found that electrically heated Ni/Al conductor layers contributed between 1.13 kJ/g and 2.26 kJ/g of additional kinetic energy compared with conductors composed only of Al, Ni, or Cu, when evaluated at the same instantaneous input electrical energy levels [7]. The simila
