Streak spectroscopy and velocimetry of electrically exploded Ni/Al laminates

Abstract

We present an experimental and theoretical study of electrically exploded nickel-aluminum (Ni/Al) laminates, lithographically patterned into bow-tie bridge regions, and encapsulated with parylene. The exothermic nature of Ni/Al reactions is well-known at typical self-heating rates of 103–106 K/s, but electrical heating allows the interrogation of phenomena at heating rates which are five to six orders of magnitude higher. The use of time-resolved streak camera emission spectroscopy revealed that Ni/Al laminates heated at these higher rates exhibited brighter emission during the first 150 ns of emission than samples composed of either Al or Ni alone, suggesting an exothermic effect which rapidly started and persisted for at least this length of time. We also measured the transduction of electrical energy into kinetic energy through velocity measurements of encapsulation layers ejected from the bridge region. An empirical model using experimental power curves and one empirical fitting parameter successfully predicted these velocities. This model agreed well with experiments from different Al and Ni samples using the same fitting parameter, but an apparent 1.2 J/mg of additional energy from the mixing of Ni and Al was necessary to accurately predict velocities from Ni/Al laminate samples. This energy quantity corresponded to a reference value for the enthalpy of mixing Ni and Al, and likely contributed to both brighter emission and higher than expected velocities observed.