Micro-heterogeneous regimes for gasless combustion of composite materials

Reactive Ni/Al composite particles with different internal microstructures were fabricated by ball milling (BM). The propagation of gasless combustion waves through the compacted composite particle media was investigated using high-speed microscope video recording (HSMVR), with a resolution of 10 μm/pixel and 21.25 μs/frame. The microstructural combustion-wave characteristics, including hesitation time, propagation step size, instantaneous velocity, intraparticle reaction time, and average combustion-wave velocity, were studied as functions of measured internal microstructural parameters. The micro-heterogeneous relay-race combustion mechanism prevails across the investigated conditions. Decreasing the metal layer thicknesses in the composite particles leads to significant decrease in hesitation time, while only weakly affecting the instantaneous velocity. Characteristic times of hesitation and thermal relaxation defined two combustion front propagation regimes limited by interparticle heat transfer and by chemical reaction kinetics. Understanding the existence of these two discrete regimes allows us to effectively control the combustion parameters in this high-energy-density system.