Micro-heterogeneous regimes for gasless combustion of composite materials

ABSTRACT

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.

KEY WORDS:

• Micro-Heterogeneous Combustion
• Gasless Combustion
• Self-Propagating High-Temperature Synthesis
• Discrete Combustion Wave

Acknowledgment

The authors acknowledge the Notre Dame Center for Environmental Science & Technology for access to the FlowCAM equipment. Special thanks to A. Shah and H. Delgado for assisting the author while performing the experimental work.

Additional information

Funding

This work was supported by the Department of Energy, National Nuclear Security Administration, under Award Number DE-NA0002377. This work was also partially supported by the Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST “MISIS” grant No. K2-2015-068.