Laser controlled combustion rate of an aluminum/copper oxide thermite

Abstract

This study demonstrates that the burn rate of an Al/CuO nanothermite can be controlled using continuous wave laser irradiation. Expanding a 532 nm laser beam through a cylindrical lens enabled the creation of a spatially varying temperature increase of up to 200 °C across the surface of a 3D printed thermite stick. Temperature distributions on the surface were monitored using an infrared camera, and the velocity of the burning front was tracked with a high-speed camera. Two-color pyrometry showed that the flame temperature was not affected by laser illumination, so the burn rate increase is attributed to the increase in initial surface temperature of the thermite. The local velocity of the front could be increased by a factor of 3 by this photothermal heating. Effective activation energies were extracted from Arrhenius plots of local velocities vs surface temperatures. The measured activation energy of ∼10 kJ/mol at the highest peak temperature probably reflects more facile mass transport in the heated regions. This study represents a proof-of-concept for measuring the temperature sensitivity of the local burn rates in nanothermite systems. It also demonstrates that visible laser irradiation provides a non-contact method to modulate combustion rates in solid-state energetic materials.