Tailoring Magnesium Nanoparticles In-Flight via Nonthermal Plasma for Enhanced Ignition*

Magnesium (Mg) solid fuels are desirable for energetics due to their high reactivity and high gravimetric energy density. However, Mg combustion is restricted to a diffusion-limited ignition process because of the native oxide layer that inherently forms on particle surfaces. As a result, the surface of Mg nanoparticles significantly impacts the energetic performance. Directly coating Mg with an oxygen-containing silicon-based shell produces a nano-thermite system at the nanoparticle interface, accelerating reaction kinetics during ignition. Hydrogenating Mg results in a reactive magnesium hydride (MgH₂) surface, which alters the ignition pathway of Mg. Our work involves the in-flight modification of Mg nanoparticles via a low-temperature plasma process to circumvent oxide layer formation and engineer reactive Mg surfaces containing silicon (Si) or hydrogen. Ex-situ characterization of Si-coated Mg and hydrogenated Mg nanoparticles was performed to assess the effectiveness of the in-flight surface functionalization process. Processing parameters were manipulated to incorporate more MgH₂ into the nanoparticles. The ignition temperature, reaction kinetics, and ignition products were analyzed to evaluate the effects of the functionalized Mg surface on the combustion characteristics of Mg nanoparticles. Our findings indicate that both a Si coating and a MgH₂ surface participate in lowering the ignition threshold of Mg while accelerating combustion.