Vaporization-Controlled Energy Release Mechanisms Underlying the Exceptional Reactivity of Magnesium Nanoparticles.

Magnesium nanoparticles (NPs) offer the potential of high-performance reactive materials from both thermodynamic and kinetic perspectives. However, the fundamental energy release mechanisms and kinetics have not been explored due to the lack of facile synthetic routes to high-purity Mg NPs. Here, a vapor-phase route to surface-pure, core-shell nanoscale Mg particles is presented, whereby controlled evaporation and growth are utilized to tune particle sizes (40-500 nm), and their size-dependent reactivity and energetic characteristics are evaluated. Extensive in situ characterizations shed light on the fundamental reaction mechanisms governing the energy release of Mg NP-based energetic composites across particle sizes and oxidizer chemistries. Direct observations from in situ transmission electron microscopy and high-speed temperature-jump/time-of-flight mass spectrometry coupled with ignition characterization reveal that the remarkably high reactivity of Mg NPs is a direct consequence of enhanced vaporization and Mg release from their high-energy surfaces that result in the accelerated energy release kinetics from their composites. Mg NP composites also demonstrate mitigated agglomeration and sintering during reaction due to rapid gasification, enabling complete energy extraction from their oxidation. This work expands the compositional possibilities of nanoscale solid fuels by highlighting the critical relationships between metal volatilization and oxidative energy release from Mg NPs, thus opening new opportunities for strategic design of functional Mg-based nanoenergetic materials for tunable energy release.