Fast reaction of aluminum nanoparticles promoted by oxide shell

Abstract

Combustion of aluminum nanoparticles (AlNPs) has long been investigated experimentally because of their use in various energetic formulations for propellants and explosives. But the limited spatiotemporal resolution in experiments, in particular, makes it challenging to explore the microstructural evolution of AlNP oxidation and associated mechanisms. Here, we perform large-scale reactive molecular dynamics simulations to study the structural evolution of AlNPs with a 2-4 nm thick oxide shell in an oxygen environment. We find the temporal hollowing processes of AlNPs for both symmetrical and asymmetrical oxidations, in which the morphological evolution can be understood by a discrepant electric field and temperature distributions for different systems. In the early time, core aluminum atoms experience a fast reaction with an oxide shell. Environmental oxygen does not react with AlNPs until the surface O/Al ratio decreases to ∼1.2. Moreover, based on our simulation results, previous experimental data agree well with the proposed model, which can well describe the relationship between combustion efficiency and oxide shell thickness, confirming that the oxide shell promotes rather than hinders the combustion of AlNPs. The molecular insights obtained here would be significant for understanding the underlying mechanism and further modeling of AlNP combustion.