Atomistic insights into two-stage combustion of a single boron nanoparticle via reactive molecular dynamics

Boron (B) is a promising energetic additive for high-energy fuels, but its poor ignition and combustion characteristics limit its application in practical systems. The nano-sized B could alleviate these problems to a large extent. In this study, a reactive molecular dynamics simulation method is employed to investigate the fundamental combustion mechanisms of a single B nanoparticle (BNP). The experimentally observed two-stage combustion is reproduced. Moreover, the first stage is further divided into the pre-heating stage and the fast evaporation stage. The second stage is dominated by the B core combustion, during which a dynamic equilibrium of the interfacial layer and the oxide/evaporation layer is reached and drives the reaction. The diffusion mechanism of the BNP combustion is revealed. The evaporation of oxides and diffusion of ambient oxygen species into the oxide/evaporation layer proceed simultaneously during the fast evaporation stage. No ambient oxygen species diffuse into the B core but the diffusion of the core B atoms into the oxide/evaporation layer occurs throughout the simulation. Additionally, the diffusion of the core B atoms is enhanced with the rising temperature. Consistent with experimental results, BO2 is found to be a dominant intermediate species during the combustion. Furthermore, our new finding is that B3O4 is also an important intermediate, which bridges the conversion of larger BxOy species to the main combustion product B2O3. The new atomistic insights obtained from the present research could potentially benefit the design and practical application of nano-sized B as additives for high-energy fuels.