Deep oxidation and rupture processes in the aging of boron particles by time-sequenced slicing approach

The energy performance of boron-based energetic materials gradually deteriorates over time, primarily influenced by the formation and evolution of the oxide layer on boron particle surfaces. However, accurately characterizing the structural evolution of this oxide layer remains challenging due to its nanoscale characteristics and inward growth, thereby limiting a comprehensive understanding of the aging process. To address this, this study integrates accelerated aging experiments with micro-nanostructure processing techniques and develops a time-sequenced slicing approach for systematically analyzing the oxidation evolution of boron particles. Experimental results indicate that the growth of the boron oxide layer follows a two-stage process: an early slow-growth phase dominated by boron‑oxygen diffusion, followed by a mid-stage accelerated growth phase driven by structural degradation. The growth rate constants of these two modes differ by approximately a factor of 17.7. During oxidation, the chemical composition of boron undergoes a transformation from elemental boron to mixed boron oxides and eventually to boric acid (B → B_nO_m → H₃BO₃), leading to a decrease in surface density, an enhancement of oxidation-induced expansion, and the formation of cracks and voids. These structural changes directly influence oxidation kinetics and account for the variation in oxidation rates between the early and mid-aging stages. This study elucidates the microscopic structural evolution mechanism of boron particles under storage conditions, providing critical theoretical insights for optimizing energy performance assessment and storage stability.