Preparation and Performance of Core–Shell Structured B@NiF₂/AP Composite Micro-Units

In this study, core–shell structured B@NiF₂/AP composite micro-units with varying mass ratios were prepared using planetary ball milling technology to optimize the energy release and combustion performance of boron (B) powder. The optimal formulation was determined to be 0.5% NiF₂, 13.3% B, and 86.2% AP. Morphological characterization revealed that NiF₂ was uniformly coated on the surface of B particles, forming a dense shell structure that significantly enhanced the moisture resistance and oxidation stability of boron. Thermal behavior analysis indicated that the NiF₂ interfacial layer, due to its high-temperature fluorination reaction (NiF₂ → Ni + 2F), released highly electronegative fluoride ions that reacted with the B₂O₃ film on the boron surface, generating boron oxyfluoride gas and forming void structures. Experimental results showed that the composite material achieved a maximum heat release of 8912 J/g, at least 6.5% higher than other samples, and a mass gain of up to 74.58%, indicating a more complete reaction. Additionally, the oxygen released from AP decomposition further promoted combustion. Ignition and combustion analysis demonstrated a minimum ignition delay of 0.618 s—over 0.04 s shorter than that of other samples—and the lowest ignition energy at 22.17 J. The ignition flame exhibited a well-defined and complete profile with significantly enhanced combustion intensity. Overall, the core–shell structured B@NiF₂/AP composite micro-units provide a novel solution for the application of boron fuel in solid propellants and pyrotechnic technologies.