Tuning energy release in boron-based energetic composites via gradient thickness control of surface fluoride layer by in situ polymerization

Boron powder exhibits exceptionally high gravimetric and volumetric calorific values, granting boron-rich propellants a significantly higher theoretical specific impulse compared to conventional hydrocarbon-based fuels. However, its practical application is severely limited by difficult ignition and incomplete combustion, resulting from the inherent oxide layer on the boron surface. Addressing these combustion inefficiencies is therefore critical. In this work, a series of modified B@FP composites with gradient fluoropolymer coating thicknesses were successfully synthesized through in situ polymerization of 1H,1H,2H,2H-perfluorooctyl acrylate (FOA) onto boron powder, where the coating mass was precisely tailored by varying the FOA monomer concentration. The surface morphology, elemental distribution, chemical composition, and hydrophobicity of the B@FP composites were comprehensively characterized. Their oxidation behavior, ignition performance, and combustion dynamics were further investigated. The results indicate that the fluoropolymer coating significantly reduces the ignition temperature of boron while increasing both the combustion heat and total exothermic enthalpy. Moreover, in combustion systems with ammonium perchlorate (AP) as oxidizer, the B@FP-1/AP mixture demonstrated higher combustion temperatures and a more vigorous reaction. Ultimately, the effect of the modified boron composites on the combustion performance of composite propellants was thoroughly evaluated, providing valuable insights for enhancing energy release efficiency in boron-containing propellant systems.