Combustion enhancement of micron-sized boron powder by three metal fluorides: Performance and mechanism

Metal fuels find extensive application in propellants and explosives due to their high energy density. Boron (B) has garnered significant attention due to its relatively ideal mass combustion heat (58.3 MJ/kg) and volumetric combustion heat (136.44 kJ/cm³). However, its practical application faces significant challenges, primarily due to the relatively low combustion efficiency of boron. To address the challenges in boron powder application, this study employed three metal fluorides (MF: Na₃AlF₆, MgF₂, and AlF₃) to enhance the ignition and combustion properties of boron powder. A series of B/MF-10% samples were prepared using a physical blending method. The TG-DSC results indicated that the addition of metal fluorides increased the degree of boron oxidation and intensified the exothermic response compared with pure B. Notably, the B/Na₃AlF6-10% sample exhibited a pre-ignition reaction at a relatively low temperature (∼576 °C). The results of the combustion heat test indicate that the combustion heat of samples containing the three metal fluorides increased by approximately 12% compared to pure B, demonstrating a significant enhancing effect. In the ignition experiment, the burning time of B/MF-10%/CuO increased by approximately 23.1% compared to pure B, with a significant increase in maximum flame area. The presence of metal fluorides also markedly enhanced the sample's combustion intensity, though they exhibited an inhibitory effect on the initial combustion stage. Furthermore, by analyzing the combustion products of different samples, the potential intrinsic mechanism is elucidated by which metal fluorides promote boron combustion.