Combustion Performance of Laser Pyrolysis-Synthesized Boron Nanoparticles with Polytetrafluoroethylene

Boron has been studied as an energetic material for future use in hybrid rocket motors, as theoretical energy release of boron combustion with oxygen is much higher than that of aluminum. However, the two-stage combustion of boron and the physics/phase behavior of its oxide layer slow its reaction and hamper ignition and combustion. Polytetrafluoroethylene (PTFE) is believed to enhance the ignition behavior of boron by gasification of the oxide layer. Fluorine species can react with B₂O₃ at a much lower temperature which accelerates the boron ignition process. In this effort, the reactivity, ignition, and combustion performance of compositions of boron with nanoscale PTFE were investigated in 20/80 wt.% B/PTFE compositions. Boron powders consisted of laser-pyrolysis synthesized nano-size boron (10-15 nm) and commercially available boron powders were used. To assess the ignitability of compositions, DSC/TGA experiments indicate that nanoscale boron based compositions oxidize / react at temperatures ~490 °C which is well below those of commercial boron based compositions. T-jump experiments were conducted at heating rates of 1×10⁵ °C/s and show that at high heating rate, nano Boron compositions have much lower ignition temperature than micron boron compositions. Reaction and combustion rate of compositions is assessed with closed vessel combustion experiments. Measured pressurization rates of synthesized and commercial boron/PTFE mixtures indicate the pressurization rate of nano-B /PTFE mixture is about 10 times higher than commercial boron/PTFE mixtures in both high pressure air and argon. We also report that nano boron is sensitive to photoflash ignition and can be ignited via broadband light exposure. Overall, mixtures of laser pyrolysis-synthesized boron with PTFE show much better performance than commercial boron compositions in respect to ignition temperature, combustion rate (pressurization rate), and unique photo-flash ignition sensitivity.