Enhanced ignition of milled boron-polytetrafluoroethylene mixtures

The combustion and physical properties of boron-polytetrafluoroethylene (PTFE) mixtures were modified by ball milling. Examination of the milled material through optical microscopy, scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) reveal that the milled mixtures are more intimately mixed and arranged into larger aggregate particles. Differential scanning calorimetry indicates the appearance of an endothermic reaction, brought on by milling. Fourier transform infrared spectroscopy provides evidence that the milling process enhances the chemical reaction of boron and PTFE. The milled boron-PTFE mixtures are demonstrated to be more reactive than those mixed by hand, despite containing larger particle sizes. Laser-ignition studies of the materials show that milling boron-PTFE mixtures results in the ignition delay times being reduced by a factor of 2. The milled mixtures were able to sustain combustion in air and emitted a strong BO2 signal while simple physical mixtures do not. Enhanced reactivity of the milled materials is attributed to a combination of decreased diffusion lengths and disruption of the boron oxide shell during the milling process. Published by Elsevier Inc. on behalf of The Combustion Institute.