Ignition and Combustion Enhancement of Boron with Polytetrafluoroethylene

The ignition and combustion properties of fuel-rich mixtures of boron and polytetrafluorethylene in air and argon were studied as a function of pressure at a heating rate of approximately 1×105 K/s to simulate heating rates that individual ingredients may be subjected to in propellant burning. Mixtures ranging from 20 to 100 wt% boron (balance polytetrafluorethylene) and pressures up to 7 MPa were considered in this study. Ignition of the samples was achieved by joule heating of a platinum filament within a pressure vessel of selected atmospheres. Ignition of the mixture was characterized by monitoring broadband light emission, whereas boron ignition specifically was verified by identification of the BO2 molecule using emission spectroscopy. At atmospheric pressure, none of the mixtures ignited within the duration of the experiment. Mixtures containing more than 80% boron did not consistently ignite under any conditions within the duration of the experiment. It was found that the ignition temperature for all of the mixtures was a function of pressure with a reduction in ignition temperature of about 300 K when increasing the pressure from 2 to 7 MPa. At pressures greater than approximately 3.5 MPa, the ignition temperature was insensitive to mixture composition for all mixtures that ignited. The results suggest that the enhancement of boron ignition is the result of sufficient polytetrafluoroethylene decomposition products to remove the oxide layer of boron.