Chemical kinetics of boron combustion in high pressure ar/f/o₂mixtures

Small crystalline boron particles (5-15 µm) are ignited in atmospheres consisting of Ar/F/O₂ at the endwall of a shock tube to study the effect of fluorine additives on ignition delay time. A reflected shock is used to obtain a pressure of 8.5 atm and a temperature of 2600 K. Visible wavelength emission data is recorded using a spectrometer coupled to a streak camera and by two photodetectors. The streak camera allows recording of multiple time-resolved spectra at rates of 100 (is per spectrum. Results indicate a rapid decrease by a factor of four in ignition and burning times as the mole fraction ration yp/yO₂-, is increased from 0 to 0.25. For values of yF/yO₂greater than 0.5 there is little change of ignition burning time with yF/yO₂- Spectroscopic data taken in pure oxygen environments show residual BO₂ emission after particle combustion, while that taken in fluorine-containing environments show little or no emission from BO₂. This is consistent with predictions from theoretical modeling efforts of other researchers. However, these same models predict the presence of BF and BF₂, which are not observed.