Shock initiation of crystalline boron in oxygen and fluorine compounds

The ignition delay and combustion of amorphous and crystalline boron particles is investigated at elevated temperatures and pressures for wet, dry, and fluorine-containing atmospheres. Micron-sized amorphous and sieved 20 μm crystalline particles are ignited in the ambient conditions produced by a reflected shock wave in a shock tube. The ignition delay and combustion times are examined as a function of temperature for pressures of 8.5, 17, and 34 atm and for oxidizer mixtures of 100% oxygen, 30% water vapor, 1-3% sulfur hexafluoride, and 6-12% hydrogen fluoride. Results indicate that pressure in the range studied does not affect the ignition delay or bum time. The additives, water vapor and sulfur hexafluoride, reduce the ignition delay time for amorphous and sub-micron crystalline boron when compared to oxygen. For 20 μm particles, H₂O and SF₆ reduce the ignition temperature limit from 2500 K in pure oxygen to 2200 K and 1900 K, respectively. Burn time is unaffected by the additives. A review of previous chemical models is also presented for comparison.