SHOCK INITIATION OF CRYSTALLINE BORON IN OXYGEN AND FLUORINE-COMPOUNDS

Tile ignition delay and combustion of amorphous and crystalline boron particles is investigated at elevated temperatures and pressures for w et, dry, and fluorine containing atmospheres, Micron-sized amorphous a nd sieved 20-mu m crystalline particles are ignited in the reflected-s hock ambient conditions produced at a Shock-tube endwall. 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. At 8.5 atm, SF6 has little effect on the ignition delay or temperature limit for 20-mu m particles, but at 34 atm the effect of S F6 is to reduce both the ignition delay time and the ignition temperat ure limit, from 1900 to 1400 K, In addition, experiments conducted wit h 1- and 20-mu m crystalline boron particles and with unsieved <200-mu m B2O3 particles show that the first and second peaks observed in 20- mu m particle combustion are associated with removal of the oxide laye r.