MICROEXPLOSIONS OF BORON AND BORON CARBON SLURRY DROPLETS

Microexplosions of suspended boron/JP-10 and boron/carbon/JP-10 slurry droplets were studied for various solids loadings (Y(s) = 0.2-0.5) in the postflame region of a flat-flame burner. While the small-particle amorphous boron slurry droplets of a low solids loading (Y(s) = 0.2) shrank considerably before microexplosion, the droplets of high loadin gs (Y(s) = 0.3-0.5) held a nearly constant diameter before considerabl e swelling and drastic disruption occurred. For a fixed surfactant con centration of 0.05, the microexplosions were observed to be most viole nt at Y(s) congruent-to 0.45. The transient internal temperature distr ibutions of small-particle amorphous boron slurry droplets (Y(s) = 0.4 ) were measured up to microexplosion with fine thermocouples at 1000 K . Measurements indicated that temperatures at the outer region of the droplets rose continuously beyond the boiling point of JP-10, resultin g from evaporation suppression by the surface shell textures. The key event appeared to be the evaporation-suppressed heating process, simil ar to the microexplosion mechanism proposed by Wong and Lin for Al/C/J P-10 slurries. The semiempirical microexplosion model of Wong and Lin was applied to an amorphous boron slurry of Y(s) = 0.4, with the empir ical factors carefully determined at initial diameters of 1330 +/- 30 mum, and an ambient temperature of 1000 K. The calculations agreed sat isfactorily with the experimental data at various droplet diameters an d ambient temperatures. The effects of carbon black on microexplosion were also examined. For small-particle amorphous B/C/JP-10 slurries of Y(s) = 0.3, a proportion of 8-12 wt.% carbon in the solids resulted i n stronger microexplosions. At larger Y(s), the advantageous effects d iminished and the addition of carbon black became unfavorable when Y(s ) greater-than-or-equal-to 0.45. For large-particle crystalline B/C/JP -10 slurries (mean boron particle diameter of about 20 mum), the addit ion of an appropriate amount of carbon black always appeared beneficia l.