Abstract
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 loadings (Y s = 0.3-0.5) held a nearly constant diameter before considerable swelling and drastic disruption occurred. For a fixed surfactant concentration of 0.05, the microexplosions were observed to be most violent at Y s ≅ 0.45. The transient internal temperature distributions 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, resulting from evaporation suppression by the surface shell textures. The key event appeared to be the evaporation-suppressed heating process, similar to the microexplosion mechanism proposed by Wong and Lin for Al/C/JP-10 slurries. The semiempirical microexplosion model of Wong and Lin was applied to an amorphous boron slurry of Y s = 0.4, with the empirical factors carefully determined at initial diameters of 1330 ± 30 μm, and an ambient temperature of 1000 K. The calculations agreed satisfactorily with the experimental data at various droplet diameters and 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 in stronger microexplosions. At larger Y s , the advantageous effects diminished and the addition of carbon black became unfavorable when Y s ≥ 0.45. For large-particle crystalline B/C/JP-10 slurries (mean boron particle diameter of about 20 μm), the addition of an appropriate amount of carbon black always appeared beneficial. © 1994.