Most of the small particles (50 to 100 micrometers in diameter) of microcrystalline beta-rhombohedral boron that quickly transit an argon plasma maintained within a radio-frequency induction-coupled torch emerge as better crystallized spheroids of the same crystalline form and nearly the same size as the starting material. A few crystals of each of four distinctive, well-faceted habits are formed along with the general product. Three of these types are monocrystals of the beta-rhombohedral polymorph, of the tetragonal-III modification, and of an unreported cubic form of boron. Specimens of the fourth type are polycrystals of another unreported form of boron, apparently consisting of many hexagonal platelets stacked in an imprecise fashion.
The phase diagram for the ternary fused-salt system LiF-BeF2-UF4 was determined from 300°C to the liquidus by differential thermal analysis, thermal-gradient quenching studies, and high-temperature filtration techniques. The samples prepared by quenching were examined by polarized-light microscopy and X-ray diffraction techniques. The experimental methods are described. The primary-phase fields for the compounds LiF, 7LiF.6UF4, LiF.4UF4, and UF4 covered most of the liquidus surface.Small areas of the liquidus surface were covered by the compounds BeF,, 2LiF.BeFz, and 4LiF.UF4. The compound 4LiF-UF4, which was stable at the binary liquidus temperature, decomposed in the ternary system when the liquidus temperature decreased below 48OOC. No ternary compounds or solid solutions were observed. Two ternary eutectics were found. The first, containing 48 mole yo LiF, 51.5 mole yo BeFz, and 0.5 mole yo UF4, melted at 350°C. The second, containing 69.5 mole yo LiF, 22.5 mole yo BeF,, and 8 mole % UF,, melted at 427°C.
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