Elemental Boron, Tungsten Bronzes, and Metal Sulfides

ELEMENTAL BORON, TUNGSTEN BRONZES, AND METAL SULFIDES 

The a-rhombohedral form of boron (a-boron) was first reported by L. V. McCarty, J. S. Kasper, F. H. Horn, B. F. Decker, and A. E. Newkirk.1 Of the many allotropic forms of boron, it has the simplest structure.2 It may be prepared by the pyrolysis of boron(III) iodide on a tantalum filament at 800-1000°C., but the product is usually contaminated by other allotropic varieties of boron.1,4 Recently, Hagenmuller and Naslain showed that boron(III) bromide may be reduced by 

H2 at 700°C. in a quartz tube to give finely divided a-rhombo-hedral boron. X-ray diffraction reveals only a single phase in the product.5- The reduction of BBr with H is described here. 

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