Boron Rich Nitride

Crystalline boron-rich boron nitrides of the compositions B25N up to B53N as well as amorphous phases of the composition B3N and B5N have also been synthesized by CVD methods [120,121]. The formation of a rhombohedral structure of the boron-rich nitride, B4N, is described in [122]. The films deposited at 1200°C on hBN substrates by a tungsten hot filament assisted vapor-phase reaction... 

Saitoh, H., Yoshida, K., and Yarborough, W., Crystal Structure of New Composition Boron Rich Boron Nitride Using Raman Spectroscopy, J. Mater. Res., 8(1) 8-11 (Jan. 1993)... 

By using a boron-nitride powder barrier (hot pressed or deposited onto graphite mold and punches), it is possible to prepare dense and pure boron and boron-rich phases, especially carbides (between B,o.4C and B4C) by hot pressing in graphite dies " . 

H Werheit. Optical properties of boron-rich solids with icosahedral structure. In R Freer, ed. The Physics and Chemistry of Carbides, Nitrides and Borides. Dordrecht Kluwer, 1990, p 705. Gmehn Handbook of Inorganic Chemistry. Vol 54. Boron Compounds. Part 20. Berlin Springer, p 224 (1979). 

Typically, Be-containing alloys and intermetallic phases have been prepared in beryllia or alumina crucibles Mg-containing products have been synthesized in graphite, magnesia or alumina crucibles. Alloys and compounds containing Ca, Sr and Ba have been synthesized in alumina , boron nitride, zircon, molybdenum, iron , or steel crucibles. Both zircon and molybdenum are satisfactory only for alloys with low group-IIA metal content and are replaced by boron nitride and iron, respectively, for group-IIA metal-rich systems . Crucibles are sealed in silica, quartz, iron or steel vessels, usually under either vacuum or purified inert cover gas in a few cases, the samples were melted under a halide flux . 

A complex nanostructured catalyst for ammonia synthesis consists of ruthenium nanoclusters dispersed on a boron nitride support (Ru/BN) with barium added as a promoter (33). It was observed that the introduction of barium promoters results in an increase of the catalytic activity by 2—3 orders of magnitude. The multi-phase catalyst was first investigated by means of conventional HRTEM, but this technique did not succeed in identifying a barium-rich phase (34). It was even difficult to determine how the catalyst could be active, because the ruthenium clusters were encapsulated by layers of the boron nitride support. By HRTEM imaging of the catalyst during exposure to ammonia synthesis conditions, it was found that the... 

Existence of a nitrogen-rich boron nitride denoted as h BN was suggested by Yoo et ai, who observed appearance of a low-density hexagonal compound after laser heating of boron in excess of nitrogen in a diamond cell [123], This compound was synthesized both in the stability fields of conventional hBN (2GPa, 1300 K) and of cubic BN (15 GPa, 1800 K). h BN is highly transparent and can be recovered as white polycrystals, which do not convert to other forms of boron nitride at ambient conditions [123]. Unfortunately, chemical composition of the compound obtained was not determined quantitatively. 

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