Preparation of Hexagonal BN

The Ba.C) N, nanotubes and fullerene-like structures have been synthesized by various laboratories in recent years. The most popular method is the plasma arc technique. The first report on the synthesis of BN nanotubes was by Zettl and coworkers (55). Since BN is an insulator, a composite anode was prepared from a tungsten rod with an empty bore in the center, which was stuffed with a pressed hexagonal BN powder. For the cathode, a water-cooled Cu rod was used. The collected gray soot contained limited amount of multi wall BN nanotubes. It is possible that in this case, the tungsten serves also as a catalyst. By perfecting this method, macroscopic amounts of double-wall BN nanotubes of a uniform diameter (2 nm)... 

Boron nitride (BN) can normally be prepared from the reaction of boric acid and urea or melamine. For example, the pyrolysis of MB can yield hexagonal BN. It is commonly referred to as white graphite because of its platy hexagonal structure similar to graphite. Under high pressure and at 1600°C, the hexagonal BN is converted to cubic BN, which has a diamond-like structure. 

In retrospect, it is ironic to it that when I met Ernst Schumacher in 1969 (he was then Professor at the University of Bern in Switzerland) we did not talk about the experiments he did at Zurich in the same building where I was at that time. Instead, his interest focussed on our work on borazine transition metal compounds and we discussed in some detail whether it would be possible to incorporate metal atoms like chromium or molybdenum between the layers of hexagonal boron nitride (BN) in a similar way as it can be done with graphite. In the course of these discussions I did not mention that, after I had moved to Zurich, we had begun to investigate the reactivity of nickelocene towards both nucleophilic and electrophilic substrates. The reason was that we were still at the beginning, and while we had been able to prepare a series of monocyclopentadienyl nickel complexes from Ni(C5H5)2 and Lewis bases, our attempts to obtain alkyl- or acyl-substituted nickelocenes by the Friedel-Crafts reaction failed. 

Intercalation of h-BN by SbF /F2 mixtures. Mixtures of h-BN, SbFg, and F2 in 6 2 1 molar ratio in a stainless steel reactor with a Whitey KS4 value were agitated at 0°C for 6 h. Some BF3 was produced. Removal of volatiles left a light blue solid, the XRDP of which indicated the presence of a hexagonal first-stage salt with a indistinguishable from that of h-BN and c = 8.01 A. Some unintercalated h-BN remained. Several preparations gave similar results and material entirely free of h-BN was never obtained. 

The cubic 2inc blende form of boron nitride is usually prepared from the hexagonal or rhombohedral form at high (4—6 GPa (40—60 kbar)) pressures and temperatures (1400—1700°C). The reaction is accelerated by lithium or alkaline-earth nitrides or amides, which are the best catalysts, and form intermediate Hquid compounds with BN, which are molten under synthesis conditions (11,16). Many other substances can aid the transformation. At higher pressures (6—13 GPa) the cubic or wurt2itic forms are obtained without catalysts (17). 

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