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STRUCTURE OF BORON NITRIDE:


(1) Diborane react with excess NH3 at temperature to form boron nitride (BN) x.while when diborane and NH3 react in 1:2 ratios at low temperature give Borazole.
(2) The thermodynamically stable phase of boron nitride, BN, consists of planar sheets of atoms like those in graphite The planar sheets of alternating B and N atoms consist of edge shared hexagons and, as in graphite, the B-N distance within the sheet (145 pm) is much shorter than the distance between the sheets (333 pm,). The difference between the structures of graphite and boron nitride, however, lies in the register of the atoms of neighboring sheets:

(3) In BN, the hexagonal rings are stacked directly over each other, with B and N atoms alternating in successive layers; in graphite, the hexagons are staggered. Molecular orbital calculations suggest that the stacking
(4) In BN stems from a partial positive charge on B and a partial negative charge on N. This charge distribution is consistent with the electronegativity difference of the two elements.
(5) As with impure graphite, layered boron nitride is a slippery material that is used as a lubricant. Unlike graphite, however, it is a colourless electrical insulator, as there is a large energy gap between the filled and vacant π bands.
(6) In contrast to graphite, layered boron nitride is stable in air up to 1000°C, making it a useful refractory material. Layered boron nitride changes into a denser cubic phase at high pressures and temperatures (60 kbar and 2000 degree centigrade)

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