Cubic boron nitride synthesis and applications

Cubic BN has the zinc-blende structure and is the second-hardest material known after diamond. It is more resistant than diamond to oxidation and to attack by hot ferrous metals and is now widely used industrially for precision grinding and cutting ('Borazon'). It is conveniently synthesized in large amounts by exposing graphitic BN to high pressure (45-55 kbar) and high temperature (1400-1700 C) with a catalyst which is usually a nitride of Li, Mg, or Ca, but many other catalysts are known. It can also be made from graphitic BN without a catalyst at pressures above about 90 kbar and temperatures above about 500 C. It can be doped to become a p- or n-type semiconductor. Large pieces suitable for high-performance cutting tools can be made by a special sintering process. 14 refs