| abstract |
Cubic boron nitride is produced by subjecting a charge of hexagonal boron nitride and an alkali(ne earth) metal and/or if boride as initiator to a pressure of 40-70 Kilobars and a temp. of 1100-2000 deg. C. The yield and crystal size of the prod. are increased if a crystalline hydrate (e.g. a salt contg. S and/or halogen and/or nitrogen) having at least 5 molecules of water of crystallisation (e.g. Al2(SO4)3.18H2O) be added to the charge. A typical charge will contain (wt.%) hexagonal BN, 72-94; initiator 5-20 and hydrate 1-8. The prod. is suitable as an abrasive, esp. for hard steels. |