CUBIC BORON-NITRIDE SYNTHESIS BY PYROLYSIS OF CERTAIN POLYAMMONIATES OF BORON HYDRIDES OF METALS AT HIGH-PRESSURE

Pyrolysis of certain polyammoniates of boron hydrides of metals (PABH Mes) at high pressures not exceeding 7.0 GPa and at a temperature not exceeding 1770 K was examined. These compounds have a general formula Me(BH4)(n).mNH(3), where n is determined by the metal valency, m = 1-8 , Me: Li, Mg, Zn, Al, Sc, La, Zr, Cr, Co. P, T regions of cubic boron nitride (cBN) synthesis in the process of PABH Me pyrolysis were deter mined. It was ascertained that the P,T regions differed widely for dif ferent compounds. The kinetics of cBN formation in the process of pyro lysis of PABH Mg and PABH Al were studied. Cubic boron nitride crystal s were examined using the method of scanning electron microscopy (SEM) . A mechanism of cubic boron nitride formation in the process of PABH Me pyrolysis is suggested. (C) 1997 Elsevier Science S.A.