HIGH-PRESSURE PHASE-TRANSFORMATIONS OF CUBIC BORON-NITRIDE FROM AMORPHOUS BORON-NITRIDE USING MAGNESIUM BORON-NITRIDE AS THE CATALYST

Results are described of high pressure phase transformations of amorph ous boron nitride (aBN) to cubic boron nitride (cBN) using magnesium b oron nitride (Mg3B2N4) as a catalyst-solvent. It was observed that amo rphous boron nitride undergoes various structural modifications under high pressures and high temperatures leading to the formation of hexag onal, cubic and wurtzitic phases of boron nitride. The minimum pressur e at which aBN starts transforming into cBN was found to be 25 kbar at 1800 degrees C. This is the lowest pressure for cBN formation employi ng the catalyst-solvent process and is reported here for the first tim e.