High pressure reactions and formation mechanism of cubic BN in the system BNMg 3N 2

Abstract

High pressure and high temperature reactions in the system BNMg 3N 2 were examined to investigate the formation mechanism of cubic boron nitride. An unidentified phase (X-phase) was obtained in the composition between Mg 3BN 3 and Mg 3N 2. The X-phase reacts with BN to form Mg 3BN 3 at high pressure. We found no evidence of the decomposition reaction of the X-phase to form cubic BN. Only Mg 3BN 3 was confirmed as an intermediate compound in the system BNMg 3BN 3. The Mg 3BN 3 showed high pressure phase transformation. The phase boundary between Mg 3BN 3(L) and Mg 3BN 3(H) was determined to be P = 7.2−0.0035 T (GPa, °C). The formation mechanism of cubic BN in this system was dissolution and precipitation of cubic BN in the eutectic liquid of the pseudobinary BNMg 3BN 3 system. We found no evidence of cubic BN formation by solid state decomposition of the intermediate compound in the system BNMg 3N 2.