Synthesis of Cubic Boron Nitride by the Reaction of Li3N and B2O3

Cubic boron nitride is synthesized by the reaction of Li3N and B2O3 under high pressure and high temperature (4.0–5.0 GPa, 1350–1500°C). The minimum pressure of cBN formation is 4.0 GPa. The present condition of cBN formation is clearly lower than the eutectic temperature of Li3BN2 and BN in the Li3N-hBN system (5.5 GPa, 1610°C). The content of cBN in the sample increases, while the content of hBN decreases with the temperature and pressure. The maximum conversion rate (5.0 GPa, 1500°C) is about 34%, which is higher than that in the hBN-Li3N system. The cBN crystals are octahedral or tetrahedral in shape and approximately 20 μm in diameter.