SOLVENT EFFECTS OF FLUORIDES IN CUBIC BN HIGH-PRESSURE SYNTHESIS

Cubic BN can be synthesized under high pressure by using various fluorides as solvents. When NH4F solvent is used, synthesis conditions are pressures above 4.0 GPa and temperatures above 800°C at 6.0 GPa. However, there exists a lower pressure limit for the synthesis, as in the case of water solvent. Synthesized cubic BN is a colorless tetrahedral crystalline powder with crystal size varying from 0.2 - 1 μm. Spark ion source mass spectrography revealed that the resulting cubic BN and hexagonal BN contain fluorine. This indicates that fluorine plays a role in the shift of the cubic-hexagonal BN equilibrium line to the higher pressure side, creating a pressure limit for the synthesis. © 1979.