SYNTHESIS OF BORON-NITRIDE BY SELF-PROPAGATING REACTIONS AT HIGH-PRESSURE

Peculiarities of the formation of BN in a self-propagating reaction be tween LiBF4 and Li3N have been studied under a wide range of p, T cond itions within the region of thermodynamic stability of cBN. Boron nitr ide crystallized mainly in the form of highly ordered hBN (1700-2100 K ), of meso-graphitic BN (2200-3000 K), or of turbostratic BN (>3000 K) . Cubic boron nitride mas obtained with a low yield (up to 14 vol%) as a result of precipitation from the metastable eutectic liquid in the BN-Li3N system. These results give further evidence for an alternative metastable behavior in the BN phase formation under high pressures.