SYNTHESIS OF BORON-NITRIDE FROM BORON-OXIDE USING SUPERCRITICAL AMMONIA

Hexagonal boron nitride was synthesized from boron oxide using super c ritical ammonia and solid CaO below the melting point of B2O3 by the f ollowing reaction: B2O3(s) + 2NH(3) (super-critical fluid) + 3CaO (s)= 2BN (s) + 3Ca(OH)(2) (s). The experiment was carried out at 623-753 K and the initial ammonia pressure was 3.0-40.0 MPa. The mean diameter o f obtained BN particles was 0.2-0.3 mu m. The yield of BN increased wi th increasing temperature, initial ammonia pressure and the addition o f CaO. The thermochemical calculation showed that the CaO addition sup pressed the decomposition loss of ammonia during the reaction.