Crystallization behavior of cubic boron nitride from an amorphous BN precursor via high pressure, high temperature treatment with controlled water addition
Abstract Crystallization behavior of cubic boron nitride (c BN) from amorphous boron nitride (a BN) by high pressure, high temperature (HP HT) treatment with the intentional addition of a controlled amount of water was studied. The a BN precursor was prepared by pyrolysis of a boric acid urea complex with urea/boric acid 2 at 1000 degC for 3 h under an ammonia atmosphere. Hexagonal BN (h BN) were initially crystallized from a BN containing 2 mass% of water after HP HT treatment at 7.7 GPa and 1200 degC, and the formation of c BN was observed after 5 min. The crystallization of c BN from a BN containing 8 mass% of water after HP HT treatment at 7.7 GPa and 1200 degC was observed even after 1 min, indicating that the crystallization of c BN was promoted by increasing the amount of water added. In addition, since neither h BN nor c BN was crystallized from a BN without intentional water addition after the same HP HT treatment, the addition of water promoted the crystallization of both h BN and c BN from a BN. Since no transformation from h BN to c BN was observed during HP HT treatment at 7.7 GPa and 1200 degC, it was concluded that c BN was directly crystallized from a BN. After HP HT treatment at 7.7 GPa and 1650 degC for 1 min, both h BN and c BN were crystallized from a BN containing 8 mass% of water. These results clearly indicate that the addition of water has a positive effect on crystallization of c BN from a BN.