Sintered BN Products Obtained from a Ground BN Powder and Its Sintering Processes

Pressureless sintered products of h-BN were fabricated by heating ground BN powders at temperatures between 900 and 2000°C. The BN products with bending strengths of 40 to 70MPa were obtained at the sintering temperatures above 1400°C, while they contained an appreciable amount of oxygen as impurity, except for the 2000°C products. The strength of sintered bodies increased with increasing sintering temperature up to 1600°C, with the release of boron compounds such as boric oxide. SEM and TEM observations indicated that grain growth or coarsening of BN particles took place above 1800°C with the vaporization of boron compounds, which reduced lowered slightly the strength of BN products.