Abstract
Amorphous boron nitride (BN) powder was prepared by mechanically milling hexagonal BN and used as a starting material for studying BN phase transformation behavior. Fabricated amorphous BN (aBN) powder was significantly reactive with humidity in the air. When it was kept under a dry nitrogen atmosphere without H2O or O2, the phase transformation from aBN to cubic BN (cBN) occurred at 7.7 GPa at temperatures above 2200 °C, whereas aBN powder treated in air transformed into cBN at 5.5 GPa at temperatures above 1500 °C. These observations suggest that H2O has a strong catalytic effect on the phase transformation behavior of aBN. Without H2O, the phase transformation from aBN to cBN is rather difficult to achieve compared with transformations starting from other crystalline phases of BN. The cBN powder produced from aBN consists of fine grains smaller than 100 nm, which are superior in purity to those obtained via the conventional route using an alkali-earth metal/solvent system.
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