Oxygen Gas-assisted Synthesis of Boron Nitride Nanotubes

Wool-like products were fabricated on the stainless-steel substrates by directly heating amorphous B powder at high temperature (1300°C) at 50 mL/min ammonia gas with different flow of oxygen gas (10, 15, 20, 40 mL/min). It was found that B powder could be oxidized by trace oxygen gas to form the intermediate B2O2 vapor, which can act as highly active boron source for the growth of BN nanotubes. When an appropriate amount of oxygen was introduced, the obtained nanotubes had an average diameter of about 80 nm and the lengths of several hundred micrometer. Both the diameter and the yield of BN nanotubes could be influenced dramatically by the flow rate of oxygen. With the increase of oxygen flow, the diameter of nanotubes was gradually increased, and the yield of nanotubes was improved obviously at first and then turned down. The formation mechanism of these nanotubes is governed by a vapor-liquidsolid (VLS) growth model.