Investigation on preparing boron nitride by nitriding pure boron at 1200–1550 °C

Boron nitride (BN) was prepared by nitriding pure boron (B) deposited on carbon substrates by chemical vapor deposition (CVD). Thermodynamic analysis of preparing BN by nitriding CVD B at 1200–1550 °C was firstly performed. And then, the effects of nitridation conditions, including temperature, nitridation atmosphere and CVD B microstructure, on the conversion of B to BN were analyzed by scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Results show that the conversion degree of B to BN firstly increased and then slightly decreased with rising temperature. The nitridation degree was controlled by mutual actions between the nitridation of B and consumption of the effective nitrogen source (NH₃). The morphology of products and the reaction mechanism between B and N were influenced by nitridation temperature. At high temperatures (1400–1500 °C), BN with highly ordered microstructure was produced. On using N₂–H₂ as nitridation atmosphere instead of NH₃–H₂–N₂, no BN was obtained in the studied temperature range. The microstructure and component of BN obtained in nitridation process were little affected by the microstructure of CVD B.