Effects of trimethylamine and ammonia on cBN content in the samples prepared by hydrothermal method

The previous results have proved that the phase-selective synthesis route is an effective method for preparing cubic boron nitride (cBN) from hydrothermal solutions. However, the experimental parameters are still required to be optimized in order to synthesize pure cBN at high yield. Here we report the results of investigating the effects of adding trimethylamine (N(CH3)3) and ammonia (NH3·H2O) (denoted as secondary nitrogen source) into the reacting solutions. It was found that the content of cBN could be increased by adding appropriate amount of N(CH3)3 and decreased with excess amount of it. On the contrary, hexagonal boron nitride (hBN) was always promoted by adding NH3·H2O into the reacting solutions. The samples were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectrum (FTIR) and high resolution transmission electron microscopy (HRTEM). The experimental results were briefly discussed based on a reported model.