Boron Carbonitride Crystal Preparation Process

In this paper, BCN compounds were synthesized under high temperature and high pressure. Catalysts were investigated to show the influence on properties of BCN composites. The precursor of B-C-N was prepared by pyrolysis process using boric and melamine. The effects of temperature, pressure, time, and catalysts on the synthesis of B-C-N ternary compounds were investigated. The XRD, SEM, EDX, and Fourier transformed infrared (FTIR) spectrometer techniques were carried out to characterize the prepared samples.Without catalysts, a B-C-N precursor with a disordered graphite structure was obtained at 800-1500 ℃ for 20 min under a pressure of 5.5 GPa With the increasing in the temperature, the B-C-N precursor gradually transformed from a disordered graphite structure to a well-crystallized hexagonal phase. BC₂N and BCN ternary compounds with fine grain size of several hundreds nano meter and a mixture of BN and graphite were obtained by high temperature and high pressure processing of the B-C-N precursor at 1200 ℃ for 20 min under a pressure of 5.5 GPa. As the temperature increased to 1500 ℃, a mixture of h-BN and graphite were obtained and no B-C-N ternary compounds were found.Using reduced-Ni powders as the catalyst a mixture of hexagonal BC2N, hexagon BN and graphite was synthesized at 1500-1600 ℃ for 15²0 min under a pressure of 5.5 GPa The lattice parameters of hexagonal BC₂N were determined as a=0.2485 nm and c=0.6626 ran, respectively. Using Mg3B2N4 as the catalyst, the precursor was processed at 800¹600 ℃ under 3⁶ Gpa. As the pressure increased to 5.5 GPa, cubic B-C-N formed at 1200 ℃, and the transition temperature from hexagonal B-C-N to cubic B-C-N was reduced with the furtherincreasing in pressure.