Microstructure and dielectric properties of hexagonal boron nitride prepared by hot pressing (uniaxial and isostatic) and by spark plasma sintering

Owing to the strong covalent B-N bonding and layered structure, complete sintering of h-BN ceramics is quite difficult to attain without using high-pressure and high-temperature processes. In this paper, a commercial pure h-BN powder was sintered by hot pressing (uniaxial – HP and isostatic – HIP) and spark plasma sintering (SPS) aiming at studying the anisometry among microstructures and their influence in the density and in the dielectric properties of this material. The results are compared to a commercial h-BN product in terms of densification, microstructure and dielectrical properties. Samples sintered by hot pressing processes presented microstructures with random alignment of the grains while the samples sintered by SPS showed an aligned microstructure with grains oriented perpendicular to the pressing direction. A higher dielectric constant was observed for the HIP sintered sample and the results of this sample show similar behaviour to the commercial h-BN ceramic component.