Low-temperature synthesis and properties of high-purity boron nitride microspheres

Boron nitride (BN) has excellent high temperature resistance, thermal conductivity, strong insulation, and wave-transparent properties. Spherical BN is an essential filler in polymer matrix composites due to good particle mobility and high filler content. In this paper, we present a large-scale preparation for BN microspheres with uniform particle size distribution in the range of 1.0–2.8 μm via solvothermal method at low cost and high yield (∼90%), which is two orders of magnitude lower than the diameter of the spherical BN prepared by other methods. BN microspheres can achieve good crystallinity (>70%) and high purity (>99.9%) at 800 °C. The temperature resistance study showed that the BN microspheres could maintain the dense particle morphology at 1200 °C. In addition, the prepared BN microspheres have good dielectric and thermal conductivity properties (dielectric constant ∼3.4, dielectric loss ∼2.0 × 10−3, and thermal conductivity of 9.8 W·m−1 K−1), which show great potential in the field of wave-transparent and thermal conductive composites. The synthesis process of BN microspheres proposed in this study provides a new idea for the preparation of ceramic micro or nano materials by polymer-derived ceramics.