Controllable preparation of boron nitride microspheres and their epoxy-based thermoconductive composites

How to prepare spherical boron nitride (BN) particle with different size is an extremely challenging work. In this paper, the controllable preparation of spherical BN particle from nanospheres to microsphere was realized by changing the synthesis temperature of trimethyl borate (B(OMe)3) and ammonia. The spherical precursor (SP) with high oxygen content was obtained first, and then it was heated under flowing ammonia atmosphere to form stable boron nitride microspheres (BNMS). The BNMS exhibits onion-like cavitation structure with a diameter of 0.8–3.4 μm. The effects of the lower reaction temperature (700–825 °C) and gas flow rate on the spherical precursor are discussed. A possible mechanism is proposed to explain the formation of precursors and the appearance of onion-like structure. It is believed that the formation of microsphere is due to the deposition and growth of BO species during the flow process of nanosphere. In addition, the effect of the addition of BNMS on the thermal conductivity of epoxy resin (EP) composites was investigated.