Boron Nitride Microspheres via Pyrolysis of Polymerized Precursors

Microspheric BN materials have high application potential because they have better fluidity and dispersion ability to endow hexagonal boron nitride (h-BN) ceramics and h-BN/polymer composites with highly desired performance. In this work, a novel synthetic route to the BN microspheres has been developed by means of a controllable pyrolysis of polymerized spherical precursors. The precursor formation mechanism is proposed to be the F-127-induced self-assembling polymerization of a boric acid-melamine-formaldehyde (MF) colloid. It is found that ammonia-annealing of an air-pyrolysis (700 degrees C) intermediate causes higher BN phase transformation within final BN microspheres with more uniform diameter distribution compared to those of direct ammonia-pyrolysis of spherical precursors at the same temperatures of 1100 and 1500 degrees C. After ammonia-annealing and ammonia-pyrolyzed treatment at 1100 and 1500 degrees C, the obtained BN microspheres have a low specific surface area (SSA) property, but replacing part of melamine with dicyandiamide could increase their SSAs to more than 1000 m2/g. We believe that this new microspherical BN preparation with more facile and controllable operation would be well suited for industrialization.