Pressure-induced vapor synthesis, formation mechanism, and thermal stability of well-dispersed boron nitride spheres

Abstract

Boron nitride spheres (BNSs) are advantageous for application of composites due to the high filler loading, high flowability, and good composite processability. However, the existing methods synthesizing the BNSs still suffer from the problems of complicated procedures, low yield, high cost of the precursors, and poor dispersibility and roundness of the spheres. Here, we report a novel and simple method to prepare the BNSs. The BNSs were synthesized by heating BH3NH3 in a sealed vessel. Pressure increase arising from the evaporation and decomposition of BH3NH3 and temperature increase results in the formation of the spherical structure. The effects of reaction temperature, loading amount of BH3NH3 in the sealed vessel, and heating rate were systemically investigated for understanding the synthesis of BNSs. The BNSs with high dispersibility and roundness were achieved by heating the BH3NH3 in the sealed vessel at a low temperature of 200 °C. After further heat treatments at higher temperature (1300 °C) in N2 in open crucible, the spherical structure is retained, indicating BNSs have high thermal stability and the crystallinity could be greatly improved. The obtained BNSs are 0.6–1.2 μm in diameter with the (002) planes concentrically arranged and possess high oxidation resistance with the onset temperature at 895 °C. The conversion yield of BH3NH3 into the BNSs is over 80%.