Design of Highly Dense Boron Nitride by the Combination of Spray-Pyrolysis of Borazine and Additive-Free Sintering of Derived Ultrafine Powders

Ultrafine boron nitride (B 1.0 N 0.9 ) powders have been prepared by the spray-pyrolysis of borazine and then used to explore their potentialities to form three-dimensional boron nitride (B 1.0 N ∼1.0 ) by additive-free conventional sintering. Complete characterization of the B 1.0 N 0.9 powders by SEM, HRTEM, X-ray diffraction (XRD), infrared spectroscopy (FTIR), and Raman demonstrated that samples form elementary blocks containing slightly agglomerated nanocrystalline particles with sizes ranging from 55 to 120 nm. On the basis of the BET specific surface area (SSA; 34.6 ± 0.7 m 2 g −1 ) and the helium density of powders ( d = 1.95 ± 0.02 g cm −3 ), an average particle size (APS) of 89 nm has been calculated. Ultrafine B 1.0 N 0.9 powders were successfully used to design microstructured disk-shaped boron nitride materials with a very high relative density (96.3%), a homogeneous microstructure, and an average hardness throughout the cross-section of 8 HV (78 MPa) at a temperature (1840 °C) lower than those currently applied to sinter boron nitride with sintering additives. Sintering resulted in the orderly arrangement of the boron nitride platelets parallel to the pressing direction.