Synthesis of (h-BN)/SiO2 core-shell powder for improved self-lubricating ceramic composites

An easy and effective preparation method has been achieved for the fabrication of core-shell-structure (h-BN)/SiO2 composite powders. Ammonium hydroxide (NH4OH) was used as a catalyst. Silica (SiO2, similar to 50-100 nm) was coated on the surface of lamellar hexagonal boron nitride (h-BN, similar to 5-10 mu m) particles via hydrolysis and condensation reaction of tetraethylorthosilicate (TEOS). The resulting composite powders were characterized using XRD (X-ray diffraction), SEM (Scanning electron microscopy), EDS (Energy-dispersive X-ray spectroscopy) and TEM (Transmission electron microscopy). A completely compact and uniform SiO2 coating binds tightly to h-BN particles. In addition, the effects of the reaction temperature and molar ratio of H2O and NH4OH between TEOS on the coating results are studied. The coating processes of the composite powders reveal that SiO2 nucleates and grows first on the surface of h-BN particles. By adding (h-BN)/SiO2 instead of h-BN as a solid-lubricant to Al2O3/TiC, the resulting microstructure, fracture-toughness and flexural strength of the composite are noticeably improved. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.