Densification of hBN with the as-coated SiO₂ nanolayer by rotary chemical vapor deposition

SiO₂ nanolayer, less than 50 nm in thickness, was coated on hexagonal boron nitride (hBN) plate powders by rotary chemical vapor deposition (RCVD) to assist densification of sinter-hard hBN. In RCVD process, tetraethylorthosilicate (TEOS) precursor heated at 110°C was carried into a reactor by argon, and then reacted with oxygen to form SiO₂ at 700°C, with by-products of CO₂ or H₂O gases vacuumed out the reactor. Full expose of the surface of hBN powders to TEOS, argon and oxygen gases by RCVD technique and stable proceeding of decomposition reaction of TEOS contributed to the uniform distribution of SiO₂ nanolayer. Viscous or liquid flow of uniform SiO₂ nanolayer sintering aids assisted densification process of hBN and elevated its relative density to a maximum value of 96.2% at 1900°C.