Enhanced electrical resistivity in SiC-BN composites with highly-active BN nanoparticles synthesized via chemical route

In order to fabricate SiC-BN composites with enhanced electrical resistivity, boric acid and urea were used as reactants for synthesizing nano-sized BN particles on the surfaces of SiC powders in flowing ammonia atmosphere. The composites containing 10 wt% BN were pressureless densified at 2150 degrees C for 1 h with B4C and C as sintering additives. The chemical route was advantageous for obtaining finer BN dispersoids and microstructures of higher homogeneity, which significantly enlarged the SiC/BN interdiffusion area. Consequently, the concentrations of dissolved B and N in SiC grains became more equivalent and the carrier concentration was further decreased through impurity compensation mechanism. The chemically processed composite exhibited a considerably high electrical resistivity (1.03 x 10(12) Omega(12) cm), which was similar to 15 times higher than that of the composite prepared by conventional powder mixing method. Besides, considerably low dielectric constant (13.88) and loss tangent (0.128) at 1 MHz, as well as good thermal conductivity (70.08W m(-1) K-1) were also achieved. (C) 2014 Elsevier Ltd. All rights reserved.