Preparation and Dielectric Properties of Si3N4/BN(CB) Composite Ceramic

Si3N4/nano-carbon black (CB) composite ceramics with boron nitride (BN) as interphase were fabricated by gelcasting. The results of scanning electron microscopy (SEM) and X-ray diffraction (XRD) showed that the structures of BN interphase and BN coated CB were formed and were uniform distributed in the Si3N4 ceramic. The permittivity (ε′ε″) of BN-coated CB was obviously lower than that of the pure CB, and the impedance of the BN-coated CB particles was close to the Z0 (Z0 = 1, Z0 is impedance under vacuum) compared with that of the CB particles; therefore, electromagnetic wave can enter into the BN-coated CB particles and be dissipated due to the high conductivity of CB particles. When incorporating the BN(CB) into Si3N4 substrate, the electromagnetic wave can pass through Si3N4/nano-CB composite ceramics easily and be absorbed by CB, so the tgδ of the composite ceramic increased as the mass content of BN(CB) increased. The tgδ of the composite ceramic was about 0.43 when the content of BN(CB) increased to 15 wt%