Preparation and dielectric properties of Si_3N_4/SiCw composite ceramic

摘要

Gelcasting was employed to fabricate Si_3N_4/SiC whisker (SiCw) composite ceramics, and the effects of heat-treatment temperature on the length-to-diameter ratio of the whiskers and SiCw content on microwave dielectric properties were studied. Compared with pure SiCw of spherical structure obtained at temperature of 1,750 ℃(Ar), pure SiCw treated at 1,600 ℃(Ar) showed rod-like structure, higher dielectric properties and more evenly distribution in Si_3N_4/SiCw composite ceramics. Both the real (ε') and imaginary (ε") permittivity of Si_3N_4/SiC whisker (SiCw) composite ceramics decreased with increasing frequency and increased as the whisker content raised owing to the interface and SiCw playing a role of dipole in the frequency range of 8.2-12.4 GHz. In addition, comparing the ceramics with lower content of SiCw, the reflectivity of the composite ceramics moved to a lower frequency; the maximum absorption peak reached -22.4 dB at the whisker content of 15 wt%.