Dielectric and mechanical properties of hot-pressed SiCN/Si ₃N₄composites

A series of high temperature radar wave-absorbing materials, SiCN/Si ₃N₄ceramics, were prepared by hot-pressing. The nanometer SiCN powder, used as an absorber in the SiCN/Si₃N₄ceramic, was synthesized through laser pyrolysis of ((CH₃) ₃Si)₂NH) and NH₃. The dielectric and mechanical properties of the prepared ceramics were investigated. XRD and SAED were conducted to study the growth of crystals in the ceramics. The results showed that the transformation of Si₃N₄from α to β was inhibited. The growth of the rod-like β -Si₃N₄grains in SiCN/Si₃N₄ceramics was retarded during hot-pressing process due to the existence of the nanometer SiCN particles. The relative density and the strength of the composites both decreased with the increase of the SiCN content in the composites. The dielectric properties of the ceramics prepared at different temperatures were very different. For the samples sintered at 1600°C and 1700°C, both the real and imaginary parts of the complex permittivity of them increased as the content of SCN powder in the sample obviously. For the sample with same concentration of SCN, the real and imaginary parts of them varied with the sintering temperature. SAED pattern revealed that structure of the SiCN in SiCN/Si₃N₄sintered at 1800°C tended to crystallize fully. Its real, imaginary parts and dissipation factor were much lower than those sintered at 1600°C and 1700°C greatly.