Dielectric properties and thermal conductivity of Si 3 N 4 –SiC composite ceramics

In this work, Si 3 N 4 –SiC composite ceramics were prepared by hot pressing sintering with Y 2 O 3 –MgO–Al 2 O 3 as sintering additives in a flowing nitrogen atmosphere. The crystal structure and microstructure of Si 3 N 4 –SiC specimens with different SiC content were studied. The XRD results show that the peaks of β-Si 3 N 4 and SiC were displayed and matched well on XRD patterns. Si 3 N 4 particles were basically long rod-shaped. Besides, the effects of SiC content on thermal conductivity and dielectric properties in W band (75–110 GHz) of sintered Si 3 N 4 –SiC ceramics were researched. The dielectric constant first decreased then increased with the increase of SiC content, while the trend of dielectric loss (tg δ ) was opposite. The dielectric constant of Si 3 N 4 –SiC composites for 35 wt% SiC reached a minimum range of 13–20 and tg δ values reached a maximum range of 0.72–0.96 in the frequency of 75–110 GHz. Meanwhile, the thermal conductivity of Si 3 N 4 –SiC composites for 35 wt% SiC was 63.008 W/(m K) at room temperature. The variation of thermal conductivity as test temperature was also studied. The thermal conductivity decreased with increasing test temperature. When the test temperature was 300 °C, the thermal conductivity of the Si 3 N 4 –SiC ceramics for 35 wt% SiC content was 36.022 W/(m K). The Si 3 N 4 –SiC composite ceramics were expected to be applied as microwave absorbing materials.