Dielectric properties and thermal conductivity of Si3N4–SiC composite ceramics

In this work, Si3N4–SiC composite ceramics were prepared by hot pressing sintering with Y2O3–MgO–Al2O3 as sintering additives in a flowing nitrogen atmosphere. The crystal structure and microstructure of Si3N4–SiC specimens with different SiC content were studied. The XRD results show that the peaks of β-Si3N4 and SiC were displayed and matched well on XRD patterns. Si3N4 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 Si3N4–SiC ceramics were researched. The dielectric constant first decreased then increased with the increase of SiC content, while the trend of dielectric loss (tgδ) was opposite. The dielectric constant of Si3N4–SiC composites for 35 wt% SiC reached a minimum range of 13–20 and tgδ values reached a maximum range of 0.72–0.96 in the frequency of 75–110 GHz. Meanwhile, the thermal conductivity of Si3N4–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 Si3N4–SiC ceramics for 35 wt% SiC content was 36.022 W/(m K). The Si3N4–SiC composite ceramics were expected to be applied as microwave absorbing materials.