A lightweight CNWs-SiO₂/3Al₂O₃·2SiO₂ porous ceramic with excellent microwave absorption and thermal insulation properties

To obtain excellent microwave absorption and thermal insulation properties, carbon nanowires reinforced SiO₂/3Al₂O₃·2SiO₂ composite ceramics (CNWs-SiO₂/3Al₂O₃·2SiO₂) were fabricated by catalytic chemical vapor deposition (CCVD) using C₂H₄ as the carbon source. The content of CNWs in SiO₂/3Al₂O₃·2SiO₂ porous ceramics can be adjusted by controlling the concentration of the catalyst precursor and the CCVD time. A higher concentration of catalyst precursor and longer CCVD time are beneficial for the growth of CNWs and for improving the electromagnetic wave (EMW) absorption properties of CNWs-SiO₂/3Al₂O₃·2SiO₂. However, CNWs are harmful to impendence matching due to the strong reflection and weak absorption when the content exceeds the threshold (30 wt%) in SiO₂/3Al₂O₃·2SiO₂ porous ceramics. CNWs are also harmful to the thermal insulation properties due to their high thermal conductivity. The results show that CNWs-SiO₂/3Al₂O₃·2SiO₂ can attain good EMW absorption and thermal insulation properties if the content of CNWs is 30 wt% when the concentration of the catalyst precursor is 3 wt% and the CCVD time is 15 min. The effective absorption bandwidth (EAB) can cover from 8.2 to 12.4 GHz (the whole X-band), and the minimum reflection coefficient (RC_min) is -31 dB at 9.1 GHz. The temperature gradient is 218 °C, which can satisfy the design requirement. Thus, the dielectric and thermal insulation properties are designable for CNWs reinforced SiO₂/3Al₂O₃·2SiO₂ porous ceramics to obtain excellent EMW absorption and thermal insulation properties.