Design and properties of ceramic–based microwave absorbing composites with carbon fibres as absorber

Abstract

To develop multifunctional microwave absorbing (MA) materials for modern military system, the technical potential of preparing ceramic–based MA composites with carbon fibres (CFs) as absorber was studied. Near–net–shape preparation of the composites was achieved by sintering the green bodies with 3.5 wt% of CaCO3 at 750 °C for 30 min followed by cooling at a rate of 18 °C/min, and the composites showed good CFs preservation owing to the prevention of CFs oxidation by the decomposition–derived CO2 from CaCO3 during sintering. As the CFs fraction increased from 0 wt% to 6.0 wt%, the composites remained essentially constant in density at 1.48–1.57 g/cm3, increased slightly in open porosity from 5.3% to 6.9%, increased in compressive strength from 54 MPa to 68 MPa, and showed the lowest mean reflection loss (RL) of –7.8 dB when the CFs fraction was 1.5 wt%. Double–layer design effectively improved the MA performance of the composites. The composites with the upper/lower–layer CFs fraction of 0.75 wt%/4.0 wt% had a mean RL of –14.7 dB, an effective absorption bandwidth of 9.2 GHz, and a minimum RL of –20.4 dB@13.2 GHz. The composites did not deteriorate in MA performance after annealing in air at 400 °C for 100 h, making them a promising MA material that is lightweight and temperature resistant up to 400 °C.