Porous SiC-Si2N2O-Si3N4 composite ceramics with excellent EMW absorption properties prepared by gelcasting and carbonthermal reduction

Porous SiC-Si2N2O-Si3N4 composite ceramics with excellent electromagnetic wave absorption properties were prepared by the combination of gelcasting and carbonthermal reduction, with the in-situ generated SiC by the reaction of PyC with SiO2 and Si3N4 as microwave absorbent and the Si2N2O fibers by the reaction of SiO2 with Si3N4 as reinforcing agent. The increase in monomer content within 5.94-20.79 wt% resulted in PyC and SiC formation, which seriously inhibited the alpha ->beta-Si3N4 phase transformation and beta-Si3N4 growth. Nevertheless, the bulk density, flexural strength and fracture toughness of porous SiC-Si2N2O-Si3N4 composite ceramics were significantly increased with the values of 1.84-2.48 g/cm(3), 115.66-220.50 MPa and 1.88-3.37 MPa m(1/2), respectively. The in-situ generated SiC effectively improved the electromagnetic wave absorption properties of porous SiC-Si2N2O-Si3N4 ceramics with reflection loss of -41.01 dB at 12.34 GHz and 2.0 mm thickness, accompanied with the effective absorption bandwidth of 10.55-12.40 GHz, demonstrating broad application prospects on electromagnetic wave absorption fields. (C) 2021 Elsevier B.V. All rights reserved.