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

• SiC-Si 2 N 2 O-Si 3 N 4 composites were achieved by gelcasting and carbonthermal reduction. • DMAA-MBAM gel as carbon resource reacted with Si 3 N 4 and SiO 2 to form SiC in situ. • PyC and SiC inhibited α→β-Si 3 N 4 phase transformation and β-Si 3 N 4 growth. • In-situ generated Si 2 N 2 O enhanced mechanical properties with 115.66–220.50 MPa. • In-situ generated SiC improved absorption properties with RL of −41.01 dB. Porous SiC-Si 2 N 2 O-Si 3 N 4 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 SiO 2 and Si 3 N 4 as microwave absorbent and the Si 2 N 2 O fibers by the reaction of SiO 2 with Si 3 N 4 as reinforcing agent. The increase in monomer content within 5.94–20.79 wt% resulted in PyC and SiC formation, which seriously inhibited the α→β-Si 3 N 4 phase transformation and β-Si 3 N 4 growth. Nevertheless, the bulk density, flexural strength and fracture toughness of porous SiC-Si 2 N 2 O-Si 3 N 4 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-Si 2 N 2 O-Si 3 N 4 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.