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 α→β-Si₃N₄ phase transformation and β-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/cm³, 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.