High-strength and low-dielectric porous Si₃N₄ ceramics prepared by gelcasting using DMAA

Herein, porous Si₃N₄ ceramics embracing excellent mechanical and dielectric properties were achieved via gelcasting using N, N-dimethylacrylamide (DMAA) gel system while acting as pore-former. The increase of monomer content (8.0–23.0 wt%) led to an increase in porosity (39.53–43.60%) and pore connectivity, which accelerated vapor phase mass transport and promoted β-Si₃N₄ grain growth, thereby improving flexural strength (212.33–245.30 MPa) and fracture toughness (3.60–3.89 MPa·m^1/2). Attributable to the pores introduced by increasing monomer content, the ε′ and tanδ were significantly reduced with the values of 4.18–4.29 to 3.95–4.06 and 1.83–2.38 × 10⁻³ to 0.37–1.96 × 10⁻³, respectively, demonstrating excellent microwave-transparent properties. This work proved the great application potential of porous Si₃N₄ ceramics fabricated by gelcasting employing DMAA gel system in the field of microwave-transparent materials.