Mechanical and dielectric properties of porous Si3N4 ceramics prepared by modified water-based gel casting

Abstract

Porous Si₃N₄ ceramics were prepared using the low-toxicity monomer HEMA (2-hydroxyethyl methacrylate) via a modified gel casting method. The rheological properties of Si₃N₄ slurries were investigated. Triethanolamine with high activity was used as a catalyst and modifier for gelation reactions, effectively improving the curing rate and suppressing the inherent surface oxygen inhibition in such process systems. With an increase in solid loading of the slurry, the drying shrinkage (12.3% to 5.4%) significantly decreased, while the green body density (44.0%–49.0%) and flexural strength (9.65–16.46 MPa) increased, demonstrating an excellent mechanical strength. After sintering at 1700°C, the porous Si₃N₄ ceramics prepared with 24–36 vol% solid loading slurry exhibited a flexural strength of 144.39–193.66 MPa and a porosity of 55.8% to 49.0%. The dielectric constant and loss tangent at 30 GHz ranged from 2.88 to 3.38 and 1.17–1.56 × 10⁻³, respectively. These ceramics show promising potential applications in high-performance structural ceramics and high-temperature wave-transparent materials.