Synthesis of fibrous β-Si3N4 structured porous ceramics using carbothermal nitridation of silica

Abstract Porous Si 3 N 4 ceramics with a fibrous interlocking microstructure were synthesized directly by carbothermal nitridation (CT/N) of SiO 2 . Carbon black was used as the carbon source and α-Si 3 N 4 was used as seed. The cold-pressed samples of powder mixtures were heated at nitrogen pressures above 0.6 MPa and temperatures exceeding 1600 °C. The addition of the α-Si 3 N 4 to the initial powder mixtures had important effects on the microstructure and mechanical properties of the porous Si 3 N 4 . Fine elongated fibrous β-Si 3 N 4 grains were developed in the seeded samples with stoichiometric C–SiO 2 ratio and Y 2 O 3 as the sintering additive, when sintered at 1700–1750 °C. A sample of outstanding strength resulted, five times stronger than the seed-free samples. Such a technique offers the possibility of synthesizing highly porous and strong Si 3 N 4 materials at considerably lower cost than at present.