Synthesis of Porous Si 3 N 4 Ceramics with Rod‐Shaped Pore Structure

Porous Si 3 N 4 ceramics were synthesized by pressureless sintering of green compacts prepared using slip casting of slurries containing Si 3 N 4 , 5 wt% Y 2 O 3 +2 wt% Al 2 O 3 , and 0–60% organic whiskers composed of phenol–formaldehyde resin with solids loading up to 60 wt%. Rheological properties of slurries were optimized to achieve a high degree of dispersion with a high solid‐volume fraction. Samples were heated at 800°C in air and sintered at 1850°C in a N 2 atmosphere. Porosities ranging from 0% to 45% were obtained by the whisker contents (corresponding to 0–60 vol% whisker). Samples exhibited a uniform pore distribution. Their rod‐shaped pore morphology originated from burnout of whiskers, and an extremely dense Si 3 N 4 matrix.