Synthesis of Mullite Whiskers and Their Application in Composites

Mullite whiskers were synthesized by a vapor‐solid reaction. Mullite composition xerogels were fired at 900° to 1600°C with AlF 3 in an airtight container. An average whisker increased in length from 7 μm at 1100°C to 10 μm at 1600°C, whereas an average whisker decreased in aspect ratio from 25 to 10 with increased firing temperature. The whiskers elongated to the c ‐axis and the side planes were the {110}. A clear lattice image corresponding to (110) lattice spacing up to the edges of the whiskers was observed with high‐resolution electron microscopy, and no droplet was observed on the tips of the whiskers. The chemical composition of the whiskers synthesized below 1100°C showed an apparent Al 2 O 3 ‐rich composition of about 72 mol%. Composites reinforced by 15 vol% of mullite whiskers in the matrix of 75 vol% mullite/25 vol% Y‐TZP enhanced the fracture toughness compared with those materials without mullite whiskers.