Characterization of ceria and yttria co-doped zirconia/alumina composites crystallized in supercritical methanol

Softly agglomerated CeO₂ and Y₂O₃ co-doped zirconia powders ((Ce, Y)-ZrO₂) were fabricated by crystallizing amorphous gels of the mixtures of end members and intermediate compositions along with the tie-lines joining 12 mol% CeO₂-doped ZrO₂ (12Ce-ZrO₂) to 2 mol% Y₂O₃-doped ZrO₂ (2Y-ZrO₂) in supercritical methanol at 250°C for 5 h before supercritical drying. (10.8 Ce, 0.2 Y)-TZP was dispersed with 0-30 mol% Al₂O₃ particles by crystallizing mixed gels in supercritical methanol and supercritical drying. Ceria and yttria co-doped zirconia and alumina composites containing less than 10 mol% Al₂O₃ could be sintered to almost full theoretical density at low temperature around 1200°C. The addition of Al₂O₃ depressed the grain growth of zirconia during sintering and improved the thermal stability of tetragonal zirconia in moist atmosphere, but degraded the sinterability. Consequently, the composites (10.8 Ce, 0.2 Y)-TZP/5∼10 mol% Al₂O₃ sintered at 1300°C for 5 h possessed excellent fracture strength, fracture toughness and thermal stability of the tetragonal phase in moist atmosphere.