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.
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