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)-Z rO2) were fabricated by crystallizing amorphous gels of the mixtures o f end members and intermediate compositions along with the tie-lines j oining 12 mol% CeO2-doped ZrO2 (12Ce-ZrO2) to 2 mol% Y2O3-doped ZrO2 ( 2Y-ZrO2) in supercritical methanol at 250 degrees C for 5 h before sup ercritical drying. (10.8 Ce, 0.2 Y)-TZP was dispersed with 0-30 mol% A l2O3 particles by crystallizing mixed gels in supercritical methanol a nd supercritical drying. Ceria and yttria co-doped zirconia and alumin a composites containing less than 10 mol% Al2O3 could be sintered to a lmost full theoretical density at low temperature around 1200 degrees C. The addition of Al2O3 depressed the grain growth of zirconia during sintering and improved the thermal stability of tetragonal zirconia i n moist atmosphere, but degraded the sinterability. Consequently, the composites (10.8 Ce, 0.2 Y)-TZP/S similar to 10 mol% Al2O3 sintered at 1300 degrees C for 5 h possessed excellent fracture strength, fractur e toughness and thermal stability of the tetragonal phase in moist atm osphere. (C) 1998 Elsevier Science B.V.