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The 40 mol% CeO2-stabilized ZrO2 ceramic was synthesized by the sol-spray pyrolysis method and aged at 1400°C-1600°C. The effects of high-temperature aging on its fracture toughness were investigated after heat treatments at 1500°C for 6-150 h in air. Characterization results indicated that the activation energy for grain growth of 40 mol% CeO2-stabilized ZrO2 was 593 ± 47 kJ/mol. The average grain size of this ceramic varied from 1.4 to 5.6 μm within the aging condition of 1500°C for 6-150 h. The Ce-lean tetragonal phase has a constant tetragonality (ratio of the c-axis to a-axis of the crystal lattice) of 1.0178 during the aging process. It was found that the fracture toughness of 40 mol% CeO2-stabilized ZrO2 was determined to be 2.0 ± 0.1 MPa·m1/2, which did not vary significantly with prolonging aging time. Since no monoclinic zirconia was detected in the regions around the indentation crack-middle and crack-tip, the high fracture toughness maintained after high-temperature aging can be attributed to the remarkable stability of the tetragonal phase in 40 mol% CeO2-stabilized ZrO2 composition. [ABSTRACT FROM AUTHOR]

Powders of zirconia doped with 8 mol% REO1.5 ( RE = Yb, Y, Gd, and Nd) were synthesized by using the sol-spray pyrolysis method. The effects of RE3+ ionic radius on monoclinic (m) phase content of powders were investigated. The XRD results showed that the metastable tetragonal (t′) phase underwent a complete phase change to form m and cubic (c) phases after a heat treatment of 50-100 h at 1450°C. A cation size-dependent reduction in the m phase content of the REO1.5 partially stabilized ZrO2 powders was observed. The SEM- EDS analysis of the powders revealed that the RE3+ concentrations in the c phases decreased with decreasing the RE3+ ionic radius. These results indicate that the stabilizer concentration of the c phase can be attributed to RE3+ ionic radii, resulting in different m phase contents. Compared to the REO1.5 single doped ZrO2, the m phase contents of 8 mol% ( RE0.5Yb0.5)- ZrO2 ( RE = Y, Gd, and Nd) powders were significantly reduced. The results prove that the stabilizer with a lower RE3+ size is effective in reducing the m phase content of partially stabilized ZrO2 after annealing at high temperatures. [ABSTRACT FROM AUTHOR]