NB2O5 AND TA2O5 CODOPED ZIRCONIA

Orthorhombic zirconia codoped with 5 mol-% Nb2O5 and 5, 7, 1O, 12 and 15 mol-% Ta2O5 as well as samples with 5 mol-% Ta2O5 and 7, 1O, 12 and 15 mol-% Nb2O5, respectively, were made fi om precursors prepared by hydrolysis of the metalalkoxide solutions in I-propanol with water. Th e amorphous, coprecipitated hydroxides were converted to the oxides at 900 degrees C. The powders were characterized by the specific surface areas, the particle size distributions and by electron microscopy. Th e codoped zirconia powders were attributed isostatically compacted and sintered at temperatures ranging fi om 1500 to 1650 degrees C. Three- point bend-strengths, Weibull moduli, fracture toughnesses, Vickers ha rdnesses, densities and phase compositions were measured for the sinte red specimens. Average three-point bend-strengths ranged between 85 an d 257 MPa. No phase transformations occurred during fracture. Fractogr aphy showed that the fracture origins were either surface flaws or por es near the tensile surface. Depending on the composition and the sint ering conditions, fracture toughnesses between 2.1 and 3.6 MPa m(1/2), Vickers hardnesses between 6.8 and 9.9 GPa and theoretical densities between 96.8 and 99.0% were observed. Increasing dopant concentrations resulted in increases in the b- and c-axes and in a decrease in the a -axis of the orthorhombic cell.