V2O5, NB2O5 AND TA2O5 DOPED ZIRCONIA CERAMICS

V2O5, Nb2O5 and Ta2O5 doped zirconia ceramics were made from precursors prepared by hydrolysis of the respective metal alkoxide solutions in 1-propanol with water. The amorphous, coprecipitated hydroxides were calcined at 900-degrees-C Oxidic zirconia powders doped with 5 and 15 mol.% V2O5 as well as powders with 1, 2, 5, 7, 10, 12, 15, 17 and 20 moL % Nb2O5 and Ta2O5, respectively, were isostatically compacted and subjected to different sintering conditions. The powders were characterized by the specific surface areas, the particle size distributions and by electron microscopy. Powders calcined at 1400-degrees-C with more than 12 mol.% Nb2O5 and Ta2O5, respectively were found to be orthorhombic. Powders with lower contents of Nb2O5 and Ta2O5, consisted of mixtures of the monoclinic and the orthorhombic phase. Increases in the doping oxides led to increases in the b- and c-axes accompanied by a decrease in the a-axis. V2O5 doped powders and sintered samples were monoclinic. The powders doped with Nb2O5 or Ta2O5 were sintered at temperatures ranging from 1500 to 1650-degrees-C Three-point bend strengths, Weibull moduli, fracture toughnesses, Vickers hardnesses, densities and phase compositions were measured for the sintered specimens. Average three-point bend strengths for samples consisting of the pure orthorhombic phase ranged between 134 and 181 MPa, samples with both monoclinic and orthorhombic phases yielded lower bend strengths. Fracture toughnesses were around 3 MPa m1/2, Vickers hardnesses between 2.3 and 9.7 GPa. Theoretical densities between 96.8 and 99.7% were observed. No phase transformations occurred during fracture.