NEW Y-TZP POWDERS FOR MEDICAL GRADE ZIRCONIA

There is interest in using zirconia for biomedical applications as bal l heads for total hip prostheses. Two potential types are under discus sion: partially stabilized zirconia (PSZ) and tetragonal zirconia poly crystals (TZP) materials. Because of its enhanced material properties, TZP stabilized with yttria is favourable. To eliminate high amounts o f natural radioactive impurities, the precursors are purified. The kin d of precursor and purification method determine the powder impurity l evel. The disadvantage of Y-TZP is that the hydrothermal decomposition reaction method is that it depends very strongly on the grain size an d the distribution of the stabilizing yttria within the zirconia grain s. Thermodynamical and kinetic investigations on high purity coprecipi tated and yttria-coated zirconia powders show different behaviours. Y- TZP materials based on yttria-coated zirconia powders show excellent m echanical strength of more than 1000 MPa, a Weibull modulus of up to 2 0 and a fracture toughness of 9 MPa root m. The material properties of Y-TZP ceramics based on coprecipitated powders and prepared under the same conditions are less attractive. It is expected that materials ba sed on yttria-coated zirconia will show enhanced properties compared t o materials derived from coprecipitated powders. Therefore Y-TZP mater ials derived from yttria-coated powders are very attractive as medical grade zirconia.