Translucent zirconia polycrystals prepared from nanometric powders

The aim of the present study was investigation of synthesis and sinterability of nanometric zirconia solid solution powders containing 8mol% and 3mol% of Y2O3. The powders were prepared by the hydrothermal treatment of the co-precipitated gels, which resulted in very fine powders with particle sizes <10 nm. The main problem in application of such fine powders is their tendency to form hard agglomerates. To overcome this obstacle, the aqueous suspensions of the powders were subjected to the freeze drying. It resulted in the powders composed of very weak agglomerates which were broken under pressure as low as ~1MPa. The powder compacts were sintered in oxygen atmosphere to the state of closed porosity and then HIP-ed at 1300?C to fully dense ceramics. The spectrophotometric investigations in the wave length range of 190-1100 nm indicated higher translucency of the 8mol% Y2O3-ZrO2 than the 3mol% Y2O3-ZrO2 ceramics. Most probably it should be related to the birefringence phenomenon which occurs in the latter case due to the tetragonal symmetry of this material. In the polycrystal containing 8mol% of Y2O3 this phenomenon does not occur due to its cubic symmetry. The other two factors which lead to the decreased optical transparency of the material containing 3mol% Y2O3 are its smaller grain sizes and the presence of some amount of the monoclinic phase.