Effect of manganese oxide on the sintered properties and low temperature degradation of Y-TZP ceramics

The sinterability of yttria-tetragonal zirconia polycrystals (Y-TZP) containing small amounts of MnO2 as sintering aid was investigated over the temperature range of 1250–1500 °C. Sintered samples were evaluated to determine bulk density, Youngʹs modulus, Vickers hardness and fracture toughness. In addition, the tetragonal phase stability of selected samples was evaluated by subjecting the samples to hydrothermal ageing in superheated steam at 180 °C/10 bar for up to 24 h. The results showed that the addition of MnO2, particularly ≥0.3 wt% was effective in aiding densification, improving the matrix stiffness and hardness when compared to the undoped Y-TZP sintered at temperatures below 1350 °C. On the other hand, the fracture toughness of Y-TZP was unaffected by MnO2 addition except for the 1 wt% MnO2-doped Y-TZP samples sintered above 1400 °C. The hydrothermal ageing resistance of Y-TZP was significantly improved with the additions of MnO2 in the Y-TZP matrix.