IADR Abstract Archives
Optimized Speed-Sintering of Monolithic Zirconia Ceramics
Objectives: To evaluate the effect of different speed-sintering cooling rates on the phase composition, microstructure, optical and mechanical properties of monolithic zirconia.
Methods: Speed-sintered ZirCAD LT_1200 (Ivoclar) (total thermal cycle: 47 min; sintering time: 15 min; dwell temperature: 1480°C; oven-door opening and air-cooling: 1200°C) and Katana STML_800 (Kuraray Noritake) (90 min; 30 min; 1560°C; 800°C) were compared to speed-sintered ZirCAD LT_300 and Katana STML_300 with slowed cooling and oven-door opening at 300°C. Density was determined according to the Archimedes principle; chemical composition was determined using X-ray fluorescence (XRF); phase composition was characterized using X-ray diffraction (XRD); grain size was measured using scanning electron microscopy (SEM); translucency Parameter (TP) was measured with a spectrophotometer. Vickers hardness, indentation fracture toughness and biaxial strength (BS) were also assessed. Statistical analysis involved one-way ANOVA and post-hoc Tukey’s HSD test (α=0.05).
Results: Regardless of slowed cooling, ZirCAD LT and Katana STML revealed similar density (≈6.05 g/cm3 and 6.03 g/cm3, respectively), chemical composition and grain size (≈0.2 µm and 1.4 µm, respectively). Both 3Y-TZP Katana ZirCAD LT_800/300 zirconia were characterized with a lower cubic-phase content (≈4.8wt%), which resulted in a lower Y2O3 amount (≈3mol%) in the remaining tetragonal ZrO2 phases, as compared to the two 5Y-PSZ Katana STML_1200/300 zirconia (≈16.4wt% and ≈5.7mol% Y2O3, respectively). TP of both ZirCAD LT and Katana STML (TP≈23 and 27, respectively) was not affected by slowed cooling. While the optimum hardness of 3Y-TZP and 5Y-PSZ was reached, slowed-cooling significantly improved their fracture toughness. On the other hand, slowed-cooling significantly diminished flexural strength (549.5±135.8 MPa) and mechanical reliability (m=4.4) of Katana STML_300, while it did not have any effect on ZirCAD LT zirconia.
Conclusions: Fast cooling during speed-sintering can negatively influence strength and mechanical reliability of 5Y-PSZ zirconia ceramics. Further studies should focus on fine-tuning the speed-sintering protocol.
Methods: Speed-sintered ZirCAD LT_1200 (Ivoclar) (total thermal cycle: 47 min; sintering time: 15 min; dwell temperature: 1480°C; oven-door opening and air-cooling: 1200°C) and Katana STML_800 (Kuraray Noritake) (90 min; 30 min; 1560°C; 800°C) were compared to speed-sintered ZirCAD LT_300 and Katana STML_300 with slowed cooling and oven-door opening at 300°C. Density was determined according to the Archimedes principle; chemical composition was determined using X-ray fluorescence (XRF); phase composition was characterized using X-ray diffraction (XRD); grain size was measured using scanning electron microscopy (SEM); translucency Parameter (TP) was measured with a spectrophotometer. Vickers hardness, indentation fracture toughness and biaxial strength (BS) were also assessed. Statistical analysis involved one-way ANOVA and post-hoc Tukey’s HSD test (α=0.05).
Results: Regardless of slowed cooling, ZirCAD LT and Katana STML revealed similar density (≈6.05 g/cm3 and 6.03 g/cm3, respectively), chemical composition and grain size (≈0.2 µm and 1.4 µm, respectively). Both 3Y-TZP Katana ZirCAD LT_800/300 zirconia were characterized with a lower cubic-phase content (≈4.8wt%), which resulted in a lower Y2O3 amount (≈3mol%) in the remaining tetragonal ZrO2 phases, as compared to the two 5Y-PSZ Katana STML_1200/300 zirconia (≈16.4wt% and ≈5.7mol% Y2O3, respectively). TP of both ZirCAD LT and Katana STML (TP≈23 and 27, respectively) was not affected by slowed cooling. While the optimum hardness of 3Y-TZP and 5Y-PSZ was reached, slowed-cooling significantly improved their fracture toughness. On the other hand, slowed-cooling significantly diminished flexural strength (549.5±135.8 MPa) and mechanical reliability (m=4.4) of Katana STML_300, while it did not have any effect on ZirCAD LT zirconia.
Conclusions: Fast cooling during speed-sintering can negatively influence strength and mechanical reliability of 5Y-PSZ zirconia ceramics. Further studies should focus on fine-tuning the speed-sintering protocol.