The effects of sintering temperature and duration on the flexural strength and grain size of zirconia.

Objective: This study investigated the effect of different sintering temperatures and times on the flexural strength and grain size of zirconia. Material and methods: Zirconia specimens (In-Coris ZI, In-Coris TZI, 120 samples) were prepared in a partially sintered state. Subsequently, the specimens were randomly divided into three groups and sintered at different final sintering temperatures and for various durations: 1510 °C for 120 min, 1540 °C for 25 min and 1580 °C for 10 min. Three-point flexural strength (for 120 samples, 20 samples per group) was measured according to the ISO 6872: 2008 standards. The grain sizes were imaged by scanning electron microscopy (SEM) and the phase transitions were determined by X-ray diffraction (XRD). The data were analyzed using one-way ANOVA and Duncan tests (p < 0.05). Results: The highest flexural strength was observed in ZI and TZI samples sintered at 1580 °C for 10 min. The differences between the ZI samples sintered at 1510 °C for 120 min and those sintered at 1540 °C for 25 min were statistically insignificant. Also, TZI samples sintered at 1510 °C for 120 min and those sintered at 1540 °C for 25 min also did not show any statistically significant differences. There were no visible differences in the grain sizes between the ZI and TZI specimens. The XRD patterns indicated similar crystalline structure for both materials subjected to the three different procedures. Conclusions: The results of this study showed that experimented high sintering temperature and short sintering time combination increases the flexural strength of zirconia.