Effect of sintering time on the microstructure, flexural strength and translucency of lithium disilicate glass-ceramics

Abstract Glass-ceramics derived from the SiO 2 –Li 2 O–K 2 O–Al 2 O 3 –ZrO 2 –P 2 O 5 system were produced by a two-stage sintering cycle with a primary thermal treatment at 700 °C followed by a secondary thermal treatment at 900 °C. The periods during which the materials were subjected to each temperature level (700 °C/900 °C) were the following: A, 1 h/1 h; B, 2 h/2 h; C, 3 h/3 h; D, 4 h/4 h; E, 5 h/5 h; F, 6 h/6 h; and G, 8 h/8 h. The X-ray diffraction results revealed that all groups had a similar crystalline structure though the sintering times were different. The main crystalline phase corresponds to Li 2 Si 2 O 5 and the minor phases correspond to Li 2 SiO 3 and Li 3 PO 4 . Scanning electron microscopy analysis showed an interlocking microstructure of rod-shaped Li 2 Si 2 O 5 crystals in all specimens. However, the glass-ceramics produced with different sintering times showed different crystal sizes and spatial distribution. The glass-ceramic sintered during 5 h in each temperature level (700 °C/900 °C) showed the highest flexural strength (308 ± 25 MPa). The translucency parameters (TP) of the glass-ceramics studied were not affected by sintering time since similar TP values were observed in all specimens.