Synthesis and properties of lithium disilicate glass-ceramics in the system SiO2-Al2O3-K2O-Li2O

The purpose of this study was the synthesis of lithium disilicate glass-ceramics in the system SiO2-Al2O3-K2O-Li2O. A total of 8 compositions from three series were prepared. The starting glass compositions 1 and 2 were selected in the leucite-lithium disilicate system with leucite/lithium disilicate weight ratio of 50/50 and 25/75, respectively. Then, production of lithium disilicate glass-ceramics was attempted via solid-state reaction between Li2SiO3 (which was the main crystalline phase in compositions 1 and 2) and SiO2. In the second series of compositions, silica was added to fine glass powders of the compositions 1 and 2 (in weight ratio of 20/100 and 30/100) resulting in the modified compositions 1-20, 1-30, 2-20, and 2-30. In the third series of compositions, excess of silica, in the amount of 30 wt.% and 20 wt.% with respect to the parent compositions 1 and 2, was introduced directly into the glass batch. Specimens, sintered at 800 degrees C, 850 degrees C and 900 degrees C, were tested for density (Archimedes' method), Vickers hardness (H-V), flexural strength (3-point bending tests), and chemical durability. Field emission scanning electron microscopy and X-ray diffraction were employed for crystalline phase analysis of the glass-ceramics. Lithium disilicate precipitated as dominant crystalline phase in the crystallized modified compositions containing colloidal silica as well as in the glass-ceramics 3 and 4 after sintering at 850 degrees C and 900 degrees C. Self-glazed effect was observed in the glass-ceramics with compositions 3 and 4, whose 3-point bending strength and microhardness values were 165.3 (25.6) MPa and 201.4 (14.0) MPa, 5.27 (0.48) GPa and 5.34 (0.40) GPa, respectively. (c) 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved.