This work proposes three different glass formula derived from the SiO2-Li2O-K2O-Al2O3 system to investigate the effect of glass compositions on their crystal formation and mechanical properties. Glass LD_1 was SiO2-Li2O-K2O-Al2O3 system with adding P2O5 and CaF2 as nucleating agents. In Glass LD_2, a few amount of MgO was mixed to improve the viscosity of the glass. Finally, an important factor of Si:Li ratio was increased in Glass LD_3. Glass batches were melted at 1500°C and cast into a graphite mold which was annealed at 400-500°C before heat treatment at 700, 750, 800 and 850°C.
XRD results can be indexed Li2Si2O5, Li2SiO3, Ca5(PO4)3F and SiO2 as an early crystallization when heat treated at 700°C. After heat treatment at 750-850°C, the intensity of SiO2 disappeared and the peaks associated to Li3PO4 appeared; meanwhile, Li2Si2O5 increased in intensity. Adding MgO resulted in decreasing the viscosity of the glass with no significant effects on the formation of lithium disilicate. By increasing Si:Li ratio, the peak of SiO2 more obviously observed. SEM results revealed the development of microstructure from plate-like to interlocking rod-shaped crystals in all glasses. The highest indentation fracture toughness and biaxial flexural strength found in all glass ceramics heat treatment at 800°C because the finest microstructure observed at this temperature, except LD_3 heat treated at 850°C, which obtained the finest microstructure. LD_1 heat treated at 850°C presented the best chemical solubility 59 μg/cm2.
Effect of increasing the Al2O3 content on the phase formation and mechanical properties of lithium disilicate glass-ceramics
