Controlled precipitation of lithium disilicate (Li2Si2O5) and lithium niobate (LiNbO3) or lithium tantalate (LiTaO3) in glass-ceramics

In the present study, the crystallization principles and phenomena of base glasses from the system of SiO₂-Li₂O-P₂O₅-Al₂O₃-K₂O-Nb₂O₅ or Ta₂O₅ were investigated. Annealing parameters such as temperature and time were varied. Annealing the base glasses 10 min at temperatures <850 °C for Nb₂O₅ or Ta₂O₅ containing samples lead to the crystallization of Li₂SiO₃. At higher annealing temperatures or longer annealing times, Li₂SiO₃ disappeared and Li₂Si₂O₅ was the main crystal phase in all glass-ceramics. After the dissolution of Li₂SiO₃, the minor crystal phases of LiNbO₃ or LiTaO₃ were precipitated. Increasing the annealing temperatures as well as the annealing times lead to higher bending strengths up to about 676 MPa and CR-values of up to 100. Increasing the contents of Nb₂O₅ or Ta₂O₅ lead to higher CR-values. The radiopacities increased up to 355% compared to aluminum.