Effect of K2O:Al2O3 Ratio on Crystallization Phenomena and Microstructure of Lithium Silicate Glass-Ceramics

Abstract

K2O plays an important role as glass modifier in glass systems. In the present study,the effect of K2O:Al2O3 ratio on crystallization and microstructural evolution in Li2O-SiO2- K2O-MgO-Al2O3-ZnO-ZrO2-P2O5 glass system has been reported. K2O mol% has been varied from 1 to 3 mol% while keeping Al2O3 at 2 mol%. The glass structure was analyzed by MAS-NMR spectroscopy. Heat treated glass systems were studied by using XRD, SEM and DTA to analyse the sintering and crystallization behavior. Increased amount of K2O modified the role of Al2O3, which acted as glass network former and formed [AlO4/2] tetrahedron unit, which eventually polymerized the glass structure. Consequently, lithium disilicate (LS2) crystallization was suppressed and crystallization of lithium metasilicate (LS) was promoted. As a result, while in the sample with 1 mol% K2O LS2 appeared as the main crystalline phase and LS as minor phase, 3 mol% K2O samples did not show any lithium disilicate throughout the sintering temperature range. The K2O:Al2O3 ratio did not have a significant impact on densification of these glass-ceramics. GRAPHICAL ABSTRACT