The role of P2O5, TiO2 and ZrO2 as nucleating agents on microstructure and crystallization behaviour of lithium disilicate-based glass

The aim of this study was to investigate the effects of different nucleating agents (P2O5, TiO2 and ZrO2) on the crystallization behaviour and the properties of a parent glass with composition 23.7 Li2O–2.63 K2O–2.63 Al2O3–71.78 SiO2 (mol%) and SiO2/Li2O molar ratio far beyond that of stoichiometric lithium disilicate (LD, Li2Si2O5). The scanning electron microscopy examination of the as-cast non-annealed glasses revealed the occurrence of liquid–liquid phase separation for all the compositions. P2O5 revealed to be effective in promoting bulk crystallization of LD, while TiO2 and ZrO2 led to surface crystallization. Moreover, ZrO2 enhances the glass polymerization and shifts Tp to higher temperatures, hindering crystallization. At 900 °C, TiO2-containing glasses feature LD and lithium metasilicate (LMS, Li2SiO3), while P2O5- and ZrO2-containing ones present monophasic LD and LMS glass–ceramics, respectively.