Nonstoichiometric crystallization of lithium metasilicate–calcium metasilicate glasses. Part 1 — Crystal nucleation and growth rates

The initial stages of the crystallization kinetics of lithium metasilicate (LS) in glasses of the Li2O·SiO2–CaO·SiO2 join – which has a simple eutectic – was investigated at high undercoolings, somewhat above the glass transition temperatures. Calcium metasilicate crystals precipitate and grow only in the advanced stages of crystallization. The variation of glass composition from the eutectic (26.5 mol% Li2O) towards lithium metasilicate (50 mol% Li2O) results in a sharp increase of the internal nucleation rate of LS crystals, whereas the growth rates increase only weakly. This strong increase of the nucleation rate is primarily caused by a decrease of the thermodynamic barrier for nucleation – due to an increase of the thermodynamic driving force for crystallization and a decrease of the nucleus/liquid interfacial energy – as the glass composition approaches the crystal composition.