Crystal growth in a multicomponent lithia aluminosilicate glass

An industrially melted glass with complex composition in the Li2O–Al2O3–SiO2 system was annealed at temperatures in the range from 700 to 1000 °C. At temperatures up to 825 °C, a β-quartz solid solution crystallized, while at higher annealing temperatures keatite was formed. Up to an annealing temperature of 850 °C, the samples were transparent. During annealing at 750 °C, the concentration of the formed β-quartz crystals increased up to a value of 80 wt%, however, the number of crystals remained constant (within the limits of error) for annealing times from 4 to 120 h. Within that period of time, a slight increase in the mean crystallite size (from 16 to 22 nm) was observed, while the lattice parameter (a-axis) decreased. As shown by Rietveld refinement, during annealing, the SiO2-concentration of the crystals increased continuously, and the β-quartz solid solution was depleted in Li2O, MgO and Al2O3. During crystallization, the viscosity of the glass phase increased which decelerated further crystal growth. Finally, the crystallization was frozen in.