Phase separation and crystallization in glasses of the lithium silicate system xLi2O · (100 − x)SiO2 (x = 23.4, 26.0, 33.5)

Abstract

The phase separation in ultimately homogenized glasses of the lithium silicate system xLi2O · (100 − x)SiO2 (where x = 23.4, 26.0, and 33.5 mol % Li2O) has been investigated. The glasses of these compositions have been homogenized using the previously established special temperature-time conditions, which provide the maximum dehydration and the removal of bubbles from the glass melt. The parameters of nucleation and growth of phase_separated inhomogeneities and homogeneous crystal nucleation have been determined. The absolute values of the stationary nucleation rates I st of lithium disilicate crystals in the 23.4Li2O · 76.6SiO2 and 26Li2O · 74SiO2 glasses with the compositions lying in the metastable phase separation region have been compared with the corresponding rates I st for the glass of the stoichiometric lithium disilicate composition. It has been established that the crystal growth rate have a tendency toward a monotonic increase with an increase in the temperature, whereas the dependences of the crystal growth rate on the time of low-temperature heat treatment exhibit an oscillatory behavior with a monotonic decrease in the absolute value of oscillations. The character of crystallization in glasses with the compositions lying in the phase separation region of the Li2O-SiO2 system is compared with that in the glass of the stoichiometric lithium disilicate composition. The inference has been made that the phase separation weakly affects the nucleation parameters of lithium disilicate and has a strong effect on the crystal growth.