Compositional onset of homogeneous nucleation in (Li, Na) disilicate glasses

Crystal nucleation and growth rates in glasses of molar batch composition xNa2O · (1 − x)Li2O · 2SiO2 are determined by optical microscopy techniques and correlated to X-ray diffraction and parallel plate rheometry results. It is observed that glasses with x⩽0.3 have internal nucleation of lithium disilicate solid solution (LS2-ss) while glasses with x>0.3 have only surface crystallization. The steady state nucleation rate (I0), the induction time (tind) and also the crystal growth rate (U0) of LS2-ss in the volume are determined as a function of temperature and glass composition. An exchange of 30% of the total lithium ions by sodium results in a decrease of I0 by eight orders of magnitude, while only changes in tind and U0 within one logarithmic unit are observed. I0s are tested for the correlation between the reduced glass transition temperature, Trg and the ability to nucleate in the volume. It is demonstrated that Trg can be used to estimate volume nucleation rates in silicate glasses.