Nanocrystallization of fresnoite glass. II. Analysis of homogeneous nucleation kinetics

We analyzed internal (homogeneous) nucleation rates in an almost stoichiometric fresnoite (2BaO · TiO2 · 2SiO2) glass using the classical nucleation theory (CNT) with experimental viscosity data and calculated thermodynamic quantities. Assuming, first, that the nucleus-melt surface energy is size and temperature-independent, σ ≡ σ∞, the CNT offered a good description of the temperature dependence of the steady-state nucleation rate Ist(T) over a wide temperature range, above and below Tg, but failed to predict the pre-exponential factor, confirming previous tests performed on other silicate glasses. The congruence between theory and experiment was restored with a (fitted) temperature-dependent σ. The main thermodynamic and kinetic parameters of the CNT were investigated to explain the extremely high nucleation rates measured in this glass: Imax ∼ 1016 m−3 s−1 (Tmax ≈ 740 °C, Tg ≈ 710 °C). The viscosity at Tmax was found to be quite close to that of other silicate glasses that display homogeneous nucleation, such as Na2O · 2CaO · 3SiO2 and 2Na2O · CaO · 3SiO2. Therefore, the lowest thermodynamic barrier for nucleation in fresnoite glass, as compared with other silicate glasses, is responsible for these high crystal nucleation rates.