Nucleation time-lag from nucleation and growth experiments in deeply undercooled glass-forming liquids

A new approach is proposed to explain the strong difference between the induction periods (nucleation time-lags) obtained from nucleation rate measurements and from crystal growth experiments for lithium silicate glasses; and their similar magnitude for a Na2O · 2CaO · 3SiO2 glass. For these two glass families, the time-lags for nucleation estimated from crystal growth kinetics were compared with those directly obtained from nucleation experiments. A theoretical analysis was performed employing analytical solutions of the Frenkel–Zeldovich equation. In such analysis, the frequently assumed condition of size-independence of the thermodynamic properties of the crystallites was used. Provided this assumption is correct, time-lag data obtained in the two above mentioned ways should coincide. Consequently the significant difference between the values of nucleation time-lag for lithium silicate glasses from nucleation and growth data gives a strong indirect evidence for the deviation of the properties of critical nuclei from the respective parameters characterizing the state of the newly evolving macrophase. For Na2O · 2CaO · 3SiO2 glass at intermediate stages of crystallization we show that the average composition of the growing crystals is close to that of the near-critical nuclei. The fact that the nucleation and growth rates of this soda–lime–silica glass refer to the same phase provides an explanation for the similarity of the induction periods estimated from nucleation and growth experiments.