| This study was undertaken with the goal of comparing the calculated nucleation rate for phase separation with experimental measurements for a simple glass system. The magnitude and the temperature dependence of the nucleation rate for a sodium silicate glass composition in the binodal regime was calculated. These calculations used a minimum of assumptions in order to determine the limits on certain thermodynamic variables, chiefly surface energy. Many of the values used in these calculations were determined from growth and coarsening measurements made on this system. Nucleation rates, as well as growth and coarsening rates, were then measured in this system for this comparison to theory.;It was found that the free energy of mixing models are unable to predict nucleation behavior at temperatures near the immiscibility boundary. In addition, these models predict that the nucleating composition lies outside of the binodal. Although the values measured for the activation energy correspond well to those in the literature, their incorporation into the nucleation expression does not correct for the temperature behavior of the free energy of mixing. It is also unlikely that a temperature dependent surface energy term could account for the poor predictive nature of classical nucleation theory at small undercoolings. |
