Effect of structural relaxation on crystal nucleation in a soda-lime-silica glass

The influence of structural relaxation on crystal nucleation has been underexplored and remains elusive. This article discusses its possible effect on the nucleation process using a stoichiometric soda-lime-silica (2Na(2)O center dot CaO center dot 3SiO(2)) glass as a model system. We show that the relaxation effect is powerful at low temperatures, close and below the glass transition, Tg, and leads to a continuous increase in the nucleation rate. At any given temperature, the nucleation rate eventually reaches its ultimate steady-state corresponding to the fully relaxed supercooled liquid (SCL). However, the time to reach the steady-state is two to three orders of magnitude longer than the average relaxation time estimated by the Maxwell relation (shear viscosity / shear modulus). The proposed nucleation mechanism and model, which take relaxation into account, and related experimental results also explain the alleged breakdown of CNT at low temperatures reported for various glasses. It confirms a few recent papers that this apparent flaw is merely because most researchers did not prolong nucleation treatments enough to complete the relaxation process to achieve a steady state. Another remarkable result is that the actual maximum nucleation temperature, Tmax, is significantly lower than the previously reported values. Finally, a comparative analysis of the kinetic coefficient using viscosity versus growth velocity favors the last. These results for this soda-lime-silica glass extend and validate recent findings for lithium disilicate on the significant (but often neglected) effect of relaxation on crystal nucleation.

Automated summary

This article discusses the influence of structural relaxation on crystal nucleation process. It shows that structural relaxation has a significant impact on nucleation rate at low temperatures, leading to a continuous increase before reaching a steady state. The study also explains the alleged breakdown of CNT at low temperatures and reveals a significantly lower actual maximum nucleation temperature than previously reported values.