The Low-Temperature Nucleation Rate Anomaly in Silicate Glasses is an Artifact.

Over the past 40 years measurements of the nucleation rates in a large number of silicate glasses have indicated a breakdown in the widely used Classical Nucleation Theory (CNT) for temperatures below that of the peak nucleation rate. The data show that instead of steadily decreasing with decreasing temperature, the work of critical cluster formation enters a plateau, and even starts to increase. While many explanations have been offered to explain this anomaly, none have provided a satisfactory answer. We present the first experimental results that demonstrate that the anomaly is not real, but is instead an artifact arising from an insufficient annealing time at the low temperatures. The time-dependent nucleation rate was measured in a 5BaO.8SiO2 glass at a temperature 50 K below the peak nucleation rate temperature for a time many times longer than any previous measurement time for a silicate glass. The new data give results that are consistent with the predictions of the CNT. Since the artifact has been widely observed in many silicate glasses, these results indicate that much of the existing nucleation rate data at low temperatures are incorrect.