Abstract
For over 40 years, measurements of the nucleation rates in a large number of silicate glasses have indicated a breakdown in the Classical Nucleation Theory at 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. Many explanations have been offered to explain this anomaly, but none have provided a satisfactory answer. We present an experimental approach to demonstrate explicitly for the example of a 5BaO ∙ 8SiO2 glass that the anomaly is not a real phenomenon, but instead an artifact arising from an insufficient heating time at low temperatures. Heating times much longer than previously used at a temperature 50 K below the peak nucleation rate temperature give results that are consistent with the predictions of the Classical Nucleation Theory. These results raise the question of whether the claimed anomaly is also an artifact in other glasses.
Highlights
For over 40 years, measurements of the nucleation rates in a large number of silicate glasses have indicated a breakdown in the Classical Nucleation Theory at temperatures below that of the peak nucleation rate
The new experimental data for 5BaO ∙ 8SiO2 instead show that the critical work of cluster formation monotonically decreases with decreasing temperature, following the trend expected from the Classical Nucleation Theory
The data confirm the suggestion by Cassar et al.[20] that the nucleation anomaly at low temperatures is not a real phenomenon in all silicate glasses, but is rather an experimental artifact, at least in this 5BaO ∙ 8SiO2 glass, due to the short nucleation times used in earlier studies
Summary
For over 40 years, measurements of the nucleation rates in a large number of silicate glasses have indicated a breakdown in the Classical Nucleation Theory at temperatures below that of the peak nucleation rate. Heating times much longer than previously used at a temperature 50 K below the peak nucleation rate temperature give results that are consistent with the predictions of the Classical Nucleation Theory These results raise the question of whether the claimed anomaly is an artifact in other glasses. The new experimental data for 5BaO ∙ 8SiO2 instead show that the critical work of cluster formation monotonically decreases with decreasing temperature, following the trend expected from the Classical Nucleation Theory. The data confirm the suggestion by Cassar et al.[20] that the nucleation anomaly at low temperatures is not a real phenomenon in all silicate glasses, but is rather an experimental artifact, at least in this 5BaO ∙ 8SiO2 glass, due to the short nucleation times used in earlier studies
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