[Paper Review] The Low-Temperature Nucleation Rate Anomaly in Silicate Glasses is an Artifact

Xinsheng Xia, D. C. Van Hoesen+3 more|arXiv (Cornell University)|May 11, 2020

Glass properties and applications29 references4 citations

TL;DR

This study demonstrates that the long-reported low-temperature nucleation rate anomaly in silicate glasses—where nucleation rates plateau or increase below the peak rate temperature—is an experimental artifact caused by insufficient annealing time at low temperatures. By extending measurements in 5BaO·8SiO2 glass far beyond prior durations, the authors show nucleation rates follow Classical Nucleation Theory (CNT) predictions, invalidating the perceived anomaly and calling into question decades of prior low-temperature data.

ABSTRACT

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.

Motivation & Objective

• To resolve the long-standing discrepancy between experimental nucleation rates in silicate glasses and predictions of Classical Nucleation Theory (CNT) at low temperatures.
• To investigate whether the observed plateau or increase in nucleation rate at low temperatures is a real physical phenomenon or an artifact of experimental methodology.
• To test the hypothesis that insufficient annealing time leads to incomplete nucleation kinetics, distorting measured rates.
• To provide definitive experimental evidence that the anomaly is not intrinsic to the material but stems from kinetic limitations in prior experiments.

Proposed method

• Conducted time-resolved nucleation rate measurements in 5BaO·8SiO2 glass at a temperature 50 K below the peak nucleation rate temperature.
• Extended the measurement duration to times significantly longer than any prior study on silicate glasses, ensuring full kinetic equilibration.
• Used standard thermal analysis techniques to monitor nucleation onset and rate over extended periods.
• Compared the observed nucleation rate evolution with predictions from Classical Nucleation Theory (CNT) to assess consistency.
• Performed multiple replicate measurements to ensure statistical reliability and reproducibility of the extended-time data.
• Analyzed the time dependence of nucleation to distinguish between transient and steady-state behavior, identifying the onset of equilibrium kinetics.

Experimental results

Research questions

• RQ1 Is the observed plateau or increase in nucleation rate at low temperatures in silicate glasses a real physical phenomenon or an experimental artifact?
• RQ2 Does insufficient annealing time at low temperatures lead to incomplete nucleation kinetics and thus erroneous rate measurements?
• RQ3 To what extent do extended measurement times restore agreement with Classical Nucleation Theory (CNT) predictions?
• RQ4 Are the widely reported low-temperature nucleation anomalies in silicate glasses systematically biased due to inadequate data collection duration?
• RQ5 Can the apparent anomaly be fully explained by kinetic limitations rather than a breakdown of CNT?

Key findings

• The nucleation rate in 5BaO·8SiO2 glass decreases monotonically with decreasing temperature over extended annealing times, consistent with Classical Nucleation Theory (CNT).
• The previously reported anomaly—where nucleation rates plateau or increase at low temperatures—disappeared when measurements were extended beyond typical durations.
• The study demonstrates that prior data showing the anomaly were obtained under conditions where nucleation had not reached equilibrium, leading to systematic underestimation of the true rate decline.
• The artifact arises from insufficient time to allow full nucleation kinetics to manifest, particularly at low temperatures where nucleation is slow.
• The results imply that much of the existing low-temperature nucleation rate data for silicate glasses are incorrect due to inadequate measurement duration.
• The findings call for a re-evaluation of all prior nucleation rate data in silicate glasses obtained at low temperatures with short annealing times.