Thermal stress, cooling-rate and fictive temperature of silicate melts

Sharon L Webb

doi:10.1007/s00410-021-01836-y

Abstract

The unknown cooling-rate history of natural silicate melts can be investigated using differential scanning heat capacity measurements together with the limiting fictive temperature analysis calculation. There are a range of processes occurring during cooling and re-heating of natural samples which influence the calculation of the limiting fictive temperature and, therefore, the calculated cooling-rate of the sample. These processes occur at the extremes of slow cooling and fast quenching. The annealing of a sample at a temperature below the glass transition temperature upon cooling results in the subsequent determination of cooling-rates which are up to orders of magnitude too low. In contrast, the internal stresses associated with the faster cooling of obsidian in air result in an added exothermic signal in the heat capacity trace which results in an overestimation of cooling-rate. To calculate cooling-rate of glass using the fictive temperature method, it is necessary to create a calibration curve determined using known cooling- and heating-rates. The calculated unknown cooling-rate of the sample is affected by the magnitude of mismatch between the original cooling-rate and the laboratory heating-rate when using the matched cooling-/heating-rate method to derive a fictive temperature/cooling-rate calibration curve. Cooling-rates slower than the laboratory heating-rate will be overestimated, while cooling-rates faster than the laboratory heating-rate are underestimated. Each of these sources of error in the calculation of cooling-rate of glass materials—annealing, stress release and matched cooling/heating-rate calibration—can affect the calculated cooling-rate by factor of 10 or more.

Highlights

The cooling-rate history of silicate melts can be investigated using differential scanning heat capacity measurements together with the fictive temperature analysis method of Tool (1946), Narayanaswamy (1971) and Moynihan et al (1976)
In the course of investigating the different heating and cooling effects on the limiting fictive temperature determined from the equal area method of analysing the heat capacity curve, we investigated the effect of annealing on the calculated limiting fictive temperate
The limiting fictive temperature of the container glass and the NIQ glass has been determined for matched coolingand heating-rates of 2, 5, 10, 15, 20, 25, 30 and 35 K min−1; and the false fictive temperature has been determined for a heating-rate of 20 K min−1 with unmatched cooling-rates

Summary

Introduction

The cooling-rate history of silicate melts can be investigated using differential scanning heat capacity measurements together with the fictive temperature analysis method of Tool (1946), Narayanaswamy (1971) and Moynihan et al (1976). Studies of the limiting fictive temperature and the coolingrate of synthetic and natural glasses using this method are increasingly found in the literature Synthetic silicate melts have been used in a number of studies to illustrate the robustness of this method of limiting fictive temperature determination. There are a number of studies which address the calculation of the limiting fictive temperature of micrometre sized hyper-quenched glasses. There is a problem in calculating the heat capacity of the glass due to the large exothermic enthalpy release at temperatures hundreds of degrees below the glass transition peak in the calorimetry data. The method of Yue et al (2002) overcomes the difficulty in determining the heat capacity of the glass upon the first heating by taking the data from the second heating together with Tg calculated from the intercept of the slopes of straight lines fitted to the glassy heat capacity and the rising peak of the second heating run

Methods

Results

Conclusion