TABLE OF CONTENTS Thermal analysis methods are used for determination of a number of important properties of glasses. The glass transformation and fictive temperatures of glasses, discussed in Chapter 7, are commonly measured using a differential scanning calorimeter ( DSC). Crystallization kinetics can be measured by a number of different methods, but the fastest and most commonly used methods rely on various techniques using the DSC. The determination of nucleation rate versus temperature curves can also be carried out using a DSC. Access to a DSC has become a requirement for any glass science laboratory.
The differential scanning calorimeter evolved from an older instrument known as a differential thermal analyzer, or DTA. The DTA, which is based on the work of Le Chatelier in 1887, was developed in 1899 for identification of specific types of clays, which are difficult to differentiate by more traditional methods. The concept of the DTA is quite simple. A differential thermocouple, which consists of two otherwise identical thermocouples connected in opposing polarities, is placed in a furnace in a position which allows the bead of one thermocouple to be inserted into an inert reference material, while the bead of the other thermocouple is inserted into the sample. The difference in temperature between the reference and sample materials is obtained directly as a function of temperature as the entire assembly is heated at a controlled, usually linear, rate. In the absence of any thermal difference between the sample and reference material, the...
