Differential Thermal Analysis and Differential Scanning Calorimetry

Abstract Differential thermal analysis (DTA) and differential scanning calorimetry (DSC) are two closely related methods in which a material under investigation is typically subjected to a programmed temperature change and thermal effects in the material are observed. (Isothermal methods are also possible though they are less common.) The term “differential” indicates that the difference in behavior between the material under study and a supposedly inert reference material is examined. In this manner the temperature at which any event either absorbs or releases heat can be found. This allows the determination of, e.g., phase transition temperatures and the study of order‐disorder transitions and chemical reactions. Similarly, heat capacity measurements can be performed, although DTA and DSC differ significantly in the ease and precision of such measurements. These two methods are ideally suited for quality control, stability, and safety studies. Measurement of heat capacity can be performed by other methods and these are discussed. In DTA, the temperature difference between a substance and a reference material is measured as a function of temperature while the substance and reference material are subjected to a controlled temperature program. The record is the differential thermal, or DTA, curve; the temperature difference should be plotted on the ordinate with endothermic reactions downward and temperature or time on the abscissa increasing from left to right. The term “quantitative differential thermal analysis” (quantitative DTA) covers those uses of DTA where the equipment is designed to produce quantitative results in terms of energy and/or any other physical parameter. In DSC, the difference in energy inputs into a substance and a reference material is measured as a function of temperature while the substance and reference material are subjected to a controlled temperature program. Two modes, power compensation differential scanning calorimetry (power compensation DSC) and heat‐flux differential scanning calorimetry (heat‐flux DSC), can be distinguished, depending on the method of measurement used. These thermal analysis methods can be conducted simultaneously with other measurement methods to provide a greatly enhanced ability to understand material behavior. There is widespread confusion in the literature and elsewhere regarding the terms DTA and DSC that stems, in part, from how these methods developed and this is discussed.