19. Thermal Properties and Thermal Analysis: Fundamentals, Experimental Techniques and Applications

The chapter provides a summary of the fundamental concepts that are needed to understand the heat capacity C_P, thermal conductivity κ, and thermal expansion coefficient α_L of materials. The C_P, κ, and α_L of various classes of materials, namely, semiconductors, polymers, and glasses, are reviewed, and various typical characteristics are summarized. A key concept in crystalline solids is the Debye theory of the heat capacity, which has been widely used for many decades for calculating the C_P of crystals. The thermal properties are interrelated through Grüneisen’s theorem. Various useful empirical rules for calculating C_P and κ have been used, some of which are summarized. Conventional differential scanning calorimetry (DSC) is a powerful and convenient thermal analysis technique that allows various important physical and chemical transformations, such as the glass transition, crystallization, oxidation, melting etc. to be studied. DSC can also be used to obtain information on the kinetics of the transformations, and some of these thermal analysis techniques are summarized. Temperature-modulated DSC, TMDSC, is a relatively recent innovation in which the sample temperature is ramped slowly and, at the same time, sinusoidally modulated. TMDSC has a number of distinct advantages compared with the conventional DSC since it measures the complex heat capacity. For example, the glass-transition temperature T_g measured by TMDSC has almost no dependence on the thermal history, and corresponds to an almost step life change in C_P.

The new Tzero DSC has an additional thermocouple to calibrate better for thermal lags inherent in the DSC measurement, and allows more accurate thermal analysis.