Differential scanning calorimetry thermodynamic principles

In previous chapters, the principles and applications of differential scanning calorimetry (DSC) have been outlined, and it should be clear that the technique is both versatile and extremely sensitive. Using DSC, it is possible to analyze a wide range of systems quickly and cheaply so that thermodynamic parameters may be obtained. These qualities have led to the widespread use of DSC for not only pure research but also for routine thermal analysis. DSC does, however, have some drawbacks. To achieve good thermal contact with a sample, most DSC instruments are equipped with a pair of sample holders into which prepared sample and reference materials are placed. These materials are usually encapsulated in crimped aluminum ampoules, a typical sample mass being 5 to 10 mg. Such a small mass of sample contributes... 

Both differential thermal analysis (DTA) and differential. scanning calorimetry (DSC) are concerned with the measurement of energy changes, and as such are applicable in principle to a wider range of processes than TG. From a practical standpoint DSC may be regarded as the method from which quantitative data are most easily obtained. The use of DSC to determine absolute thermodynamic quantities is discussed in Sections 26.2.3.2 and 26.2.4.1. Types of processes amenable to study by these methods are summarized in Table 2. 

While in DTA (differential thermal analy ) the difference in temperature between sample and reference is detected for a given heat input, making it possible to determine phase transition temperatures very accurately, it is appropriate for thermodynamic analysis to work isothermally and to measure the energy input (e.g. electric current), necessary to keep the temperatures between sample and reference the same. This is the measurement principle of DSC (differential scanning calorimetry). 

Practically, the technique utilizes the principle of differential heat flux calorimetry, with which it is possible to operate under four thermodynamic situations where the perfectly controlled variation (or perturbation) of one of the three state variables (p, V, or T) is simultaneously recorded with the thermal effect resulting from the generated perturbation of the system under investigation. The principle of scanning transitiometry [23] offers the possibility to scan, in the measuring calorimetric cell, one of the three independent thermodynamic variables (p, V, or T)... 

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