Instrument design differential thermal analysis

We shall describe the design and performance of multiple sample instruments for differential thermal analysis which do runs on several samples simultaneously The first of these is a five-sample DTA system that served as a basis for the DSC system. Following this is a description of the principles of operation of the isothermal boundaries that were formed as integral parts of the heating block and thermoelectric disk of a heat flow type multiple sample DSC cell. 

With Figs. 4.4 to 4.6, six different, commercial, advanced differential thermal analysis instruments are introduced. They were picked because of the change in design from instrument to instrument. This selection by no means covers all available commercial equipment. Only the most prominent types of... 

Figure 10.4 Differential scanning calorimetry (DSC) instrumentation design (a) heat flux DSC and (b) power compensation DSC. A, furnace B, separate heaters and C, sample and reference holders. (Reproduced with permission from E.L. Charsley and S.B. Warrington, Thermal Analysis Techniques and Applications, Royal Society of Chemistry, Cambridge, UK. 1992 Royal Society of Chemistry.)...

The term differential scanning calorimetry has become a source of confusion in thermal analysis. This confusion is understandable because at the present time there are several entirely different types of instruments that use the same name. These instruments are based on different designs, which are illustrated schematically in Figure 5.36 (157). In DTA. the temperature difference between the sample and reference materials is detected, Ts — Tx [a, 6, and c). In power-compensated DSC (/), the sample and reference materials are maintained isothermally by use of individual heaters. The parameter recorded is the difference in power inputs to the heaters, d /SQ /dt or dH/dt. If the sample is surrounded by a thermopile such as in the Tian-Calvet calorimeter, heat flux can be measured directly (e). The thermopiles surrounding the sample and reference material are connected in opposition (Calvet calorimeter). A simpler system, also the heat-flux type, is to measure the heat flux between the sample and reference materials (d). Hence, dqjdi is measured by having all the hot junctions in contact with the sample and all the cold junctions in contact with the reference material. Thus, there are at least three possible DSC systems, (d), (c), and (/), and three derived from DTA (a), [b), and (c), the last one also being found in DSC. Mackenzie (157) has stated that the Boersma system of DTA (c) should perhaps also be called a DSC system. 

The results of thermal analysis by differential scanning calorimetry (DSC) are influenced by various experimental parameters. Instruments designed and constructed by different manufacturers have distinct operating principles, but all instruments provide support for two crucibles of small volume in a single or a matched pair of furnaces that allow the temperature of the sample and a reference material to be subjected to a predefined temperature program. Various authors (Turi, 1981 Haines, 2002 Ehrenstein et al., 2004 Wunderlich, 2005 Brown and GaUacher, 2008 Menczel and Bruce Prime, 2009) have provided extensive descriptions of specific details of commercial instruments and therefore further aspects of equipment design will not be discussed in this chapter. 

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