DTA: Differential Thermal Analysis
Definition:Differential thermal analysis, Differentialthermoanalyse
Explanation:DTA experiments measure the temperature difference between a sample and an inert standard as a function of temperature or time at constant heating or cooling rate. It is a powerful tool to gain information on chemical and physical processes that involve enthalpy changes. The sample and reference crucibles are respectively connected to thermocouples. The voltage difference between the thermocouples is proportional to the temperature difference of the crucibles, which remains almost constant as long as the sample does not undergo any chemical or physical process involving heat transfer. Therefore, a deviation from the reference curve indicates the occurrence of either exothermic or endothermic reaction, depending on the deviation direction of the measured curve (Fig. 1). As the temperature is raised, processes, such as melting, sublimation, evaporation, etc. result in endothermic peaks. On the other hand, the reverse processes lead to exothermic deviations as the temperature is lowered. Moreover, the investigations on glass transitions, chemical reactions, sample decomposition, solidus and liquidus temperatures, polymorphic transitions, etc. are also possible. In addition, characteristic DTA-curves can be used to identify compounds and phase impurities by the detection of multiple consecutive melting points (Fig. 2), and also to gain calorimetric information such as heat capacities.
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(a) Heating and cooling schemes in DTA, (b) DTA heating curve of a mixture of two phases with different melting points.
SFB-Link:DTA is used to determine transition temperature and verify phase diagrams by various synthesis projects within the SFB.
References:[1] Normausschuß Materialprüfung (NMP) im DIN Deutsches Institut für Normung e.V.- Deutsche Norm DIN 51007, Thermische Analyse (TA), Differenzthermoanalyse (DTA), Grundlagen. Beuth Verlag GmbH, Berlin (Juli 1997).
[2] Normausschuß Materialprüfung (NMP) im DIN Deutsches Institut für Normung e.V.- Deutsche Norm DIN 51005, Thermische Analyse (TA), Begriffe. Beuth Verlag GmbH, Berlin (August 2005).
[3] W. J. Boettinger, U. R. Kattner, K.-W. Moon und J. H. Perepezko. NIST Recommended Practice Guide, Special Publication 960-15. National Institute of Standards and Technology, Washington, DC (November 2006).