Differential scanning calorimetry

The differential scanning calorimetry ( DSC, english differential scanning calorimetry, DSC ) is a method of thermal analysis for the measurement of actual output or recorded amount of heat a sample at heating, cooling or isothermal process.

Measurement principles

An encapsulated container called crucible, with a sample ( 5-40 mg) and a second identical container without contents (reference) are suspended together in a heating bath to the same temperature change of the program. This leads due to the heat capacity of the sample and the endothermic or exothermic processes, or phase changes, such as melting or vaporization to temperature differences between sample and reference, since in the process under study, thermal energy flows into or out of the sample.

In contrast to the older differential thermal analysis ( DTA), this temperature difference is not used directly as a measurement signal in the DSC, but it closed on the heat flow as a benchmark. For this, two methods are available.

Dynamic Wärmestromdifferenzkalorimetrie

This also heat flux DSC -called type the enthalpy ( heat flow ) can be calculated by integrating the delta T TRef curve. In this case, shelves for sample and reference are in the oven on a disk (English disktype measuring system ), which has good thermal conductivity and under which sit the temperature sensor., The furnace is heated, the heat flow through the sample / reference to the disc and is removed there by means of the sensor:

  • Sample and reference are identical, the flow of the same size heat flow through the glass, the heat flow difference is therefore zero.
  • Varies during the measurement, a sample, for example by conversion, melting or evaporation, the result is a difference in the heat flow which is proportional to the temperature difference:

With

  • ΦFP the heat flow of the sample
  • ΦFR the heat flow to the reference
  • DELTA.T the temperature difference.

Dynamic Leistungsdifferenzkalorimetrie

This also power compensating DSC -called type sample and reference crucibles are placed in thermally insulated furnaces and this is controlled so that there is always the same temperature on both sides. The necessary electric power is plotted as a function of temperature.

Applications

With DSC, the following provisions may be made, inter alia:

  • Melting and glass transition temperatures (especially for plastic)
  • Degree of crystallization
  • Kinetic considerations of chemical reactions
  • Specific heat capacity
  • Phase transitions
  • Decomposition
  • Identification of plastic

Another typical field of application is the determination of the purity of substances due to the melting point of change occurring due to impurities. Purity examination of the change in melting point, however, is only possible when the pure substance is a eutectic mixture with the impurity.

Simultaneous applications

For special studies there are now ways to examine a sample during DSC measurement also gravimetrically. This combination is called DSC -TG (TG = thermogravimetry ) or STA (simultaneous thermal analysis ). It is recorded next to the DSC signal yet of the mass loss. In addition, it evolved gases can be analyzed even by infrared spectroscopy or mass spectrometry.

Exothermic reaction Thermogravimetric analysis
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