National Physical Laboratory

Differential Scanning Calorimetry

Differential Scanning Calorimetry (DSC) measures the temperatures and heat flow associated with transitions in materials as a function of time and temperature. The technique provides qualitative and quantitative information about physical and chemical changes that involve endothermic or exothermic processes or changes in heat capacity using minimal amounts of sample. It has many advantages including fast analysis time, typically thirty minutes, easy sample preparation, applicability to both liquids and solids, a wide range of temperature applicability and excellent quantitative capability. There are two types of DSC instruments curently used; 'heat flux' and 'power compensation' instruments. Although they are fundamentally different in design, the data produced are comparable.

DSC trace

DSC trace indicating the transitions that can be measured

Some measurements that the DSC can make are:

  • Glass Transitions
  • Melting and Boiling Points
  • Crystallisation time and temperature
  • Percent Crystallinity
  • Heats of Fusion and Reactions
  • Specific Heat and Heat Capacity
  • Oxidative Stability
  • Rate and Degree of Cure
  • Reaction Kinetics
  • Percent Purity
  • Thermal Stability

DSC has been used in the evaluation of small transitions such as multiple phase transitions in liquid crystals and those due to side chains in polymers which can not be resolved by most other techniques.

It allows accurate determination of temperatures associated with thermal events. Temperature can be calibrated with respect to one or more standards which allows highly accurate, precise and reproducible values.

The technique reveals the thermal history imparted to thermoplastics as a result of different processing conditions. The information generated can be used to vary heating rates to deliver the required degree of crystallinity.

Heat evolved during cure can be related to the degree of cure in thermosetting materials. Percent conversion with time at a given temperature or for the same time under varying temperatures can be determined.

Reaction kinetics can be studied to determine Arrhenius parameters, such as Activation Energy, the pre-exponential term, rate constant and reaction order. Experiments can be carried out isothermally at temperatures of interest.

DSC finds application in the pharmaceutical and health care industry as a means to determine purity of highly pure chemicals. Presence of an impurity leads to a decrease in melting point which can be related to percent purity. Water in oil emulsions can be evaluated by following the depression in freezing point of water.

DSC is used to evaluate metal alloys and provide data required to prepare phase diagrams.

Greases and lubricants can be evaluated in terms of the transitions of interest, glass transition, wax dissolution, polyethylene melt, soap melt and decomposition in a single run allowing the determination of use window. Quantitative analysis of the different constituents can be made by measuring the areas under the different peaks.

Contact

For further information, please contact Sam Gnaniah

Last Updated: 16 Jun 2016
Created: 30 Apr 2010

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