Differential Scanning Calorimetry (DSC)

Differential scanning calorimetry is similar to differential thermal analysis the main change in the apparatus is that the two furnaces have separate and individual temperature control. Thus, if the temperature of the material in one furnace lags behind that of the other, extra heat can be injected into the sample to keep the temperature difference zero. Thus, if a phase change occurs such as melting or crystallization then either heat is evolved or absorbed by the system causing the sample to require more or less heat to maintain the same temperature as the reference standard. By calibration, the heat adsorbed or evolved during a phase change can be directly rated to the change in energy supplied to the reference oven to maintain the temperature of the reference standard the same as that of the sample. A commercially available differential scanning calorimeter is shown in figure 9.

Figure 9. A Differential Scanning Calorimeter

A diagrammatic representation of a differential scanning curve for glass is shown in figure 10. Glass is chosen to demonstrate a DSC curve as it shows, in the results of one experiment three different types of energy change that that can be monitored and identified by this technique.

Figure 10. A Diagramatic Differential Scanning Curve for Glass

The first downward step results from some transition that causes a change in heat capacity of the sample but does not necessarily represent a recognized phase change. The positive peak is the result of a phase change and represents the evolution of the latent heat of crystallization as the amorphous mass begins to crystallize. The negative peak represents the absorption of heat as the sample begins to melt and, in fact, represents the latent heat of melting.

The DSC technique has an ever-widening field of application. Including the polymer and pharmaceutical industries, food science and forensic studies.