Differential scanning calorimeter

In a differential scanning calorimeter, the heat flow into a sample -usually contained in a small aluminum capsule or 'pan'- is measured differentially, i.e. by comparing it to the flow into an empty reference pan.

Both pans sit on a small slab of material with a known (calibrated) heat resistance K. The temperature of the calorimeter is raised linearly in time (scanned), i.e. the heating rate dT/dt = β is kept constant This requires good design and good (computerized) temperature control.

Heat flows into the two pans by conduction. The flow of heat into the sample is larger because of its heat capacity C_p. The difference in flow dq/dt induces a small temperature difference ΔT across the slab. This temperature difference is measured using a thermocouple. The heat capacity can in principle be determined from this signal:

Δ T = K dq/dt = K.C_pbeta

The first part of this formula is analogous to Ohm's law of electric flow: ΔV = R. dQ/dt = R.I, but it is much older (Newton's law of heat flow)

When a sudden change in the heat capacity occurs, e.g. when the sample melts the signal will respond and form a peak. From the integral of this peak the enthalpy of melting can be determined, from its onset the melting temperature.

The technique is a major workhorse technique in many field, particularly in polymer characterization.