Differential scanning calorimeter
A differential scanning calorimeter (DSC) is a scientific instrument used by many types of scientists to investigate certain temperature-related properties of a material. In a DSC, 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 with time (scanned), i.e. the heating rate
dT/dt = β
is kept constant. This time linearity 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 Cp. 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:
Note that this formula (equivalent to Newton's law of heat flow) is analogous to, and much older than, Ohm's law of electric flow:
ΔV = R dQ/dt = R I.
When a sudden change in the heat capacity occurs (e.g. when the sample melts), the signal will respond and exhibit a peak. From the integral of this peak the enthalpy of melting can be determined, and from its onset the melting temperature.
Differential scanning calorimetry is a workhorse technique in many fields, particularly in polymer characterization.
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