Differential Scanning Calorimetry
Definition and meaning of Differential Scanning Calorimetry in chemistry.
Differential Scanning Calorimetry (DSC) is a thermal analysis technique that measures the heat flow into or out of a sample, relative to an inert reference, as both are heated or cooled at a controlled rate.
In more detail
The instrument keeps the sample and reference at the same temperature and records the extra power needed to do so; any deviation from a flat baseline signals a physical or chemical transition. Endothermic events (melting, glass transitions, dehydration, endothermic decomposition) absorb heat and appear as upward or downward peaks depending on convention, while exothermic events (crystallization, oxidation, curing) release heat. The area under a peak gives the transition enthalpy in joules per gram. DSC is central to characterizing polymers, pharmaceuticals, and metals, since it reveals purity, polymorphism, and thermal stability without destroying chemical identity.
Key facts
| Field | Analytical Chemistry |
|---|---|
| Abbreviation | DSC |
| Measures | Differential heat flow (mW or W/g) vs. temperature or time |
| Typical uses | Melting point, glass transition (Tg), crystallinity, purity, reaction enthalpy |
Heating a sample of crystalline polyethylene in a DSC pan produces a sharp endothermic peak near 130°C corresponding to melting; integrating the peak area yields the enthalpy of fusion, which can be compared to a 100%-crystalline reference value to estimate the sample's percent crystallinity.
Frequently asked questions
How does DSC differ from differential thermal analysis (DTA)?
DTA records the temperature difference between sample and reference and is largely qualitative, whereas DSC measures actual heat flow and gives quantitative enthalpy values in joules.
Why use an inert reference in DSC?
The reference (often an empty pan or an inert material with no transitions in the studied range) provides a baseline, so any extra heat flow measured for the sample can be attributed to a real physical or chemical change.