Editing Differential scanning calorimetry (section)

==Examples==
The technique is widely used across a range of applications, both as a routine quality test and as a research tool. The equipment is easy to calibrate, using low melting [[indium]] at 156.5985&nbsp;°C for example, and is a rapid and reliable method of thermal analysis.{{Citation needed|date=February 2021}}

===Polymers===
[[File:Thermal transitions in amorphous and semicrystalline polymers.tif|thumb|Thermal transitions in '''(A)''' amorphous and '''(B)''' semicrystalline polymers. As the temperature increases, both amorphous and semicrystalline polymers go through the [[glass transition]] (''T''<sub>g</sub>). Amorphous polymers '''(A)''' do not exhibit other phase transitions. However, semicrystalline polymers '''(B)''' undergo crystallization and melting (at temperatures ''T''<sub>c</sub> and ''T''<sub>m</sub>, respectively).]]
DSC is used widely for examining [[polymer]]ic materials to determine their thermal transitions. Important thermal transitions include the glass transition temperature (''T''<sub>g</sub>), crystallization temperature (''T''<sub>c</sub>), and melting temperature (''T''<sub>m</sub>). The observed thermal transitions can be utilized to compare materials, although the transitions alone do not uniquely identify composition. The composition of unknown materials may be completed using complementary techniques such as IR spectroscopy. [[Melting point]]s and [[glass transition temperature]]s for most [[polymer]]s are available from standard compilations, and the method can show [[polymer degradation]] by the lowering of the expected melting temperature. ''T<sub>m</sub>'' depends on the [[molecular weight]] of the polymer and thermal history.{{Citation needed|date=February 2021}}

The percent crystalline content of a polymer can be estimated from the crystallization/melting peaks of the DSC graph using reference heats of fusion found in the literature.<ref>{{cite book | vauthors = Wunderlich B | title = Macromolecular Physics | year = 1980 | volume =  3 | chapter = Chapter 8, Table VIII.6 }}</ref> DSC can also be used to study thermal degradation of polymers using an approach such as Oxidative Onset Temperature/Time (OOT); however, the user risks contamination of the DSC cell, which can be problematic. [[Thermogravimetric Analysis]] (TGA) may be more useful for decomposition behavior determination. Impurities in polymers can be determined by examining thermograms for anomalous peaks, and [[plasticiser]]s can be detected at their characteristic boiling points. In addition, examination of minor events in first heat thermal analysis data can be useful as these apparently "anomalous peaks" can in fact also be representative of process or storage thermal history of the material or polymer physical aging. Comparison of first and second heat data collected at consistent heating rates can allow the analyst to learn about both polymer processing history and material properties. (see ''J.H.Flynn.(1993) Analysis of DSC results by integration. Thermochimica      Acta, 217, 129-149.)''  {{Citation needed|date=February 2021}}

===Liquid crystals===
DSC is used in the study of [[liquid crystal]]s. As some forms of matter go from solid to liquid they go through a third state, which displays properties of both phases. This [[anisotropic]] liquid is known as a liquid crystalline or mesomorphous state. Using DSC, it is possible to observe the small energy changes that occur as matter transitions from a solid to a liquid crystal and from a liquid crystal to an [[isotropic]] liquid.<ref name=Pugnor/>

===Oxidative stability===
Using differential scanning calorimetry to study the stability to [[oxidation]] of samples generally requires an airtight sample chamber. It can be used to determine the [[oxidative-induction time]] (OIT) of a sample. Such tests are usually done isothermally (at constant temperature) by changing the atmosphere of the sample. First, the sample is brought to the desired test temperature under an inert atmosphere, usually [[nitrogen]]. Oxygen is then added to the system. Any oxidation that occurs is observed as a deviation in the baseline. Such analysis can be used to determine the stability and optimum storage conditions for a material or compound.<ref name=Dean/> DSC equipment can also be used to determine the Oxidative-Onset Temperature (OOT) of a material. In this test a sample (and a reference) are exposed to an oxygen atmosphere and subjected to a constant rate of heating (typically from 50 to 300&nbsp;°C). The DSC heat flow curve will deviate when the reaction with oxygen begins (the reaction being either [[exothermic]] or [[endothermic]]). Both OIT and OOT tests are used as a tools for determining the activity of [[antioxidant]]s.

===Safety screening===
DSC makes a reasonable initial safety screening tool. In this mode the sample will be housed in a non-reactive crucible (often [[gold]] or gold-plated steel), and which will be able to withstand [[pressure]] (typically up to 100 [[bar (unit)|bar]]). The presence of an [[exothermic]] event can then be used to assess the [[chemical stability|stability]] of a substance to heat. However, due to a combination of relatively poor sensitivity, slower than normal scan rates (typically 2–3&nbsp;°C/min, due to much heavier crucible) and unknown [[activation energy]], it is necessary to deduct about 75–100&nbsp;°C from the initial start of the observed exotherm to ''suggest'' a maximal temperature for the material. A much more accurate data set can be obtained from an [[Calorimeter#Adiabatic calorimeters|adiabatic calorimeter]], but such a test may take 2–3 days from [[Ambient temperature|ambient]] at a rate of a 3&nbsp;°C increment per half-hour.{{Citation needed|date=February 2021}}

===Drug analysis===
DSC is widely used in the [[pharmaceutical]] and [[polymer]] industries. For the polymer chemist, DSC is a handy tool for studying [[curing (chemistry)|curing]] processes, which allows the fine tuning of polymer properties. The [[cross-link]]ing of polymer molecules that occurs in the curing process is exothermic, resulting in a negative peak in the DSC curve that usually appears soon after the glass transition.<ref name=Dean/><ref name=Pugnor/><ref name=Skoog/>

In the pharmaceutical industry it is necessary to have well-characterized [[Medication|drug]] compounds in order to define processing parameters. For instance, if it is necessary to deliver a drug in the amorphous form, it is desirable to process the drug at temperatures below those at which crystallization can occur.<ref name=Pugnor/>

===General chemical analysis===
[[Freezing-point depression]] can be used as a '''purity analysis''' tool when analysed by differential scanning calorimetry. This is possible because the temperature range over which a mixture of compounds melts is dependent on their relative amounts. Consequently, less pure compounds will exhibit a broadened melting peak that begins at lower temperature than a pure compound.<ref name=Pugnor/><ref name=Skoog/>