Tips & Tricks

Tips for Sample Preparation for DSC Measurements

Careful sample preparation ensures reproducible and reliable DSC results.

The following factors can influence a DSC measurement:

Pan material:

• The pan material should feature good Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity and not interact with the sample material. One of the most common materials of choice is Aluminum which can be used to approx. 600°C.
• For temperature ranges higher than that, or for samples with special requirements, pans made of materials such as platinum or platinum alloys, gold, silver, alumina, graphite, steel and quartz glass are available.
• When determining the oxidative stability of cable sheathing, it is sometimes mandatory to employ copper pans [ASTM D3895]. Chemical reactions like Curing (Crosslinking Reactions)Literally translated, the term “crosslinking“ means “cross networking”. In the chemical context, it is used for reactions in which molecules are linked together by introducing covalent bonds and forming three-dimensional networks.curing sometimes require using mid- or high-pressure pans made of stainless steel or titanium.

Lids:

• Oxidative-Induction Time (OIT) and Oxidative-Onset Temperature (OOT)Oxidative Induction Time (isothermal OIT) is a relative measure of the resistance of a (stabilized) material to oxidative decomposition. Oxidative-Induction Temperature (dynamic OIT) or Oxidative-Onset Temperature (OOT) is a relative measure of the resistance of a (stabilized) material to oxidative decomposition.OIT measurements are mostly carried out in open pans; all other DSC measurements in pans with lids. Applying a lid results in a more homogeneous heat distribution in the pan.
• Aluminum pans with lids are usually used in cold-welded form. If the samples to be measured allow it, the lids are preferable pierced to prevent bursting at higher temperatures.

Sample:

• For DSC measurements on compact samples, a single sample specimen is ideal.
• In order to achieve good heat transfer between the sample and the pan bottom, the sample should have one surface with an area as smooth as possible which allows it to lie flat at the bottom of the pan. It is particularly easy to cut polymer granulates, for example, with the SampleCutter.
• Overall, the sample should not be too high, in order to ensure that the bottom does not become deformed when the pan is pressed. For powders, it has been determined to be a good idea to compact these when possible.

Sample mass:

• Most standards for the testing of polymers – such as ISO 11357, DIN 53765 and ASTM D3895 (OIT) – recommend a mass between 5 mg and 20 mg. For determination of the Glass Transition TemperatureThe glass transition is one of the most important properties of amorphous and semi-crystalline materials, e.g., inorganic glasses, amorphous metals, polymers, pharmaceuticals and food ingredients, etc., and describes the temperature region where the mechanical properties of the materials change from hard and brittle to more soft, deformable or rubbery.glass transition, it is usually recommended for the mass to be a little bit higher (10 mg to 20 mg) than for the investigation of melting and CrystallizationCrystallization is the physical process of hardening during the formation and growth of crystals. During this process, heat of crystallization is released.crystallization phenomena (5 mg to 10 mg).