Influencing factors
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In a calorimetric determination, many factors have to be considered. Their influence varies according to the type of DTA, DSC or calorimeter that is used for the measurement. Below is a table summarising the main influencing factors.

Factor Influence

Temperature

Temperature is one of the main influencing factors, as thermal analysis techniques cover a wide range, from very low to very high temperature. Temperature will affect the sensitivity of the detector, the stability of the baseline, the choice of container and type of sample to be investigated (e.g. solid or liquid).
Heat capacity also varies with temperature.

Sample mass

The choice of sample mass depends on the type of calorimetric detector used for the test. For DTA and plate DSC types, a small sample mass (some mg) has to be used in order to guarantee a good heat transfer through the bottom of the crucible. By increasing the mass, the heat leakages are more important and the detector has to be recalibrated. The heat calibration factor for such detectors depends on the sample mass.
For DSC or calorimeters using a surrounding-type detector, larger sample masses can be used without affecting the calibration factor.

Sample type

Both solid and liquid samples are investigated with calorimetric techniques.
When a solid sample is heated in a closed and tight container, an internal pressure can build up in the crucible, produced by moisture from the sample or its decomposition. Care is needed to prevent explosion of the container.
With a liquid sample in a tight crucible, the problem is identical. If the crucible is not tight, the heating of the liquid sample will generate a leak of vapour, producing an endothermic effect that can mask the transition to be measured.

Crucible

The nature of the crucible (aluminium, stainless steel, glass) has to be selected according to different parameters:
   - good thermal conductivity
   - no interaction between the sample and carrier gas
   - type of closing (tight or not tight)
   - pressurisation
The type of crucible can affect the calibration factor

Carrier gas

Different carrier gases can be selected: inert, oxidative, reducing.
As the thermal conductivity of gases are different, the calibration factor can be affected. It is also necessary to check that there is no interaction between the gas and the detector or crucible.

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