This contribution deals with the calibration of a DSC apparatus between −100 and 0°C using compounds with well-known temperature
and heat of transition. Only a few suitable substances are mentioned in literature. For that reason another compound, adamantane,
is proposed with a solid-solid transition at −64.56°C and a heat of reaction being 24.78 J/g.
Gas reactions, catalyzed by solid catalysts, can be measured by DSC. In the experimental set-up an open sample pan with catalyst (powder or pellet) is placed on the sample side of the DSC sensor. The reactive gas mixture flows through the cell and reacts on the catalyst surface. The heat effect, caused by this reaction, results into a DSC signal.
A practical Thermal Analysis Course is described, lasting one full week, in which the stuents are performing at least 10 experiments from different kinds, covering a broad range of possible applications. In combination with the elaboration of the experiments a number of lectures is given about the practice of thermal analysis. So a course is obtained, in which the students learn a lot of the possibilities (and impossibilities) of thermal analysis techniques, particularly by experiments, performed by their own.
The activity of copper containing catalysts for the formation of methanol from CO and H2 is investigated by DSC measurement of the methanol decomposition. Calibration of the DSC signal can be performed by melting experiments with tin under reaction conditions. Comparison of catalysts is well possible by measurement of the standard activity at 240°, the apparent activation energy for the methanol decomposition reaction and the aging of the catalyst samples.
A number of compounds are investigated for DSC calibration during cooling. Adamantane and Zn show fast reversible transitions
and can be applied both for temperature and for heat calibration. A third compound, namely 4,4′-azoxyanisole, has a liquid
crystal to isotropic liquid transition at 409 K. This compound can be used for temperature calibration. Heat calibration with
this compound is more problematic because of the small heat effect and the construction of the baseline. Two other compounds,
namely Hg and Pb, show a slight undercooling. Nevertheless they can be used for heat calibration, and possibly also for temperature
calibration during cooling.
Two compounds are described with interesting properties for use in DSC. The first compound is adamantane (C10H16), with a reversible solid-solid transition at 208.62 K , suitable for DSC calibration at this low temperature . The second compound is 4,4'-azoxyanisole (C14H14N2O3), with a liquid crystal range between 390 and 407 K . This compound shows two transitions on heating, with a large heat effect at 390 K and a small heat effect at 407 K. For this reason, this substance is well suitable for testing the sensitivity and the resolution of DSC instruments . For both compounds not only the heating, but also the cooling behaviour is investigated.
For a large number of DSC calibration substances the vapour pressure at room temperature or at transition temperature (whichever is the highest) is given. It is important to know the vapour pressure of substances, because a DSC measurement on a substance with a high vapour pressure requires encapsulation of the substance in a hermetically sealed crucible to prevent evaporation. Because the calibration procedure must be performed using the same type of sample pan as will be used during the actual measurements, the presented information allows one to decide which calibration substances and/or what type of sample pan should be used for calibration.