With DSC and STA, the primary areas of investigation include melting, crystallization, phase transitions, specific heat, oxidation, and thermostability of non-metallic, inorganic compounds and elements. Also, the desorption and adsorption behavior of minerals and catalyzers are important application areas for TGA or STA.
The coefficient of thermal expansion and the expansion rate as well as phase transitions are measured with dilatometry.
Knowledge of the thermal diffusivity and conductivity of geological layers is becoming increasingly important for studies regarding global warming.
Lanthanum oxide (La2O3) is of great interest as catalyst material, but is also used in applications such as the manufacturing of high-quality optical glasses and the production of lanthanum metal. Lanthanum oxide is hygroscopic and can therefore absorb water from its surroundings.
In the case shown here, 643.4 mg of La2O3, contaminated with some carbonate impurities, was weighed in a beaker (volume: 3.5 ml) and heated to 1120°C at 50 K/min in a nitrogen atmosphere. The larger crucible is ideal when measuring samples which are low in contaminant concentration or are not very homogeneous.
The TGA curve reveals several steps. There are some smaller overlapped ones in the temperature range up to 400°C, followed by two well separated steps at 510°C and 705°C (both temperature values correspond to DTG peaks). The total mass loss amounts to 0.43%. Evaluation of the experimental FT-IR spectra identifies water and carbon dioxide as the main gases released.
The plot shows that the dehydration takes place primarily in the first part of the measurement, prior to 400°C; the formation of carbon dioxide is directly related to the two-step decomposition taking place between 400°C and 800°C.
With the help of this information, the total water loss can be specified as 0.22% (or 1.41 mg) and the amount of CO2 released as 0.21%. (measurement with PERSEUS® STA 449 F1/F3)
Natural materials such as rocks are difficult to analyze with regard to their chemical composition. Such materials are generally a mixture of different oxides, sulfates or carbonates. Volcanic rocks are generally solidified from molten magma and their main contents are different oxides. This example shows a DSC measurement result for such a material. It can clearly be seen that it solidified almost completely amorphous. The glass transition was between 623°C and 655°C. Cold crystallization and melting were detected at 884°C and 1111°C (peak temperature). The heat released during crystallization was comparable to the heat of fusion, indicating the highly amorphous nature of this mixture. (measurement with DSC 404 F1 Pegasus®)
The DSC 200 F3 Maia® allows tests up to 600°C with excellent baseline stability and reproducibility. Presented here are three runs on a mixture of crystalline SiO2 (quartz) and potassium sulphate (K2SO4). The result clearly proves the out-standing temperature and enthalpy reproducibility of this cost-effective differential scanning calorimeter even at the limits of the temperature range.