Thermogravimetric analysis (TGA)

Thermogravimetric analysis (TGA)

Change in mass of a material as a function of time and temperature
Thermogravimetry is an analytical method for examining the change in mass of a sample as a function of temperature and time. For this purpose, the sample is exposed to a constant temperature or a temperature ramp with a defined temperature increase per unit of time for a long time. During the gravimetric investigation, the sample space can be flushed with different gases. In order to prevent an oxidation reaction of the sample, pure nitrogen is used as the flushing medium in most cases. In order to promote oxidation, it is again flushed with oxygen or ambient air.

The sample is placed in a crucible made of a heat-resistant material such as aluminum oxide.
Heating the sample material can lead to decomposition, conversion and chemical reactions of the material.
Possible scenarios are:
  • Loss of mass due to the change in the physical state:
    Parts of the material to be examined are evaporated or sublimed. These gaseous components leave the balance area and are no longer detected.
  • Loss of mass as a result of thermal decomposition:
    The material is irreversibly destroyed. This leads to the formation of volatile components, which are released into the environment and leave the balance area.
  • Loss of mass due to a chemical reaction:
    A chemical reaction occurs in the sample material, favored by a higher temperature and activation energy, in which volatile substances are formed which are released into the environment.
  • Increase in mass due to a chemical reaction:
    A chemical reaction occurs in the sample material, aided by a higher temperature and activation energy, in which the sample material or parts of it reacts with the surrounding flushing medium. As a result of the atomic increase, there is also an increase in weight.
Based on the sample-specific change in mass, conclusions can be drawn about the composition of the material.

Example of a TG analysis:

On the basis of the percentage mass distribution depending on the temperature, it can be concluded that the material to be examined contains three components which decompose at different temperatures. The percentage difference can be used to determine the proportion of these components in the sample at the beginning of the test.
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