Thermogravimetry determines the mass loss of a sample as a function of time, temperature and, if applicable, surrounding atmosphere. Typical thermogravimetric parameters include moisture, dry matter, volatile substances, loss on ignition or ash. Different temperatures and measurement times are applied in accordance with the sample matrix.
THERMOGRAVIMETRIC ANALYSIS – FUNCTIONAL
Thermogravimetric analysis is carried out on a huge variety of samples, ranging from organic materials such as food, soil, wood, plastic and coal to inorganic materials such as cement or ceramics.
After the weight of the original sample has been determined, it is heated to a defined temperature between 40 °C and 1,000 °C. Depending on the type of sample and the selected temperature and atmosphere, the sample is dried or oxidized or the volatile components escape, all of which reduces the weight of the material. When the mass of the sample remains constant under the selected conditions, it is again weighed and the mass loss is documented.
THERMOGRAVIMETRIC ANALYSIS EXPLAINED
There are various ways of carrying out thermogravimetric analyses, depending on the technical requirements. One possibility is to weigh each sample manually, put it into the drying cabinet or muffle furnace and then weigh it again. If several parameters need to be determined (for example, moisture and ash in flour), several furnaces with different temperatures (105 °C and 550 °C) are required as well as additional weighing. This method is fairly time-consuming.
A much more convenient and time-saving alternative is offered by thermogravimetric analyzers such as ELTRA’s TGA Thermostep.These analyzers combine furnace and balance thus allowing for automated measurement of a variety of thermogravimetric parameters.
The user fills various samples into the ceramic crucibles and places them in the carousel inside the analyzer where they are weighed by the integrated balance and automatically analyzed. According to the selected program the samples are dried or reduced to ashes until they have the desired constant weight. No manual weighing is required. After the thermogravimetric analysis is finished, the relevant data can be directly transferred to a laboratory information management system (LIMS).
EXAMPLE OF AN AUTOMATED TGA MEASUREMENT
It is also possible to run a complex analysis program with a thermogravimetric analyzer. An example: coal is dried at 105 °C (parameter: moisture), then heated under nitrogen atmosphere to 950 °C (parameter: volatile components); after cooling down to 750 °C it is combusted at this temperature under oxygen atmosphere (parameter: ash). The whole analysis cycle runs fully automatically, including documentation of the measurement results.