Thermogravimetric analysis (TGA) is an experimental technique in which the weight or, strictly speaking, the mass of a sample is measured as a function of sample temperature or time. The sample is typically heated at a constant heating rate (so-called dynamic measurement) or held at a constant temperature (isothermal measurement), but may also be subjected to non-linear temperature programs such as those used in sample controlled TGA (so-called SCTA) experiments. The choice of temperature program will depend upon the type of information required about the sample. In this technique, the change in the weight of the sample with respect to the temperature and time is monitored when heated under a controlled program. Additionally, the atmosphere used in the TGA experiment plays an important role and can be reactive, oxidizing or inert. Changes in the atmosphere during a measurement may also be made.

The program is often of linear increase in temperature or time. This technique is quantitative and is very useful to study the curing reactions/degradations taking place while heating the sample. The results of a thermogravimetric analysis (TGA) measurement are usually displayed as a TGA curve in which mass or per cent mass is plotted against temperature and/or time. An alternative and complementary presentation is to use the first derivative of the TGA curve with respect to temperature or time. This shows the rate at which the mass changes and is known as the differential thermogravimetric or DTG curve. Providing information about physical phenomena such as phase transitions, absorption, and desorption, as well as chemical phenomena including chemisorptions, thermal decomposition, and solid-gas reactions (e.g., oxidation or reduction).

Mass changes occur when the sample loses material in one of several different ways or reacts with the surrounding atmosphere. This produces steps in the TGA curve or peaks in the DTG (differential thermogravimetric) curve. Different effects can cause a sample to lose, or even gain, mass and so produce steps in the TGA curve. These include the following:

• Evaporation of volatile constituents; drying; desorption and adsorption of gases, moisture and other volatile substances; loss of water of crystallization. See Figure 1.

• Oxidation of metals in air or oxygen.

• Oxidative decomposition of organic substances in air or oxygen.

• Thermal decomposition in an inert atmosphere with the formation of gaseous products. With organic compounds, this process is known as pyrolysis or carbonization.

• Heterogeneous chemical reactions in which a starting material is taken up from the atmosphere, for example reduction reactions with a purge gas containing hydrogen. Furthermore, reactions in which a product is evolved, for example decarboxylation or condensation reactions.

• Ferromagnetic materials. The magnetic properties of some materials change with temperature (Curie transition). If the sample is measured in an inhomogeneous magnetic field, the change in magnetic attraction at the transition generates a TGA signal. The magnetic field is produced by placing a permanent magnet in close proximity to the furnace close to the sample.

• Uptake or loss of water in a humidity-controlled experiment.

Figure 1. Stepwise decomposition of calcium oxalate monohydrate: sample mass 19 mg, heating rate 30 K/min, nitrogen. The TGA curve has been normalized (divided by the sample weight) and therefore begins at 100%. The temperature range of the three mass losses is particularly clear in the normalized first derivative or DTG curve.

Thermogravimetric analysis (TGA) can interface with a mass spectrometer to identify and measure volatile substances generated during mass changes of the test sample. Thermogravimetric analysis (TGA)  determines temperature and weight change in decomposition reactions, facilitating quantitative composition analysis, and it may be used to determine water content or detect residual solvents in a material. Thermogravimetric analysis (TGA) allows identification of organic materials by measuring the temperature of bond scission in inert atmospheres or of oxidation in air or oxygen.

For ceramic and glass science, the technique can be used to study the following: calcination, binder burn out, decomposition, pyrolysis, weight changes during crystallization or transformation, weight changes during oxidation or decomposition of ceramics, glasses and high temperature ceramics and composites. Thus, the technique can be used to aid the understanding of the kinetics and mechanisms of various physico-chemical processes involved in materials processing or materials degradation. Experiments can be carried out in complex gas environments as well as in neutral or inert gas environments.

Besides, others like inorganic materials, metals, polymers and plastics, and composite materials can be analyzed. Samples can be analyzed in the form of powder or small pieces to maintain an interior sample temperature close to the measured gas temperature. An accurate analysis of various polymeric blends and filler contents can also be performed successfully using this analytical technique.

In summary, thermogravimetric analysis (TGA) precisely measures the thermal stability and decomposition behavior of materials and the decomposition rate during the heating and cooling cycle of the material. This instrument has the potential to identify the minimal presence of volatile molecules such as water and residual solvents generated during the heating of polymeric samples. The thermal stability of a material can be studied at various heating rates including isothermal or dynamic conditions using this technique.