Thermogravimetric analysis
Method measuring sample mass change with temperature or time.
Thermogravimetric analysis (TGA) tracks how a sample’s mass changes over time as its temperature is altered. This technique reveals physical processes like phase transitions, absorption, adsorption, and desorption, alongside chemical events such as chemisorption, thermal decomposition, and solid-gas reactions (for instance, oxidation or reduction). The instrument used, a thermogravimetric analyzer, constantly records mass while the sample’s temperature is varied over time. Mass, temperature, and time are the core measurements in TGA, with other values derived from them.
A typical analyzer includes a precision balance holding a sample pan inside a furnace with a programmable temperature controller. The temperature is usually raised at a steady rate—or, in some cases, held to maintain a constant mass loss—to trigger a thermal reaction. These reactions can occur in various atmospheres, such as ambient air, vacuum, inert gas, oxidizing or reducing gases, corrosive or carburizing gases, liquid vapors, or a self-generated atmosphere. Pressures can range from high vacuum to high pressure, and may be constant or controlled.
Data from a thermal reaction is plotted as a TGA curve, with mass or percentage of initial mass on the y-axis and temperature or time on the x-axis. This curve is often smoothed. Its first derivative, the Differential Thermogravimetry (DTG) curve, highlights inflection points for deeper analysis and differential thermal studies. TGA helps characterize materials by revealing their decomposition patterns. It is especially useful for polymers, including thermoplastics, thermosets, elastomers, composites, plastic films, fibers, coatings, paints, and fuels.
There are three types of thermogravimetry. Isothermal or static thermogravimetry records sample weight over time at a constant temperature. Quasistatic thermogravimetry raises the temperature in steps, with isothermal intervals where mass stabilizes before the next ramp. Dynamic thermogravimetry heats the sample in an environment where temperature changes linearly.
TGA assesses thermal stability: if a material shows no mass change over a temperature range, it is stable, and the TGA trace has little or no slope. This also indicates the material’s upper use temperature, beyond which degradation begins. In polymer analysis, most polymers melt or degrade below 200 °C, but thermally stable polymers
- field
- Thermal analysis
- known_for
- Measuring mass change as a function of temperature or time to study material properties
- types
- Isothermal, quasistatic, dynamic thermogravimetry
- applications
- Thermal stability, oxidation and combustion, thermogravimetric kinetics
Lore & Background
Thermogravimetric analysis is performed using a thermogravimetric analyzer, which consists of a precision balance with a sample pan inside a furnace with programmable temperature control. The temperature is generally increased at a constant rate, though for some applications it is controlled for constant mass loss. The thermal reaction may occur under various atmospheres, including ambient air, vacuum, inert gas, oxidizing/reducing gases, corrosive gases, carburizing gases, vapors of liquids, or self-generated atmosphere, as well as under a variety of pressures such as high vacuum, high pressure, constant pressure, or controlled pressure.
Reader's Guide
Thermogravimetric analysis is significant for materials characterization through analysis of characteristic decomposition patterns. It is especially useful for studying polymeric materials, including thermoplastics, thermosets, elastomers, composites, plastic films, fibers, coatings, paints, and fuels. TGA can evaluate thermal stability, giving the upper use temperature of a material beyond which degradation begins. It is also used to study oxidation and combustion, as oxidative mass losses are the most common observable losses in TGA. The technique can be combined with other instruments, such as Fourier-transform infrared spectroscopy and mass spectrometry, for gas analysis as samples are heated to temperatures up to 2000 °C. Thermogravimetric kinetics can be explored for insight into reaction mechanisms of thermal decomposition in pyrolysis and combustion processes, with activation energies calculable using the Kissinger method.
Did You Know?
- TGA can be used to evaluate the thermal stability of a material; negligible mass loss corresponds to little or no slope in the TGA trace.
- Combustion during TG analysis is identifiable by distinct traces in TGA thermograms, such as when as-produced unpurified carbon nanotubes with metal catalyst cause a dramatic slope change.
- Different weight losses on the same sample at different points can be used to diagnose sample anisotropy, such as detecting sedimentation.
- TGA can be coupled with Fourier-transform infrared spectroscopy and mass spectrometry for gas analysis at temperatures up to 2000 °C.
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