Of the different thermal analysis techniques, thermogravimetric analysis (TGA) is one of the most prominent. Its goal is to measure the dependence of one or more system variables on temperature, with the sample’s weight as the primary measurement of interest. The instrument measures the mass of the sample as the temperature changes, generally through the loss of volatile compounds liberated from the sample.

A TGA system’s operation is relatively straightforward, with the sample introduced into a crucible of known weight, and generally made of aluminum, platinum, steel or gold. The sample is heated in an insulated electric oven, which allows for excellent temperature control and enables tests that vary the temperature with time in a reproducible fashion. Most commonly, TGA tests involve a simple linear increase in temperature.

Most standard TGA systems have different electric furnace options. Standard furnaces typically reach maximum temperatures of about 1,000° C, while the range of high-temperature systems can extend to 1,500° C or more. Refrigeration can also extend the temperature range. To prevent unwanted chemical reactions, like oxidation, that would interfere with the measurements, a purge gas is often used to keep the sample in an inert environment. The choice of crucible material may also be critical to avoid reactions. In other cases, chemical reactions with the surrounding gas or air may be of interest, and the oxidation of a sample may actually lead to a gain in mass. Ultimately, weight is determined by a precision balance.

As the increased temperature volatilizes different components of the sample into gaseous form, the mass of the sample decreases. The TGA curve indicates when different components begin their evolution, where the rate of evolution is greatest, and when evolution is complete. TGA libraries can be used to separate different components, and this information is used to identify and quantify the evolved gases. Alternatively, the addition of an IR spectrometer or MS system can allow more definitive identification of the evolved gases in a hyphenated instrumental technique.

TGA is frequently used in polymer analysis; the stability and degradation characteristics of polymeric materials can be directly measured with TGA. Pharmaceutical formulations can be tested for thermal stability or for the evolution of residual solvents. Other potential analyses include chemicals, coal, asphalt, elastomers, cements, adhesives, paints and various foodstuffs.

The total market for TGA, including systems, aftermarket and service, was about $160 million in 2014. Waters’s TA Instruments division is the market leader, followed by thermal analysis specialist company NETZSCH. Mettler-Toledo is also a major supplier. PerkinElmer is another significant vendor. Other competitors include Eltra, Hitachi High-Technologies, Instrument Specialists, LECO, Navas, Setaram and Shimadzu.

Thermogravimetric Analysis at a Glance:

Leading Suppliers

• TA Instruments (Waters)

• NETZSCH

• Mettler-Toledo

Largest Markets

• Polymers

• Pharmaceuticals

• Chemicals

Instrument Cost

• $20,000–$120,000