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Scientists characterize many materials with thermogravimetric analysis, often adding new methods of detection.
The characterization of materials could be one of the oldest interests in all of science, and there’s a lot to characterize. “The materials characterization universe is as large and multifaceted as the materials and engineering fields combined,” wrote Julie Cross, a physicist at Argonne National Laboratory, and her colleagues.1 “Many methods have evolved over decades, or even centuries, from quite rudimentary tools to extremely sophisticated instruments.” Many of those methods, including thermogravimetric analysis (TGA), involve heating.
Many materials—minerals, pharmaceuticals, and more—can be studied with thermogravimetric analysis. (Image courtesy of the author.)According to “TGA Technique—Basic Principles and Applications” (https://www.mt.com/us/en/home/library/on-demand-webinars/lab-analytical-instruments/Thermogravimetric_Analysis.html) from Mettler Toledo (Columbus, OH), “The TGA technique measures the mass of a sample as it is heated, cooled, or held at a constant temperature in a defined atmosphere.” The web page adds that TGA “is ideal for characterizing the thermal properties of materials such as plastics, elastomers and thermosets, mineral compounds and ceramics, as well as for chemical and pharmaceutical products.” Moreover, the web page points out that scientists use TGA to measure a material’s “composition, purity, decomposition reactions, decomposition temperatures, and absorbed moisture content.”
This technology offers other benefits to scientists. “The ability to easily collect and analyze the evolved gas from a sample being tested in a TGA is one of the most recent technological advancements that has significantly improved the amount of information that can be gathered in a single experiment,” says Jason Saienga, senior thermal product specialist at TA Instruments (New Castle, DE).
Various instruments, such as the TGA 5500 (right) and Thermo Fisher FTIR (left) can be combined when doing thermogravimetric analysis. (Image courtesy of TA Instruments.)Combining technologies
Beyond running TGA alone, scientists also use it in hyphenated techniques, such as combining TGA with gas chromatography, GC/MS, or FTIR. “While the technique of TGA combined with the analysis of the evolved gas products with a MS or FTIR has been an option for many years, the added ability to connect a technique like the GC/MS, which can provide fragment separation and quantification, is a relatively new accessory for the TGA,” Saienga explains.
To combine some of these technologies, vendors develop the needed products. For example, Bruker (Billerica, MA) makes a TG-FTIR interface that can couple many of its spectrometers—TENSOR, INVENIO, and VERTEX Series FTIR spectrometers—to a TGA system.
When asked about the latest advance in thermogravimetric analyzers from Mettler Toledo, materials characterization market manager Chris Arko says that it’s “the expansion of hyphenated techniques to include the new MicroGC/MS.” He adds, “The TGA-MicroGC/MS coupling permits the rapid qualitative and quantitative analysis of evolved gases derived from almost any material, including polymers, organics, and inorganics.” For example, Arko notes that MicroGC is especially well-suited to detecting small molecules—such as carbon monoxide, carbon dioxide, and water—which cannot be detected—or only with great difficulty—with ordinary GC. “The MicroGC/MS option starts to become really interesting with analysis of medium compounds,” such as 4–10 carbon hydrocarbons and small acids, Arko notes.
The MicroGC/MS technique is also fast, producing results in just three minutes. As Arko states, it also “enables immediate result assessment” and “improved efficiency and comprehensive results” when analyzing multiple gases. This technology, says Arko, also delivers “linear results over a wide range” and with a modular concept “users may add up to three MicroGC modules, according to their needs.”
Depending on the experimental requirements, a scientist might want to use various forms of analysis from one TGA platform. “TA Instruments has implemented a system that allows a user to connect the industry-leading Discovery TGA 5500 with any combination of evolved-gas analysis techniques: FTIR, GC/MS or both,” says Saienga. “The unique transfer line adapted to the Discovery TGA allows the user to run a TGA experiment and analyze the off-gas with serial analysis or any combination of FTIR, GC/MS, or direct MS without any hardware changes.” He adds, “This modular connection to the TGA will provide an unprecedented new level of information about the structure and decomposition mechanism of materials all from a single TGA experiment.”
Balancing the options
A variety of companies create TGAs worth mulling over. The TGA from Mettler Toledo, for example, is described as providing “fast and accurate TGA results through seamless workflows” and uses “the world’s best Mettler Toledo micro- and ultra-micro balances with sub-microgram resolution over the whole measurement range,” which goes up to 5 grams.
The TGA Thermostep from ELTRA (Haan, Germany) determines various parameters such as moisture, volatiles, and ash at user-defined temperatures and atmospheres in a single analysis,” the company notes. One analysis can include 19 samples, each weighing as much as 5 grams. “A special feature of the TGA Thermostep is the management of crucible covers,” according to ELTRA. “The analyzer can place and remove the covers of the crucibles during analysis.” The company recommends this platform for analyzing coal, coke, food, limestone, plastics, and more.
Shimadzu (Columbia, MD) invests considerable time and resources in TGA. The company’s website notes: “Shimadzu has been pursuing what thermal analysis instruments should be since developing the DT-1 in 1958, the first differential thermal analyzer in Japan.” It adds, “Today, Shimadzu thermal analysis systems offer unmatched flexibility in material characterization with either complete standalone functionality or multisystem operation for up to four units.”
For instance, Shimadzu’s DTG-60 series platforms provide TGA and differential thermal analysis at the same time. Also, the available models come with various capabilities and options. The DTG-60AH, for instance, allows a temperature range of ambient to 1500 °C and an autosampler that handles as many as 24 samples. As Shimadzu notes: “The advanced balance, high-quality detectors, and excellent furnace temperature distribution combine to provide a measurable mass change of ±500 mg, a mass readability of 0.1 µg, a maximum sample quantity of 1 g, and a measurable differential thermal range of ±1000 µV.” Plus, these platforms can be connected to Shimadzu’s TA-60WS thermal analysis workstation, which provides experimental control, data acquisition, and analysis.
The increasing use of new detectors and other techniques downstream from TGA will drive the need for more ways to easily and completely analyze the data. Also, scientists will look for simple and fast ways to change out options and adjust the analysis. That will drive ongoing changes in TGA and associated devices.
Reference
- Cross, J.O.; Opila, R.L. et al. MRS Bulletin 2015. 40, 1019–34.
Mike May is a freelance writer and editor living in Texas. He can be reached at [email protected]