Parameters which typically are measured via TGA are:
% Moisture
% Volatile
% Ash
% Lost on ignition
Thermogravimetric analysis or thermal gravimetric analysis (TGA) is an analytical method that has been developed over a century ago and maintained its basic principles throughout its history. At its core, TGA determines the mass loss of a sample as a function of time, temperature and, if applicable, surrounding atmosphere.
With advanced instrumentation and measurement techniques the precision of TGA measurements has significantly enhanced. As a result, TGA has solidified its status as an important analytical tool over the years.
In contemporary applications, this quantitative technique yields critical insights into the curing reactions and decomposition processes occurring during material heat treatment. TGA's versatility allows the examination of sample behaviour under both inert and oxidative conditions, depending on the equipment and methodology employed. This enables TGA to deliver temperature-dependent data on a wide array of physical phenomena, including phase transitions, adsorption, and desorption, as well as chemical processes like chemisorption, thermal decomposition, and solid-gas reactions such as oxidation and reduction.
Consequently, TGA stands as a vital method for understanding material properties and reactions under varying thermal conditions.
As the measuring principle of (automated) TGA is based on the change in mass as a function of temperature, the essential components of a thermogravimetric analysis instrument remain the same, regardless of which device is used:
The core concept of the thermogravimetric analysis is to measure how the weight of a material changes as it is heated, cooled, or held at a constant temperature. However, the behaviour of the sample does not depend exclusively on the temperature program used. The atmosphere in the sample chamber also has a decisive influence on the mass change mechanism. In an inert environment using gases such as nitrogen or argon, for example, materials lose weight as the temperature rises. This may involve evaporation, sublimation, dissociation, desorption or decomposition. The presence of a continuous gas flow in the furnace chamber prevents the possible occurrence of back reactions that could influence the result. In this way, samples can be tested for moisture content, volatile components or thermal stability. When thermogravimetric analysis (TGA) is conducted under oxidative conditions (oxygen atmosphere or air), this leads for the most part in more pronounced mass loss compared to inert conditions due to combustion or oxidation processes. The decomposition patterns of the material offer insights into its oxidative stability by observing the rate of the mass loss during the reaction. In addition, the residue obtained by oxidative reactions can provide information on inorganic components of the sample, such as ash content, for example. Overall, TGA under oxidative conditions provides information regarding material performance, stability, and safety in oxidative environments.
The functional principle of thermal gravimetric analysis using the ELTRA THERMOSTEP can be summarized as follows:
Most thermogravimetric analysis instruments available in the market fall into one of two categories: Micro or Macro TGAs. The main distinction between these categories is the size of the sample they are intended to analyse. Micro TGAs, which feature a smaller furnace chamber, are tailored for analysing samples in the range of micrograms to a few milligrams and usually measure only one sample simultaneously for TGA parameters. On the other hand, Macro TGAs, like the ELTRA THERMOSTEP, are designed to handle multiple larger samples, up to several grams each.
With a large furnace chamber multiple measurements can be carried out by Macro TGA simultaneously and larger sample quantities reduce measurement uncertainty due to potential inhomogeneity of the sample. For this reason, Macro TGAs are more suited for industrial applications or when the bulk properties of a material are of interest, whereas Micro TGAs are often used in research applications with studying materials only being available in small quantities.
Coupled Techniques (mainly used in combination with MICRO TGAs): For enhanced detection and analysis of volatiles, thermogravimetric analysis (TGA) can be coupled with gas analysis techniques such as Fourier Transform Infrared Spectroscopy (FTIR), Mass Spectrometry (MS), or Gas Chromatography (GC). These techniques allow for the real-time analysis of gases evolved during the TGA run.
TGA-FTIR: Identifies functional groups in the evolved gases, providing insights into the composition of volatiles.
TGA-MS: Offers mass-to-charge ratio information, helping to identify the molecular structure of evolved gases.
TGA-GC: Separates the evolved gases, allowing for detailed compositional analysis.
Thermogram is a graphical representation of the obtained TGA measurement data that shows the relationship between the mass change of a sample and temperature or time under controlled conditions. Thermograms are unique for each compound and provide detailed insights into the thermal behaviour of materials, enabling the observation of decomposition, oxidation, dehydration, or other mass-altering reactions during thermal exposure.
The Y-axis (vertical axis) in the diagram represents the sample weight, which can be displayed as either the percentage of the original mass remaining or the absolute mass in grams/milligrams. With proceeding analysis time, the change in the sample weight due to thermal treatment is plotted along this axis. Since the measuring principle of thermogravimetric analysis is based on weight change as a function of temperature and time, the X-axis (horizontal axis) therefore represents either temperature or time.
The thermogram generally consists of several consecutive sections of slopes and plateaus which allow the thermal behaviour of the respective materials to be analysed.
Weight Loss (gain) Steps: As the sample is heated, it may undergo various processes such as dehydration (loss of water), decomposition (breakdown of the material), or oxidation (reaction with oxygen). These processes result in a decrease in the sample's mass, which appears as steps or slopes in the thermogram. It should be noted that in certain instances, particularly with metallic compounds, oxidation results in a higher oxidation state and an increase in the sample weight.
An inert atmosphere, such as nitrogen or argon, is often used when the goal is to prevent oxidation or combustion of the sample. This environment is suitable for detecting the thermal decomposition products of the sample without interference from reactions with oxygen:
An oxidative atmosphere (air or pure oxygen) is chosen when the interest lies in studying oxidative degradation or combustion products.
It is important to note that the exact temperatures and phenomena observed depend on the specific material type being analysed and on the experimental conditions.
Stability Regions: Flat regions or plateaus on the thermogram indicate temperatures where the sample's mass remains constant, suggesting thermal stability within that temperature range.
Onset and Endset Temperatures: The temperatures at which a weight loss step begins, and ends are crucial for determining the thermal stability and decomposition temperatures of the material.
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 analysis instruments such as ELTRA’s TGA THERMOSTEP.
These analysers 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 analyser where they are weighed by the integrated balance and automatically analysed. 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).
It is also possible to run a complex analysis program with a thermogravimetric analyser. 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.
Due to its ability to precisely measure the mass change of a material as a function of temperature or time, thermogravimetric analysis (TGA) has become indispensable across a wide range of industries, being used for material characterization, quality control and research and development of novel products. TGA is thus 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.
Coal, Biomass, Fuel Development: Quality control of coal, biomass and other fuels by analysing moisture, volatile content, combustible residue and ash content. Evaluating thermal behaviour and potential energy content.
Studying thermal stability and degradation behaviour of polymers. Determination of compositional properties: filler content, polymer content, and moisture.
Determination of moisture and ash content and study of thermal properties in a wide range of food products.
Analysing the organic and inorganic components and evaluating thermal behaviour and potential energy content (as a potential source of alternative energy) in various types of waste.
Evaluating thermal stability and decomposition behaviour of ceramic, glass and advanced materials.
Cement and concrete analysis: thermal stability and decomposition behaviour, determination of moisture content. Analysing the loss of CO2 from carbonates in concrete.
Bitumen: studying thermal behaviour and measuring the content of volatiles.
Wood: analysing thermal degradation patterns and determining the moisture, volatile and ash content.
Thermogravimetric analysis or thermal gravimetric analysis (TGA) is an analytical method that measures mass change of a sample as a function of time and temperature in a specific atmosphere (inert or oxidative). This method is highly sensitive, making it an important tool for understanding a wide range of material properties and behaviours during heat treatment. It provides valuable insights into curing reactions and decomposition processes.
The parameters typically measured through TGA include the percentage of moisture, volatile substances, ash content and loss on ignition (LOI). These measurements are crucial for determining the composition of a material, its thermal stability and its behaviour during heating, which can include physical phenomena (such as phase transitions, adsorption and desorption) and chemical processes (including reactions like oxidation and reduction).
Thermogravimetric analysis instruments operate on the principle of measuring and recording weight changes in a material as it undergoes thermal treatment within a controlled environment. The essential components of a TGA analyser include a furnace chamber for heating the sample, a built-in balance for weight measurement, an external gas supply for creating inert or oxidative conditions, and a computer with software to record and evaluate data. The sample's weight is measured as it is heated, cooled, or maintained at a constant temperature, under inert or oxidative conditions, to gain information on its thermal stability, moisture content, volatile components, and more.
Thermogravimetric analysis (TGA) is of a great importance across various fields of scientific and industrial applications such as Energy Sector, Food Industry, Construction Industry, Environmental and Material Science. It provides important data on the thermal stability and composition of materials. By understanding how a material decomposes, reacts, or changes state upon heating, researchers and engineers can make conclusions about its ability to be used in certain areas, its durability and how it might behave under varying thermal and atmospheric conditions. In the area of research and development this is very important for designing materials with tailored properties to ensure safety, efficiency and durability of these upcoming products.
Furthermore, TGA is an essential tool for quality control. By ensuring that materials meet their specified thermal properties and composition, manufacturers can maintain product quality, comply with regulatory standards and avoid potential failures during the production.
Thermogravimetric analysis (TGA) offers several significant advantages over a muffle furnace. This includes automated measurement process, reducing the need for manual intervention such as weighing samples before and after heating. Unlike a muffle furnace thermogravimetric analysis instrument allows for continuous monitoring of mass change during the heating process, providing real-time measurement data. With pre-set material specific measurement applications automated analysis of samples at sequential specific temperature levels is possible.
Furthermore, TGA can operate under various controlled atmospheres (inert or oxidative). Control over the atmosphere is crucial for studying processes under inert conditions as well as oxidative or reductive behaviour of the materials. The TGA software can automatically calculate and present results such as moisture content, volatiles, ash content and loss on ignition (LOI), making the analysis process and the following calculation of the measured data easier for the operator.
ELTRA offers elemental analyzers for a wide range of solid materials.
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