What Is Thermal Analysis?

Thermal analysis is used to study how a material’s physical or chemical properties change with temperature or time. Depending on the technique, it can reveal phase transition such as melting, crystallization, glass transitions, thermal decomposition, oxidation, dehydration, dimensional changes, and other temperature-dependent behavior.

Because many materials undergo characteristic changes when heated or cooled, thermal analysis is widely used for material identification, formulation development, stability studies, failure analysis, quality control, and process optimization. It can be applied to polymers, pharmaceuticals, ceramics, metals, foods, batteries, chemicals, and many other materials.

Each thermal analysis technique measures a different property of a sample as temperature changes.

Thermogravimetric analysis (TG or TGA) measures changes in sample mass and is useful for studying processes such as dehydration, volatilization, oxidation, and thermal decomposition.

Differential scanning calorimetry (DSC) measures changes in heat flow associated with transitions such as melting, crystallization, glass transition, and chemical reactions.

Differential thermal analysis (DTA) measures temperature differences between a sample and a reference, making it useful for detecting thermal events such as melting, crystallization, and reactions.

Thermomechanical analysis (TMA) measures dimensional or mechanical changes under a controlled load, making it useful for determining properties such as thermal expansion, softening, shrinkage, and sintering behavior.

The appropriate technique depends on which property or transition needs to be characterized.

Thermogravimetric analysis measures changes in a sample’s mass with temperature or time. A sample is heated, cooled, or held at a specified temperature while a sensitive balance continuously monitors its mass.

Mass loss can indicate processes such as evaporation of moisture or solvents, decomposition of organic components, or release of gases. Mass gain may occur during processes such as oxidation.

Because different components can undergo mass changes at different temperatures, TG can also help characterize multicomponent materials and evaluate thermal stability. When TG is combined with another technique, such as DSC or evolved gas analysis, researchers can correlate mass changes with thermal events or identify the gases released during decomposition. Rigaku offers simultaneous TG-DSC as well as coupled evolved-gas-analysis systems for this purpose.

Differential scanning calorimetry measures changes in heat flow as a sample is heated or cooled according to a controlled temperature program. It can detect both endothermic and exothermic events associated with physical transitions and chemical reactions.

Common DSC measurements include melting temperature, crystallization temperature, glass transition temperature, crystal transition temperature, reaction temperatures, and the amount of heat associated with these processes.

DSC is particularly valuable for polymers, pharmaceuticals, foods, chemicals, and other materials whose performance depends on thermal history or physical state. For example, it can be used to compare formulations, evaluate crystallinity, investigate curing reactions, or determine whether processing has altered a material.

Advanced DSC configurations can also extend measurements to lower or higher temperatures and allow direct observation of changes occurring in the sample during analysis.

Thermomechanical analysis measures changes in a sample’s dimensions or mechanical behavior while the sample is subjected to a controlled temperature program and an applied load.

TMA can determine properties such as thermal expansion, coefficient of thermal expansion, softening temperature, glass transition behavior, shrinkage, and sintering behavior.

These measurements are especially useful when materials must maintain dimensional stability over a range of operating temperatures. Applications include polymers, ceramics, glasses, electronic materials, composites, and other engineered materials.

For example, TMA can reveal whether two materials used together have significantly different thermal expansion behavior, which may contribute to warping, cracking, delamination, or other reliability problems during temperature cycling.

Simultaneous thermal analysis measures two or more thermal properties of the same sample during the same temperature program. A common example is simultaneous thermogravimetry and differential scanning calorimetry, or TG-DSC.

TG measures changes in sample mass, while DSC measures changes in thermal energy. Measuring both at the same time makes it easier to determine whether a thermal event is associated with a mass change.

For example, a DSC peak accompanied by mass loss may indicate decomposition or volatilization, while a thermal event without a corresponding mass change may instead represent melting, crystallization, or a solid-state transition.

Because the measurements are performed on the same sample under identical conditions, simultaneous analysis can make interpretation more straightforward than comparing separate experiments. Rigaku's STAvesta systems combine TG and DSC measurements in a single instrument.

Evolved gas analysis identifies gases released from a material as it is heated or decomposes. It is commonly coupled with thermogravimetric analysis so that changes in sample mass can be correlated with the chemical species being released.

Techniques such as mass spectrometry, gas chromatography-mass spectrometry, and Fourier transform infrared spectroscopy can be combined with thermal analysis. For example, TG-FTIR can identify gases produced at different temperatures, while TG-GCMS provides more detailed separation and identification of complex mixtures.

This additional chemical information can be valuable when TG alone shows that mass has been lost but cannot determine what substance caused the change. Applications include polymer degradation, pharmaceutical characterization, identification of additives or contaminants, and investigation of complex decomposition reactions.

Thermal analysis and X-ray diffraction provide complementary information about materials.

Thermal analysis measures changes that occur as a material is heated, cooled, or held at a particular temperature. Depending on the method, it can detect changes in mass, heat flow, or dimensions, as well as thermal events such as decomposition.

X-ray diffraction (XRD) can be used to characterize crystalline structure and phases. It can identify crystalline materials, distinguish polymorphs, quantify phases, and provide information about crystallinity and structural changes.

Combining thermal analysis with XRD can provide a more comprehensive understanding of material changes. For example, DSC may show that a transition occurs at a particular temperature, while XRD can determine whether that transition corresponds to a change in crystal structure or phase composition.