Thermal analysis is a field within materials science for investigating how material properties transform in response to changes in temperature. It is crucial when developing materials that are used or processed in low or high temperatures, including polymers, metals, food, and pharmaceuticals.
Factors to consider in method selection
Thermal analysis techniques offer remarkable versatility in terms of the properties that can be evaluated, enabling the characterization of substances in solid, semi-solid, and liquid states. When choosing an appropriate method, the following should be considered:
Properties to be determined
Type of material
Temperature range
Sample state
Table 1 lists key properties determinable through thermal analysis, along with the techniques suitable for analyzing them. More information on each technique’s ideal applications and technical specifications is provided further on in the article.
Table 1: Analysis techniques for determining selected thermal properties
Property | DSC | TGA | EGA | TMA | DMA | Dilatometry |
Specific heat capacity | x | |||||
Enthalpy changes | x | |||||
Melting and crystallinity | x |
|
| x | x | |
Glass transition (Tg) | x |
|
| x | x | |
Purity | x | (x) | (x) | |||
Expansion coefficient |
|
|
| x |
| x |
Polymorphism | x |
|
| x | ||
Evaporation, sublimation, desorption | x | x | x | |||
Composition (fillers, ash, moisture) | x | x | x | |||
Degradation, decomposition, pyrolysis | (x) | x | x | |||
Reaction enthalpies/kinetics | x | x | ||||
Crosslinking |
| x |
|
| x | |
Stability | (x) | x | x | |||
Oxidation and oxidative degradation | x | x | ||||
Viscoelasticity |
|
|
| (x) | x | |
Elastic and shear modulus |
|
|
|
| x | |
Damping |
|
|
|
| x |
x denotes a technique ideal for determining the property, whereas (x) denotes a technique that can be used but is not optimal.
Thermal analysis with DSC
Differential scanning calorimetry (DSC) is a powerful analysis technique that measures the amount of heat released or absorbed by the sample as it undergoes heating or cooling. DSC is affordable and provides information on a wider range of properties than most other thermal analysis methods, which makes it a good starting point in thermal characterization.
Ideal applications of DSC include determining the melting point (Tm), crystallization point (Tc), glass transition (Tg), thermal stability, and heat capacity of samples including polymers, pharmaceuticals, food, and inorganic compounds. The method also provides insight into chemical reactions, such as oxidation, and can help detect changes in sample composition, purity, and crystallinity.
Technical specifications:
Typical temperature range: -170 °C – 600 °C
Heat-up rate: 0.1°C–200°C/min.
Atmosphere: nitrogen. For oxidation analysis: oxygen or air.
Required sample mass: 100 mg
Thermal analysis with TGA and EGA
Thermogravimetric analysis (TGA) measures the mass change of a sample as it is heated or cooled under a controlled environment. The method is ideal for determining thermal stability and composition in terms of moisture, ash, filler, and volatile content of materials including polymers, food, pharmaceuticals, construction materials, and environmental samples.
TGA is highly sensitive, requires only a small amount of sample material, and provides quantitative, reproducible results. However, it may be challenging to determine the cause of the measured mass change with TGA alone, as it does not directly distinguish between physical and chemical phenomena occurring during temperature changes. A more comprehensive understanding of material behavior can be achieved in combination with other techniques, such as DSC, FTIR, or MS.
Technical specifications:
Typical temperature range: RT – 1100 °C
Heat-up rate: 0.1 °C–200 °C/min.
Atmosphere: inert nitrogen at lower temperatures, air or oxygen in higher temperatures (> 600 °C)
Required sample mass: 10 mg
The combination of TGA with FTIR, MS, or GC/MS is known as evolved gas analysis (EGA). EGA enables identifying the gasses that are released from a sample when it is heated, the amounts evolved, and the temperatures they are released at, providing additional insight into the thermal stability of the material under heating.
Thermal analysis with TMA
Thermomechanical analysis (TMA) measures the dimensional changes (strain) of solid materials with respect to time/temperature, or when a load is applied within a given temperature range. Properties determinable using TMA include glass transition (Tg), coefficient of linear thermal expansion (CLTE), shrinkage force, Young’s modulus, heat deflection under loading (HDUL), heat deflection temperature (HDT), stress relaxation modulus, and creep compliance.
When determining the Tg of polymers, TMA can give more accurate results than DSC for materials with a high crosslink density or large filler content. TMA is also highly useful for determining the CLTE of composites in situations where the thermal expansion of two interconnected materials might result in a strain induced by thermal stress. The main limitation is relatively complex sample preparation, as samples need to be manufactured in defined geometries, depending on the type of load applied.
Technical specifications:
Typical temperature range: -150 – 1100 °C
Force range: 0.001N – 2N
Atmosphere: Ambient (air)
Sample requirements: Variable geometry of solid material depending on the test.
Thermal analysis with DMA
Dynamic mechanical analysis (DMA), also known as dynamic mechanical thermal analysis (DMTA), is similar to TMA but utilizes an oscillatory/sinusoidal application of stress or strain to determine viscoelastic properties, such as storage modulus (E’), loss modulus (E”), and damping factor (tan(δ)), along with the way they change at different temperatures. DMA is often used to compare the toughness, impact strength, rigidity, and flexibility of materials with one another. It can also help determine the appropriate temperature range where these properties are optimal for the material's intended application.
DMA provides a full viscoelastic profile of the material, from which considerably more information can be obtained than is possible with TMA. DMA is also the most accurate method for determining glass transition (Tg), but it is more expensive than DSC and TMA and tends to have a lower maximum temperature than the latter.
Technical specifications:
Typical temperature range: -150 – 600 °C
Parameters: Temperature rate of increase, frequency, and force negotiable.
Atmosphere: Ambient (air)
Sample requirements: Variable geometry of solid material depending on the test.
Thermal analysis with dilatometry
Dilatometry measures dimensional changes associated with heating or cooling the sample within a temperature range of -180 to 1,000 °C. The measurement can be done either visually, with an optical dilatometer, or physically, with a push rod dilatometer. The primary application of dilatometry is determining the coefficient of linear thermal expansion (CLTE, α) of materials that are rigid or solid within the given temperature range.
Dilatometry can also measure the temperature at which chemical reactions or phase changes occur when the preceding phenomena are accompanied by a change in volume but not in mass, making TGA measurement unfeasible. For most other thermal properties, such as glass transition (Tg) and melting temperature (Tm), DSC is a cheaper and more accurate alternative.
Technical specifications:
Typical temperature range: -180 – 1000 °C
Resolution: 0.1 µm (inorganics) – 3.5 µm (plastics)
Atmosphere: Ambient (air), oxygen, nitrogen, or helium
Sample requirements: Specified cylindrical or rectangular geometry
Measurlabs offers thermal characterization services with all the methods described above. Do not hesitate to contact our experts through the form below to discuss your analysis needs and to request a quote for your material.