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Thermal Science is regarded as a “mature science” because of the continuous advancements in research and application for more than a decade. All thermal analytical techniques measure the changes of a particular material property as a function of temperature. Even though various techniques are available, the different thermal analysis types depend on the properties of the material under consideration.
Scientists have developed various methods associated with thermal analysis (TA). These include temperature modulation, online data analysis, sample-controlled regimes, and robotic operational regimes.
TA is widely used in various fields of science, for example, in pharmaceutical sciences. Some of the widely used TA techniques in pharmaceutical science are differential scanning calorimetry (DSC), differential thermal analysis (DTA), dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA). Advancements in material science have brought about continuous changes in TA techniques.
Common Types of Thermal Analysis and their Applications
Scientists use TA techniques for the characterization of different materials. There are different types of TA, each bearing some advantages and disadvantages. Some of the common types of TA techniques used for various materials and their widespread applications are discussed below:
Thermomechanical Analysis (TMA)
TMA is a type of TA that involves studying viscoelastic materials' physical properties under mechanical loading as a function of temperature and time. In this technique, measurements are carried out in compression or tension mode, with a probe applying force to the sample.
A typical viscoelastic material generally changes its volume with ramping temperature. As the sample changes its structure, the probe moves around and measures the change in the sample's length. Subsequently, the measured length is correlated with other properties such as expansion, shrinkage, swelling, and softening. TMA has many applications, including:
- Determination of softening point (Tg) of polymers
- Measure coefficient of thermal expansion (CTE) of polymers, composites, ceramics, inorganics, and metals. It can also characterize CTE differences of polymers in the glassy and rubbery states
- Characterization of shrinkage property and dimensional stability in oriented films
Thermogravimetric Analysis (TGA)
TGA is a type of TA that involves measuring the changes in sample weight in a controlled thermal environment as a function of temperature or time. The changes in sample weight can be owing to modifications in chemical or physical properties. This technique is useful for analyzing the thermal stability of solids and liquids. A sensitive microbalance measures the change in the sample's mass as it is heated or placed isothermally in a furnace. The purgative gas surrounding the sample can be chemically inert or reactive. TGA instruments are designed so that they can switch gases during the test, as a result of which they provide wide-ranging information in a single experiment. Some of the standard applications of TGA are as follows:
- Thermal stability/degradation studies
- Quantitation of volatiles and moisture
- Vaporization and sublimation
- Decomposition kinetics
Differential Scanning Calorimetry (DSC)
DSC involves the calculation of quantitative calorimetric measurements of solid, liquid, or semisolid samples. Heat flux DSC measures the difference in temperature (T) between the sample and an inert reference. It calculates the quantity of heat flow (q), in or out of the sample, using equation q = DT/R, where R is the transducer's thermal resistance.
Two basic types of DSC instruments that are commercially available are heat-flux DSC and power compensation DSC. Some of the typical applications of DSC are listed below:
- Measure the heat capacity of pure compounds and mixtures
- Identify unknown materials
- Estimate percent crystallinity
- Determine percentage purity of relatively pure organics
- Evaluate eutectic point
- Characterize polymorphic materials
Differential Thermal Analysis (DTA)
DTA is a thermoanalytical technique, which is similar to DSC. In this process, the sample under consideration and an inert reference undergo similar thermal cycles, and the temperature difference between the sample and the reference is recorded.
The data is used to plot a thermogram that provides information about the transformations such as glass transitions, crystallization, melting, and sublimation. DTA is widely used in the pharmaceutical and food industries. It is also used in research involving cement chemistry, archaeological materials, and mineralogical research.
Evolved Gas Analysis (EGA)
EGA is used to detect the gasses released from heated samples undergoing decomposition or desorption. Evolved gas detection (EGD) is generally performed by coupling EGA with mass spectrometry, gas chromatography, Fourier transform spectroscopy or Optical In-Situ Evolved Gas Analysis.
Dynamic Mechanical Analysis (DMA)
DMA is used to measure viscoelastic properties under the influence of a low mechanical force. The viscoelasticity of polymers is dependent on temperature and time. Generally, polymers respond (elastic and viscous response) differentially to the energy of motion. Some of the common applications of DMA are as follows:
- Evaluation of viscoelastic spectrum.
- Determination of glass transition (Tg) of polymers
- Characterization of dissipation of mechanical energy through internal motion
- Comparative and failure analysis of polymers
Other Applications of Thermal Analysis
Pharmaceutical Sciences
TA methods are widely used to test samples that are solid, semi-solid, or liquid, and most applications are directed towards pharmaceutical research. One of the standard applications is the characterization of physicochemical properties of crystalline solids. It is also used to identify polymorphic forms and to study lyophilization effects.
Soil and Metal Science
Thermal analysis techniques are used in the study of clay mineralogy. Scientists have suggested that soil thermograms represent characteristic properties of soil. This technology is also used to produce many metals such as cast iron, ductile iron, compacted graphite iron, copper alloys, and silver.
Food Research
The influence of temperature on food is enormous. Therefore, a better understanding of temperature’s effect on various food properties will help food manufacturers optimize the processing conditions and improve product quality.
References and Further Reading
Feist, M. (2015) Thermal analysis: basics, applications, and benefit. ChemTexts, 1, 8. https://doi.org/10.1007/s40828-015-0008-y
Stodghill, P.S. (2010) Thermal Analysis – A Review of Techniques and Applications in the Pharmaceutical Sciences. American Pharmaceutical Review, 13 (12), Available at: https://www.americanpharmaceuticalreview.com/Featured-Articles/36776-Thermal-Analysis-A-Review-of-Techniques-and-Applications-in-the-Pharmaceutical-Sciences/
Hill, J.O. (2005) Thermal analysis-Overview, Editor(s): Paul Worsfold, Alan Townshend, Colin Poole, Encyclopedia of Analytical Science (Second Edition), Elsevier, pp. 17-22 https://doi.org/10.1016/B0-12-369397-7/00613-0
Pyramides, G., Robinson, J.W. and Zito, S.W. (1995) The combined use of DSC and TGA for the thermal analysis of atenolol tablets. Journal of Pharmaceutical and Biomedical Analysis. 13(2), pp.103-10. https://doi.org/10.1016/0731-7085(94)00112-f
Instrument Specialist Incorporated. Thermal Analysis. [Online]. Available at: https://instrument-specialists.com/thermal-analysis-applications/
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