This article considers the use of the differential thermal analysis method applied to technical ceramics as well as recent research and developments.
Scientist and thermogravimetric/differential thermal analyzer. Image Credit: Image Source Trading Ltd/Shutterstock.com
The invention of thermocouples led to the development of the Differential Thermal Analysis (DTA) method. DTA has progressed through systematic scientific development, and now researchers use state-of-the-art equipment and can perform analyzes for different types of materials using this method. Moreover, this technique is essential to control the atmospheric composition and the pressure of the furnace and to analyze the thermodynamics and the kinetics of the chemical reactions. Although DTA is performed on a variety of materials, the most common application of DTA is the analysis of engineered ceramics.
Thermal analysis of materials
Thermal analysis is the study of a change in the property of a material due to a variation in temperature. When the material is heated, the thermal changes that occur in the material include melting, phase transition, sublimation, and decomposition, which can be studied using thermal analysis methods.
Thermogravimetric (TG) analysis studies the properties of materials during heating in a controlled atmosphere. TG measures the changes in mass of a material as a function of temperature or time, and its main applications are the analysis of the thermal stability and the examination of the composition of a material. The properties measured using TG are dehydration, decomposition, desorption and oxidation of materials. Several industries and scientists use the DTA method to perform TG analysis of materials.
In DTA analysis, the test sample and an inert reference are heated and cooled under identical conditions, and the temperature differences between the two are recorded. The difference in heat flux between the reference and the sample is calculated by plotting the differential temperature curves and the phase diagrams. The curves are plotted taking time, temperature and heat flux as variables. Accordingly, the absorption or evolution of heat from the sample can be detected with reference to the inert sample.
Studies on phase diagrams, transition temperatures and qualitative analyzes of materials are carried out using the DTA method, and it is mainly used for materials such as metals, oxides, salts, ceramics , glasses, minerals and soils.
DTA Analysis of Ceramics
A DTA curve can be used to analyze structural similarity, which is difficult to study using diffraction experiments. Additionally, mass and temperature changes in ceramics can also be investigated using DTA curves.
The main advantage of DTA analysis of ceramics is that it can be used in high temperature analysis using very sensitive instruments. Additionally, the reaction temperatures of ceramics can be accurately determined using the DTA. The limitation is that the temperature difference of the reference sample and the test sample estimated during the analysis may be inaccurate, which affects the main results. Moreover, the difference between the heat variation of the reference samples and the tested sample can also cause errors during the experiment.
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In the DTA analysis of ceramic material, the shape, temperature and intensity of the low-temperature endothermic loop of the DTA curve are associated with water loss and mainly depend on the exchange cations. Similarly, the high temperature exothermic loop is associated with the formation of new compounds and also depends on the exchange cations. In addition, the temperature of the medium temperature endothermic loop is influenced by the partial pressure of the water.
In a recent study published in the journal MetalsChinese researchers have examined the influence of Fe2O3 on the crystallization behavior of glass-ceramics. In the study, DTA analysis was used to examine changes in crystallization temperature and transition temperature of glass with respect to Fe2O3 volume.
In another study published in the journal Open ceramic, researchers conducted a study to analyze the effect of boron sources on the thermal behavior of clay-based ceramics. Based on DTA analysis, researchers examined the behavior of boron oxide sources as fluxing agents.
Technological development in DTA
Measuring the dimensional change of the material under study is the most appropriate method to examine the ceramic sintering process, as it directly represents the densification process. However, traditional thermal analysis techniques such as DTA and TG analysis cannot provide complete information about the sintering rate of ceramic material.
Dimensional changes can be effectively measured using the dual beam optical dilatometer during DTA analysis. In a dual-beam optical dilatometer, two independent optical systems focus on the edges of the sample, optimizing the sensitivity and accuracy of the experiment.
In this process, changes in the top of the sample are measured using the first optical path and a stepper motor. The second optical path is focused on the sample holder and serves as a reference beam to compensate for the mechanical drift of the sample holder. Therefore, this process can effectively examine the sintering rate of ceramics.
The sections above develop the DTA analysis of technical ceramics and its importance in the study of phase diagrams, transition temperatures and qualitative analyzes of materials. They also discuss technological developments in DTA analysis to estimate the rate of sintering in ceramics.
References and further reading
Rowland, RA Differential thermal analysis of clays and carbonates. Clay miner. 1, 151–163 (1952). DOI: https://link.springer.com/article/10.1346/CCMN.1952.0010118
Pomeroy, Michael J. “Thermal Analysis Techniques for Technical Ceramics and Glasses.” (2021): 676-688. DOI: https://www.sciencedirect.com/science/article/pii/B978012818542100059X?via%3Dihub
Li, X.; Zang, X.; Xing, X.; Li, J.; Can.; Li, T. Effect of Fe2O3 on the crystallization behavior of glass-ceramics produced from secondary nickel slag. Metals 2022, 12, 164. DOI: https://www.mdpi.com/2075-4701/12/1/164
Mari.F. Hernández, PV López, Marí.S. Conconi, Nicolá.M. Rendtorff, Effect of boron sources on the thermal behavior of clay-based ceramics, Open Ceramics (2022), DOI: https://www.sciencedirect.com/science/article/pii/S2666539522000104
Non-contact optical measurement for the analysis of ceramic materials during rapid heat treatments. https://www.azom.com/article.aspx?ArticleID=11524