Ceramics are inorganic, nonmetallic materials that are essential in daily life. Common types of ceramics are typically composed of carbides, nitrides, and oxides. Selenides, tellurides, phosphides, borides, and silicides are also used for ceramics production.1 These materials are widely used in various products, such as watches, automobiles, and phone lines.2
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What Are Ceramic Materials?
Ceramics possess a diverse range of properties that enable their use in various applications. These include low thermal conductivity, high heat capacity, corrosion resistance, oxidation resistance, and wear resistance. Additionally, most ceramics are hard, strong, chemically stable, brittle, and nonmagnetic and serve as thermal and electrical insulators.2,3
The properties of ceramic materials are influenced by the types of atoms present, the bonding between these atoms, and their arrangement. Most ceramics consist of two or more elements, with prevalent bonding mechanisms being covalent and ionic bonds.2 These mechanisms often coexist within the same material, and each bonding type results in different characteristics.3
Ionic bonds typically occur between nonmetallic and metallic elements with significant differences in electronegativity, resulting in structures with high melting points due to their non-directional and strong nature. Covalent bonds form between nonmetallic elements with smaller electronegativity differences.3
Compounds dominated by either covalent or ionic bonding tend to have higher melting points than those with mixed bonding. For example, magnesium oxide (73 % ionic character, 27 % covalent character) melts at 2798 °C, silicon carbide (11 % ionic, 89 % covalent) at 2500 °C, and silicon dioxide (49 % covalent, 51 % ionic) at 1715 °C.3
The properties of ceramics influenced by bonding mechanisms include low ductility, high wear strength, poor thermal conductivity, elevated modulus and fusion temperatures, as well as high hardness, brittleness, and tenacity.4
Ceramic Production
Ceramic production involves synthesizing powder, mixing, shaping, and thermal treatment, where sintering occurs through intergranular-liquid phase formation or solid-state diffusion. Ceramic powders are obtained through synthetic routes, such as precipitation or sol-gel processes, or by treating natural raw materials like rock minerals.4
The next step involves forming ceramic particles into specific shapes with low mechanical strength and high porosity by adding water or binders, followed by various shaping processes.5 Common forming techniques include injection molding, tape casting, axial and isostatic dry pressing, slip casting, and extrusion.4,5
The goal is to achieve low porosity and high particle packing, with the choice of process depending on the desired product, costs, and time considerations.4 After the ceramic particles are formed, these "green" ceramics undergo thermal treatment to produce a rigid final product.5
Compact densification occurs during the sintering process, which can occur via three mechanisms: reactive sintering, liquid-phase sintering, or solid-state sintering. The initial density of green ceramics is typically 40–60 % of the theoretical density, while the final density can reach 85–100 %.4
Types of Ceramics
Ceramics can be classified into advanced (technical) ceramics and traditional ceramics. Traditional ceramics are based on silicates, such as refractories and clay products, produced in large volumes using raw materials from natural deposits.4
Clay is the most commonly used raw material in traditional ceramics as it is easily formed and has abundant natural availability. It primarily consists of hydrated aluminum silicates. Additionally, most clay products include inexpensive fillers, such as quartz, and feldspar/flux, which forms glass to bind ceramic particles during heat treatment.6
Clay is utilized in whitewares like sanitaryware, tableware, and pottery, as well as in structural clay products such as tiles, pipes, and bricks. Its workability stems from the plate-like shape of its particles.
The electrical charge on clay particles attracts water molecules, causing them to wedge between neighboring particles.6 The water acts as a lubricating layer between the plate-like particles during molding, allowing them to slide over one another with minimal friction while maintaining an atomic bridge that holds the particles together.6
Advanced ceramics are produced from artificial raw materials that undergo significant chemical processing to achieve high purity and enhance their physical properties.4 Examples of advanced ceramics include oxides such as zirconia and alumina, nitrides like titanium nitride and silicon nitride, borides, carbides such as silicon carbide, and various ceramics with superconducting, piezoelectric, ferroelectric, and magnetic applications.
These advanced ceramics demonstrate exceptional mechanical properties under extreme conditions, including high wear strength, resistance to aggressive chemicals, and durability in corrosive environments.4,7
They also possess unique electrical, magnetic, and optical properties, along with remarkable resistance to high temperatures and chemical attacks.4,7 As a result, advanced ceramics have significant potential for applications in sound, electricity, heat, light, biology, magnetism, and chemistry.7
The Future of Ceramics
In addition to existing applications, ceramics also hold significant potential in aerospace, electronics, and sustainability.8,9 For example, ceramic materials are ideal for lightweight hot-section components in aircraft turbine engines and thermal protection systems for space vehicles due to their lower densities compared to metals.8
Advanced ceramics also play a vital role in electronics. They are commonly used for sensors, capacitors, superconductors, semiconductors, varistors, ionic conductors, and substrate/packaging applications. For instance, boron nitride, aluminum nitride, and alumina serve as electronic substrates, while titanate compositions are employed in sensors, actuators, ferroelectrics, and capacitors.9
In summary, ceramics have significantly influenced history, evolving from traditional pottery to advanced technological applications, highlighting their versatility and importance. Ongoing innovations are expected to further enhance the role of ceramics in diverse fields such as aerospace, electronics, and sustainable energy solutions, showcasing their potential for future advancements.
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References and Further Reading
- U.S. Environmental Protection Agency. (n.d.). Ceramic Products Manufacturing. [Online] Available at https://www3.epa.gov/ttn/chief/ap42/ch11/final/c11s07.pdf (Accessed on 17 September 2024)
- University of Washington. (n.d.). Ceramics. [Online] University of Washington. Available at https://depts.washington.edu/matseed/mse_resources/Webpage/Ceramics/ceramics.htm (Accessed on 17 September 2024)
- University of Illinois. (n.d.). Scientific Principles [Online] University of Illinois. Available at https://matse1.matse.illinois.edu/ceramics/prin.html (Accessed on 17 September 2024)
- Eliche-Quesada, D., Pérez-Villarejo, L., José Sánchez-Soto, P. (2019). Introduction to Ceramic Materials: Synthesis, Characterization, Applications, and Recycling. Ceramic Materials-Synthesis, Characterization, Applications and Recycling. Available at: https://www.researchgate.net/publication/331493333_Introduction_to_Ceramic_Materials_Synthesis_Characterization_Applications_and_Recycling
- University of Washington. (n.d.). Ceramic Processing. [Online] University of Washington. Available at https://depts.washington.edu/matseed/mse_resources/Webpage/Ceramics/ceramicprocessing.htm (Accessed on 17 September 2024)
- UNSW Sydney. (n.d.). Traditional ceramics. [Online] UNSW Sydney. Available at https://www.unsw.edu.au/science/our-schools/materials/engage-with-us/high-school-students-and-teachers/online-tutorials/ceramics/forming-and-processing/traditional-ceramics (Accessed on 17 September 2024)
- Ayode Otitoju, T., Ugochukwu Okoye, P., Chen, G., Li, Y., Onyeka Okoye, M., Li, S. (2020). Advanced ceramic components: Materials, fabrication, and applications. Journal of Industrial and Engineering Chemistry. DOI: 10.1016/j.jiec.2020.02.002, https://www.sciencedirect.com/science/article/abs/pii/S1226086X20300757
- Zhu, D. (2018) Aerospace Ceramic Materials: Thermal, Environmental Barrier Coatings and SiC/SiC Ceramic Matrix Composites For Turbine Engine Applications. [Online] NASA. Available at https://ntrs.nasa.gov/citations/20180002984 (Accessed on 17 September 2024)
- Science Direct. (n.d.). Electronic Ceramics. [Online] Science Direct. Available at https://www.sciencedirect.com/topics/materials-science/electronic-ceramics (Accessed on 17 September 2024)
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