Ceramics

Summary

Ceramics is a specialty field of materials engineering that includes traditional and advanced ceramics, which are inorganic, nonmetallic solids typically created at high temperatures. Ceramics form components of various products used in multiple industries and new applications are constantly being developed. Examples of these components are rotors in jet engines, containers for storing nuclear and chemical waste, and telescope lenses.

Definition and Basic Principles

Ceramic engineering is the science and technology of creating objects from inorganic, nonmetallic materials. A specialty field of materials engineering, ceramic engineering involves the research and development of products such as space shuttle tiles and rocket nozzles, building materials, ball bearings, glass, spark plugs, and fiber optics.

Ceramics can be crystalline in nature; however, in the broader definition of ceramics (which includes glass, enamel, glass ceramics, cement, and optical fibers) they can also be noncrystalline. The most distinguishing feature of ceramics is their ability to resist extremely high temperatures. This makes ceramics very useful for tasks where materials such as metals and polymers alone are unsuitable. For example, ceramics are used in the manufacture of disk brakes for high-performance cars (such as race cars) and for heavy vehicles (such as trucks, trains, and aircraft). These brakes are lighter and more durable and can withstand greater heat and speed than conventional metal-disk brakes. Ceramics can also be used to increase the efficiency of turbine engines used to operate helicopters. These aircraft have a limited travel range and cannot carry a great deal of weight because of the stress these activities place on engines made of metallic alloys. However, turbine engines using ceramic parts and thermal barrier coatings have been developed and show superior performance when compared with existing engines. The ceramic engine parts are from 30 to 50 percent lighter than their metallic counterparts, and the thermal coatings increase the engine operating temperatures to 1,650 degrees Celsius (C). These qualities are expected to enable future helicopters to travel farther and carry more weight.

Background and History

One of the oldest industries on Earth, ceramics dates back to prehistoric times. The earliest known examples of ceramics, animal and clay figures that were fired in kilns, date back to 24,000 Before the Common Era (BCE). These ceramics were earthenware that had no glaze. Glazing was discovered by accident, and the earliest known glazed items date back to 5000 BCE. Chinese potters studied glazing and first developed a consistent glazing technique. Glass was first produced around 1500 BCE. The development of synthetic materials with better resistance to very high temperatures in the 1500s enabled the creation of glass, cement, and ceramics on an industrial scale. The ceramics industry has grown in leaps and bounds since then.

Many notable innovators have contributed to the growth of advanced ceramics. In 1709, Abraham Darby, a British brass worker and key player in the Industrial Revolution, first developed a smelting process for producing pig iron using coke instead of wood as fuel. Coke is now widely used in the production of carbide ceramics. In 1888, Austrian chemist Karl Bayer first separated alumina from bauxite ore. This method, known as the Bayer process, is still used to purify alumina. In 1893, Edward Goodrich Acheson, an American chemist, electronically fused carbon and clay to create carborundum, also known as synthetic silicon carbide, a highly effective abrasive.

Other innovators include brothers Pierre and Jacques Curie, French physicists who discovered piezoelectricity around 1880; French chemist Henri Moissan, who combined silicon carbide with tungsten carbide around the same time as Acheson; and German mathematician Karl Schröter, who in 1923 developed a liquid-phase sintering method to bond cobalt with the tungsten-carbide particles created by Moissan.

The need for high-performance materials during World War II helped accelerate ceramic science and engineering technologies. Development continued throughout the 1960s and 1970s when new types of ceramics were created to facilitate advances in atomic energy, electronics, and space travel. This growth continues as new uses for ceramics are researched and developed.

How It Works

There are two main types of ceramics: traditional and advanced. Traditional ceramics are so-called because the methods for producing them have existed for many years. The familiar methods of creating these ceramics—digging clay, molding the clay by hand, or using a potter's wheel, firing, and then decorating the object—have been around for centuries and have only been improved and mechanized to meet increasing demand. Advanced ceramics, which cover the more recent developments in the field, focus on products that make full use of specific properties of ceramic or glass materials. For example, ferrites, a type of advanced ceramics, are very good conductors of electricity and are typically used in electrical transformers and superconductors. Zirconia, another type of advanced ceramics, is strong, tough, very resistant to wear and tear, and does not cause an adverse reaction when introduced to biological tissue. This makes it ideal for use in creating joint replacements in humans. It works particularly well in hip replacements, but it is also useful for knee, shoulder, and finger joint replacements. The unique qualities of these and other advanced ceramics, and the research into the variety of ways they can be applied, are what differentiate them from traditional ceramics.

There are seven basic steps to creating traditional ceramics. They are described in detail below.

Raw Materials. In this first stage, the raw materials are chosen to create a ceramic product. The type of ceramic product to be created determines the type of raw materials required. Traditional ceramics use natural raw materials, such as clay, sand, quartz, and flint. Advanced ceramics require the use of chemically synthesized powders.

Beneficiation. Here, the raw materials are treated chemically or physically to make them easier to process.

Batching and Mixing. In this step, the parts of the ceramic product are weighed and combined to create a more chemically and physically uniform material to use in forming, the next step.

Forming. The mixed material is consolidated and molded to create a cohesive body of the determined shape and size. Forming produces a “green” part, which is soft and pliable and, if left at this stage, will lose its shape over time.

Green Machining. This step eliminates rough surfaces, smooths seams, and modifies the size and shape of the green part to prepare for sintering.

Drying. Here, the water or other binding agent is removed from the formed material. Drying is a carefully controlled process that should be done as quickly as possible. After drying, the product will be smaller than the green part. It is also very brittle and must be handled carefully.

Firing or Sintering. The dried parts now undergo a controlled heating process. The ceramic becomes denser during firing, as the spaces between the individual particles of the ceramic are reduced as they heat. It is during this stage that the ceramic product acquires its heat-resistant properties.

Assembly. This step occurs only when ceramic parts need to be combined with other parts to form a complete product. It does not apply to all ceramic products.

This is not a comprehensive list. More steps may be required depending on the type of ceramic product being made. For advanced ceramics production, this list of steps will either vary or expand. For example, an advanced ceramic product may need to have forming or additives processes completed in addition to the standard forming processes. It may also require a post-sintering process such as machining or annealing.

Applications and Products

Traditional Ceramics. Applications and products include whiteware, glass, structural clay items, cement, refractories, and abrasives. Whiteware, so named because of its white or off-white color, includes dinnerware (plates, mugs, and bowls), sanitary ware (bathroom sinks and toilets), floor and wall tiles, dental implants, and decorative ceramics (vases, figurines, and planters). Glass products include containers (bottles and jars), pressed and blown glass (wineglasses and crystal), flat glass (windows and mirrors), and glass fibers (home insulation). Structural clay products include bricks, sewer pipes, flooring, and wall and roofing tiles. Cement is used in the construction of concrete roads, buildings, dams, bridges, and sidewalks. Refractories are materials that retain their strength at high temperatures. They are used to line furnaces, kilns, incinerators, crucibles, and reactors. Abrasives include natural materials such as diamonds and garnets and synthetic materials such as fused alumina and silicon carbide, which are used for precision cutting as well.

Advanced Ceramics. Advanced ceramics focus on specific chemical, biomedical, mechanical, or optical uses of ceramic or glass materials.

Advanced ceramics fully came into being starting in the late twentieth century (beginning in the 1960s), and research and development are ongoing. The field has produced a wide range of applications and products. In aerospace, ceramics are used in spacecraft tiles, aircraft instrumentation and control systems, missile nose cones, rocket nozzles, and thermal insulation. Automotive applications include spark plugs, brakes, clutches, filters, heaters, fuel pump rollers, and emission control devices. Biomedical uses for ceramics include replacement joints and teeth, artificial bones and heart valves, hearing aids, pacemakers, dental veneers, and orthodontics. Electronic devices that use ceramics include insulators, magnets, cathodes, antennae, capacitors, integrated circuit packages, and superconductors. Ceramics are used in the chemical and petrochemical industry for ceramic catalysts, catalyst supports, rotary seals, thermocouple protection tubes, and pumping tubes. Laser and fiber-optics applications for ceramics include glass optical fibers (used for very fast data transmission), laser materials, laser and fiber amplifiers, lenses, and switches. Environmental uses of ceramics include solar cells, nuclear fuel storage, solid oxide fuel cells, hot gas filters (used in coal plants), and gas turbine components. Ceramic coatings include self-cleaning coatings for building materials, coatings for engine components, cutting tools, industrial wear parts, optical materials (such as lenses), and anti-reflection coatings.

Other products in the advanced ceramics segment include water-purification devices, particulate or gas filters, and glass-ceramic stovetops. The ceramics industry continues to innovate. Advances in 3D printing using ceramics and new materials, including functional and bioactive ceramics, have provided innovations across many fields. The use of ceramics for environmental projects, such as air purification or the creation of increased-efficiency batteries, is also being studied.

Careers and Course Work

Ceramic scientists and engineers work in various industries, as their skills are applicable in various contexts. These fields include aerospace, medicine, mining, refining, electronics, nuclear technology, telecommunications, transportation, and construction. A bachelor's degree is required for entrance into the above-mentioned fields. A master's degree in ceramic engineering qualifies the holder for managerial, consulting, sales, research, development, and administrative positions.

Pursuing a career in this field requires an aptitude for the sciences. Most colleges require that high school coursework includes four years of English, four years of math (at least one of which should be an advanced math course), at least three years of science (one of which should be a laboratory science), and at least two years of a foreign language.

Typical course work for a bachelor's degree in ceramics engineering includes calculus, physics, chemistry, statistics, materials engineering, and glass engineering. It also includes biology, mechanics, English composition, process design, and ceramic processing.

Only a few universities in the United States offer bachelor's degrees in ceramic engineering. These include the Inamori School of Engineering at Alfred University and Missouri University of Science and Technology. Other universities, such as Iowa State University and Ohio State University, offer a bachelor's degree in materials engineering with a specialization in ceramics engineering. Additionally, some schools offer a combined-degree option: Undergraduate students can combine undergraduate and graduate coursework to earn a bachelor's and a master's or doctorate in materials engineering with a concentration in ceramics simultaneously.

An alternative to acquiring a bachelor's degree in ceramics engineering is to acquire a degree in a related field and then pursue a master's degree in ceramics engineering. Examples of related fields include biomedical engineering, chemical engineering, materials engineering, chemistry, physics, and mechanical engineering.

Several universities in the United States offer master's degrees in ceramic engineering. Admission into these programs is extremely competitive. Graduate students focus primarily on research and development, though they are required to take classes. Doctoral candidates also focus on research and development, and after they have been awarded their degree, they can choose to teach or continue working in research.

Social Context and Future Prospects

As mentioned in the preceding sections, the advanced ceramics segment of the field, which is the primary focus of ceramic engineering, has plenty of room for growth. The number of materials engineers (including ceramic engineers) employed nationally and the small number of ceramic engineers teaching in colleges continued to grow. The number of job openings is expected to exceed the number of engineers available. Men vastly outnumber women in this field.

Many industries in which ceramic engineers work—stone, clay, and glass products; primary metals; fabricated metal products; and transportation equipment industries—are expected to experience little employment growth during the 2020s and beyond. However, employment opportunities are expected to grow in service industries (research and testing, engineering and architectural). This is primarily because more firms, and by extension, more ceramic engineers, will be hired to develop improved materials for industrial customers. Increasingly, a computer modeling and simulation background is needed in ceramic engineering as the technology replaces more traditional laboratory testing of new materials. 

Bibliography

Barsoum, M. W. Fundamentals of Ceramics. 2nd ed. London: Inst. of Physics, 2020.

Callister, William D. Jr., and David G. Rethwisch. Materials Science and Engineering: An Introduction. 10th ed. Hoboken: Wiley, 2020.

“Brief History of Ceramics and Glass.” The American Ceramic Society, ceramics.org/about/what-are-engineered-ceramics-and-glass/brief-history-of-ceramics-and-glass. Accessed 24 May 2024.

Griggs, Jason A. "Recent Advances in Materials for All-Ceramic Restorations." Dental Clinics of North America, vol. 51, no. 3, 2007, p. 713, doi.org/10.1016/j.cden.2007.04.006. Accessed 24 May 2024.

King, Alan G. Ceramic Technology and Processing. Norwich: Noyes, 2002.

Kingery, W. D., H. K. Bowen, and D. R. Uhlmann. Introduction to Ceramics. 2nd ed. New York: Wiley, 1976.

Rahaman, M. N. Ceramic Processing and Sintering. 2nd ed. New York: Dekker, 2003.

Richerson, David W. and William E. Lee. Modern Ceramic Engineering: Properties, Processing, and Use in Design. 4th ed. CRC Press, 2018.

Xiang, Huimin, et al. "High-Entropy Ceramics: Present Status, Challenges, and a Look Forward." Journal of Advanced Ceramics, vol. 10, 2021, pp. 385–441. DOI: 10.1007/s40145-021-0477-y. Accessed 28 Feb. 2022.