Ceramics: Definition, Properties, Types, Applications

Ceramics are a broad class of materials identified for their amazing qualities that distinguish them from metals and polymers. These non-metallic, inorganic compounds have a distinct set of properties, such as high melting temperatures, extraordinary hardness, superior electrical insulation, and resistance to chemical corrosion. Ceramics are brittle when compared to metals, yet they have excellent thermal stability and low heat conductivity. Ceramics’ qualities make them useful in a variety of applications, ranging from advanced electronics and aircraft components to everyday goods such as pottery and tiles.

What are Ceramics?

• The word ceramics comes from the Greek word keramos, which meaning ‘potter’s clay’.
• Ceramics, an ancient and flexible art medium, has captured humanity’s curiosity and inventiveness for millennia. Ceramics, which dates back to prehistoric times, encompasses a wide range of materials and techniques used to create practical and ornamental pieces. Ceramics, ranging from delicate porcelain to durable earthenware, provide a unique combination of durability, aesthetic appeal, and functionality. This art form has evolved across cultures, leaving an everlasting mark on human history and influencing how we perceive and interact with our surroundings.
• A ceramic is a non-metallic inorganic solid formed by combining powdered ingredients to form clay, which is then heated in a furnace to form goods.
• Ceramics are typically produced using more than one ingredient.
• Clay, earthy materials, powders, and water are the ingredients of ceramics. To complete the fabrication, these elements are mixed, molded into the required shape, and then heated in some way, such as firing. Depending on the desired qualities of the ceramic product, several types and amounts of materials may be used.
• Ceramics have the following characteristics: high hardness, chemical inertness, and compressive strength. Ceramics are refractory. In other words, they can resist extreme temperatures while remaining durable. They are also known for their low ductility and tensile strength, as well as their poor heat and electrical conductivity.
• There are two types of ceramics: advanced ceramics, which are more modern, and traditional ceramics, which are similar to those found in pottery. Advanced ceramics are designed to possess particular attributes. Many, for instance, are designed to be robust and long-lasting. Usually, ceramics are formed at room temperature and then heated to a high temperature, often known as “firing,” to produce strong, resilient materials that are resistant to corrosion, heat, and wear. Once a material, no matter how heated, is no longer soluble in water, it is deemed ceramic.

What Are Ceramics Made Of?

Clay, water, and powdered earthy elements or minerals such as silicone, fireclay, alumina, magnesia, calcia, feldspar, titanium dioxide, etc. are commonly used to make ceramics. Particular inorganic, non-metallic components are combined to create them; clay is usually used as a base ingredient.

• Metal oxides, which are mixtures of metallic elements and oxygen, are typically the building blocks of ceramics. But in a lot of ceramics, especially sophisticated ceramics, they are metal compounds containing sulfur, carbon, or nitrogen.
• After shaping the mixture into the required shape, the fabrication process is finished by heating or firing it.
• The intended qualities of the finished product determine the composition of ceramics. While some ceramics are made entirely of clay, others are enhanced to increase their qualities with the addition of silica or feldspar.
• Advanced ceramics intended for specific applications employ more exotic materials like zirconia or tungsten carbide.
• In general, ceramic materials can be divided into oxide and non-oxide categories. Metallic and metalloid oxides make up oxide ceramics, whereas nitrides, carbides, and borides are the main constituents of non-oxide ceramics. While both types are important, non-oxide ceramics are harder and have better electrical conductivity than oxide ceramics.

Properties of Ceramics

• Bond: The remarkable strength and stability of ceramics are attributed to their atomic structure’s special blend of covalent and ionic bonding. Because of these linkages, ceramics have a strong lattice structure and are therefore very resistant to deformation. Ceramics can be used in severe conditions because of their exceptional chemical stability, which is a result of their ionic and covalent interactions.
• Strength: For applications needing rigidity and durability, ceramics offer significant strength, but metals often demonstrate better tensile and compressive strength. The strength-to-weight ratio of ceramics can be useful in some engineering applications. Ceramics are ideally suited for situations where load-bearing capability is crucial due to their remarkable compressive strength.
• Brittleness: Because ceramics are inherently fragile, stress can cause them to fracture without causing considerable plastic deformation. In applications that need hardness and resilience, this brittleness may be a hindrance. When developing components, it’s crucial to take ceramics’ brittleness into account to avoid catastrophic failures.
• Corrosiveness: Because of its atomic structure’s preexisting chemical stability and lack of corrosiveness, ceramics have an inherent resistance to environmental corrosion. Ceramics are useful in areas where exposure to corrosive substances is a problem because of this resistance. Ceramics can offer durable corrosion resistance in situations that include strong chemicals.
• Electrical connectivity: Since their ionic or covalent connection limits the free electron flow, ceramics generally have limited electrical conductivity. Because of this characteristic, ceramics are useful as electrical insulators in a variety of engineering settings. Electrical resistivity in ceramics can be precisely adjusted for particular semiconductor and electronic applications.
• Thermal conductivity: Because of their well-known poor thermal conductivity, ceramics are useful in applications requiring thermal insulation or tolerance to high temperatures. Ceramics can tolerate high temperatures despite having weak thermal conductivity, which makes them appropriate for use in engines and furnaces. Ceramics are useful for applications like ceramic tiles on spacecraft and furnace linings because of their thermal characteristics.
• Density: The relatively low weight and mass properties of ceramics can be attributed to their density, which is between that of metals and polymers. This characteristic may influence the choice of material in situations where weight is an important factor. The low density of ceramics is advantageous in situations where strength and weight must be balanced, like in aeronautical components.
• Hazardous properties: Because they don’t emit any dangerous compounds or contribute to pollution, ceramics are regarded as environmentally benign. Their usage in sustainable engineering solutions is supported by their environmentally beneficial quality. Because ceramics are inert, they can be used in industries with high hygiene standards like food processing and pharmaceuticals.
• Recyclability: Ceramics are difficult to recycle because of their rigidity and durability, which prevents them from being recycled using standard recycling methods. Novel approaches are being investigated to enhance the recycling of ceramics and minimize waste in certain applications. Reusing ceramics for particular non-structural applications, like refractories or abrasive materials, can be a sustainable way to dispose of them.

Types of Ceramics

There are numerous varieties of ceramics, each with unique uses and characteristics. Primary categories of ceramics consist of:

1. Traditional Ceramics
   • Three basic ingredients are used to make traditional ceramics: feldspar, clay minerals, and silicates (or compounds based on silica).
   • Water, dissolved carbon dioxide, and organic acids all play a role in the weathering of igneous rocks, forming clay minerals like kaolinite.
   • The largest deposits are caused by feldspar being eroded from rocks like granite, deposited in lake beds, and changing into clay.
   • Because clay minerals are the main source of aluminosilicates and have distinctive plate-shaped, micrometer-sized particles, they are essential to traditional ceramics. These particles show unique rheological behavior when combined with water, opening up new processing techniques including plastic forming and slip casting.
   • Other vital ingredients in traditional pottery are feldspar and silica. When silica is added as quartz sand, it serves as a filler, giving the unfired object strength and preserving its shape while it is being fired. As fluxing agents, feldspars, which are aluminosilicates containing calcium, potassium, or sodium, lower the melting temperatures of aluminosilicate phases. All these ingredients work together to give traditional ceramics their formability and firing properties.
   • Earthenware, sanitary ware, porcelain, vitrified tiles, conventional refractories, and cordierite-based goods are all made with traditional ceramics.
2. Advanced Ceramics
   • Alumina (aluminum oxide)
     • It is known for its versatility and white color.
     • Because of its high melting point, hardness (which is used in the manufacturing of aluminum metal), and purity, it has been used for decades in mechanical and electrical applications (acting as a refractory material).
     • Because of these characteristics, it is a robust and well-liked option for a wide range of applications, including: bearings; pump seals; lithium-ion batteries; electrical insulators (like spark plugs); glass production; armor protection; and wear- and heat-resistant liners.
   • Zirconia (zirconium dioxide)
     • Zirconia, also known as zirconium dioxide, is a cutting-edge ceramic substance that comes in black or white.
     • It is prized for its exceptional qualities, which include resistance to corrosion, high heat shock resistance, remarkable mechanical strength, low thermal conductivity, and good wear and abrasion resistance.
     • Zirconia is used in the production of cutting tools and instruments, microengineering, filters, oxygen gas sensors, electronics, aircraft parts, and medical devices.
   • Silicon carbide
     • The mineral moissanite contains the rare substance silicon carbide.
     • It is the only known chemical combination of silicon and carbon. Refractory, electric, and abrasive resistors are all functions of silicon carbide.
     • It has high energy economy, good thermal management, and high operating frequency and temperature (up to 200 °C connections).
     • Because of its ability to tolerate high voltage, it finds use as a semiconductor and is well-suited for power applications.
     • It is used in the production of sealing materials for power supplies, battery chargers, converters, motor control systems, and pump shafts.
   • Silicon nitride
     • Silicon nitride, which is well-known in the field of rocket science for its capacity to endure extreme shock and temperature changes, is used in many structural applications because of its many beneficial qualities, which include oxidation resistance, low density, mechanical fatigue and creep resistance, and exceptional wear resistance.
     • Because of its heat stability, hardness, and wear resistance, it is used to make cutting and shaping tools, ball bearings, micro shutters, and engine parts for the automotive sector.
   • Cubic boron nitride
     • CBN, the second hardest substance, has a structure similar to that of a diamond and is used to make engine and car parts, tools, armor, and grinding wheels.
     • It functions as a heat sink and insulator in a variety of electronic equipment. It provides excellent chemical and thermal stability, high electrical resistivity, high temperature stability, thermal conductivity, and chemical inertness.
     • With a broad bandgap, it functions as a good insulator and has a low coefficient of friction.
3. Refractory ceramics: Inorganic materials with high-temperature engineering, refractory ceramics provide resilience to high temperatures without melting or deforming. These ceramics have qualities such as strong refractoriness, the generation of electrical charge, and chemical modification properties. Typical instances include the following:
   • Zirconia is comparable to hafnium. It stands out for having good refractoriness, or thermal stability, and respectable strength at high temperatures. It is used in optical coatings, especially in the film-making process.
   • Sapphire ceramics are used in a variety of optical and electronic applications, watch crystals, jewel bearings, and lasers.
   • The special property of piezoelectric ceramics is their capacity to produce an electrical charge in response to a load. Consequently, they find widespread usage in various applications such as piezoelectric motor development, load sensors, pressure sensors, and microactuator.
   • Powdered yttria, also known as yttrium oxide, is used as an additive in a variety of applications, such as phosphor formation, ceramic strengthening, and the creation of microwave and lasing garnets. Their characteristics are in line with those of rare earth oxides.
4. Glass and Glass-Ceramics
   • Advanced materials called glass ceramics are made of crystals embedded in a glassy matrix.
   • They are made by quickly cooling glass after it has been heated to high temperatures. Customizable properties are made possible by the unique combination of crystalline and amorphous states that are produced by this method.
   • Glass ceramics are well recognized for their exceptional hardness, strength, and resistance to thermal shock.
   • Originally, they were created for the mirrors and mounts of astronomical telescopes. Nonetheless, they are now widely found in commonplace products including bakeware, cookware, cooktops, and high-performance reflectors for digital projectors.
5. Piezoelectric Ceramics
   • A particular substance called a piezoelectric ceramic has the capacity to convert mechanical effects, such pressure, movement, or vibration, into electrical signals and the other way around.
   • Because of its special electromechanical characteristic, piezoelectric ceramics are used in many different applications. These include active vibration dampeners, high-frequency loudspeakers, watches, lithotripters (medical devices for breaking kidney stones), motion sensors, ultrasonic power transducers, and actuators for atomic force microscopes.
   • The three types of piezoelectric ceramic materials that are most frequently used are strontium, barium, and lead zirconate titanate.
6. Bioceramics
   • One class of materials called bioceramics is utilized to replace or restore damaged bone tissue.
   • Depending on the particular use, they can interact directly with the surrounding tissue to promote tissue growth or stimulate the regeneration of new tissue.
   • Alumina, zirconia, hydroxyapatite, glass ceramics, bioactive glass, and resorbable calcium phosphates are a few examples of bioceramics.
   • These ceramics are used in dentistry to treat bone abnormalities, fill in apical spaces, restore roots, act as endodontic sealers, seal perforations, and support the processes of regeneration.
   • Biocompatibility, dimensional stability, non-toxicity, and bio-inert qualities—which are especially important in endodontic applications—are a few of their essential characteristics.

Purpose of Using Ceramics

• Ceramics play a crucial role across various industries thanks to their distinct blend of properties. By altering their composition, a wide array of ceramics with unique characteristics and applications can be produced.
• Ceramics are highly valued for their hardness, strength, resistance to wear, chemical stability, and ability to provide thermal and electrical insulation. These diverse properties determine their suitability for different industrial uses. For instance, their resilience to heat, toughness, and long-lasting nature make them perfect for applications like pottery, tiles, and structural elements in construction projects.
• Ceramics are also indispensable in manufacturing cutting tools, bearings, and electronic components, owing to their resistance to wear and ability to insulate against electricity.
• In the medical sector, ceramics are utilized in dental implants and prostheses due to their compatibility with biological systems.
• In specialized areas like aerospace, advanced ceramics such as zirconia and tungsten carbide are vital, given their exceptional strength and ability to withstand high temperatures.

ISO Standard of Ceramics

The International Classification for Standards (ICS) is a database of worldwide, national, and regional standards. Ceramics are classified under ICS 81.060. The ISO 81.060 series focuses on ceramics, especially glass ceramics. A few subsets of 81.060 are devoted to various ceramic kinds or classifications; each has its own ISO standards that apply to a certain category.

• 81.060.01 deals broadly with ceramics and encompasses ISO standards such as ISO 9385:1990 (concerning the Knoop hardness test for glass and glass-ceramics) and ISO 14719:2011 (addressing the chemical analysis of refractory material glass and glazes).
• Standard 81.060.10 focuses on raw materials, including ISO standards like ISO 14720:2013, which cover testing methods for ceramic raw and basic materials in two parts.
• Within the 81.060.20 category, which addresses ceramic products like tiles, building materials, and sanitary products, several ISO standards apply, such as ISO/FDIS 5644, ISO 6486-1:2019, ISO 6486-2:1999, ISO 8391-1:1986, and ISO 8391-2:1986.
• Moving on to 81.060.30, it pertains to advanced ceramics, featuring ISO standards like ISO 3169:2023, ISO 3180:2023, and ISO 4825-1:2023.
• Lastly, the final category, 81.060.99, titled “Other standards related to ceramics,” encompasses miscellaneous standards in the field.

Application of Ceramics

• Electronics: Ceramics are extensively used in electronics for manufacturing insulating components like capacitors, resistors, and substrates for integrated circuits (ICs). They are also used in piezoelectric devices for generating precise electric signals, such as in sensors, actuators, and ultrasound machines.
• Automotive industry: Because ceramics can tolerate high temperatures and corrosive environments, they are used in the automotive sector as engine components such as engine blocks and spark plug insulators. Automotive parts with ceramic coatings have increased wear resistance and decreased friction, which improves engine performance and fuel economy.
• Aerospace and Defense: In aerospace and defense, ceramics are utilized in manufacturing lightweight components for aircraft engines, missile nose cones, and heat shields due to their high strength-to-weight ratio and resistance to extreme temperatures. They are also used in armor plating for military vehicles and personnel protection due to their excellent ballistic properties.
• Medical applications: Because of their biocompatibility and resistance to physiological fluids, ceramics are essential in medical applications, including the manufacturing of orthopedic implants (e.g., hip and knee replacements), surgical instruments, and dental implants. To encourage bone growth and regeneration, bioactive ceramics are employed in tissue engineering and bone graft procedures.
• Refractory materials: Ceramics are widely used as refractory materials in industries such as steel, glass, and cement manufacturing where they are employed in lining furnaces, kilns, and reactors due to their high melting points and thermal shock resistance.
• Building and construction: Because of their strength, resistance to water, and visual appeal, ceramics are widely employed in the architecture and construction sector to create tiles, bricks, and sanitaryware. Piezoelectric ceramics, an advanced ceramic material, is also utilized in smart building applications for structural health monitoring and energy harvesting.
• Energy sector: Ceramics are employed in the energy sector to produce parts for the generation, transmission, and storage of power. For instance, ceramic membranes are employed in fuel cells and batteries for energy conversion and storage, whereas ceramic insulators are used in high-voltage transmission lines. In order to increase performance and efficiency, thermal barrier coatings for gas turbines also employ ceramic materials.
• Chemical processing: Ceramics are utilized in chemical processing industries for manufacturing vessels, pipes, and linings for handling corrosive chemicals and high temperatures. They are also used in catalyst supports and membranes for chemical reactions and separation processes due to their chemical inertness and stability.
• Consumer goods: Ceramics are used in consumer goods including cookware, kitchenware, and ornamental objects because of their easy-to-clean nature, temperature resilience, and attractive appearance. High-performance blades, cutting tools, and bearings are also made with advanced ceramics like alumina and zirconia for increased performance and durability.
• Environmental applications: Applications for ceramics in the environment include gas sensors that identify contaminants in the atmosphere, catalytic converters that lower car emissions, and filtration systems that purify water and air. To generate power sustainably, they are also utilized in renewable energy technologies like fuel cells and solar panels.

Advantages of Ceramics

• High Hardness: Ceramics are known for their exceptional hardness, making them suitable for applications where wear and abrasion resistance are essential, such as cutting tools and armor plating.
• High-Temperature Resistance: Ceramics are perfect for use in high-temperature situations like gas turbines and furnaces because they can tolerate extremely high temperatures without melting or deforming.
• Chemical Stability: Many ceramics exhibit excellent chemical stability, resisting corrosion and degradation when exposed to harsh chemicals or acidic environments, which is beneficial in chemical processing industries.
• Biocompatibility: Certain ceramics are biocompatible, which means that living tissues can accept them without experiencing negative side effects. Because of this characteristic, they can be used in medical applications like as orthopedic prosthesis and dental implants.
• Electrical Insulation: Ceramics are excellent electrical insulators, making them indispensable in electronics for manufacturing components like capacitors, resistors, and insulating substrates for integrated circuits.
• Aesthetic Appeal: Ceramics offer a wide range of colors, textures, and finishes, making them popular choices for decorative items, architectural tiles, and kitchenware.

Limitations of Ceramics

• Brittleness: Ceramics are inherently brittle materials, meaning they are prone to fracture or shattering under impact or stress, limiting their use in applications where toughness and ductility are required.
• Low Tensile Strength: Compared to metals and polymers, ceramics usually have a lower tensile strength, which can make them less suitable for use in structural applications where tensile loads are applied.
• Processing Challenges: Ceramics can be difficult and costly to manufacture due to their high hardness and brittleness, requiring specialized processes such as sintering and hot pressing.
• Limited Design liberty: Because ceramics are frequently created by powder processing processes and can be difficult to shape into complex geometries, they have less design freedom than other materials like metals and polymers.
• Surface Roughness: Ceramics can have relatively rough surfaces compared to other materials, which may require additional processing or surface treatments to achieve the desired surface finish.
• Susceptibility to Thermal Shock: In applications where sudden fluctuations in temperature occur, like in thermal barrier coatings, certain ceramics are susceptible to thermal shock, which means they may fracture or shatter when exposed to fast temperature changes.

References

• https://www.xometry.com/resources/materials/ceramics/
• https://byjus.com/gate/ceramics/
• https://www.pmaimperio.com/en/blog/what-is-ceramic-its-properties-types-and-usage
• https://www.studysmarter.co.uk/explanations/engineering/materials-engineering/ceramic-materials/
• https://www.preciseceramic.com/blog/types-and-applications-of-all-kinds-of-ceramic-materials.html
• https://testbook.com/mechanical-engineering/properties-of-ceramics
• https://clubtechnical.com/ceramics#google_ vignette
• https://www.thomasnet.com/articles/custom-manufacturing-fabricating/ceramics/