Ceramics are made up of mixtures of clay, earthen elements, powders, and water, solidified into desired forms or shapes.
They have been used for thousands of years in various applications, from pottery to advanced engineering solutions. Due to their unique mechanical and physical properties, ceramics are used in various industries such as construction, medicine, automobile, and aerospace engineering.
Our today’s article focuses on ceramics starting from how we define ceramics, what are their properties, and their advantages. Let’s dive right into it!
Ceramics Definition: What is Ceramic?
Image Caption: What is Ceramic?
Scientifically, “Ceramics” are non-metallic and inorganic materials, that are formed by a sintering process involving heat to compact and solidify.
Typically, ceramics offer a combination of hardness, thermal stability, and chemical resistance making them useful in many technological fields.
Generally, we differentiate into two types of ceramics, based on their use case:
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Traditional ceramics
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Advanced ceramics
Traditional ceramics are composed of natural or earthly elements such as feldspar, quartz, clay, etc. They find applications in many day-to-day household items, such as jugs, vases, pots, planters, home construction items, tiles, tableware, etc., created through the wet molding process. One differentiating feature of their microstructure is that not highly uniform or smooth as in the case of advanced ceramics. Also, the microstructure varies depending on the clay’s composition.
Advanced ceramics are new types of ceramics made from highly pure inorganic compounds artificially synthesized and under strict control by molding, sintering, and other required treatments. They are designed for high performance with properties like hard-wearing, strong, extremely tough, and heat and chemical resistivity.
Ceramics Material Composition
Ceramics are made from combinations of many different substances which could include a mix of clay, water, and a few additive powders for specific enhancements, among others. The mechanical, thermal, and chemical properties of ceramics change with the types and ratios of raw substances mixed together in specific compositions. This specific composition of mixtures in turn decides the specific property and application of the end ceramics.
Image Caption: Microstructure of Ceramics
Key Ingredients
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Clay: These provide plasticity and enable easy shaping of the ceramic before firing.
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Silica (SiO₂): A major component of many ceramics, highly contributes to the hardness and thermal resistance of ceramics.
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Alumina (Al₂O₃): Additive for high strength, wear resistance, and thermal stability.
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Zirconia (ZrO₂): Mainly used for structural ceramics, known for adding toughness.
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Carbides and Nitrides: Such as silicon carbide (SiC) and boron nitride (BN), which provide high wear resistance and thermal stability.
Types of Raw Materials
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Natural: Clay, feldspar, quartz, kaolin, and other minerals extracted from the earth.
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Synthetic: Alumina, zirconia, silicon carbide, and engineered materials designed for high-performance applications.
Types of Ceramics
Various types of ceramics are classified into several categories, majorly based on their chemical composition and application.
Oxide Ceramics
“Oxide Ceramics” are composted of metal oxides such as aluminum (Al), zirconium (Zr), titanium (Ti), magnesium (Mg), etc., and are known for their high thermal stability, corrosion resistance, and electrical insulation properties.
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Examples: Alumina (Al₂O₃), Zirconia (ZrO₂)
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Applications: Biomedical implants, refractories, cutting tools, and electrical insulators.
Carbide Ceramics
“Carbide Ceramics” are composed of carbon atoms bonded with metals. They are processed through a sintering process. With properties like extreme hardness, wear resistance, and thermal stability, they are used as high-performance materials in advanced engineering.
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Examples: Silicon Carbide (SiC), Boron Carbide (B₄C)
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Applications: Abrasives, armor plates, high-temperature components, and semiconductor components.
Nitride Ceramics
“Nitride Ceramics” contains nitrogen atoms along with metallic bonds with metals. They are well-known for their high-temperature resistance, excellent mechanical strength, and good electrical properties.
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Examples: Silicon Nitride (Si₃N₄), Boron Nitride (BN)
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Applications: Aerospace, bearings, electronic components, and high-temperature applications.
Unique Properties of Ceramics
As mentioned earlier, the properties of ceramics depend on their specific compositions and the atomic microstructure. In general, ceramic materials tend to be:
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High Hardness
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Wear-resistant
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Corrosion-resistant
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Good Thermal and Electrical Insulation
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Anti-Ferromagnetism ( i.e. Nonmagnetic in nature)
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Oxidation-resistant
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Inert & Chemically stable
Mechanical Properties of Ceramic Materials
Image Caption: Physical Properties of Ceramics
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Wear Resistance & High Hardness: Ceramics possess high hardness and highly wear-resistant qualities. This makes them highly useful for manufacturing power-cutting tools and abrasive substances. For example, Tungsten carbide (WC), a carbide ceramic, is widely used in industrial drill bits and cutting tools.
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Low ductility and Brittleness: Scientifically speaking, ductility is a material’s ability to deform permanently without breaking when stretched. Unlike most metals, ceramics do not exhibit plastic deformation simply due to their low tensile strength. This means ceramics deforms when stress is applied, due to their brittle nature. They are vulnerable to breaking instead of deforming. Even a minor presence of microcracks in ceramics can cause sudden stress concentration causing brittle fracture. However, there are some ceramics that are ductile at ambient temperatures such as MgO, SrTiO3, etc.
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High Compressive Strength: Generally ceramic ‘s properties allow them to withstand extreme compressive loads, which comes in handy for structural applications. This property allows ceramics to be used in the construction sector.
Thermal Properties of Ceramics Materials
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Thermal Conductivity: Ceramics showcase low thermal conductivity in general. These properties are specially used in processes where thermal insulation or resistance to extreme temperatures is required. For example, firebricks made of refractory ceramics are used in kilns and furnaces acting as insulators. However, some ceramics (e.g., Silicon Carbide - SiC, Aluminum Nitride - AlN) have high thermal conductivity, making them useful in heat dissipation (electronics, heat exchangers).
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High Melting Points: As mentioned earlier, ceramics have a high melting point, allowing good operational tendency in high-temperature setups.
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Poor Thermal Shock Resistance: Thermal Shock Resistance is about any material’s ability to handle sudden temperature changes. Most ceramics, especially traditional ones, have poor thermal shock resistance properties. It means they are vulnerable to cracking under sudden temperature changes.
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Low Thermal Expansion: Some ceramics exhibit minimal expansion with temperature changes ( e.g. Fused Silica), promoting dimensional stability. Again, there are exceptions to his property. Some ceramics do showcase high thermal expansion, such as Zirconia (ZrO₂), which expands significantly with temperature changes.
Chemical Properties of Ceramics Materials
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High Resistance to Corrosion: Most ceramics are very chemically stable, and are inert to nature. This adds to their strongly chemically resistant property to acids, alkalis, and other aggressive environments. They are also inherently corrosion-resistant.
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Inert Nature: Their inert nature to environmental factors such as humidity, heat, etc., makes them ideal for biomedical and chemical processing applications. Bioceramic hydroxyapatite is used in bone grafts as it does not react with body fluids. Similarly, Zirconia (ZrO₂), a corrosion-resistant ceramic, is used in chemical processing plants across the globe.
Application of Ceramic Materials
Biomedical Applications
As ceramics possess useful properties like biocompatibility, strength, and wear resistance, they are actively used in medical implants.
Some of the applications are:
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Prosthetics and Implants (due to their biocompatibility, they are used in hip and knee replacement implants)
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Bone Grafts and Fillers (i.e. few ceramics like hydroxyapatite (HA) show natural bone-like structure)
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Dental Applications (because of their aesthetic and mechanical properties, most of the dental implants are made up of ceramics such as Zirconia)
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Medical Devices (found in pacemakers, surgical tools, and drug delivery systems)
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Bioactive Glasses ( they also stimulate cell growth helpful in tissue regeneration and injury/wound healing)
Aerospace Applications
Many aerospace engineering components such as turbine blades, heat shields, or nose cones, require advanced material properties that are also capable of precision cutting. Advanced ceramics make a good fit due to their properties like thermal conductivity, high melting points, high hardness, etc.
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Structural Materials (due to high strength, many ceramics like Silicon carbide (SiC) are used for lightweight, high-strength aerospace components)
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Thermal Protection Systems or TPS (ceramic tiles made of silica and alumina are used in spacecraft to withstand extreme temperatures during re-entry)
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Ablative Ceramics for Heat Shields (these types of ceramics protect spacecraft during atmospheric re-entry by gradually eroding to absorb heat)
Electronics and Insulators
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Multilayer Ceramic Capacitors (MLCCs) and Resistors (ceramics such as aluminum oxide, are crucial in, providing insulation and dissipating energy as heat making use of MLCC and resistors)
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ICs and Semiconductors (ceramic subtracts are thin and flat, along a low dielectric constant and dielectric loss, high thermal conductivity, and good chemical stability)
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Semiconductors and Ceramic PCBs (ceramics have low electrical conductivity and are used in semiconductors and PCBs demanding high in-electric insulation)
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High-voltage Insulators (in high-voltage functionalities, Porcelain, and Alumina-based ceramics are essential for power transmission lines)
Construction Materials
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Bricks and Tiles (due to their properties like durability, fire resistance, and thermal insulation, clay-based ceramics are widely used in bricks and tiles construction)
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Sanitary Ware (Most toilets, sinks, and bathtubs itinerary are made from vitrified ceramics, as they showcase inert properties like resistance to moisture, stains, and bacterial growth)
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Glass Ceramics (ceramic materials like Lithium Alumino-Silicate are used in countertops and architectural applications for their aesthetic and heat-resistant properties)
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Facade and Coating (ceramics are used as facade and coating materials in buildings as they offer the necessary thermal and acoustic insulation properties)
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Cement and Concrete Additives (to improve the strength, durability, and efficiency of cement or concrete mixtures, ceramic additives like fly ash and silica fume are commonly used as additives)
Advantages of Ceramic Materials
Image Caption: Advantages of Ceramics
Durability and Longevity
As mentioned earlier, ceramics have a durable life because of their high hardness and inert nature. This means unlike metals, ceramics do not oxidize or corrode in harsh environments. Also, most ceramic substances are resistant to acids, alkalis, and other aggressive chemicals.
Lightweight Properties
Along with high harnesses, ceramics are very lightweight making them useful in aerospace engineering and the automotive industry. For example, SiC is being used in aircraft brake discs due to its high strength-to-weight ratio.
Aesthetic Versatility
By mixing different substances during forming, various visually aesthetic properties like colors, textures, and finishes, are possible with ceramics. For example, Porcelain tiles are quite famous due to their visually appealing structure. Some ceramics are also used in optics and display ( such as Sapphire glass (Al₂O₃) used to build tempered glasses for smart screens) due to their transparency and optical properties.
Limitations of Ceramic Materials
Brittleness and Fragility
Image Caption: Brittle microstructure of Ceramics
Although generally, they have high compressive strength, their very low ductile or tensile strength makes them brittle and fracture-prone under stress rather than deform plastically like ductile materials like metals.
Production Costs
Ceramics formations undergo the process of sintering (i.e. requiring high-temperature processing, sometimes up to 1500 degree centrigates). This high-temperature maintenance increases the overall production costs of ceramics. Also, for advanced ceramics, fabrication costs and high precision cutting with CNCs or 3-D printing also lead to a high cost in production. Precision manufacturing involves expensive techniques like hot pressing, chemical vapor deposition (CVD), and spark plasma sintering (SPS).
However, it’s to be noted that the overall outcomes are highly advantageous to us humans due to their unique properties.
Conclusion
We became familiar with ceramic materials, their associated properties, and their advantages. Ceramic materials offer a significant role in our daily lives due to their unique properties, such as durability, heat resistance, and chemical stability.
With the advancements in material sciences, more advanced ceramics with better constructible properties will become available to us.