Ceramics: Definition, Properties, Types, and Applications
Ceramics are a class of materials that humans have used for thousands of years. Applications range from pottery to advanced aerospace components. They are valued for their hardness, strength, wear resistance, electrical and thermal insulation, and chemical stability. In this article, we will provide a comprehensive overview of ceramics, including their definition, properties, types, and applications.
What Are Ceramics?
Ceramics are a diverse group of materials that you’ll find in products such as: tiles, bricks, plates, glass, and toilets. The term, “ceramic materials,” is a wide-ranging category largely defined by a lack of organic substances (those based around carbon-hydrogen bonds) and metallic elements. Absent those components, ceramics may be composed of: clay, minerals, oxides, and other compounds. Essentially, ceramics are the materials that remain when we exclude organic and metallic materials.
Ceramics are refractory, meaning they are durable and can withstand high temperatures. They also resist high pressures and most chemical compounds and are generally poor electrical conductors. Most ceramics are non-magnetic. Some ceramics shatter easily, while others are very tough.
Ceramics are divided into two categories: traditional (like those found in pottery) and more modern ceramics (advanced ceramics). Advanced ceramics are engineered to have specific properties. Many, for example, are meant to be hard and durable. Ceramics are typically shaped at moderate temperatures and then heated or “fired” at high temperatures to create hard, durable materials that resist heat, wear, and corrosion. The material is considered to be ceramic once it is no longer soluble in water even if heated.
It is important here to differentiate between water solubility and porosity. Some ceramics are still porous, meaning that they will still absorb water, but they are not water-soluble. Ceramics can be found in a wide variety of products and applications including: tiles, bricks, engineering ceramics used in electronic devices, and aerospace components. Figure 1 is an example of familiar household ceramics:
Image Credit: Shutterstock.com/Chzu
Is Ceramics the Same as Pottery?
No, ceramics are not the same as pottery. The terms pottery and ceramics are sometimes used interchangeably, but despite being related terms, they are not the same. Ceramics is an umbrella term used for a wide range of materials and products. Pottery is simply one subdivision of ceramics.
It can be hard to define ceramics because it's such a broad term. Many substances can be classified as ceramic, including, but not limited to cement and bricks. However, by definition, ceramic refers to a material that is non-metallic and inorganic in nature.
Pottery, on the other hand, is simply a category of functional containers made of clay. Vessels like coffee mugs, vases, or cereal bowls are classified as ceramic pottery. Pottery can also serve artistic purposes. These items are considered to be the oldest forms of ceramics. That is why pottery is referred to as traditional ceramics.
What Are Ceramics Made Of?
Ceramics are made of clay, earthen elements, powders, and water. These components are combined, molded into the desired shape, and then fired or otherwise heated to finish the fabrication. The specific types and proportions of materials involved can vary depending on the desired characteristics of the ceramic product. For example, some ceramics may be made from pure clay while others may be blended with additives such as feldspar or silica to enhance their properties. Advanced ceramics intended for specialized applications may be made from more exotic materials such as tungsten carbide, or zirconia.
What Are the Properties of Ceramics?
The properties of ceramics, like those of any material, depend on the types of atoms involved, the bonds between them, and their arrangement. This atomic structure determines the material’s characteristics. Ceramic materials tend to be:
- Harder and more brittle than metals
- Good thermal and electrical insulators
- Chemically stable
Let’s consider the mechanical and chemical properties of ceramics in more detail below:
What Are the Mechanical Properties of Ceramics?
The mechanical properties of ceramics include:
- Poor impact strength
- High compressive strength
- Extremely stiff and rigid structure with little or no yielding
- The presence of microcracks can cause local stress concentrations and brittle fracture
- Hardness and strength in compression, with a high softening temperature
- Poor thermal shock resistance
- Brittle nature
What Are the Chemical Properties of Ceramics?
Compared to most engineering materials, most ceramics are very chemically stable. They inherently resist chemical reactions and corrosion. Ceramics are also generally inert and do not react with acids or bases. However, the chemical properties can vary depending on the specific composition and type of ceramic; some ceramics may be susceptible to corrosion or degradation under certain conditions while others may be highly resistant to chemical attack. Additionally, certain ceramics exhibit unusual chemical properties such as the ability to conduct electricity or act as catalysts. The general chemical behavior of ceramics can be summarized as:
- Mostly resistant to chemical attacks by gasses, liquids, and even high-temperature melts.
- Generally inert and non-reactive with acids or bases.
What Are the Different Types of Ceramics?
Ceramics typically fall under two categories:
- Traditional Ceramics: These are made from natural materials like feldspar, quartz, or clay. Their structure depends on the composition of the clay which makes them more imperfect compared to the uniform microstructure of advanced ceramics. Traditional ceramics are manufactured by wet molding. They are mainly used in daily-use items and building materials.
- Advanced Ceramics: These use synthetic powders such as aluminum oxide, silicon carbide, and silicon nitride. They are designed and engineered to have specific properties for high-performance applications. Advanced ceramics are typically made from a mixture of high-purity powders that are processed using specialized techniques to give the final product unique properties such as high strength, toughness, wear resistance, high-temperature stability, and chemical inertness. Each of these ceramics is known for its ability to serve specific purposes, such as permeability, magnetism, insulation, and conductivity.
Many different materials and ceramic types fall under each of these categories (traditional and advanced). We’ll discuss some of them in the sections below. For the purposes of this article, we will consider pottery as a traditional ceramic and compare it to advanced ceramics.
Some common types of advanced ceramics are listed below:
Silica (SiO2) is a material widely recognized for its remarkable thermal shock resistance and leachability. It is a popular choice for aerospace and energy applications for the production of investment casting shells and cores.
2. Tungsten Carbide
Tungsten carbide items are composed of tungsten carbide particles bonded with a metal binder. The material is known for its ability to maintain its properties at high temperatures. Tungsten carbide often gets mixed with high percentages of cobalt or nickel as a second metallic phase to form materials known as "cermets." Pure tungsten carbide can also be produced as an advanced technical ceramic using a high-temperature hot isostatic pressing process. This extremely hard and wear-resistant material is used in cutting tools, abrasive water jet nozzles, and other applications where strength and toughness are critical. However, its weight can limit its use in certain applications.
3. Fire Bricks
Fire bricks are made from a refractory material and get used to line high-temperature furnaces, fireboxes, fireplaces, and kilns. They are typically made from a mixture of clay and other materials and are designed to withstand extreme heat without cracking or breaking down. They also exhibit low thermal conductivity so they naturally save energy. The refractory nature of these bricks makes them ideal for applications that focus on heat resistance and durability. Fire bricks are used in a wide variety of industrial applications, including steelmaking, glassmaking, and ceramics production.
4. Bone China
Bone china, also referred to as fine china, is a porcelain variety renowned for its strength, chip resistance, and translucency. The material is composed of bone ash, kaolin, and feldspathic material. It was first created by Josiah Spode, an English ceramicist, in the 1800s. Due to its superior durability, bone china can be molded into thinner shapes than porcelain. It undergoes vitrification during production, but its transparency results from differences in mineral properties. Bone china is often used for fine dinnerware and decorative objects because of its elegant appearance and durability.
5. Silicon Carbide
Silicon carbide (SiC) is an advanced ceramic material known for its high wear resistance and exceptional thermal conductivity. It is composed of silicon and carbon atoms. It is typically produced by heating a mixture of sand (silicon dioxide) and petroleum coke (carbon) at high temperatures. Due to its outstanding chemical resistance and high strength, SiC is an ideal choice for thermal processing applications. This material is specifically used in advanced ceramic applications that need a highly durable material with exceptional thermal conductivity. Specific examples include cutting tools, abrasives, and semiconductor devices.
6. Titanium Carbide
Titanium carbide is a type of advanced ceramic that is used in cutting tools, wear-resistant coatings, and other applications that require extreme strength and hardness. It is composed of titanium and carbon atoms and is typically produced by heating a mixture of titanium dioxide and carbon at high temperatures. Titanium carbide is known for having stable properties even at high temperatures and in harsh environments.
7. Glass Ceramics
Glass-ceramics are composite materials with crystals embedded in a glassy matrix. These advanced ceramics are made by heating glass to a high temperature and then cooling it rapidly to form a crystalline material. This unique combination of amorphous and crystalline states makes for customizable properties. Many varieties are especially known for their high strength, toughness, and resistance to thermal shock.
They were initially developed for the mirrors and mounts of astronomical telescopes. Glass ceramics have gained wider popularity, though, and are now found in everyday products such as cooktops, cookware, bakeware, and high-performance reflectors for digital projectors.
Pottery ceramics, otherwise referred to as traditional ceramics, can be divided into three categories:
Porcelain is made from a specific type of clay called kaolin, which is known for its fine particle size and high plasticity. Porcelain is typically white or translucent in appearance. It is known for its hardness, strength, and durability. It is fired at a high temperature, usually between 1200 and 1450 °C, which causes the clay to vitrify and become non-porous. Porcelain is often used for decorative or fine art objects and practical items such as dinnerware, electrical insulators, and dental implants.
Stoneware ceramic materials are made from a mixture of clay and other materials such as feldspar, quartz, and bone ash. It is typically fired at a high temperature(1200-1300 °C), which causes the clay to become vitrified and non-porous. Stoneware is known for its strength, durability, and resistance to chipping and scratching, and is often used for practical items such as dinnerware, bakeware, and pottery.
Earthenware is made from clay and fired at a lower temperature than other types of ceramics — typically below 1180 °C. This results in a porous material that is less durable than stoneware or porcelain, but which has a unique, rustic appearance. Earthenware is often used for decorative pottery, vases, and figurines, as well as for practical items such as flower pots and cookware. It can be glazed or left unglazed and is often decorated with colored slips, underglazes, or painted designs.
What Are the Different Advanced Applications of Ceramics?
Advanced ceramics have a wide range of applications in various industries. Some examples include:
- Aerospace: Ceramics make up some high-temperature components such as turbine blades, heat shields, and nose cones. Although these materials are hard to shape using conventional manufacturing methods, 3D printing is now being used to build aerospace parts out of ceramics.
- Biomedical: Ceramics show up in medical implants due to their biocompatibility, strength, and wear resistance.
- Electronics: Electronic devices receive ceramic components because of the material’s electrical insulation properties and ability to dissipate heat.
- Energy: Ceramic materials are important to energy applications such as fuel cells, solar panels, and thermal insulation due to their thermal stability and temperature resistance.
How Is 3D Printing Being Applied to Create Aerospace Parts Made from Ceramics?
3D printing presents a potential way to create complex and detailed parts that cannot be achieved using traditional machining or molding techniques. There are several 3D printing processes available for ceramics, including stereolithography (SLA), selective laser sintering (SLS), material jetting, laminated object manufacturing (LOM), and fused deposition modeling (FDM). Each process requires a different form of ceramic feedstock. For example, SLA printers use ceramic slurry or paste as feedstock, which is a mixture of photosensitive resins and ceramic powder. Ceramic components are built up by successive layers using a laser to polymerize the paste, after which the parts are subjected to heat treatment for debinding and densification.
Other related technologies that use ceramic pastes or slurries include direct light printing (DLP) and lithography-based ceramic manufacturing (LCM) technology. A ceramic powder can also be used in material jetting printers, while solid ceramic filament can be used for LOM and FDM. Of these processes, stereolithography or related photopolymerization techniques are the most common because they can achieve nice surface finishes. For more information, see our How Does 3D Printing Work guide.
What Are the Advantages of 3D Printing to Create Aerospace Parts from Ceramics?
Printing 3D aerospace parts has some distinct advantages over making them via conventional manufacturing methods:
- Design Flexibility and Innovation: One of the key benefits of additive manufacturing is the ability to create complex parts, geometric shapes, and patterns. This is more critical for ceramic materials than others because these ceramics are more difficult to shape.
- Time and Cost Savings: Production using additive manufacturing is often cheaper and requires less lead time than other methods.
- Replacement Parts with Better Properties: 3D-printed ceramic parts are now being used to replace polymer or metal components. In some cases, the materials are selected not for their properties, but because they are easier to shape using a printer.
- Material Availability and Environmental Impact: Ceramic materials are readily available, can be locally sourced, and are environmentally friendly.
What Are Examples of 3D Printed Materials Made from Ceramics for Aerospace?
A few 3D-printed ceramic materials show up more often than others in aerospace components. Here are some of the most common:
- Silica: Silica is known for its remarkable thermal shock resistance and leachability, making it a popular choice for the investment casting of aerospace shells and cores.
- Alumina: This is a ceramic material with high stiffness and strength, excellent wear resistance, and good chemical resistance. It is used in high-temperature electrical insulation, engine components, and cutting tools.
- Silicon Nitride: This ceramic material has excellent thermal shock resistance, high strength, and good toughness. Turbine blades, cutting tools, and wear-resistant parts get made from silicon nitride.
- Zirconia: This is a ceramic material with high strength, toughness, and wear resistance. It is used in cutting tools, thermal barrier coatings, and engine components.
- Glass-ceramics: These are formed by the controlled crystallization of glasses. They have good mechanical properties, excellent thermal stability, and low thermal expansion. They are used in applications such as optical components and high-temperature sensors.
Are 3D Printed Ceramics tested for Ductility?
No, 3D-printed ceramic parts are not usually tested for ductility. Ceramics are non-ductile in general and therefore are not normally selected when a ductile 3D-printed part is required.
Are 3D Printed Ceramics tested for Brittleness?
Yes, 3D-printed ceramics are usually tested for brittleness. Ceramics are known for being brittle, so printed parts need testing so engineers know they will meet their strength requirements. These tests should be performed on the part itself, as the design of the part, as well as printing and material parameters all play a role in the overall brittleness.
What Are the Benefits of 3D Printed Ceramics Over Metals?
3D-printed ceramics offer a unique combination of properties that make them attractive for various aerospace, medical, and industrial applications. 3D printed ceramics are preferable to metals in several regards:
- High-Temperature Resistance: Ceramics can withstand high temperatures without melting, even at points where metals would lose their strength and shape.
- Lightweight: Ceramics are generally lighter per unit volume than metals, which is beneficial in industries like aviation where weight is a concern.
- Corrosion Resistance: Unlike many metals that oxidize quickly, ceramics are highly resistant to corrosion.
For more information, see our guide on What Are Metalloids.
What Are the Advantages of 3D Printed Ceramics Compared to Plastics?
3D printed ceramics have the following advantages over plastics:
- Higher Temperature Resistance: Ceramics can withstand much higher temperatures than plastics without degrading.
- Superior Strength and Durability: Ceramics are generally stronger and more durable than plastics.
- Better Chemical Resistance: Ceramics are less likely to react with chemicals than plastics.
- Longer Lifespan: Ceramics are more durable and have a longer life expectancy than plastics.
This article presented ceramics, explained what it is, and discussed its types and applications. To learn more about ceramics, contact a Xometry representative.
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