Ceramic Definition and Examples


Ceramic Definition and Examples
A ceramic in an inorganic, non-metallic material.

Ceramics play a crucial role in materials science and engineering, offering unique properties and applications across various industries. From ancient pottery to cutting-edge biomedical applications, they play a key role numerous fields and industries.

Simple Definition of Ceramics

In simple terms, ceramics are non-metallic, inorganic materials that are typically made by shaping and then firing a non-metal, such as clay, at high temperatures. This process results in a hard, brittle material.

Technical Ceramic Definition

From a technical standpoint, ceramics combine metallic (e.g., aluminum, magnesium) and non-metallic (e.g., oxygen, carbon) elements. They exhibit crystalline or partly crystalline structures and display a range of high-temperature stability, low electrical conductivity, resistance to corrosion, and high hardness.

Origin of the Term “Ceramic”

The word “ceramic” originates from the Greek word “keramikos,” meaning “of pottery” or “for pottery.” This reflects the material’s historical association with earthenware.

Examples of Ceramics

Many everyday materials are ceramics. So are numerous technical materials. Examples include:

  • Traditional Ceramics: Traditional ceramics are clay-based items like pottery, bricks, stoneware, porcelain, and tiles.
  • Advanced Ceramics: Some examples of advanced ceramics are silicon carbide, boron nitride, alumina, and zirconia.

Composition and Properties of Ceramics

Ceramics typically consist of metallic and non-metallic elements, forming sturdy and stable crystal structures. Their properties include:

  • Crystalline or partially crystalline
  • High melting points
  • Low thermal and electrical conductivity
  • Resistance to chemical attack and wear
  • High compressive strength
  • Brittle, with weak shear strength
  • Interesting electrical properties (semiconductors, superconductors, ferroelectric materials, piezoelectric materials, etc.)

Classification of Ceramics

One way of classifying ceramics is by their material composition:

  • Oxide Ceramics: Such as alumina and zirconia.
  • Non-Oxide Ceramics: Includes carbides, borides, and nitrides like silicon carbide and boron nitride.
  • Composite Ceramics: Mixtures of ceramics and other materials to enhance specific properties.

Another classification method is by use:

  • Structural: Such as tiles, bricks, pipes
  • Whitewares: Such as pottery, cookware, tableware
  • Refractories: Crucibles, kiln linings, fire radiants
  • Technical or Advanced: Such as vehicle armor, biomedical implants, bearings, spacecraft tiles, nuclear fuel pellets, turbine blades

Ceramics in Nature

In the broadest sense, ceramics are non-metallic and inorganic materials, and many such materials occur in nature. Some examples of natural ceramics include:

  • Minerals: Many minerals that are key components of rocks are essentially ceramics. For example, feldspar and quartz, common in granite, have ceramic properties. Flint is another example of a natural ceramic.
  • Clays: Clay minerals, like kaolinite, occur naturally and are the basis for many traditional ceramic products.
  • Gemstones: Many gemstones, such as diamonds and rubies, are ceramics due to their crystalline structure and inorganic composition.
  • Glass: Obsidian, a type of naturally occurring volcanic glass, is an example of a natural ceramic. While not crystalline like most traditional ceramics, it shares many properties such as brittleness and hardness.
  • Bioceramics: Some substances in animal skeletons, like hydroxyapatite in bones and teeth, are bioceramics. They are inorganic, non-metallic materials found in nature and have similar properties to synthetic ceramics.

Uses of Ceramics

The applications of ceramics are endless:

  1. Industrial Applications: In machinery and automotive industries for insulation, bearings, spark plugs, brake pads, and cutting tools.
  2. Electronics: As insulators, semiconductors, and in superconducting materials.
  3. Biomedical: For implants and prosthetics due to their bio-compatibility.
  4. Construction: In bricks, tiles, and pipes for structural applications.
  5. Household Items: Like dishes, pottery, and decorative items.

Is Glass a Ceramic?

Whether or not glass is a ceramic is a topic of debate in materials science. Glass is hard and brittle, but it differs from most ceramics. Traditionally, ceramics are crystalline or partly crystalline, while glass has an amorphous structure. This relates to the way glass forms.

  • Ceramics: The production of ceramics involves the process of heating (firing) followed by cooling. During firing, the material undergoes significant changes, including the development of a crystalline structure.
  • Glass: Glassmaking involves heating materials until they melt and then cooling them rapidly, a process known as quenching. This rapid cooling prevents the formation of a regular crystalline structure, resulting in an amorphous solid.

Quartz is a form of silicon dioxide (SiO2) that definitely qualifies as a ceramic. Whether or not glass (also typically SiO2) is a ceramic depends on who you ask and their definition of the material.

How Are Ceramics Made?

The process of ceramic manufacturing varies greatly depending on the type of produce and its intended use. A typical process involves the following steps:

1. Raw Material Preparation

  • Selection and Procurement: Ceramics typically start as clay, minerals, elements, and other raw materials.
  • Purification and Mixing: The next step is purification and mixing in specific proportions. Additives like fluxes, binders, or plasticizers modify the properties of the mixture.

2. Forming

  • Shaping: The prepared material gets shaped into the desired form. There are various methods such as:
    • Hand Building: For artistic ceramics, where the material is shaped manually.
    • Wheel Throwing: For round ceramic wares.
    • Slip Casting: Involves pouring a liquid clay mixture (slip) into molds.
    • Extrusion: Forcing clay through a mold.
    • Pressing: Using presses to shape the material.
  • Drying: The shaped material dries, reducing moisture content and preparing it for firing.

3. Firing

  • Kiln Firing: A kiln fires the dried ceramic at high temperatures. The temperature and duration depend on the type of material and desired properties.
  • Chemical and Physical Changes: During firing, several changes occur:
    • Dehydration: Removal of remaining water.
    • Oxidation: Some materials react with oxygen.
    • Vitrification: The material melts and solidifies into a glass-like structure, increasing its strength.
    • Sintering: Particles fuse together and porosity decreases.

4. Glazing and Decoration (Optional)

  • Application of Glazes: After the first firing, a glaze adds color, texture, and waterproofing.
  • Second Firing: After glazing, a second firing melts the glaze and fuses it to the surface.

5. Cooling and Finishing

  • Cooling: Post firing, ceramics cool slowly to prevent cracking.
  • Finishing Touches: Additional decoration, polishing, or machining achieves the final appearance and specifications.

Variations

  • Advanced Ceramics: For technical or advanced ceramics, the process often involves more complex raw materials and specialized sintering processes, such as hot pressing or reactive bonding.

References

  • Burakov, B.E.; Ojovan, M.I.; Lee, W.E. (2010). Crystalline Materials for Actinide Immobilisation. Materials for Engineering. Vol. 1. Imperial College Press. ISBN 978-1-84816-418-5. doi:10.1142/p652
  • Carter, C. B.; Norton, M. G. (2007). Ceramic Materials: Science and Engineering. Springer. ISBN 978-0-387-46271-4.
  • Gohardani, A. S.; Gohardani, O. (2012). “Ceramic engine considerations for future aerospace propulsion”. Aircraft Engineering and Aerospace Technology. 84 (2): 75. doi:10.1108/00022661211207884
  • Heimann, Robert B. (2010). Classic and Advanced Ceramics: From Fundamentals to Applications. John Wiley & Sons. ISBN 9783527630189.
  • Rahaman, M.N. (2003). Ceramic Processing and Sintering (2nd ed.). Marcel Dekker Inc.. ISBN 0-8247-0988-8.