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Published on July 16th, 2018 | By: pwray@ceramics.org


Structure and Properties of Ceramics

Published on July 16th, 2018 | By: pwray@ceramics.org

[Image above] Credit: allispossible.org.uk; Flickr CC BY 2.0


The properties of ceramic materials, like all materials, are dictated by the types of atoms present, the types of bonding between the atoms, and the way the atoms are packed together. The type of bonding and structure helps determine what type of properties a material will have.

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Ceramics usually have a combination of stronger bonds called ionic (occurs between a metal and nonmetal and involves the attraction of opposite charges when electrons are transferred from the metal to the nonmetal); and covalent (occurs between two nonmetals and involves sharing of atoms). The strength of an ionic bond depends on the size of the charge on each ion and on the radius of each ion.

The greater the number of electrons being shared, is the greater the force of attraction, or the stronger the covalent bond.


These types of bonds result in high elastic modulus and hardness, high melting points, low thermal expansion, and good chemical resistance. On the other hand, ceramics are also hard and often brittle (unless the material is toughened by reinforcements or other means), which leads to fracture.


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In general, metals have weaker bonds than ceramics, which allows the electrons to move freely between atoms. Think of a box containing marbles surrounded by water. The marbles can be pushed anywhere within the box and the water will follow them, always surrounding the marbles. This type of bond results in the property called ductility, where the metal can be easily bent without breaking, allowing it to be drawn into wire. The free movement of electrons also explains why metals tend to be conductors of electricity and heat.


Plastics or polymers of the organic type consist of long chains of molecules which are either tangled or ordered at room temperature. Because the forces (known as van der Waals) between the molecules are very weak, polymers are very elastic (like a rubber band), can be easily melted, and have low strength. Like ceramics, polymers have good chemical resistance, electrical and thermal insulation properties. They are also brittle at low temperatures. The following table provides a general comparison of the properties between the three types of materials.


General Comparison of Materials

Property Ceramic Metal Polymer
Hardness Very High Low Very Low
Elastic modulus Very High High Low
High temperature strength      
Thermal expansion High Low Very Low
Ductility Low High High
Corrosion resistance High Low Low
Wear resistance High Low Low
Electrical conductivity Depends on material High Low
Density Low High Very Low
Thermal conductivity Depends on material High Low
Magnetic Depends on material High Very Low


Note: For general comparison only; specific properties depend on the material’s specific composition and how it is made.


These three material types can also be combined in various ways to form composites to take advantage of each material’s properties. For instance, ceramic particles or fibers can be added to a ceramic or metal matrix to improve the mechanical properties and/or produce a special property the matrix by itself generally would not have. Polymers are also reinforced with glass fibers for a wide range of construction and structural applications.



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2 Responses to Structure and Properties of Ceramics

  1. April Gocha, PhD says:

    While a molecule is a group of atoms that is the repeating unit of a substance, a unit cell is the simplest repeating unit of a crystal. Unit cells consist of several molecules, atoms, or ions that make up the smallest repeating unit of a crystal.

  2. negin says:

    What is the difference between crystals(unit cell) and molecules?

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