About Ceramics From The American Ceramic Society

 

When the average person hears the word ceramics, usually an image of pottery (or at the other extreme even space shuttle tiles) appears. But what many people don’t realize is that ceramics play an important role almost everywhere you look and sometimes where you can’t. Besides the everyday objects of dinnerware, glassware, floor and wall tile, and other consumer products, ceramics are helping computers and other electronic devices operate, improving people’s health in various ways, providing global telecommunications, and protecting soldiers during combat. And the list goes on.

Definition of Ceramics

Merriam-Webster’s online dictionary defines it as a clay material that is fired at a high temperature to form such products as earthenware, porcelain or brick. The word itself can be traced back to the Greek term keramos, meaning potter’s clay or pottery. Keramos in turn is related to an older Sanskrit root meaning “to burn.” Ceramus or Keramos was also an ancient city on the north coast of the Aegean Sea in what is currently Turkey. (The word Keramos lives on as the name for the national professional ceramic engineering fraternity.

In the most simple of terms, ceramics can be defined as inorganic, nonmetallic materials. They are typically crystalline in nature (have an ordered structure) and are compounds formed between metallic and nonmetallic elements such as aluminum and oxygen (alumina, Al₂O₃), calcium and oxygen (calcia, CaO), and silicon and nitrogen (silicon nitride, Si₃N₄).

In broader terms ceramics also include glass (which has a non-crystalline or amorphous random structure), enamel (a type of glassy coating), glass-ceramics (a glass containing ceramic crystals), and inorganic cement-type materials (cement, plaster and lime). However, as ceramic technology has developed over time, the definition has expanded to include a much wider range of other compositions used in a variety of applications.

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.

Microstructure

Another characteristic that plays an important factor in the final property of a material is called microstructure. The microstructure of a material is usually too small to be seen with the naked eye. For ceramics, the microstructure is made up of small crystals called grains. In general, the smaller the grain size, the stronger and denser is the ceramic material. In the case of a glass material, the microstructure is non-crystalline. When these two materials are combined (glass-ceramics), the glassy phase usually surrounds small crystals, bonding them together. The wide variety of applications for ceramic results from its unique properties. In many respects this properties cannot be achieved by other materials. Among the many properties that ceramic products take advantage of include:

• High hardness
• High mechanical strength
• Dimensional stability
• Resistance to wear
• Resistance to corrosion or chemical attack
• weathering resistance
• High working temperature
• Low or high thermal conductivity
• Good electrical insulation
• Dielectric and ferroelectric properties

Depending on the composition and the processing of the raw materials, as well as the fabrication and firing conditions, the properties of the material can often be closely tailored to the desired application.