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Ceramics refer to polycrystalline materials and products formed by baking natural clays and
mineral admixtures at a high temperature and also by sintering oxides of various metals and
inorganic substances having high melting point. The word is of Greek origin and derives its
name from Keromos meaning potter ’s earth or clay. But, nowadays the term ceramic is applied
to a wide range of silicates, metallic oxides and their combinations. Carbon, boron, silicon,
certain carbides, silicates, refractory hydrides and sulphides are also considered to be ceramics.
As a building material, ceramics, may include brick, stone, concrete, glass, abrasives, porcelain,
high temperature refractories, etc. Clay is the most common example of ceramic materials.
Magnesium oxide can withstand high temperatures (1650–2500°) without melting and is used
extensively as a refractory.
Ceramics are usually hard and brittle and are in the form of amorphous (non-crystalline) or
glassy solids. The bond in these materials is mixed ionic and covalent and while these can be
made in single crystal forms, their more common structure is glassy. Because of covalent ionic
bond the electrons are not free which makes the ceramics, thermal and electrical insulators. At
low temperatures, ceramics behave elastically. However, under proper conditions of stress and
temperature these deform by viscous flow.
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On the basis of their internal structure the ceramics are classified as clay products, refractories
and glasses. Clay products have been dealt in detail in Chapter 2. Refractories and glasses
are described in the sections to follow.
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