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.On the basis of their internal structure the ceramics are classified as clay products, refractories
and glasses.
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