The word ceramic is derived from the Greek word keramikos, meaning "of pottery," which is itself descended from an even older Sanskrit root referring to a burning or firing process. Today, the term ceramic applies to any inorganic nonmetallic solid material that involves heating at high temperature during its fabrication. This definition means that, apart from clay, other naturally occurring materials such as rutile (titanium oxide), and chemically synthesized ones such as silicon carbide may also be classed as ceramic.
There is a tendency to think of ceramics as synonymous with pottery or, alternatively, in the traditional roles of earthenware, porcelain, furnacining bricks, and so on. Most of these products start with clay or sand and are then shaped in a wet plastic state followed by firing at high temperature to give the article its final strength. Today, ceramic materials are used in such diverse applications as crockery, insulators, rocket nose cones, machine tools, nuclear fuels, lasers, and magnetic memory cores for computers. These important modern extensions of the uses of ceramics, however, should not overshadow the importance of traditional ceramics to the comfort and convenience of everyday life as we know it.
Properties
Ceramic materials have two important characteristics: they are chemically inert compared with most metals and carbon based (organic) materials, and they have a more complex internal structure. This crystal structure generally involves a number of different elements joined together by strong electrovalent (ionic) bonds. Magnesium oxide (more familiar as the antacid magnesia) is a simple ceramic material that is made up from positive magnesium ions and negative oxygen ions arranged as a cubic lattice.
This structural strength combined with a lack of chemical reactivity gives rise to useful properties. Ceramic materials are harder than metals or plastics and make useful abrasives. Furthermore, although they have the drawback of being brittle in tension, they are very strong in compression, retaining these properties to temperatures close to their melting points (for example, alumina, Al2O3, melts at 3630°F, or 2000°C). This property makes them useful where high-temperature strength is required, in furnace linings or rocket nose cones and, if they can be made cheaply enough, as building blocks such as bricks. Ceramic materials have low electrical conductivity, which makes them ideal as insulators, for example, in power-supply substations, and their low chemical reactivity makes them extremely resistant to corrosion in chemically hazardous environments. They are therefore useful for containing molten metals, acids, and alkalis as well as for resisting oxidation at high temperatures.
Heavy clay products
Heavy clay products include building materials such as bricks, roof and floor tiles, and sewer pipes. The raw materials used vary depending on the availability of a clay or hard carbonaceous shale (a type of clay rock). The essential features are cheap raw materials capable of being fired at moderately low temperatures of 1650 to 2010°F, (900–1100°C) to give the required mechanical strength. The trend has been to increase the mechanical stresses on these products, as in the case of bricks used for high-rise buildings, so greater technical expertise is now required to produce optimum strength and erosion resistance.
