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Ceramics - A Definition
Ceramics are defined as products made from inorganic materials having non-metallic properties, usually processed at a high temperature at some time during their manufacture.
The word "ceramics" comes from the Greek word "Keramos" meaning "Pottery," "Potter's Clay," or "a Potter." This Greek word is related to an old Sanskrit root meaning "to burn" but was primarily used to mean "burnt stuff."
The technical definition of ceramics encompasses a much greater variety of products than is normally realized. To most people, the word ceramics means dinnerware, figureines, vases, and other objects of ceramic art.
The majority of ceramic products not generally recognized as such are much more recent in development and are, in general, utilitarian rather than aesthetic. Examples are bathtubs, washbowls, sinks, electrical insulating devices, water and sewerage pipes, bricks, hollow tile, glazed building tile, floor and wall tile, earthenware, porcelain enamel and glass.
Ceramic products have a number of outstanding properties which determine their usefulness. One of the most unusual of these is their great durability. This durability can be divided into three types: chemical, mechanical and thermal.
Chemical Durability
The high chemical durability of the great majority of ceramic products makes them resistant to almost all acids, alkalies, and organic solvents. Of further importance is the fact that ceramic materials are not affected by oxygen. The materials generally contained in the ceramic products have already combined with all of the oxygen for which they have an affinity, and therefore, are not affected further by the presence of oxygen in their environment.
Mechanical Durability
The mechanical durability of ceramics is evidenced by their strength and hardness. The compressive strengths of ceramic materials are extremely high, normally 50,000 to 100,000 lbs/sq. in. This hardness makes ceramic materials very resistant to abrasion. It is this property which makes them useful for floors, and for the grinding of metals and other materials.
Thermal Durability
Most ceramics have the ability to withstand high temperatures. This is why they are useful in the production of all types of heat-containing equipment such as kilns for the ceramic industry, and such products as the inner linings of fireplaces and home heating furnaces.
Historical Background
The history of tiles dates back as far as the fourth millenium BC where in Egypt tiles were used to decorate various houses. In those days, clay bricks were dried beneath the sun or baked, and the first glazes were blue in color and were made from copper.
As early as 4,000 BC ceramics were also found in Mesopotamia. These ceramics bore decorations which were white and blue striped and later possesed more varied patterns and colors.
In China, the great center of ceramic art, a fine, white stoneware with the earliest Chinese glaze was produced during the Shang-Yin Dynasty (1523-1028 BC).
Through the centuries, tile decoration was improved upon as were methods of tile manufacture. For example, during the Islamic period, all methods of tile decoration were brought to perfection in Persia. Throughout the known world, in various countries and cities, ceramic tile production and decoration reached great heights. The tile mosaics of Spain and Portugal, the floor tiles of Rennaisance Italy, the faiences of Antwerp, the development of tile iconography in the Netherlands, and the ceramic tiles of Germany are all prominent landmarks in the history of ceramic tile.
In the early days, the tiles were hand-made - that is to say - each tile was hand-formed and hand-painted, thus each was a work of art in its own right. Ceramic tile was used almost everywhere - on walls, floors, ceilings, fireplaces, in murals, and as an exterior cladding on buildings.
Today ceramic tile in the United States as it is throughout the world is not "hand-made" or "hand-painted" for the most part. Automated manufacturing techniques are used and the human hand does not enter into the picture until it is time to install the tile.
As in the early days, ceramic tile is still used indoors as well as outdoors. It can be found on floors, walls, counters, fireplaces, fountains, exterior building walls, etc.
Ceramics - Raw Materials
The majority of raw materials used by the ceramic industry are the oxides of metals. The three metals which have been the mainstays of the industry for many years are clay, flint, and feldspar. These are the major materials contained in what is sometimes referred to in the industry as "classical ceramic bodies."
Clay
Clays are hydrated aluminosilicates and are the end-product of the weathering of feldspathic rock. The most important clay mineral is Kaolinite which has the composition AL2O3 - 2SiO2 - 2H2O. Clay is the material that gives a ceramic composition the plasticity which facilitates the fabrication of the material into the desired form prior to heat-treating.
Flint
Flint is a form of silicon dioxide (SiO2) usually produced from quartzite, sand or rock. It is used in a finely pulverized form as a filler to give the clay and final product the desired properties.
Feldspar
Feldspar is a broad, generic name applied to a group of alkali-aluminosilicates. For example, feldspars in which the alkali is potassium (K2O - Al2O3 - 6SiO2) are called "potash feldspars," and those containing sodium (Na2O - Al2O3 - 6SiO2) are called "soda feldspars." Most feldspars, however, are combinations of these two types. Feldspar is used and known as a "flux" in the ceramic industry. The flux is the material which starts to melt at the lowest temperature during the heat-treating process, thereby acting as the cementing element which gives the ceramic body its strength.
A great many other naturally-occurring minerals and some synthetically produced chemicals are used as raw materials by the ceramic industry. A few of the more important ones, along with their chemical formulas, are now presented:
Raw Materials Listing
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