| Ceramics (Ancient Greek: κέραμος - clay) represents items made from inorganic, non-metallic materials (for example clay) and their mixture with mineral additives, manufactured at high temperatures with subsequent cooling.
In narrow sense, the word "ceramics" means clay, which had undergone burning. However, modern use of this term widens its meaning to the inclusion of all inorganic non-metallic materials. Ceramic materials can be transparent or partially transparent in structure and can be made from glass (see glass ceramics). The earliest ceramics were used as clay vessels or compounded with other materials. At the moment ceramics are used in industrial materials (engineering industry, instrument making, aircraft industry, etc.) as building materials, art and widely used as a material in medicine and science. In the 20th century, new ceramic materials were created for use in the semi-conductor industry and other fields.
Types of ceramics:
Depending upon the structure, ceramic is found in the form of fine ceramics (vitreous or fine-grained crockery) and coarse (coarse-grained crockery). Basic types of fine ceramics are porcelain, semi-porcelain, faience and majolica. The main type of coarse ceramics is earthenware ceramics. Besides the above, carbide, boride and silicide etc types of ceramics are also found.
Porcelain possesses compactly sintered white color crockery (sometimes with a bluish tint) with low water absorption (up to 0.2 %) and generates a highly melodious sound on tipping and can be transparent in thin layers. Glaze does not cover the edge of the crimp or base of the porcelain item. Raw materials for porcelain are china clay, sand, feldspar and other additives.
Faience produces porous white crockery with a yellowish shade. The porosity of the crockery is 9 - 12 %. Due to the high porosity, items made from faience completely become covered with an achromatic glaze of low thermal stability. Faience is used in manufacturing dinnerware for daily use. Raw materials for manufacture of faience are white-burning clay with mixture of chalk and quartz sand.
With respect to properties, semi-porcelain occupies the intermediate position between porcelain and faience, with white crockery having 3 - 5 % water absorption and is used in the manufacture of dishware.
Majolica has porous crockery, has about 15 % water absorption and the item possess a smooth surface, luster, less wall thickness, covered with color glazes and can have decorative embossing. Casting is used for the manufacturing of majolica. Raw materials are white-burning clay (faience majolica) or red-burning clay (earthenware majolica), fusible matter, chalk and quartz sand.
Earthenware ceramics create crockery of a reddish brown color (red-burning clay is used), high porosity and water absorption of up to 18 %. Items can be covered with achromatic glazes or painted with a clay color - engobes and usually used for kitchen and household ware and decorative articles.
History:
Ceramics has been used from ancient times and is, probably, the first material created by man. Ceramics date back to the Mesolithic and Neolithic ages.
Separate types of ceramics were formed gradually through improvisation and experimentation, and upon the properties of raw materials and treatment conditions being used.
Historically, ceramic articles were solid, porous and fragile.
Most ancient aspects of ceramics - the ordinary pottery with earthy, colored and porous attributes. This household pottery was improved by various methods. For example pattern stamping was applied and engraving, a glossy layer added (Greek ceramics and Roman Terra sigillata) and with color glazes ("Gafnerkeramika" of Renaissance).
Originally, all ceramics was made manually. The invention of the potter's wheel in 3000 B.C. allowed people to make articles with much thinner walls.
By the end of the XVI century, majolica (depending on the origin, it is also often called faience) appeared in Europe. It was porous crockery containing iron and lime, but with a white faience substance and it was covered with two glazes: opaque, with high tin content and a transparent glossy lead glaze.
Decorators wrote on majolica, when the glaze was still wet, before burning the item at a temperature of up to 1000°C. Paints for painting were taken from the same chemical compositions as that of the glaze. However, the significant part was made up of metal oxides, which withstood high temperatures (so called refractory paints - dark blue, green, yellow and violet). Starting from the 18th century, it became a practice to use so called glass colors, which were applied on an already burnt glaze. They were also used for painting porcelain.
In the 16th century, manufacture of stoneware was widespread in Germany. White (for example, in Siegburg) or colored (for example, in Raeren), was dense crockery that consisted of clay, mixed with feldspar and other substances. After burning at a temperature of 1200-1280°C, the stoneware became solid and practically non porous.
Stoneware was also manufactured by Wedgwood in England. Fine faience is a special quality of ceramic with white porous crockery, covered with white glaze, and appeared in England in the first half of the 18th century. Faience, depending on the firmness of crockery, is divided into soft fine faience with high lime content and average - with less content and solid without lime. The last one, in relation to composition and firmness of the crockery, compares to stoneware or porcelain.
Cement, another type of ceramic, was widely used in construction. Clay and limestone mixed with water form the composition of raw materials for cement.
|
