Ceramic

A Ming Dynasty porcelain vase dated to 1403–1424
Fire test furnace insulated with firebrick and ceramic fibre insulation.
Mid-16th century ceramic tilework on the Dome of the Rock, Jerusalem
Spherical Hanging Ornament, 1575-1585, Ottoman Period. Brooklyn Museum.
Fixed partial porcelain denture, or "bridge"

A ceramic is an inorganic, nonmetallic[lower-alpha 1] solid material comprising metal, nonmetal or metalloid atoms primarily held in ionic and covalent bonds. The crystallinity of ceramic materials ranges from highly oriented to semi-crystalline, and often completely amorphous (e.g., glasses). Varying crystallinity and electron consumption in the ionic and covalent bonds cause most ceramic materials to be good thermal and electrical insulators and extensively researched in ceramic engineering. Nevertheless, with such a large range of possible options for the composition/structure of a ceramic (e.g. nearly all of the elements, nearly all types of bonding, and all levels of crystallinity), the breadth of the subject is vast, and identifiable attributes (e.g. hardness, toughness, electrical conductivity, etc.) are hard to specify for the group as a whole. However, generalities such as high melting temperature, high hardness, poor conductivity, high moduli of elasticity, chemical resistance and low ductility are the norm,[1] with known exceptions to each of these rules (e.g. piezoelectric ceramics, glass transition temperature, superconductive ceramics, etc.). Many composites, such as fiberglass and carbon fiber, while containing ceramic materials, are not considered to be part of the ceramic family.[2]

The word "ceramic comes from the Greek word κεραμικός (keramikos), "of pottery" or "for pottery",[3] from κέραμος (keramos), "potter's clay, tile, pottery".[4] The earliest known mention of the root "ceram-" is the Mycenaean Greek ke-ra-me-we, "workers of ceramics", written in Linear B syllabic script.[5] The word "ceramic" may be used as an adjective to describe a material, product or process, or it may be used as a noun, either singular, or, more commonly, as the plural noun "ceramics".[6]

The earliest ceramics made by humans were pottery objects, including 27,000-year-old figurines, made from clay, either by itself or mixed with other materials like silica, hardened, sintered, in fire. Later ceramics were glazed and fired to create smooth, colored surfaces, decreasing porosity through the use of glassy, amorphous ceramic coatings on top of the crystalline ceramic substrates.[7] Ceramics now include domestic, industrial and building products, as well as a wide range of ceramic art. In the 20th century, new ceramic materials were developed for use in advanced ceramic engineering, such as in semiconductors.

Types of ceramic products

By usage

For convenience, ceramic products are usually divided into four main types; these are shown below with some examples:

Ceramics made with clay

Main article: Pottery

Frequently, the raw materials of modern ceramics do not include clays.[9] Those that do are classified as follows:

Classification of technical ceramics

Technical ceramics can also be classified into three distinct material categories:

Each one of these classes can develop unique material properties because ceramics tend to be crystalline.

Other applications of ceramics

Types of ceramic material

Main article: Ceramic materials
A low magnification SEM micrograph of an advanced ceramic material. The properties of ceramics make fracturing an important inspection method.

A ceramic material is an inorganic, non-metallic, often crystalline oxide, nitride or carbide material. Some elements, such as carbon or silicon, may be considered ceramics. Ceramic materials are brittle, hard, strong in compression, weak in shearing and tension. They withstand chemical erosion that occurs in other materials subjected to acidic or caustic environments. Ceramics generally can withstand very high temperatures, such as temperatures that range from 1,000 °C to 1,600 °C (1,800 °F to 3,000 °F). A glass is often not understood as a ceramic because of its amorphous (noncrystalline) character. However, glassmaking involves several steps of the ceramic process and its mechanical properties are similar to ceramic materials.

Traditional ceramic raw materials include clay minerals such as kaolinite, whereas more recent materials include aluminium oxide, more commonly known as alumina. The modern ceramic materials, which are classified as advanced ceramics, include silicon carbide and tungsten carbide. Both are valued for their abrasion resistance, and hence find use in applications such as the wear plates of crushing equipment in mining operations. Advanced ceramics are also used in the medicine, electrical and electronics industries.

Crystalline ceramics

Crystalline ceramic materials are not amenable to a great range of processing. Methods for dealing with them tend to fall into one of two categories – either make the ceramic in the desired shape, by reaction in situ, or by "forming" powders into the desired shape, and then sintering to form a solid body. Ceramic forming techniques include shaping by hand (sometimes including a rotation process called "throwing"), slip casting, tape casting (used for making very thin ceramic capacitors, e.g.), injection molding, dry pressing, and other variations. Details of these processes are described in the two books listed below. A few methods use a hybrid between the two approaches.

Noncrystalline ceramics

Noncrystalline ceramics, being glass, tend to be formed from melts. The glass is shaped when either fully molten, by casting, or when in a state of toffee-like viscosity, by methods such as blowing into a mold. If later heat treatments cause this glass to become partly crystalline, the resulting material is known as a glass-ceramic, widely used as cook-top and also as a glass composite material for nuclear waste disposal.

Ceramics in archaeology

Ceramic artifacts have an important role in archaeology for understanding the culture, technology and behavior of peoples of the past. They are among the most common artifacts to be found at an archaeological site, generally in the form of small fragments of broken pottery called sherds. Processing of collected sherds can be consistent with two main types of analysis: technical and traditional.

Traditional analysis involves sorting ceramic artifacts, sherds and larger fragments into specific types based on style, composition, manufacturing and morphology. By creating these typologies it is possible to distinguish between different cultural styles, the purpose of the ceramic and technological state of the people among other conclusions. In addition, by looking at stylistic changes of ceramics over time is it possible to separate (seriate) the ceramics into distinct diagnostic groups (assemblages). A comparison of ceramic artifacts with known dated assemblages allows for a chronological assignment of these pieces.[11]

The technical approach to ceramic analysis involves a finer examination of the composition of ceramic artifacts and sherds to determine the source of the material and through this the possible manufacturing site. Key criteria are the composition of the clay and the temper used in the manufacture of the article under study: temper is a material added to the clay during the initial production stage, and it is used to aid the subsequent drying process. Types of temper include shell pieces, granite fragments and ground sherd pieces called 'grog'. Temper is usually identified by microscopic examination of the temper material. Clay identification is determined by a process of refiring the ceramic, and assigning a color to it using Munsell Soil Color notation. By estimating both the clay and temper compositions, and locating a region where both are known to occur, an assignment of the material source can be made. From the source assignment of the artifact further investigations can be made into the site of manufacture.

See also

Notes

  1. Involving no metallic bonding, and so not having metallic properties as a material.

References

  1. Black, J. T. & Kohser, R. A. (2012). DeGarmo's materials and processes in manufacturing. Wiley. p. 226. ISBN 978-0-470-92467-9.
  2. Carter, C. B. & Norton, M. G. (2007). Ceramic materials: Science and engineering. Springer. pp. 3 & 4. ISBN 978-0-387-46271-4.
  3. κεραμικός, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus Digital Library
  4. κέραμος, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus Digital Library
  5. Palaeolexicon, Word study tool of ancient languages
  6. "ceramic". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005. (Subscription or UK public library membership required.)
  7. Carter, C. B. & Norton, M. G. (2007). Ceramic materials: Science and engineering. Springer. pp. 20 & 21. ISBN 978-0-387-46271-4.
  8. "Whiteware Pottery". Encyclopædia Britannica. Retrieved 30 June 2015.
  9. Greg Geiger Introduction To Ceramics, American Ceramic Society
  10. Ceramic in Watchmaking. Watches.infoniac.com (2008-01-09). Retrieved on 2011-11-28.
  11. Mississippi Valley Archaeological Center, Ceramic Analysis, Retrieved 04-11-12

Further reading

External links

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