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What Is Ceramic?

The word ceramic is derived from the Greek word κεραμικός (keramikos). The term covers inorganic non-metallic materials whose formation is due to the action of heat. Up until the 1950s or so, the most important of these were the traditional clays, made into pottery, bricks, tiles and the like, along with cements and glass. The traditional crafts are described in the article on pottery. A composite material of ceramic and metal is known as cermet. The word ceramic can be an adjective, and can also be used as a noun to refer to a ceramic material, or a product of ceramic manufacture. Ceramics is a singular noun referring to the art of making things out of ceramic materials.

Many ceramic materials are hard, porous and brittle. The study and development of ceramics includes methods to mitigate problems associated with these characteristics, and to accentuate the strengths of the materials as well as to investigate novel applications.

The American Society for Testing and Materials (ASTM) defines a ceramic article as “an article having a glazed or unglazed body of crystalline or partly crystalline structure, or of glass, which body is produced from essentially inorganic, non-metallic substances and either is formed from a molten mass which solidifies on cooling, or is formed and simultaneously or subsequently matured by the action of the heat.”

Comments (2) 21.01.2007. 23:18

Types of Ceramic Materials

For convenience ceramic products are usually divided into four sectors, and these are shown below with some examples:

• Structural, including bricks, pipes, floor and roof tiles
• Refractories, such as kiln linings, gas fire radiants, steel and glass making crucibles
• Whitewares, including tableware, wall tiles, decorative art objects and sanitaryware
• Technical, is also known as Engineering, Advanced, Special, and in Japan, Fine Ceramics. Such items include tiles used in the Space Shuttle program, gas burner nozzles, ballistic protection, nuclear fuel uranium oxide pellets, bio-medical implants, jet engine turbine blades, and missile nose cones. Frequently the raw materials do not include clays.

Examples of Structural ceramics

• Bricks (mostly aluminium silicates), used for construction.

Examples of Whiteware Ceramics

• Bone china
• Earthenware, which is often made from clay, quartz and feldspar
• Porcelain, which usually contains the clay mineral kaolinite
• Stoneware

Comments (2) 20.01.2007. 08:38

Classification of Technical Ceramics

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

• Oxides: Alumina, zirconia.
• Non-oxides: Carbides, borides, nitrides, silicides.
• Composites: Particulate reinforced, combinations of oxides and non-oxides.

Each one of these classes can develop unique material properties.

Examples of Technical Ceramics

• Barium titanate (often mixed with strontium titanate) displays ferroelectricity, meaning that its mechanical, electrical, and thermal responses are coupled to one another and also history-dependent. It is widely used in electromechanical transducers, ceramic capacitors, and data storage elements. Grain boundary conditions can create PTC effects in heating elements.
• Bismuth strontium calcium copper oxide, a high-temperature superconductor.
• Boron carbide (B4C), which is used in ceramic plates in some personal, helicopter and tank armor.
• Boron nitride is structurally isoelectronic to carbon and takes on similar physical forms: a graphite-like one used as a lubricant, and a diamond-like one used as an abrasive.
• Ferrite (Fe3O4), which is ferrimagnetic and is used in the magnetic cores of electrical transformers and magnetic core memory.
• Lead zirconate titanate is another ferroelectric material.
• Magnesium diboride (MgB2), which is an unconventional superconductor.
• Silicon carbide (SiC), which is used as a susceptor in microwave furnaces, a commonly used abrasive, and as a refractory material.
• Silicon nitride (Si3N4), which is used as an abrasive powder.
• Steatite is used as an electrical insulator.
• Uranium oxide (UO2), used as fuel in nuclear reactors.
• Yttrium barium copper oxide (YBa2Cu3O7-x), another high temperature superconductor.
• Zinc oxide (ZnO), which is a semiconductor, and used in the construction of varistors.
• Zirconium dioxide (zirconia), which in pure form undergoes many phase changes between room temperature and practical sintering temperatures, can be chemically "stabilized" in several different forms. Its high oxygen ion conductivity recommends it for use in fuel cells. In another variant, metastable structures can impart transformation toughening for mechanical applications; most ceramic knife blades are made of this material.

Comments (0) 20.01.2007. 07:38

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