Ceramic Definition and Chemistry

Ceramic Definition and Chemistry The word ceramic comes from the Greek word keramikos, which means of pottery. While the earliest ceramics were pottery, the term encompasses a large group of materials, including some pure elements. A ceramic is an inorganic, nonmetallic solid, generally based on an oxide, nitride, boride, or carbide, that is fired at a high temperature. Ceramics may be glazed prior to firing to produce a coating that reduces porosity and has a smooth, often colored surface. Many ceramics contain a mixture of ionic and covalent bonds between atoms. The resulting material may be crystalline, semi-crystalline, or vitreous. Amorphous materials with similar composition are generally termed glass. The four main types of ceramics are whitewares, structural ceramics, technical ceramics, and refractories. Whitewares include cookware, pottery, and wall tiles. Structural ceramics include bricks, pipes, roofing tiles, and floor tiles. Technical ceramics are also know as special, fine, advanced, or engineered ceramics. This class includes bearings, special tiles (e.g. spacecraft heat shielding), biomedical implants, ceramic brakes, nuclear fuels, ceramic engines,  and ceramic coatings. Refractories are ceramics used to make crucibles, line kilns, and radiate heat in gas fireplaces. How Ceramics Are Made Raw materials for ceramics include clay, kaolinate, aluminum oxide, silicon carbide, tungsten carbide, and certain pure elements. The raw materials are combined with water to form a mix that can be shaped or molded. Ceramics are difficult to work after they are made, so usually they are shaped into their final desired forms. The form is allowed to dry and is fired in an oven called a kiln. The firing process supplies the energy to form new chemical bonds in the material (vitrification) and sometimes new minerals (e.g., mullite forms from kaolin in the firing of porcelain). Waterproof, decorative, or functional glazes may be added prior to the first firing or may require a subsequent firing (more common). The first firing of a ceramic yields a product called the bisque. The first firing burns off organics and other volatile impurities. The second (or third) firing may be called glazing. Examples and Uses  of Ceramics Pottery, bricks, tiles, earthenware, china, and porcelain are common examples of ceramics. These materials are well-known for use in building, crafting, and art. There are many other ceramic materials: In the past, glass was considered a ceramic, because its an inorganic solid that is fired and treated much like a ceramic. However, because glass is an amorphous solid, glass is usually considered to be a separate material. The ordered internal structure of ceramics plays a large role in their properties.Solid pure silicon and carbon may be considered to be ceramics. In a strict sense, a diamond could be called a ceramic.Silicon carbide and tungsten carbide are technical ceramics that have high abrasion resistance, making them useful for body armor, wear plates for mining, and machine components.Uranium oxide (UO2 is a ceramic used as a nuclear reactor fuel.Zirconia (zirconium dioxide) is used to make ceramic knife blades, gems, fuel cells, and oxygen sensors.Zinc oxide (ZnO) is a semiconductor.Boron oxide is used to make body armor.Bismuth strontium copper oxide and magnesium diboride (MgB2) are superconductors.Steatite (magnesium silicate) is used as an electrical insulator.Barium titanate is used to make heating elements, capacitors, transducers, and data storage elements. Ceramic artifacts are useful in archaeology and paleontology because their chemical composition can be used to identify their origin. This includes not only the composition of clay, but also that of the temper the materials added during production and drying. Properties of Ceramics Ceramics include such a wide variety of materials that its difficult to generalize their characteristics. Most ceramics exhibit the following properties: High hardnessUsually brittle, with poor toughnessHigh melting pointChemical resistancePoor electrical and thermal conductivityLow ductilityHigh modulus of elasticityHigh compression strengthOptical transparency to a variety of wavelengths Exceptions include superconducting and piezoelectric ceramics. Related Terms The science of the preparation and characterization of ceramics is called ceramography. Composite materials are made up of more than one class of material, which may include ceramics. Examples of composites include carbon fiber and fiberglass. A cermet is a type of composite material containing ceramic and metal. A glasss of glass-ceramics include glass stove tops and the glass composite used to bind nuclear waste for disposal.