Ceramics Explanation and Uses

The term ceramic comes from the Greek word for pottery. It is used to describe a broad range of materials that include glass, enamel, concrete, cement, pottery, brick, porcelain, and chinaware. This class of materials is so broad that it is often easier to define ceramics as all solid materials except metals and their alloys that are made by the high-temperature processing of inorganic raw materials.
Ceramics can be either crystalline or glass-like. They can be either pure, single-phase materials or mixtures of two or more discrete substances. Most ceramics are polycrystalline materials, with abrupt changes in crystal orientation or composition across each grain in the structure. Ceramics can have electrical conductivities that resemble metals, such as ReO₃ and CrO_2. Ceramics can also make excellent insulators, such as the glass-ceramics used in spark plugs.

Spark Plug Diagram

One of the most distinctive features of ceramics is their resistance to being worked or shaped after they are fired. With certain exceptions, such as glass tubing or plate glass, they can't be sold by the foot or cut to fit on the job. Their size and shape must be decided on before they are fired and they must be replaced, rather than repaired, when they break.

The primary difference between ceramics and other materials is the chemical bonds that hold these materials together. Although they can contain covalent bonds, such as the Si O Si linkages in glass, they are often characterized by ionic bonds between positive and negative ions. When they form crystals, the strong force of attraction between ions of opposite charge in the planes of ions make it difficult for one plane to slip past another. Ceramics are therefore brittle. They resist compression, but they are much weaker to stress applied in the form of bending.

The use of ceramics traces back to Neolithic times, when clay was first used to make bowls that were baked in campfires. Clay is formed by the weathering of rock to form shinglelike particles of alumina and silica that cling together when wet to form clay minerals, such as kaolinite, which has the formula Al₄Si₄O₁₀(OH)₈.

A Ming Dynasty porcelain vase dated to 1403–1424

Today, ceramics play an important role in the search for materials that can resist thermal shock, act as abrasives, or have a better weight-strength ratio. Alumina ceramics are used for missile and rocket nose cones, silicon carbide (SiC) and molybdenum disilicide (MoSi₂) are used in rocket nozzles, and ceramic tiles are used for thermal insulation to protect the Space Shuttle on re-entry through the Earth's atmosphere.


Ceramic Heat Shield on botton of Space Shuttle Discovery

Ceramics made from uranium dioxide (UO₂) are being used as the fuel elements for nuclear power plants. Ceramics are also used as laser materials, from the chromium-doped crystals that emit a coherent monochromatic pulse of light to the optics through which the light passes. BaTiO₃ is used to make ceramic capacitors that have a very high capacitance. It is also used to make piezoelectric materials that develop an electric charge when subjected to a mechanical stress, which are the active elements of phonograph cartridges, sonar, and ultrasonic devices. Magnetic ceramics formed by mixing ZnO, FeO, MnO, NiO, BaO, or SrO with Fe₂O₃ are used in permanent magnets, computer memory, and telecommunications.

Questions:
1. What are the positive and negative  aspects of using ceramics in industry?
2. Research the Space Shuttle Columbia to find out what happened to it on February 1, 2003. Can you think of another material to use or a way to prevent this from ever happening again?
3. What future uses can you come up with for ceramics?

Source: Purdue University