The term "ceramic" once referred only to clay-based materials. However, new generations of ceramic materials have tremendously expanded the scope and number of possible applications. Many of these new materials have a major impact on our daily lives and on our society.
Ceramic materials are inorganic compounds, usually oxides, nitrides, or carbides. The bonding is very strong--either ionic or network covalent. Many adopt crystalline structures, but some form glasses. The properties of the materials are a result of the bonding and structure.
Ceramics can withstand high temperatures, are good thermal insulators, and do not expand greatly when heated. This makes them excellent thermal barriers, for applications that range from lining industrial furnaces to covering the space shuttle to protect it from high reentry temperatures.
Glasses are transparent, amorphous ceramics that are widely used in windows, lenses, and many other familiar applications. Light can induce an electrical response in some ceramics, called photoconductivity. Fiber optic cable is rapidly replacing copper for communications, as optical fibers can carry more information for longer distances with less interference and signal loss than traditional copper wires.
Ceramics are strong, hard, and durable. This makes them attractive structural materials. The one significant drawback is their brittleness, but this problem is being addressed by the development of new materials such as composites.
Ceramics vary in electrical properties from excellent insulators to
superconductors. Thus, they are used in a wide range of applications. Some
are capacitors, others semiconductors in electronic devices. Piezoelectric
materials can convert mechanical pressure into an electrical signal and
are especially useful for sensors. There is now a strong research effort
to discover new high Tc superconductors and to develop possible
applications.
| Material | Uses |
|---|---|
| Al2O3 (aluminum oxide) | Spark-plug insulating bodies,
substrates for microelectronic packaging |
| MgO (magnesium oxide) | electrical insulators, refractory brick |
| SiO2 (Silicon dioxide) | cookware, optical fibers |
| ZrO2 (zirconium oxide) | cubic zirconia, oxygen sensors |
| SiC (silicon carbide) | kiln parts, heating elements,
abrasives |
| Si3N4 (silicon nitride) | turbocharger rotors, piston valves |
The processing of crystalline ceramics follows the basic steps that
have been used for ages to make clay products. The materials are selected,
prepared, formed into a desired shape, and sintered at high temperatures.
Glasses are processed by pouring in a molten state, working into shape
while hot, and then cooling. New methods such as chemical vapor deposition
and sol-gel processing are presently being developed. Ceramics has advanced
far beyond its beginnings in clay pottery. Ceramic tiles cover the space
shuttle as well as our kitchen floors. Ceramic electronic devices make
possible high-tech instruments for everything from medicine to entertainment.
Clearly, ceramics are our window to the future.