Ceramic | Research & Encyclopedia Articles

Ceramic

Linked to synthetic metals and plastics in their versatility and durability, ceramics comprise a broad category of such specially shaped and heated products as pottery, porcelain, china, and ceramic tile; ceramics may also be found in cement, plumbing and construction materials, and spacecraft components.

The basic ingredient in all forms of ceramics are silicates, minerals which are so common and widespread that it is virtually impossible to completely trace their history. When silicates (feldspar and silica, for example) are combined with a liquid such as water, they form a mixture that can be kneaded and shaped into any form. After shaping, the object is dried and fired in a high-temperature oven called a kiln. A glaze (a glass-like substance that makes the surface glossy and nonporous) may be added between drying and firing.

From ancient days to the present, this process has survived almost unchanged, save for the addition of mechanical aids. The oldest examples of pottery, found in Moravia and dating back to 25,000 b.c., are animal shapes made of fired clay. Similar figures, dating from around 5500 b.c., have been found in the Near East, and Japanese pots, made as early as 9000 b.c., have also been discovered. Pottery was originally dried in the sun or fired in bonfires, which produced articles that were ultimately too porous. Only kilns (which first appeared in Mesopotamia, as did the first potter's wheels, around 3000 b.c.), which allowed for articles to be fired at high temperatures followed by slow cooling, could harden clay enough that it became airtight. Decorative techniques, which developed concurrently with the making of pottery, included the use of mineral-based glazes to produce various colors; etching with sticks, fingernails, or shells; and painting before glazing. Some of the most fascinating pottery in history was made by the ancient Greeks, whose vases were skillfully decorated in the "black figure" (black paint applied to red clay) or "red figure" (black paint covering all but the design, which stood out in red clay) methods. The early Islamic potters of the Middle East produced colorful, imaginatively glazed tiles and other items. Their elaborate pictorial designs have provided archeologists with many clues to their daily lives. Perhaps the most renowned potters of all time, however, are the Chinese, who developed the finest form of pottery known as porcelain.

Porcelain is made of a clay called kaolin mixed with a petuntse, which is comprised of feldspar, aluminum silicate, and potash or soda. It is fired at an extremely high temperature to achieve its smooth finish. The result is a milky white ceramic material that is uniformly translucent and glasslike. Porcelain was first made in T'ang Dynasty China ( a.d. 618-906) and by a.d. 1000 it was being mass-produced in the city of Ching-te Chen. Much later, increased trade with China brought porcelain to the attention of Europeans. At the same time, Middle Eastern methods of glazing were introduced to Europe through Spanish Moors and adapted into such forms as the Italian majolica and the French faience. These were vibrantly colored, glazed floor tiles. Europeans had seen porcelain as early as the fifteenth century but it remained quite rare until the English, French, and Dutch East India Companies began the widespread, economical importation of chinaware. As the use of china cups gained in popularity, potters in Italy, France, Germany, England, and the United States searched for ways to reproduce fine Chinese porcelain. Their efforts produced an imitative material called soft porcelain, for which a factory at Sèvres, France, became famous during the eighteenth century. Johann Friedrich Böttger (1682-1719), a German apothecary's apprentice, discovered how to make true or hard-paste porcelain in 1709 and established a factory in Dresden the next year.

One of the best-known contributors to the development of ceramics was English potter Josiah Wedgwood (1730-1795). In his early twenties he began developing a highly scientific approach to his craft, and after going into business for himself succeeded in developing a cream-colored earthenware that, because of Queen Charlotte's patronage, became known as Queen's ware. Simple, elegant, and durable, this product eventually became popular worldwide. In 1768, Wedgwood entered into a partnership with Thomas Bentley and began making jasperware, unglazed stoneware of various colors with white relief figures for which he became renowned. Wedgwood also produced items in finely textured, unglazed black basalt decorated with red painting to imitate the red figure vases of ancient Greece, and he developed bone china, which is made of clay mixed with bone ash. Finally, Wedgwood is remembered as the inventor of the pyrometer (a high-temperature gauge) and as the first pottery craftsman to utilize a steam-powered engine in his factory.

Ceramics began to be used for industrial purposes with the development of other technologies during the early twentieth century. A high demand for military materials during World War II hastened the science's evolution, and ceramics are now commonly found in a wide variety of products, including abrasives, bathroom fixtures, and electrical insulation. During the 1960s and 1970s, the burgeoning fields of atomic energy, electronics, communication, and space travel increased demands for more sophisticated ceramic products--for instance, spacecraft requiring "skins" and engine linings that are highly heat-resistant.

In the 1980s, research to develop ceramic engine parts that would better withstand heat than metal and thus burn fuel more efficiently was undertaken. As recently as 1990, a team of scientists at Japan's Government Industrial Research Institute found further applications for ceramics by developing stretchable compounds made from silicon carbide, silicon nitride, and other materials. When made into strips and heated, this special ceramic material can be stretched to two-and-a-half times its original length without losing its hardness and durability. Such ceramic fibers have revolutionary applications in the automotive and aerospace industries. One company, Thermal Ceramics Inc., has introduced a series of ceramic fiber products for use in transportation equipments such as automotive air bags, turbochargers, plastic gasoline tanks and fuel lines. In addition, they have developed ceramic fiber papers which are lightweight, durable, cost-effective alternatives to traditional insulating, friction, and filtering media.

Two other exciting developments have been made in the ceramic industry in the late 1990s. The first is a new ceramic gelcasting process developed by scientists at Oak Ridge National Laboratory. Their procedure is a simple process that allows the formation of complete ceramic components without machining. In 1997 General Motors Corp. engineers began to explore this process as a new way to manufacture improved ceramic components for turbines. Turbine engineers hope this technology can be used in the future to produce high quality ceramic nozzles, blades, rotors and other parts economically. The second breakthrough came from chemist Andrew R. Barron, an inorganic chemist at Rice University in Houston, and his colleagues C. Jeff Harlan and Rhonda L. Callender who found a way to break down the aluminum-oxide particles found in ceramics. Their process eliminates potentially hazardous waste by creating small sub-units that easily and safely dissolve in water. The impact of these two discoveries on the ceramics remains to be seen.