Discovering a Hidden Industry
Geiger, Greg, The World and I
Advanced ceramics are the enabling materials of a silent revolution that's enhancing our quality of life in numerous ways.
One of the oldest materials known to humankind is clay. People of ancient cultures discovered that this material, when soft, can be molded into various shapes, but it hardens irreversibly when heated by fire. And they took advantage of these properties to make various types of utensils for holding water or grain and cooking food. The earliest known functional pottery made in this manner dates back to 10,000 B.C. Thus began the opening chapter in the history of materials that we call ceramics. It is a history that has grown richer with time.
For most people today, the word ceramics evokes images of coffee mugs, dinner plates, figurines, and decorative pottery. Some may add brick, floor and wall tile, and certain plumbing fixtures to the list. These products illustrate what are known as traditional or silicate-based ceramics. On the other hand, over the past five decades, a new class of ceramics--called advanced ceramics--has emerged, playing a major role in novel and exciting applications. Yet, development of the advanced ceramics industry has gone largely unnoticed by the general public, prompting some to call it the "hidden industry."
Applications of advanced ceramics span such diverse fields as medicine, aerospace, automotive, environmental protection, military defense, and fiber-optic communication. For instance, NASA's space shuttle program would not be possible without the 34,000 lightweight, reusable ceramics tiles that protect the shuttle from temperatures up to 2,300 [degrees] F as it reenters the atmosphere. Advanced ceramics are also vital for electronic products such as personal computers and cell phones. And these materials are being used to make automotive catalytic converters, which help convert noxious hydrocarbons and carbon monoxide into harmless carbon dioxide and water.
In 1996, the U.S. market for advanced ceramics was estimated to be $6.3 billion. This figure is expected to rise to $9.2 billion by the year 2001.
What are ceramics?
The word ceramic can be traced back to the Creek term keramos, meaning "potter's clay" or "pottery," and keramos in turn is related to an older Sanskrit root that means "to burn." Thus the early Greeks used the term to mean "burned stuff" or "burned earth," when referring to products obtained through the action of fire on earthly materials.
Ceramics constitute one of three large classes of solid materials used by engineers. The other two are metals and polymers. In chemical terms, ceramics are inorganic, nonmetallic materials that are typically produced by the high-temperature firing of naturally occurring minerals or artificially processed powders. Ceramics are generally crystalline in nature and include compounds between elements such as aluminum and oxygen (alumina, [Al.sub.2][O.sub.3]), silicon and nitrogen (silicon nitride, [Si.sub.3][N.sub.4]), and silicon and carbon (silicon carbide, SIC).
Advanced ceramics are variously described as technical ceramics, engineering ceramics, or (in Japan) fine ceramics. Whatever the name, they are far superior to traditional ceramics in terms of their mechanical, thermal, electrical, optical, or magnetic properties, and their resistance to corrosion or oxidation. Advanced ceramics are also superior to metals and plastics in many of these properties. In fact, if it were not for the high melting point and corrosion resistance of ceramics, the production of metal and alloy products we use today would not be possible. Among the disadvantages of ceramics are their brittleness and relatively poor tensile strength.
There are several categories of advanced ceramics. They include structural ceramics; ceramic coatings; chemical processing and environmental ceramics; and electrical or electronic ceramics. Structural ceramics are useful in applications such as industrial wear parts (bearings and dies), biomedical parts (bone and dental implants), cutting tools (drills and end mills), armor (bulletproof vests and military equipment), and engine components (turbine rotors and valves). …