Page 218 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

Section 8.2 The Structure of Ceramics

This chapter describes the general characteristics and applications of those
ceramics, glasses, and glass ceramics that are of importance in engineering applica-
tions and in manufacturing. Because of their unique properties and uses, the various
forms of carbon-namely, graphite, diamond, and carbon nanotubes-are also dis-
cussed here. The manufacturing of ceramic and of glass components and various
shaping and finishing operations are detailed in Chapter 18. Composites, which are
another important group of materials, are described in Chapter 9.

8.2 The Structure of Ceramics

Ceramics are compounds of metallic and nonmetallic elements. The term ceramics
(from the Greek words /eemmos, meaning “potter’s clay,” and /zeramikos, meaning
“clay products”) refers both to the material and to the ceramic product itself. Because
of the large number of possible combinations of elements, a wide variety of ceramics
now is available for a broad range of consumer and industrial applications. The ear-
liest use of ceramics was in pottery and bricks, dating back to before 4000 B.C.
Ceramics have been used for many years in automotive spark plugs, both as an elec-
trical insulator and for their high-temperature strength. They have become increas-
ingly important in tool and die materials, heat engines, and automotive components
(such as exhaust-port liners, coated pistons, and cylinder liners).
Ceramics can be divided into two general categories:

I. Traditional ceramics, such as whiteware, tiles, brick, sewer pipe, pottery, and
abrasive wheels.
2. Industrial ceramics (also called engineering, high-tech, or fine ceramics), such
as turbine, automotive, and aerospace components (Fig. 8.1); heat exchangers;
semiconductors; seals; prosthetics; and cutting tools.
The structure of ceramic crystals (containing various atoms of different sizes)
is among the most complex of all material structures. The bonding between these
atoms is generally covalent or ionic (see Section 1.2) and as such are much stronger

(H) (D)

FIGURE 8.l A variety of ceramic components. (a) High-strength alumina for high-
temperature applications. (b) Cas-turbine rotors made of silicon nitride. Source: Courtesy of
Wesgo Div., GTE.