Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

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14.7 Fabrication and Processing of Glasses and Glass–Ceramics • 589

(%EL) versus tempering temperature for four diameters—viz. 12.5 mm (0.5 in.),

25 mm (1 in.), 50 mm (2 in.), and 100 mm (4 in.).

Fabrication of Ceramic

Materials

One chief concern in the application of ceramic materials is the method of fabri-

cation. Many of the metal-forming operations discussed earlier in this chapter rely

on casting and/or techniques that involve some form of plastic deformation. Since

ceramic materials have relatively high melting temperatures, casting them is nor-

mally impractical. Furthermore, in most instances the brittleness of these materials

precludes deformation. Some ceramic pieces are formed from powders (or partic-

ulate collections) that must ultimately be dried and fired. Glass shapes are formed

at elevated temperatures from a fluid mass that becomes very viscous upon cooling.

Cements are shaped by placing into forms a fluid paste that hardens and assumes a

permanent set by virtue of chemical reactions. A taxonomical scheme for the several

types of ceramic-forming techniques is presented in Figure 14.15.

14.7 FABRICATION AND PROCESSING

OF GLASSES AND GLASS–CERAMICS

Glass Properties

Before we discuss specific glass-forming techniques, some of the temperature-

sensitive properties of glass materials must be presented. Glassy, or noncrystalline,

materials do not solidify in the same sense as do those that are crystalline. Upon cool-

ing, a glass becomes more and more viscous in a continuous manner with decreasing

temperature; there is no definite temperature at which the liquid transforms to a solid

Glass forming

processes

Particulate forming

processes

Cementation

Pressing Blowing Drawing Fiber

forming

Powder

pressing

Hydroplastic

forming

Slip

casting

Ta pe

casting

Hot Uniaxial Isostatic

Drying

Firing

Figure 14.15 A Ceramic fabrication techniques

classification scheme

for the ceramic-

forming techniques

discussed in this

chapter.