GTBL042-14 GTBL042-Callister-v3 October 2, 2007 13:45
2nd Revised Pages594 • Chapter 14 / Synthesis, Fabrication, and Processing of MaterialsStress (10^3 psi)− 120 − 80 − 40 400 80 120− 20 − 10 100 20Compression Stress (MPa) TensionFigure 14.20 Room-temperature residual
stress distribution over the cross section of
a tempered glass plate. (From W. D.
Kingery, H. K. Bowen, and D. R. Uhlmann,
Introduction to Ceramics, 2nd edition.
Copyright©c1976 by John Wiley & Sons,
New York. Reprinted by permission of
John Wiley & Sons, Inc.)Concept Check 14.4How does the thickness of a glassware affect the magnitude of the thermal stresses
that may be introduced? Why?[The answer may be found at http://www.wiley.com/college/callister (Student Companion Site).]Fabrication and Heat Treating of Glass–Ceramics
The first stage in the fabrication of a glass-ceramic ware is forming it into the desired
shape as a glass. Forming techniques used are the same as for glass pieces, as described
previously—viz. pressing and drawing. Conversion of the glass into a glass–ceramic
(i.e., crystallation, Section 13.5) is accomplished by appropriate heat treatments. One
such set of heat treatments for a Li 2 O–Al 2 O 3 –SiO 2 glass–ceramic is detailed in the
time-versus-temperature plot of Figure 14.21. After melting and forming operations,
nucleation and growth of the crystalline phase particles are carried out isothermally
at two different temperatures.14.8 FABRICATION AND PROCESSING
OF CLAY PRODUCTS
As Section 13.6 noted, this class of materials includes the structural clay products
and the whitewares. In addition to clay, many of these products also contain other
ingredients. After having been formed, pieces most often must be subjected to drying
and firing operations; each of the ingredients influences the changes that take place
during these processes and the characteristics of the finished piece.The Characteristics of Clay
The clay minerals play two very important roles in ceramic bodies. First, when water
is added, they become very plastic, a condition termedhydroplasticity.This property
is very important in forming operations, as discussed below. In addition, clay fuses
or melts over a range of temperatures; thus, a dense and strong ceramic piece may
be produced during firing without complete melting such that the desired shape is