Callister - An introduction - 8th edition

528 • Chapter 13 / Applications and Processing of Ceramics
Fabrication and Processing of Clay Products
• Clay minerals assume two roles in the fabrication of ceramic bodies:
When water is added to clay it becomes pliable and amenable to forming.
Clay minerals melt over a range of temperatures; thus, during firing, a dense
and strong piece is produced without complete melting.
• For clay products, two common fabrication techniques are hydroplastic forming
and slip casting.
For hydroplastic forming, a plastic and pliable mass is formed into a desired
shape by forcing the mass through a die orifice.
With slip casting, a slip (suspension of clay and other minerals in water) is
poured into a porous mold. As water is absorbed into the mold, a solid
layer is deposited on the inside of the mold wall.
• After forming, a clay-based body must be first dried and then fired at an elevated
temperature to reduce porosity and enhance strength.
Powder Pressing
• Some ceramic pieces are formed by powder compaction; uniaxial, isostatic, and
hot pressing techniques are possible.
• Densification of pressed pieces takes place by a sintering mechanism (Figure
13.16) during a high-temperature firing procedure.
Tape Casting
• With tape casting, a thin sheet of ceramic of uniform thickness is formed from a
slip that is spread onto a flat surface using a doctor blade (Figure 13.18). This
tape is then subjected to drying and firing operations.
Processing/Structure/Properties/Performance Summary
In this chapter we discussed the manner in which the viscosity of a glass is influenced
by both composition and temperature (Figure 13.7). This information is important
inasmuch as the ability of a glass to melt and be formed is a function of its
viscosity.
Furthermore, the role of continuous cooling transformation diagrams in the
heat treatment and control of microstructure was presented (for iron–carbon alloys)
in Chapter 10. We also discussed how this type of diagram is employed in designing
heat treatments to crystallize glass-ceramics. The following schematics represent
relationships for these processing procedures.
Glass-Ceramics
(Processing)
Concept/definition
of viscosity
(Chapter 12)
Temperature dependence
of viscosity
(Chapter 13)
Melting
(Chapter 13)
Form glass piece
(Chapter 13)
Continuous cooling
transformation diagrams
(Chapter 10)
Cooling rate for
crystallization
(Chapter 13)