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

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Important Terms and Concepts • 613

and processing of a glass of given composition. Five of the more common glass-

forming techniques—pressing, blowing, drawing, and sheet and fiber forming—were

discussed briefly. After fabrication, glasses may be annealed and/or tempered to

improve mechanical characteristics.

Fabrication and Processing of Clay Products

For clay products, two fabrication techniques that are frequently utilized are hy-

droplastic forming and slip casting. After forming, a body must be first dried and then

fired at an elevated temperature to reduce porosity and enhance strength. Shrinkage

that is excessive or too rapid may result in cracking and/or warping, and a worthless

piece. Densification during firing is accomplished by vitrification, the formation of a

glassy bonding phase.

Powder Pressing

Tape Casting

Some ceramic pieces are formed by powder compaction; uniaxial and isostatic tech-

niques are possible. Densification of pressed pieces takes place by a sintering mech-

anism during a high-temperature firing procedure. Hot pressing is also possible in

which pressing and sintering operations are carried out simultaneously.

Thin ceramic substrate layers are often fabricated by tape casting.

Polymerization

Polymer Additives

The final sections of this chapter treated synthesis and fabrication techniques for

polymeric materials. Synthesis of large molecular weight polymers is attained by

polymerization, of which there are two types: addition and condensation. The prop-

erties of polymers may be further modified by using additives; these include fillers,

plasticizers, stabilizers, colorants, and flame retardants.

Forming Techniques for Plastics

Fabrication of plastic polymers is usually accomplished by shaping the material in

molten form at an elevated temperature, using at least one of several different mold-

ing techniques—compression, transfer, injection, and blow. Extrusion and casting

are also possible.

Fabrication of Fibers and Films

Some fibers are spun from a viscous melt, after which they are plastically elon-

gated during a drawing operation, which improves the mechanical strength. Films

are formed by extrusion and blowing, or by calendering.

IMPORTANT TERMS AND CONCEPTS

Addition polymerization

Annealing

Annealing point (glass)

Austenitizing

Cold working

Colorant

Condensation polymerization

Drawing

Extrusion

Filler

Firing

Flame retardant

Forging

Full annealing

Glass transition temperature