The Science and Engineering

of Materials, 4th ed
Donald R. Askeland – Pradeep P. Phulé

Chapter 8 – Ceramic Materials

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 Objectives of Chapter 8
o To examine the synthesis, processing, and
applications of ceramic materials.
o Recapitulate processing and applications of
inorganic glasses and glass-ceramics.

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 Chapter Outline
o 14.1
Applications of Ceramics
o 14.2
Properties of Ceramics
o 14.3
Synthesis of Ceramic Powders
o 14.4
Powder Processing
o 14.5
Characteristics of Sintered
Ceramics
o 14.6 Inorganic Glasses

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 Chapter Outline (Continued)
o 14.7 Processing and Applications
of Glasses
o 14 8 Glass-Ceramics
o 14.9 Processing and Applications
of Clay Products
o 14.10 Refractories
o 14.11 Other Ceramic Materials

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 Section 14.1
Applications of Ceramics
o Ceramics are used in a wide range of technologies such
as refractories, spark plugs, dielectrics in capacitors,
sensors, abrasives, magnetic recording media, etc.
o The space shuttle makes use of ~25,000 reusable,
lightweight, highly porous ceramic tiles that protect the
aluminum frame from the heat generated during re-
entry into the Earth’s atmosphere.

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6
Table 14-1 (Continued)

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 Section 14.2
Properties of Ceramics

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 Section 14.3
Synthesis of Ceramic Powders
o Slip casting - Forming a hollow ceramic part by
introducing a pourable slurry into a mold.
o Green ceramic - A ceramic that has been shaped into a
desired form but has not yet been sintered.
o Leaching - A process in which acids or alkalis are used to
dissolve a mineral, conducted typically to get the metal
or mineral of interest in solution.
o Calcination - Heating of chemicals to decompose and or
react with different chemicals; used in traditional
synthesis of ceramics.

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encountered in the
processing of ceramics.
Figure 14.1 Typical steps
 Figure 14.2 Schematic
of the jaw, rotary,
crushing rollers, and
hammermill crushing
equipment and ball mill
(grinding) equipment.
(Jaw, rotary, crushing,
and hammermill:
Source: From Principles
of Ceramics Processing,
Second Edition, by J.S.
Reed, p. 314, Figs. 17-
1 and 17-2. Copyright
© 1995 John Wiley &
Sons, Inc. Reprinted by
permission. Ball mill
grinding: Source: From
Modern Ceramic
Engineering, by D.W.
Richerson, p. 387, Fig.
9-3. Copyright © 1992
Marcel Dekker, Inc.)

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 Section 14.4
Powder Processing
o Powder metallurgy - Powder processing routes used for
converting metal and alloy powders into useful shapes.
o Reaction bonding - A ceramic processing technique by
which a shape is made using one material that is later
converted into a ceramic material by reaction with a
gas.
o Tape casting - A process for making thin sheets of
ceramics using a ceramic slurry consisting of binders,
plasticizers, etc. The slurry is cast with the help of a
blade onto a plastic substrate.
o Injection molding - A processing technique in which a
thermoplastic mass (loaded with ceramic powder) is
mixed in an extruder-like setup and then injected into a
die to form complex parts. In the case of ceramics, the
thermoplastic is burnt off.
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Figure 14.3

for processing of
advanced ceramics.
Different techniques
Figure 14.4 (a) Uniaxial powder compaction showing the
die-punch assembly during different stages. Typically, for
small parts these stages are completed in less than a
minute. (Source: From Materials and Processes in
Manufacturing, Eighth Edition, by E.P. DeGarmo, J.T. Black,
and R.A. Koshe, Fig. 16-4. Copyright © 1997 Prentice Hall.
Reprinted by permission Pearson Education, Inc.) (b)
Microstructure of a barium magnesium tantalate (BMT)
ceramic prepared using compaction and sintering. (Courtesy
Heather Shivey.)

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Figure 14.4 (c) Different diffusion mechanisms involved in sintering.
The grain boundary and bulk diffusion (1, 2 and 5) to the neck
contribute to densification. Evaporation-condensation (4) and surface
diffusion (3) do not contribute to densification. (Source: From Physical
Ceramics: Principles for Ceramic Science and Engineering, by Y.M.
Chiang, D. Birnie, and W.D. Kingery, Fig. 5-40. Copyright © 1997
John Wiley & Sons, Inc. This material is used by permission of John
Wiley & Sons, Inc.)

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 Section 14.5
Characteristics of Sintered Ceramics
o Typically, ceramics with a small grain size are stronger
than coarse-grained ceramics. Finer grain sizes help
reduce stresses that develop at grain boundaries due to
anisotropic expansion and contraction.
o Apparent porosity - The percentage of a ceramic body
that is composed of interconnected porosity.
o True porosity - The percentage of a ceramic body that is
composed of both closed and interconnected porosity.
o Bulk density - The mass of a ceramic body per unit
volume, including closed and interconnected porosity.

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 Example 14.4
Silicon Carbide Ceramics
Silicon carbide particles are compacted and fired at a high
temperature to produce a strong ceramic shape. The specific
gravity of SiC is 3.2 g/cm3. The ceramic shape subsequently is
weighed when dry (360 g), after soaking in water (385 g), and
while suspended in water (224 g). Calculate the apparent
porosity, the true porosity, and the fraction of the pore volume
that is closed.
Example 14.4 SOLUTION

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Example 14.4 SOLUTION (Continued)
The closed-pore percentage is the true porosity minus the
apparent porosity, or 30 - 15.5 = 14.5%. Thus:

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 Section 14.6
Inorganic Glasses
o Glass temperature - The temperature below which an
undercooled liquid becomes a glass.
o Glass formers - Oxides with a high-bond strength that
easily produce a glass during processing.
o Intermediates - Oxides that, when added to a glass,
help to extend the glassy network; although the oxides
normally do not form a glass themselves.

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Figure 14.8 When

silica crystallizes on
cooling, an abrupt
change in the
density is observed.
For glassy silica,
however, the change
in slope at the glass
temperature
indicates the
formation of a glass
from the
undercooled liquid.
Glass does not have
a fixed Tm or Tg.
Crystalline materials
shave a fixed Tm and
they do not have a
Tg.

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Figure 14.9 The expansion of quartz, in addition to the

regular-almost linear-expansion, a large, abrupt expansion
accompanies the α- to β-quartz transformation. However,
glasses expand uniformly.

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Figure 14.10 The effect of Na20 on the silica glass network.

Sodium oxide is a modifier, disrupting the glassy network and
reducing the ability to form a glass.

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Figure 14.11 The

Si02-Na20 phase
diagram.
Additions of soda
(Na20) to silica
dramatically
reduce the
melting
temperature of
silica, by forming
eutectics.

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 Section 14.7
Processing and Applications
of Glasses
o Parison - A crude glassy shape that serves as an
intermediate step in the production of glassware. The
parison is later formed into a finished product.
o Devitrification - The crystallization of glass.
o Tempered glass - A high-strength glass that has a
surface layer where the stress is compressive, induced
thermally during cooling or by the chemical diffusion of
ions.

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effect of
temperature and
Figure 14.12 The

viscosity of glass.
composition on the
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Figure 14.13 Techniques for manufacturing sheet and plate

glass: (a) rolling and (b) floating the lass on molten tin.

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Figure 14.14 Techniques for forming lass products: (a)

pressing, (b) press and blow process, and (c) drawing of
fibers.

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 Section 14.8
Glass-Ceramics

o Green ceramic - A ceramic that has been shaped into a

desired form but has not yet been sintered.

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 Figure 14.17 Producing a
glass-ceramic: (a)
Cooling must be rapid to
avoid the start of
crystallization.
Isothermal and
continuous cooling
curves for lunar glass.
(b) The rate of nucleation
of precipitates is high at
low temperatures,
whereas the rate of
growth of the
precipitates is high at
higher temperatures. (c)
A typical heat-treatment
profile for glass-ceramics
fabrication, illustrated
here for Li20-Al203-Si02
glasses.

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33
 Section 14.9
Processing and Applications
of Clay Products
o Vitrification - Melting, or formation, of a glass.
o Hydroplastic forming - A number of processes by which a
moist ceramic clay body is formed into a useful shape.
o Firing - Heating a ceramic body at a high temperature to
cause a ceramic bond to form.
o Ceramic bond - Bonding ceramic materials by permitting
a glassy product to form at high-firing temperatures.

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Figure 14.18 Processes for shaping crystalline ceramics: (a)

pressing, (b) isostatic pressing, (c) extrusion, (d) jiggering,
and (e) slip casting.

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Figure 14.19 The

change in the
volume of a
ceramic body as
moisture is
removed during
drying.
Dimensional
changes cease
after the
interparticle water
is gone.

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Figure 14.20 During firing, clay and other fluxing materials

react with coarser particles to produce a glassy bond and
reduce porosity.

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 Section 14.10
Refractories
o Refractories - A group of ceramic materials capable of
withstanding high temperatures for prolonged periods of
time.
o Acid Refractories - Common acidic refractories include
silica, alumina, and fireclay (an impure kaolinite).
o Basic Refractories - A number of refractories are based
on MgO (magnesia, or periclase).
o Neutral Refractories - These refractories, which include
chromite and chromite-magnesite, might be used to
separate acid and basic refractories, preventing them
from attacking one another.
o Special Refractories - Other refractory materials include
zirconia (ZrO2), zircon (ZrO2 · SiO2), and a variety of
nitrides, carbides, and borides.

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Figure 14.21 A simplified Si02-Al203 phase diagram, the

basis for alumina silicate refractories.

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Figure 14.22 The Mg2Si04-Fe2Si04 phase diagram, showing

complete solid solubility.

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 Section 14.11
Other Ceramic Materials
o Cements - Ceramic raw materials are joined using a binder
that does not require firing or sintering in a process called
cementation.
o Coatings - Ceramics are often used to provide protective
coatings to other materials.
o Thin Films and Single Crystals - Thin films of many complex
and multi-component ceramics are produced using different
techniques such as sputtering, sol-gel, and chemical-vapor
deposition (CVD).
o Fibers - Fibers are produced from ceramic materials for
several uses: as a reinforcement in composite materials, for
weaving into fabrics, or for use in fiber-optic systems.
o Joining and Assembly of Ceramic Components - Ceramics
are often made as monolithic components rather than
assemblies of numerous components.

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through the
bonded with

cementation
photograph of

sodium silicate
Figure 14.23 A

silica sand grains

mechanism (x60).