Ceramic Materials.ppt

1
The Science and Engineering
of Materials
Chapter 14 – Ceramic Materials

2
Objectives of Chapter 14
 To examine the synthesis, processing, and
applications of ceramic materials.
 Recapitulate processing and applications of
inorganic glasses and glass-ceramics.

3
Chapter Outline
 14.1 Applications of Ceramics
 14.2 Properties of Ceramics
 14.3 Synthesis of Ceramic Powders
 14.4 Powder Processing
 14.5 Characteristics of Sintered
Ceramics
 14.6 Inorganic Glasses

4
 14.7 Processing and Applications
of Glasses
 14 8 Glass-Ceramics
 14.9 Processing and Applications
of Clay Products
 14.10 Refractories
 14.11 Other Ceramic Materials
Chapter Outline (Continued)

5
 Ceramics are used in a wide range of technologies such
as refractories, spark plugs, dielectrics in capacitors,
sensors, abrasives, magnetic recording media, etc.
 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.
Section 14.1
Applications of Ceramics

8
Section 14.2
Properties of Ceramics

10
 Slip casting - Forming a hollow ceramic part by
introducing a pourable slurry into a mold.
 Green ceramic - A ceramic that has been shaped into a
desired form but has not yet been sintered.
 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.
 Calcination - Heating of chemicals to decompose and or
react with different chemicals; used in traditional
synthesis of ceramics.
Section 14.3
Synthesis of Ceramic Powders

11
©2003
Brooks/Cole,
a
division
of
Thomson
Learning,
Inc.
Thomson
Learning
™
is
a
trademark
used
herein
under
license.
Figure 14.1 Typical steps
encountered in the
processing of ceramics.

12
Figure 14.2 Schematic
of the jaw, rotary,
crushing rollers, and
hammermill crushing
equipment and ball mill
(grinding) equipment.
(Jaw, rotary, crushing,
and hammermill:

13
We want to make 1000 kilograms of BaTiO3 ceramic from BaCO3
and TiO2. How much barium carbonate and titanium dioxide
should be ball milled and calcined?
Example 14.1 SOLUTION
Even though the actual formation of BaTiO3 involves many
different intermediate phases, we can write the final reaction as:
BaCO3(s) + TiO2(s)  BaTiO3(s) + CO2(g)
Molecular weights are:
BaCO3: 137(Ba) + 12 (C) + (3  16(O)) = 197 g/mol
TiO2: 48(Ti) + (2  16) = 80 g/mol
BaTiO3: 137(Ba) + 48(Ti) + (3  16(O)) = 233 g/mol
CO2: 12(C) + 2  16(O) = 44 g/mol
Example 14.1
Formation of a Barium Titanate Formulation

14
Example 14.1 SOLUTION (Continued)
Thus, 197 g of BaCO3 reacts with 80 g of TiO2 to form
233 g of BaTiO3 and 44 g of CO2.
Since 233 g of BaTiO3 is produced using 197 g of
BaCO3, for 1000 kilograms of BaTiO3, we will need 845.5
kilograms of BaCO3.
Similarly, since 233 g of BaTiO3 is produced using
80 grams of TiO2, for 1000 kilograms of BaTiO3, we will
need 343.3 kilograms of TiO2.

15
 Powder metallurgy - Powder processing routes used for
converting metal and alloy powders into useful shapes.
 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.
 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.
 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.
Section 14.4
Powder Processing

16
©2003
Brooks/Cole,
a
division
of
Thomson
Learning,
Inc.
Thomson
Learning
™
is
a
trademark
used
herein
under
license.
Figure 14.3
Different techniques
for processing of
advanced ceramics.

17
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.)

18
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.)

20
Figure 14.5 Schematic of a tape casting machine. (Source:
From Principles of Ceramics Processing, Second Edition, by
J.S. Reed, p. 532, Fig. 26-6. Copyright © 1995 John Wiley &
Sons, Inc. Reprinted by permission.)

21
Figure 14.6 Steps in slip
casting of ceramics.
(Source: From Modern
Ceramic Engineering, by
D.W. Richerson, p. 462,
Fig. 10-34. Copyright ©
1992 Marcel Dekker.
Reprinted by permission.)

22
Figure 14.7 PLZT ceramics
made using compaction and
sintering. (Courtesy of Dr.
Gene Haertling.)

23
A manufacturer of PZT ceramics wants to make 100,000
cylindrical pieces (5 mm in diameter and 10 mm in height)
per day. These pieces are to be used for a gas igniter. Since
PZT is piezoelectric, it can be squeezed to generate a charge
and the charge can be used to make a spark (Chapter 18).
The manufacturer has access to several different types of
powders (e.g., traditional, hydrothermal, and sol-gel). The
manufacturer also can invest in various processing techniques
(e.g., tape casting, slip casting, uniaxial pressing, or
sintering). What type of synthesis and processing techniques
would you suggest for the manufacturing of these elements?
Example 14.2
Sintering of Lead Zirconium Titanate (PZT)
Ceramics for Barbeque Grill Gas Igniters

24
The application of PZT here is for making gas igniter pieces,
so to keep the cost low, we will choose conventionally
prepared powders.
For powder processing, we choose uniaxial pressing
and sintering since the pieces are cylindrical and can be
produced easily using this technique.
In sintering PZT, we must carefully consider using
binders to achieve higher green density.
Following sintering, the PZT ceramics may have to
undergo some machining.

25
A manufacturer of barium zinc tantalate (Ba(Zn1/3Ta2/3)O3 or
BZT ceramics) produces cylindrical, puck-shaped devices known
as dielectric resonators. The particular pucks made in this case
are 2 inches in diameter and 1/2 inch tall and they have a 1/2
inch hole at the center. The sintering of these pieces is
conducted at 1500o
C, using additives. The manufacturing
process used to make these pieces is well established.
Suddenly, one day, a batch of the dielectric resonators comes
out of the furnace with cracks and must be rejected. The plant
manager determines that the material has reached 98% of the
theoretical target level of densification. What could be the
reason for the cracks?
Example 14.3
Sintering of Microwave Dielectrics

26
Problems such as these have to be traced back through
the manufacturing process starting with the raw
materials, blending, compaction, and the use of binders.
In a quality manufacturing operation (such as the
one having a ISO 9000 certification), all raw materials,
manufacturing steps, procedures, and suppliers must be
traceable.
Discussions with the furnace operator revealed
that he had increased the speed of the furnace conveyer
belt so that he could get off work an hour early, causing
the parts to cool too quickly. The resultant dielectric
resonators developed microcracks because of rapid
cooling from the sintering temperature. The problem, in
this case, turned out to be due to a human error.

27
 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.
 Apparent porosity - The percentage of a ceramic body
that is composed of interconnected porosity.
 True porosity - The percentage of a ceramic body that is
composed of both closed and interconnected porosity.
 Bulk density - The mass of a ceramic body per unit
volume, including closed and interconnected porosity.
Section 14.5
Characteristics of Sintered Ceramics

28
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
Silicon Carbide Ceramics

29
The closed-pore percentage is the true porosity minus the
apparent porosity, or 30 - 15.5 = 14.5%. Thus:

30
 Glass temperature - The temperature below which an
undercooled liquid becomes a glass.
 Glass formers - Oxides with a high-bond strength that
easily produce a glass during processing.
 Intermediates - Oxides that, when added to a glass,
help to extend the glassy network; although the oxides
normally do not form a glass themselves.
Section 14.6
Inorganic Glasses

31
©2003
Brooks/Cole,
a
division
of
Thomson
Learning,
Inc.
Thomson
Learning
™
is
a
trademark
used
herein
under
license.
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.

32
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
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.

34
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.

35
©2003
Brooks/Cole,
a
division
of
Thomson
Learning,
Inc.
Thomson
Learning
™
is
a
trademark
used
herein
under
license.
Figure 14.11 The
Si02-Na20 phase
diagram.
Additions of soda
(Na20) to silica
dramatically
reduce the
melting
temperature of
silica, by forming
eutectics.

36
We produce good chemical resistance in a glass when we introduce
B2O3 into silica. To assure that we have good glass-forming
tendencies, we wish the O:Si ratio to be no more than 2.5, but we
also want the glassware to have a low-melting temperature to
make the glass-forming process easier and more economical.
Design such a glass.
Let us determine the amount of B2O3 we must add to obtain
exactly an O:Si ratio of 2.5. Let fB be the mole fraction of B2O3
added to the glass, and (1 – fB) be the mole fraction of SiO2:
Example 14.5
Design of a Glass

37
Therefore, we must produce a glass containing no more
than 14.3 mol% B2O3. In weight percent:

38
 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.
 Devitrification - The crystallization of glass.
 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.
Section 14.7
Processing and Applications
of Glasses

39
©2003
Brooks/Cole,
a
division
of
Thomson
Learning,
Inc.
Thomson
Learning
™
is
a
trademark
used
herein
under
license.
Figure 14.12 The
effect of
temperature and
composition on the
viscosity of glass.

40
Figure 14.13 Techniques for manufacturing sheet and plate
glass: (a) rolling and (b) floating the lass on molten tin.

42
Figure 14.14 Techniques for forming lass products: (a)
pressing, (b) press and blow process, and (c) drawing of
fibers.

43
Figure 14.15 Tempered glass is cooled rapidly to produce
compressive residual stresses at the surface.

44
©2003
Brooks/Cole,
a
division
of
Thomson
Learning,
Inc.
Thomson
Learning
™
is
a
trademark
used
herein
under
license.
Figure 14.16
The liquidus
plot for the
Si02-Ca0-Na20
phase diagram.
The
compositions
corresponding
to points A, B,
and C refer to
those
discussed in
Example 14-6.

45
Design a soda-lime glass capable of being cast at a
temperature of 1000o
C.
Example 14.6
Design of a Soda-Lime Glass
©2003
Brooks/Cole,
a
division
of
Thomson
Learning,
Inc.
Thomson
Learning
™
is
a
trademark
used
herein
under
license.
Figure 14.16 The
liquidus plot for
the Si02-Ca0-
Na20 phase
diagram. The
compositions
corresponding
to points A, B,
and C refer to
those discussed
in Example 14.6.

46
For casting, the glass should be heated above its liquidus
temperature. Its viscosity should be low enough so that it
flows easily into the mold. Therefore, if we want to pour
the liquid at 1000o
C, we might select a glass composition
that has a lower liquidus-say 900o
C. Suppose we used the
following compositions (indicated on the silica-soda-lime
phase diagram, Figure 14.16):
Glass A: 74% SiO2-13% CaO-13% Na2O
Glass B: 74% SiO2-6% CaO-20% Na2O
Glass C: 80% SiO2-7% CaO-13% Na2O
From the liquidus plot, we find that glass A has a
liquidus of 1200o
C, glass B has a liquidus of 900o
C, and
glass C has a liquidus of 1300o
C. Of these three glasses,
glass B is our obvious choice.

47
 Green ceramic - A ceramic that has been shaped into a
desired form but has not yet been sintered.
Section 14.8
Glass-Ceramics

48
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.

49
 Vitrification - Melting, or formation, of a glass.
 Hydroplastic forming - A number of processes by which a
moist ceramic clay body is formed into a useful shape.
 Firing - Heating a ceramic body at a high temperature to
cause a ceramic bond to form.
 Ceramic bond - Bonding ceramic materials by permitting
a glassy product to form at high-firing temperatures.
Section 14.9
Processing and Applications
of Clay Products

50
Figure 14.18 Processes for shaping crystalline ceramics: (a)
pressing, (b) isostatic pressing, (c) extrusion, (d) jiggering,
and (e) slip casting.

51
©2003
Brooks/Cole,
a
division
of
Thomson
Learning,
Inc.
Thomson
Learning
™
is
a
trademark
used
herein
under
license.
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.

52
Figure 14.20 During firing, clay and other fluxing materials
react with coarser particles to produce a glassy bond and
reduce porosity.

53
 Refractories - A group of ceramic materials capable of
withstanding high temperatures for prolonged periods of
time.
 Acid Refractories - Common acidic refractories include
silica, alumina, and fireclay (an impure kaolinite).
 Basic Refractories - A number of refractories are based
on MgO (magnesia, or periclase).
 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.
 Special Refractories - Other refractory materials include
zirconia (ZrO2), zircon (ZrO2 · SiO2), and a variety of
nitrides, carbides, and borides.
Section 14.10
Refractories

55
Figure 14.21 A simplified Si02-Al203 phase diagram, the
basis for alumina silicate refractories.

56
Figure 14.22 The Mg2Si04-Fe2Si04 phase diagram, showing
complete solid solubility.

57
 Cements - Ceramic raw materials are joined using a binder
that does not require firing or sintering in a process called
cementation.
 Coatings - Ceramics are often used to provide protective
coatings to other materials.
 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).
 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.
 Joining and Assembly of Ceramic Components - Ceramics
are often made as monolithic components rather than
assemblies of numerous components.
Section 14.11
Other Ceramic Materials

58
©2003
Brooks/Cole,
a
division
of
Thomson
Learning,
Inc.
Thomson
Learning
™
is
a
trademark
used
herein
under
license.
Figure 14.23 A
photograph of
silica sand grains
bonded with
sodium silicate
through the
cementation
mechanism (x60).

59
Figure 14.10 (Repeated for Problem 14.57) 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.

60
©2003
Brooks/Cole,
a
division
of
Thomson
Learning,
Inc.
Thomson
Learning
™
is
a
trademark
used
herein
under
license.
Figure 14.16
(repeated for
Problem 14.58.)
The liquidus plot
for the Si02-Ca0-
Na20 phase
diagram.

Ceramic Materials.ppt

More Related Content

What's hot

Similar to Ceramic Materials.ppt

Recently uploaded

Ceramic Materials.ppt