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Applications and Processing of Ceramics - imeng.ndhu.edu.t file4 Applications and Processing of...
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CHAPTER
13
Applications and
Processing of Ceramics
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Applications and Processing of Ceramics
ISSUES TO ADDRESS...
• How do we classify ceramics?
• What are some applications of ceramics?
• How is processing of ceramics different than for metals?
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Content
Introduction
Glasses
Glass-ceramics
Clay products
Refractories
Abrasives
Cements
Advanced ceramics
Fabrication and processing of glasses and glass-ceramics
Fabrication and processing of clay products
Powder pressing
Tape casting
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Glasses Clay
products
Refractories Abrasives Cements Advanced
ceramics
-optical
- composite reinforce
- containers/ household
-whiteware
- structural
-bricks for high T
(furnaces)
-sandpaper
- cutting - polishing
-composites
- structural
-engine
rotors valves
bearings -sensors
Classification of Ceramics
Ceramic Materials
Fireclay
Silica
Basic
Special
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Traditional Ceramics
• Made up of clay, silica and feldspar
• Clay: Provide workability and
hardness.
• Silica: Provide better temperature
resistance and MP.
• Potash Feldspar: Makes glass when
ceramic is fired.
SEM of Porcelain
Quartz
grain High-silica
glass Figure 11.35
Source: F. Norton, Elements of Ceramics, 2nd ed., Addision-Wesley,1974, p.140. 7
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Engineering Ceramics
• Alumina (Al2O3): Aluminum oxide is doped with
magnesium oxide, cold pressed and sintered.
Uniform structure. Used for electric applications.
• Silicon Nitride (Si3N4): Compact of silicon powder is
nitrided in a flow of nitrogen gas.
Moderate strength and used for parts of advanced engines.
• Silicon Carbide (SiC): Very hard refractory carbide,
sintered at 21000C.
Used as reinforcement in composite materials.
• Zirconia (ZrO2): Polymorphic and is subject to cracking.
Combined with 9% MgO to produce ceramic with high
fracture toughness.
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Insulation for Space Shuttle Orbital
• About 70% of external surface is protected from heat by
24000 ceramic tiles.
• Material: Silica fiber compound.
• Density is 4kg/ft3 and withstands temperature up to 12600C
• Space Shuttle Columbia disaster occurred on February 1, 2003
• Space Shuttle Challenger disaster occurred on January 28, 1986
Courtesy of NASA 9
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tensile force
A o
A d die
die
• Die blanks: -- Need wear resistant properties!
• Die surface: -- 4 mm polycrystalline diamond
particles that are sintered onto a
cemented tungsten carbide
substrate.
-- polycrystalline diamond gives uniform
hardness in all directions to reduce
wear.
Adapted from Fig. 11.8(d),
Callister & Rethwisch 8e.
Courtesy Martin Deakins, GE
Superabrasives, Worthington,
OH. Used with permission.
Ceramics Application: Die Blanks
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• Tools: -- for grinding glass, tungsten,
carbide, ceramics
-- for cutting Si wafers
-- for oil drilling
blades oil drill bits
Single crystal
diamonds
polycrystalline
diamonds in a resin
matrix.
Photos courtesy Martin Deakins,
GE Superabrasives, Worthington,
OH. Used with permission.
Ceramics Application: Cutting Tools
• Materials: -- manufactured single crystal
or polycrystalline diamonds
in a metal or resin matrix.
-- polycrystalline diamonds
resharpen by microfracturing
along cleavage planes.
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• Example: ZrO2 as an oxygen sensor
• Principle: Increase diffusion rate of oxygen
to produce rapid response of sensor signal to
change in oxygen concentration
Ceramics Application: Sensors
A substituting Ca2+ ion
removes a Zr 4+ ion and
an O2- ion.
Ca 2+
• Approach: Add Ca impurity to ZrO2: -- increases O2- vacancies
-- increases O2- diffusion rate
reference gas at fixed oxygen content
O 2-
diffusion
gas with an unknown, higher oxygen content
- + voltage difference produced!
sensor • Operation: -- voltage difference produced when
O2- ions diffuse from the external
surface through the sensor to the
reference gas surface.
-- magnitude of voltage difference
partial pressure of oxygen at the
external surface
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Content
Introduction
Glasses
Glass-ceramics
Clay products
Refractories
Abrasives
Cements
Advanced ceramics
Fabrication and processing of glasses and glass-ceramics
Fabrication and processing of clay products
Powder pressing
Tape casting
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Glasses
• Combination of transparency, strength, hardness and
corrosion resistance.
• Glass is an inorganic product of fusion that has cooled
to a rigid condition without crystallization.
• Glass does not crystallize
up on cooling.
• Up on cooling, it transforms
from rubbery material to
rigid glass.
Figure 10.52
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• Quartz is crystalline
SiO2:
• Basic Unit: Glass is noncrystalline (amorphous)
• Fused silica is SiO2 to which no
impurities have been added
• Other common glasses contain
impurity ions such as Na+, Ca2+,
Al3+, and B3+
(soda glass)
Glass Structure
Si0 4 tetrahedron 4-
Si 4+
O 2 -
Si 4+
Na +
O 2 -
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Structure of Glasses
• Glass-Forming Oxides: Fundamental subunit of glass is
SiO44- tetrahedron. (B2O3)
• Si 4+ ion is covalently ionically bonded to four oxygen atoms.
• In cristobalite, Si-O tetrahedron are joined corner to corner
to form long range order.
• In simple silica glass, tetrahedra are joined corner to corner
to form loose network.
Cristobailite Simple silica glass SiO4
4-
Courtesy of Corning Glass Works 16
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Glass Modifying Oxides and Intermediate Oxides
• Network modifiers: Oxides that breakup the glass
network.
Added to glass to increase workability.
Examples:- Na2O, K2O, CaO, MgO.
Oxygen atom enters network and other ion stay
in interstices.
• Intermediate oxides: Cannot form glass network by
themselves but can join into an existing network.
Added to obtain special properties.
Examples: Al2O3, Lead oxide.
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Composition of Glasses
• Soda lime glass: Very common glass (90%).
71-73% SiO2, 12-14% Na2O, 10-12% CaO.
Easier to form and used in flat glass and containers.
• Borosilicate glass: Alkali oxides are replaced by boric oxide in silica glass network.
Known as Pyrex glass and is used for lab equipments and piping.
• Lead glass: Lead oxide acts as network modifier and network former.
Low melting point – used for solder sealing.
Used in radiation shields, optical glass and TV bulbs.
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Content
Introduction
Glasses
Glass-ceramics
Clay products
Refractories
Abrasives
Cements
Advanced ceramics
Fabrication and processing of glasses and glass-ceramics
Fabrication and processing of clay products
Powder pressing
Tape casting
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Glass-Ceramics
• Glass-ceramics are initially fabricated as glasses, and
– then, by heat treatment,
– crystallized to form fine-grained polycrystalline
materials
• Two properties of glass-ceramics that make them
superior to glass are
– improved mechanical strengths and
– lower coefficients of thermal expansion
• (which improves thermal shock resistance).
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Continuous cooling transformation of a lunar glass
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Clay products
• Clay is the principal component of
– the whitewares
• pottery and tableware
– structural clay products
• building bricks and tiles
• Ingredients (in addition to clay) may be added
– such as feldspar and quartz
– these influence changes that occur during firing
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• Clay is inexpensive
• When water is added to clay -- water molecules fit in between
layered sheets -- reduces degree of van der Waals
bonding -- when external forces applied – clay
particles free to move past one
another – becomes hydroplastic
• Structure of
Kaolinite Clay:
Hydroplasticity of Clay
weak van der Waals bonding
charge neutral
charge neutral
Si 4+
Al 3 +
- OH
O 2-
Shear
Shear
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Content
Introduction
Glasses
Glass-ceramics
Clay products
Refractories
Abrasives
Cements
Advanced ceramics
Fabrication and processing of glasses and glass-ceramics
Fabrication and processing of clay products
Powder pressing
Tape casting
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• Materials to be used at high temperatures (e.g., in
high temperature furnaces).
• Consider the Silica (SiO2) - Alumina (Al2O3) system.
• Silica refractories - silica rich - small additions of alumina
depress melting temperature (phase diagram):
Fig. 12.27, Callister &
Rethwisch 8e. (Fig. 12.27
adapted from F.J. Klug and
R.H. Doremus, J. Am. Cer.
Soc. 70(10), p. 758, 1987.)
Refractories
Composition (wt% alumina)
T(ºC)
1400
1600
1800
2000
2200
20 40 60 80 100 0
alumina +
mullite
mullite + L
mullite Liquid
(L)
mullite + crystobalite
crystobalite + L
alumina + L
3Al2O3-2SiO2
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Acidic and Basic Refractories
• Acidic refractories:
Silica refractories have high mechanical strength
and rigidity.
Fireclays: Mixture of plastic fireclay, flint clay and
grog. Particles vary from coarse to very fine.
High aluminum refractories: Contain 50-90%
alumina and have higher fusion temperature.
• Basic refractories: consists mainly of MgO and CaO.
Have high bulk densities, melting temperature and
resistance to chemical attack.
used for lining in basic-oxygen steelmaking process.
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Content
Introduction
Glasses
Glass-ceramics
Clay products
Refractories
Abrasives
Cements
Advanced ceramics
Fabrication and processing of glasses and glass-ceramics
Fabrication and processing of clay products
Powder pressing
Tape casting
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Ceramic Abrasive Materials
• Ceramics are hard and can be used as abrasives
for cutting, grinding and polishing
• Examples:- Al2O3, SiC
• Diamond and c-BN are superabrasives
• By combining ceramics, improved abrasives can be
developed
• Example:- 25% ZrO2 + 75% Al2O3
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Hardness of Selected Materials
0
20
40
60
80
100
Alu
min
um
43
40
Ste
el
To
ol
Ste
el
TiN
TiC
cBN
Su
per
latt
ice
Dia
mo
nd
Ha
rd
ness
, G
Pa
Ultra-hard
Hard
Ha
rdn
ess,
GP
a
Superhard
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Increasing feed rate
Increa
sing
cuttin
g sp
eed
PCD
CBN
Ceramics
Cermets
Cemented
Carbides
High Speed
Tool Steel
Relative Machining Application ranges of
Cutting Tool Materials
Polycrystalline diamond
Polycrystalline cubic boron nitride
Al2O3, Si3N4, SiAlON
(Ti,Mo/W)CN, (Ti, Mo,/W, Nb,Ta)CN
94WC-6Co, 72WC-8TiC-11.5TaC-8.5Co
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Content
Introduction
Glasses
Glass-ceramics
Clay products
Refractories
Abrasives
Cements
Advanced ceramics
Fabrication and processing of glasses and glass-ceramics
Fabrication and processing of clay products
Powder pressing
Tape casting
36
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Cements
• Portland cement is produced by heating a mixture of clay and
lime-bearing minerals in a rotary kiln.
– The resulting “clinker” is ground into very fine particles to which a
small amount of gypsum is added.
• When mixed with water, inorganic cements form a paste that is
capable of assuming just about any desired shape.
• Subsequent setting or hardening is a result of chemical
reactions involving the cement particles and occurs at the
ambient temperature.
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Content
Introduction
Glasses
Glass-ceramics
Clay products
Refractories
Abrasives
Cements
Advanced ceramics
Fabrication and processing of glasses and glass-ceramics
Fabrication and processing of clay products
Powder pressing
Tape casting
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Advanced Ceramics:
Materials for Automobile Engines
• Advantages:
– Operate at high temperatures
– high efficiencies
– Low frictional losses
– Operate without a cooling
system
– Lower weights than current
engines
• Disadvantages:
– Ceramic materials are
brittle
– Difficult to remove internal
voids (that weaken
structures)
– Ceramic parts are difficult
to form and machine
• Potential candidate materials: Si3N4, SiC, & ZrO2
• Possible engine parts: engine block & piston coatings
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Advanced Ceramics:
Materials for Ceramic Armor
Components: -- Outer facing plates
-- Backing sheet
Properties/Materials: -- Facing plates -- hard and brittle
— fracture high-velocity projectile
— Al2O3, B4C, SiC, TiB2
-- Backing sheets -- soft and ductile
— deform and absorb remaining energy
— aluminum, synthetic fiber laminates
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Content
Introduction
Glasses
Glass-ceramics
Clay products
Refractories
Abrasives
Cements
Advanced ceramics
Fabrication and processing of glasses and glass-ceramics
Fabrication and processing of clay products
Powder pressing
Tape casting
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• Specific volume (1/r) vs Temperature (T):
• Glasses: -- do not crystallize
-- change in slope in spec. vol. curve at
glass transition temperature, Tg
-- transparent - no grain boundaries to
scatter light
• Crystalline materials: -- crystallize at melting temp, Tm
-- have abrupt change in spec.
vol. at Tm
Adapted from Fig. 13.6,
Callister & Rethwisch 8e.
Glass Properties
T
Specific volume
Supercooled Liquid
solid
Tm
Liquid (disordered)
Crystalline (i.e., ordered)
Tg
Glass
(amorphous solid)
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Glass Properties: Viscosity
• Viscosity, h: -- relates shear stress () and velocity gradient (dv/dy):
h has units of (Pa-s)
dydv /
h
velocity gradient
dv
dy
glass dv
dy
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Vis
co
sity [P
a-s
]
1
10 2
10 6
10 10
10 14
200 600 1000 1400 1800 T(ºC)
Working range:
glass-forming carried out
annealing point
Tmelt
strain point
• Viscosity decreases with T
Log Glass Viscosity vs. Temperature
• fused silica: > 99.5 wt% SiO2
• soda-lime glass: 70% SiO2
balance Na2O (soda) & CaO (lime)
• Vycor: 96% SiO2, 4% B2O3
• borosilicate (Pyrex):
13% B2O3, 3.5% Na2O, 2.5% Al2O3
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Viscous Deformation of glasses.
• Viscous above Tg and viscosity decreases with increase in
temperature.
η* = η0e+Q/RT η*
η0
= Viscocity of glass (Pa. s)
= preexponential constant (Pa. s)
Q = Activation energy
1. Working point: 103 Pa. s – glass
fabrication can be carried out
2. Softening point: 107 Pa. s – glass
flows under its own weight.
3. Annealing point: 1012 Pa. s – Internal
stresses can be relieved..
4. Strain point: 10 13.5 Pa. s – glass is
rigid below this point.
Figure 10.55
After O. H. Wyatt and D. Dew-Hughes, “Metals Ceramics and Polymers,” Cambridge, 1974, p.259. 46
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• Blowing of Glass Bottles:
GLASS
FORMING
Ceramic Fabrication Methods (i)
Gob
Parison mold
Pressing operation
Suspended parison
Finishing mold
Compressed air
• Fiber drawing:
wind up
PARTICULATE
FORMING
CEMENTATION
-- glass formed by application of
pressure
-- mold is steel with graphite
lining
• Pressing: plates, cheap glasses
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Sheet Glass Forming
• Sheet forming – continuous casting
– sheets are formed by floating the molten glass on a pool of molten
tin
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• Annealing: -- removes internal stresses caused by uneven cooling.
• Tempering: -- puts surface of glass part into compression
-- suppresses growth of cracks from surface scratches.
-- sequence:
Heat Treating Glass
at room temp.
tension
compression
compression
before cooling
hot
initial cooling
hot
cooler
cooler
-- Result: surface crack growth is suppressed.
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Content
Introduction
Glasses
Glass-ceramics
Clay products
Refractories
Abrasives
Cements
Advanced ceramics
Fabrication and processing of glasses and glass-ceramics
Fabrication and processing of clay products
Powder pressing
Tape casting
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Processing of Ceramics
• Produced by compacting powder or particles into shapes and heated to bond particles together
• Agglomeration of particles
• Basic steps in ceramic processing
– Material preparation: Particles and binders and lubricants are (sometimes ground) and blend wet or dry.
– Forming: Formed in dry, plastic or liquid conditions
– Thermal treatment by drying and firing
• Cold forming process is predominant.
• Pressing, slipcasting and extrusion are the common forming processes.
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• Mill (grind) and screen constituents: desired particle size
• Extrude this mass (e.g., into a brick)
• Dry and fire the formed piece
ram billet
container
container force
die holder
die
A o
A d extrusion Adapted from
Fig. 12.8(c),
Callister &
Rethwisch 8e.
Ceramic Fabrication Methods (iia)
GLASS
FORMING
PARTICULATE
FORMING
CEMENTATION
Hydroplastic forming:
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• Mill (grind) and screen constituents: desired particle size
• Slip casting operation
• Dry and fire the cast piece
Ceramic Fabrication Methods (iia)
solid component
Adapted from Fig.
13.12, Callister &
Rethwisch 8e. (Fig.
13.12 is from W.D.
Kingery, Introduction
to Ceramics, John
Wiley and Sons, Inc.,
1960.)
hollow component
pour slip
into mold
drain
mold “green
ceramic”
pour slip into mold
absorb water into mold
“green ceramic”
GLASS
FORMING
PARTICULATE
FORMING
CEMENTATION
Slip casting:
• Mix with water and other constituents to form slip
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Slip Casting
• Powdered ceramic material and a liquid mixed to
prepare a stable suspension (slip).
• Slip is poured into porous mold and liquid portion is
partially absorbed by mold.
• Layer of semi-hard material
is formed against mold
surface.
• Excess slip is poured out
of cavity or cast as solid
• The material in mold is
allowed to dry and then fired
Figure 10.27
After W. D. Kingery, “ Introduction to Ceramics,” Wiley, 1960, p.52. 54
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Pressing
• Dry Pressing: Simultaneous uniaxial compaction and shaping of power along with binder.
Wide variety of shapes can be formed rapidly and accurately.
• Isostatic pressing: Ceramic powder is loaded into a flexible chamber and pressure is applied outside the chamber with hydraulic fluid.
Examples: Spark plug insulators, carbide tools.
Figure 10.24
Figure 10.25
After J. S. Reed and R. B Runk, “ Ceramic Fabrication Process,” vol 9: “1976, p.74. 55
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Extrusion
• Single cross sections and hollow shapes of ceramics can
be produced by extrusion
• Plastic ceramic material is forced through a hard steel or
alloy die by a motor driven auger
• Examples: Refractory brick, sewer pipe, hollow tubes
Figure 10.28
After W. D. Kingery, “ Introduction to Ceramics,” Wiley, 1960. 56
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Typical Porcelain Composition
(50%) 1. Clay
(25%) 2. Filler – e.g. quartz (finely ground)
(25%) 3. Fluxing agent (Feldspar)
-- aluminosilicates plus K+, Na+, Ca+
-- upon firing - forms low-melting-temp. glass
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• Clay is inexpensive
• When water is added to clay -- water molecules fit in between
layered sheets -- reduces degree of van der Waals
bonding -- when external forces applied – clay
particles free to move past one
another – becomes hydroplastic
• Structure of
Kaolinite Clay:
Adapted from Fig. 12.14, Callister &
Rethwisch 8e. (Fig. 12.14 is adapted from
W.E. Hauth, "Crystal Chemistry of
Ceramics", American Ceramic Society
Bulletin, Vol. 30 (4), 1951, p. 140.)
Hydroplasticity of Clay
weak van der Waals bonding
charge neutral
charge neutral
Si 4+
Al 3 +
- OH
O 2-
Shear
Shear
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• Drying: as water is removed - interparticle spacings decrease
– shrinkage . Adapted from Fig.
13.13, Callister &
Rethwisch 8e. (Fig.
13.13 is from W.D.
Kingery, Introduction
to Ceramics, John
Wiley and Sons, Inc.,
1960.)
Drying and Firing
Drying too fast causes sample to warp or crack due to non-uniform shrinkage
wet body partially dry completely dry
• Firing: -- heat treatment between
900-1400ºC
-- vitrification: liquid glass forms
from clay and flux – flows
between SiO2 particles. (Flux
lowers melting temperature). Adapted from Fig. 13.14, Callister & Rethwisch 8e.
(Fig. 13.14 is courtesy H.G. Brinkies, Swinburne
University of Technology, Hawthorn Campus,
Hawthorn, Victoria, Australia.)
Si02 particle
(quartz)
glass formed around the particle
mic
rog
rap
h o
f p
orc
ela
in
70 mm
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Content
Introduction
Glasses
Glass-ceramics
Clay products
Refractories
Abrasives
Cements
Advanced ceramics
Fabrication and processing of glasses and glass-ceramics
Fabrication and processing of clay products
Powder pressing
Tape casting
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Powder Pressing: used for both clay and non-clay compositions.
• Powder (plus binder) compacted by pressure in a mold
-- Uniaxial compression - compacted in single direction
-- Isostatic (hydrostatic) compression - pressure applied by
fluid - powder in rubber envelope
-- Hot pressing - pressure + heat
Ceramic Fabrication Methods (iib)
GLASS
FORMING
PARTICULATE
FORMING
CEMENTATION
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Sintering
Adapted from Fig. 13.16,
Callister & Rethwisch 8e.
Aluminum oxide powder: -- sintered at 1700ºC
for 6 minutes. Adapted from Fig. 13.17, Callister
& Rethwisch 8e. (Fig. 13.17 is from
W.D. Kingery, H.K. Bowen, and
D.R. Uhlmann, Introduction to
Ceramics, 2nd ed., John Wiley and
Sons, Inc., 1976, p. 483.)
15 mm
Sintering occurs during firing of a piece that has
been powder pressed
-- powder particles coalesce and reduction of pore size
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Content
Introduction
Glasses
Glass-ceramics
Clay products
Refractories
Abrasives
Cements
Advanced ceramics
Fabrication and processing of glasses and glass-ceramics
Fabrication and processing of clay products
Powder pressing
Tape casting
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Tape Casting
• Thin sheets of green ceramic cast as flexible tape
• Used for integrated circuits and capacitors
• Slip = suspended ceramic particles + organic liquid
(contains binders, plasticizers)
Fig. 13.18, Callister &
Rethwisch 8e.
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• Hardening of a paste – paste formed by mixing cement
material with water
• Formation of rigid structures having varied and complex
shapes
• Hardening process – hydration (complex chemical
reactions involving water and cement particles)
Ceramic Fabrication Methods (iii)
GLASS
FORMING
PARTICULATE
FORMING
CEMENTATION
• Portland cement – production of:
-- mix clay and lime-bearing minerals
-- calcine (heat to 1400ºC)
-- grind into fine powder
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• Categories of ceramics: -- glasses -- clay products
-- refractories -- cements
-- advanced ceramics
• Ceramic Fabrication techniques: -- glass forming (pressing, blowing, fiber drawing).
-- particulate forming (hydroplastic forming, slip casting,
powder pressing, tape casting)
-- cementation
• Heat treating procedures -- glasses—annealing, tempering
-- particulate formed pieces—drying, firing (sintering)
Summary