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Chapter 13: Applications and

Classification of Ceramics
Processing of Ceramics
Ceramic Materials
ISSUES TO ADDRESS...
• How do we classify ceramics?
Glasses Clay Refractories Abrasives Cements Advanced
• What are some applications of ceramics ? products ceramics
-optical -whiteware -bricks for -sandpaper -composites -engine
• How is processing of ceramics different than for metals ? -composite -structural high T -cutting -structural rotors
reinforce (furnaces) -polishing valves
-containers/ Adapted from Fig. 13.1 and discussion in
bearings
household Section 13.2-8, Callister & Rethwisch 9e. -sensors

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Ceramics Application:
Ceramics Application: Die Blanks
Cutting Tools
• Die blanks: die Ad • Tools:
-- Need wear resistant properties! Ao tensile -- for grinding glass, tungsten,
force
die carbide, ceramics
• Die surface: Adapted from Fig. 11.9(d),
-- for cutting Si wafers
Callister & Rethwisch 9e.
-- 4 μm polycrystalline diamond -- for oil drilling
particles that are sintered onto a
cemented tungsten carbide • Materials: oil drill bits blades
substrate. -- manufactured single crystal
-- polycrystalline diamond gives uniform or polycrystalline diamonds Single crystal
diamonds
hardness in all directions to reduce in a metal or resin matrix.
wear. -- polycrystalline diamonds
polycrystalline
resharpen by microfracturing
diamonds in a resin
along cleavage planes. matrix.
Courtesy Martin Deakins, GE
Photos courtesy Martin Deakins,
Superabrasives, Worthington,
GE Superabrasives, Worthington,
OH. Used with permission.
OH. Used with permission.

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Ceramics Application: Sensors Refractories

• Example: ZrO2 as an oxygen sensor • Materials to be used at high temperatures (e.g., in
Ca 2+
• Principle: Increase diffusion rate of oxygen high temperature furnaces).
to produce rapid response of sensor signal to • Consider the Silica (SiO2) - Alumina (Al2O3) system.
change in oxygen concentration • Silica refractories - silica rich - small additions of alumina
• Approach: A substituting Ca2+ ion depress melting temperature (phase diagram):
removes a Zr 4+ ion and
Add Ca impurity to ZrO2: an O2- ion. 2200
-- increases O2- vacancies 3Al2O3-2SiO2
T(ºC)
-- increases O2- diffusion rate 2000
mullite
Liquid
• Operation: sensor (L) alumina + L
-- voltage difference produced when gas with an Fig. 12.25, Callister & Rethwisch 9e.
reference 1800
O2- ions diffuse from the external unknown, higher gas at fixed mullite alumina
[Adapted from F. J. Klug, S. Prochazka, and
oxygen content O2- crystobalite R. H. Doremus, “Alumina–Silica Phase
surface through the sensor to the diffusion
oxygen content
+L +L +
Diagram in the Mullite Region,” J. Am.
Ceram. Soc., 70[10], 758 (1987). Reprinted
reference gas surface. 1600 mullite by permission of the American Ceramic
Society.]
mullite
-- magnitude of voltage difference + crystobalite
 partial pressure of oxygen at the + -
voltage difference produced!
1400
0 20 40 60 80 100
external surface Composition (wt% alumina)
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Advanced Ceramics: Advanced Ceramics:

Materials for Automobile Engines Materials for Ceramic Armor
Components:
• Advantages: • Disadvantages:
-- Outer facing plates
– Operate at high – Ceramic materials are
-- Backing sheet
temperatures – high brittle
efficiencies – Difficult to remove internal
– Low frictional losses voids (that weaken Properties/Materials:
– Operate without a cooling structures) -- Facing plates -- hard and brittle
system – Ceramic parts are difficult — fracture high-velocity projectile
– Lower weights than to form and machine — Al2O3, B4C, SiC, TiB2
current engines -- Backing sheets -- soft and ductile
— deform and absorb remaining energy
• Potential candidate materials: Si3N4, SiC, & ZrO2 — aluminum, synthetic fiber laminates
• Possible engine parts: engine block & piston coatings

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Nanocarbons Nanocarbons (cont.)

• Fullerenes – spherical cluster of 60 carbon atoms, C 60 • Graphene – single-atomic-layer of graphite
– Like a soccer ball – composed of hexagonally sp2 bonded carbon atoms
• Carbon nanotubes – sheet of graphite rolled into a tube
– Ends capped with fullerene hemispheres
Fig. 12.19, Callister
& Rethwisch 8e.

Fig. 13.9, Callister & Rethwisch 9e.

Fig. 13.7, Callister & Rethwisch 9e. Chapter 13 - 9 Chapter 13 - 10

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Ceramic Fabrication Methods (i) Sheet Glass Forming

• Sheet forming – continuous casting
GLASS PARTICULATE CEMENTATION – sheets are formed by floating the molten glass on a pool of
FORMING FORMING molten tin

• Blowing of Glass Bottles: • Pressing: plates, cheap glasses

Pressing -- glass formed by application of
Gob
operation
pressure
Parison
-- mold is steel with graphite
mold lining
• Fiber drawing:
Compressed
air

Suspended
parison

Finishing Fig. 13.14, Callister & Rethwisch 9e.

wind up (Courtesy of Pilkington Group Limited.)
mold
Fig. 13.13, Callister & Rethwisch 9e. (Adapted from C.J. Phillips, Glass: The
Miracle Maker. Reproduced by permission of Pittman Publishing Ltd., London.)
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Glass Structure Glass Properties

• Basic Unit: Glass is noncrystalline (amorphous)
• Specific volume (1/ρ) vs Temperature (T):
4- • Fused silica is SiO2 to which no
Si0 4 tetrahedron impurities have been added • Crystalline materials:
Specific volume
Si 4+ • Other common glasses contain -- crystallize at melting temp, Tm
impurity ions such as Na+, Ca2+, -- have abrupt change in spec.
O2- Supercooled Liquid
vol. at Tm
Al3+, and B3+ Liquid (disordered)

• Quartz is crystalline • Glasses:

Na + Glass
SiO2: (amorphous solid)
-- do not crystallize
Si 4+
Crystalline -- change in slope in spec. vol. curve at
O2- (i.e., ordered) solid
glass transition temperature, Tg
Tg Tm T -- transparent - no grain boundaries to
(soda glass) scatter light
Adapted from Fig. 13.11,
Adapted from Fig. 12.11, Callister & Rethwisch 9e.
Callister & Rethwisch 9e.

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Glass Properties: Viscosity Log Glass Viscosity vs. Temperature

• soda-lime glass: 70% SiO2
• Viscosity decreases with T
• Viscosity, η: balance Na2O (soda) & CaO (lime)
-- relates shear stress (τ) and velocity gradient (dv/dy): • borosilicate (Pyrex):
13% B2O3, 3.5% Na2O, 2.5% Al2O3
• Vycor: 96% SiO2, 4% B2O3
τ • fused silica: > 99.5 wt% SiO2
Viscosity [Pa-s]

dy dv 10 14
glass dv
strain point
dy annealing point
τ 10 10
velocity gradient

η has units of (Pa-s) 10 6 Working range:

glass-forming carried out
10 2 Fig. 13.12, Callister & Rethwisch 9e.
Tmelt (From E.B. Shand, Engineering Glass,
1 Modern Materials, Vol. 6, Academic Press,
New York, 1968, p. 262.)
200 600 1000 1400 1800 T(ºC)

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Heat Treating Glass Ceramic Fabrication Methods (iia)

• Annealing:
-- removes internal stresses caused by uneven cooling. GLASS PARTICULATE CEMENTATION
• Tempering: FORMING FORMING
-- puts surface of glass part into compression
-- suppresses growth of cracks from surface scratches. Hydroplastic forming:
-- sequence: • Mill (grind) and screen constituents: desired particle size
before cooling initial cooling at room temp. • Extrude this mass (e.g., into a brick)
cooler compression
hot hot tension
cooler compression Ao
container die holder
-- Result: surface crack growth is suppressed. force Fig. 11.9 (c),
ram billet extrusion Ad Callister &
Rethwisch 9e.
container die

• Dry and fire the formed piece

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Ceramic Fabrication Methods (iia) Typical Porcelain Composition

GLASS PARTICULATE CEMENTATION

(50%) 1. Clay
FORMING FORMING
(25%) 2. Filler – e.g. quartz (finely ground)
Slip casting:
(25%) 3. Fluxing agent (Feldspar)
• Mill (grind) and screen constituents: desired particle size
-- aluminosilicates plus K+, Na+, Ca+
• Mix with water and other constituents to form slip
• Slip casting operation -- upon firing - forms low-melting-temp. glass
pour slip absorb water pour slip drain “green
into mold into mold into mold mold ceramic” Fig. 13.17, Callister
“green & Rethwisch 9e.
ceramic” (From W.D. Kingery,
Introduction to Ceramics,
Copyright © 1960 by
John Wiley & Sons, New
York. Reprinted by
permission of John Wiley
& Sons, Inc.)
solid component hollow component

• Dry and fire the cast piece

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Hydroplasticity of Clay Drying and Firing

• Drying: as water is removed - interparticle spacings decrease
• Clay is inexpensive Shear – shrinkage .
• When water is added to clay Fig. 13.18, Callister
& Rethwisch 9e.
-- water molecules fit in between (From W.D. Kingery,
Introduction to Ceramics,
layered sheets charge Copyright © 1960 by
John Wiley & Sons, New
-- reduces degree of van der Waals neutral York. Reprinted by
permission of John Wiley
& Sons, Inc.)
bonding
wet body partially dry completely dry
-- when external forces applied – clay
Drying too fast causes sample to warp or crack due to non-uniform shrinkage
particles free to move past one
weak van
another – becomes hydroplastic

micrograph of porcelain
Si02 particle
der Waals • Firing: (quartz)
• Structure of bonding -- heat treatment between glass formed
4+ 900-1400°C around
Kaolinite Clay: charge Si the particle
3+ -- vitrification: liquid glass forms
Fig. 12.14, Callister & Rethwisch 9e. neutral Al from clay and flux – flows
[Adapted from W.E. Hauth, "Crystal Chemistry -
of Ceramics", American Ceramic Society OH between SiO2 particles. (Flux 70μm
Bulletin, Vol. 30 (4), 1951, p. 140.] 2-
O lowers melting temperature). Fig. 13.19, Callister & Rethwisch 9e.
(Courtesy H.G. Brinkies, Swinburne University of
Technology, Hawthorn Campus, Hawthorn,
Victoria, Australia.)
Shear Chapter 13 - 21 Chapter 13 - 22

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Ceramic Fabrication Methods (iib) Sintering

Sintering occurs during firing of a piece that has
been powder pressed
GLASS PARTICULATE CEMENTATION
-- powder particles coalesce and reduction of pore size
FORMING FORMING

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
Fig. 13.21, Callister &
-- Isostatic (hydrostatic) compression - pressure applied by Rethwisch 9e.

fluid - powder in rubber envelope Aluminum oxide powder:

-- Hot pressing - pressure + heat -- sintered at 1700°C Fig. 13.22, Callister & Rethwisch 9e.
for 6 minutes. (From W. D. Kingery, H. K. Bowen, and D.
R. Uhlmann, Introduction to Ceramics, 2nd
edition, p. 483. Copyright © 1976 by John
Wiley & Sons, New York. Reprinted by
permission of John Wiley & Sons, Inc.)

15 μm
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Tape Casting Ceramic Fabrication Methods (iii)

• Thin sheets of green ceramic cast as flexible tape
GLASS PARTICULATE CEMENTATION
• Used for integrated circuits and capacitors FORMING FORMING
• Slip = suspended ceramic particles + organic liquid
• Hardening of a paste – paste formed by mixing cement
(contains binders, plasticizers)
material with water
• Formation of rigid structures having varied and complex
shapes
• Hardening process – hydration (complex chemical
reactions involving water and cement particles)
• Portland cement – production of:
-- mix clay and lime-bearing minerals
-- calcine (heat to 1400°C)
-- grind into fine powder
Fig. 13.23, Callister &
Rethwisch 9e.
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Summary

• 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)

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