Chapter 13: 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?
Chapter 13 - 1
Classification of Ceramics
Ceramic Materials
Glasses
Clay Refractories
products
Abrasives Cements
Advanced
ceramics
-optical
-whiteware -bricks for -sandpaper -composites -engine
-composite -structural high T
-cutting
-structural
rotors
(furnaces) -polishing
reinforce
valves
-containers/
bearings
Adapted from Fig. 13.1 and discussion in
-sensors
household
Section 13.2-8, Callister & Rethwisch 8e.
Chapter 13 - 2
Ceramics Application: Die Blanks
• 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.
die
Ao
die
Ad
tensile
force
Adapted from Fig. 11.8(d),
Callister & Rethwisch 8e.
Courtesy Martin Deakins, GE
Superabrasives, Worthington,
OH. Used with permission.
Chapter 13 - 3
Ceramics Application:
Cutting Tools
• Tools:
-- for grinding glass, tungsten,
carbide, ceramics
-- for cutting Si wafers
-- for oil drilling
• Materials:
-- manufactured single crystal
or polycrystalline diamonds
in a metal or resin matrix.
-- polycrystalline diamonds
resharpen by microfracturing
along cleavage planes.
oil drill bits
blades
Single crystal
diamonds
polycrystalline
diamonds in a resin
matrix.
Photos courtesy Martin Deakins,
GE Superabrasives, Worthington,
OH. Used with permission.
Chapter 13 - 4
Ceramics Application: Sensors
• Example: ZrO2 as an oxygen sensor
Ca 2+
• Principle: Increase diffusion rate of oxygen
to produce rapid response of sensor signal to
change in oxygen concentration
• Approach:
A substituting Ca2+ ion
removes a Zr 4+ ion and
an O2- ion.
Add Ca impurity to ZrO2:
-- increases O2- vacancies
-- increases O2- diffusion rate
• Operation:
-- voltage difference produced when
sensor
gas with an
reference
O2- ions diffuse from the external unknown, higher
gas at fixed
O2surface through the sensor to the oxygen content
oxygen content
diffusion
reference gas surface.
-- magnitude of voltage difference
 partial pressure of oxygen at the
+
voltage
difference
produced!
external surface
Chapter 13 - 5
Refractories
• 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):
2200
T(ºC)
2000
3Al2O3-2SiO2
Liquid
(L)
1800
mullite
alumina + L
mullite
+L
crystobalite
+L
1600
1400
mullite
+ crystobalite
0
20
alumina
+
mullite
40
60
80
100
Composition (wt% alumina)
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.)
Chapter 13 - 6
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
Chapter 13 - 7
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
Chapter 13 - 8
Ceramic Fabrication Methods (i)
PARTICULATE
CEMENTATION
GLASS
FORMING
FORMING
• Blowing of Glass Bottles:
• Pressing: plates, cheap glasses
Gob
Pressing
operation
Parison
mold
-- glass formed by application of
pressure
-- mold is steel with graphite
lining
• Fiber drawing:
Compressed
air
Suspended
parison
Finishing
mold
Adapted from Fig. 13.8, Callister & Rethwisch 8e. (Fig. 13.8 is adapted from C.J.
Phillips, Glass: The Miracle Maker, Pittman Publishing Ltd., London.)
wind up
Chapter 13 - 9
Sheet Glass Forming
• Sheet forming – continuous casting
– sheets are formed by floating the molten glass on a pool of
molten tin
Adapted from Fig. 13.9,
Callister & Rethwisch 8e.
Chapter 13 - 10
Glass Structure
• Basic Unit:
4Si0 4 tetrahedron
Si 4+
O2-
• Quartz is crystalline
SiO2:
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+
Na +
Si 4+
O2-
(soda glass)
Adapted from Fig. 12.11,
Callister & Rethwisch 8e.
Chapter 13 - 11
Glass Properties
• Specific volume (1/r) vs Temperature (T):
• Crystalline materials:
Specific volume
Liquid
(disordered)
Supercooled
Liquid
• Glasses:
Glass
(amorphous solid)
Crystalline
(i.e., ordered)
Tg
-- crystallize at melting temp, Tm
-- have abrupt change in spec.
vol. at Tm
Tm
Adapted from Fig. 13.6,
Callister & Rethwisch 8e.
solid
T
-- do not crystallize
-- change in slope in spec. vol. curve at
glass transition temperature, Tg
-- transparent - no grain boundaries to
scatter light
Chapter 13 - 12
Glass Properties: Viscosity
• Viscosity, h:
-- relates shear stress () and velocity gradient (dv/dy):

dy
glass

dv
dv
dy

h
dv / dy
velocity gradient
h has units of (Pa-s)
Chapter 13 - 13
Log Glass Viscosity vs. Temperature
• Viscosity decreases with T
• soda-lime glass: 70% SiO2
balance Na2O (soda) & CaO (lime)
• borosilicate (Pyrex):
13% B2O3, 3.5% Na2O, 2.5% Al2O3
• Vycor: 96% SiO2, 4% B2O3
Viscosity [Pa-s]
• fused silica: > 99.5 wt% SiO2
10 14
10 10
10 6
10 2
1
200
strain point
annealing point
Working range:
glass-forming carried out
Tmelt
600 1000 1400 1800 T(ºC)
Adapted from Fig. 13.7, Callister & Rethwisch
8e. (Fig. 13.7 is from E.B. Shand,
Engineering Glass, Modern Materials, Vol. 6,
Academic Press, New York, 1968, p. 262.)
Chapter 13 - 14
Heat Treating Glass
• Annealing:
-- removes internal stresses caused by uneven cooling.
• Tempering:
-- puts surface of glass part into compression
-- suppresses growth of cracks from surface scratches.
-- sequence:
before cooling
hot
initial cooling
at room temp.
cooler
hot
cooler
compression
tension
compression
-- Result: surface crack growth is suppressed.
Chapter 13 - 15
• Ceramic Fabrication
techniques:
-- glass forming (pressing,
blowing, fiber drawing).
-- particulate forming
(hydroplastic forming, slip
casting, powder pressing, tape
casting)
-- cementation
Chapter 13 - 16
Ceramic Fabrication Methods (iia)
GLASS
FORMING
PARTICULATE
FORMING
CEMENTATION
Hydroplastic forming:
• Mill (grind) and screen constituents: desired particle size
• Extrude this mass (e.g., into a brick)
Ao
force
container
ram
billet
container
die holder
extrusion
die
Ad
Adapted from
Fig. 12.8(c),
Callister &
Rethwisch 8e.
• Dry and fire the formed piece
Chapter 13 - 17
Ceramic Fabrication Methods (iia)
GLASS
FORMING
PARTICULATE
FORMING
CEMENTATION
Slip casting:
• Mill (grind) and screen constituents: desired particle size
• Mix with water and other constituents to form slip
• Slip casting operation
pour slip
into mold
absorb water
into mold
“green
ceramic”
solid component
pour slip
into mold
drain
mold
“green
ceramic”
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
• Dry and fire the cast piece
Chapter 13 - 18
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
Chapter 13 - 19
Hydroplasticity of Clay
• Clay is inexpensive
• When water is added to clay
Shear
-- 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.)
charge
neutral
weak van
der Waals
bonding
4+
charge
neutral
Si
3+
Al
OH
2O
Shear
Chapter 13 - 20
Drying and Firing
• 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.)
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).
micrograph of porcelain
Drying too fast causes sample to warp or crack due to non-uniform shrinkage
Si02 particle
(quartz)
glass formed
around
the particle
70mm
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.)
Chapter 13 - 21
Ceramic Fabrication Methods (iib)
GLASS
FORMING
PARTICULATE
FORMING
CEMENTATION
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 (
Chapter 13 - 22
Sintering
Sintering occurs during firing of a piece that has
been powder pressed
-- powder particles coalesce and reduction of pore size
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
Chapter 13 - 23
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.
Chapter 13 - 24
Ceramic Fabrication Methods (iii)
GLASS
FORMING
PARTICULATE
FORMING
CEMENTATION
• 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)
• Portland cement – production of:
-- mix clay and lime-bearing minerals
-- calcine (heat to 1400ºC)
-- grind into fine powder
Chapter 13 - 25
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)
Chapter 13 - 26
ANNOUNCEMENTS
Reading:
Core Problems:
Self-help Problems:
Chapter 13 - 27