1. Ceramic Their Properties and Material Behavior
Engr 2110
Dr. R. Lindeke

2. Taxonomy of Ceramics • Properties: • Applications: • Fabrication
Glasses
Clay
products
Refractories
Abrasives
Cements
Advanced
ceramics
-optical -
composite
reinforce
containers/
household
-whiteware
bricks
-bricks for
high T
(furnaces)
-sandpaper
cutting
polishing
-composites
structural
engine
rotors
valves
bearings
-sensors
Adapted from Fig and discussion in Section , Callister 7e.
• Properties:
-- Tm for glass is moderate, but large for other ceramics.
-- Small toughness, ductility; large moduli & creep resist.
• Applications:
-- High T, wear resistant, novel uses from charge neutrality.
• Fabrication
-- some glasses can be easily formed
-- other ceramics can not be formed or cast.

3. Ceramic Bonding • Bonding: • Large vs small ionic bond character:
-- Mostly ionic, some covalent.
-- % ionic character increases with difference in
electronegativity (remember!?!).
• Large vs small ionic bond character:
CaF2: large
SiC: small
Adapted from Fig. 2.7, Callister 7e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the Chemical Bond, 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by
Cornell University.

4. Ceramic Crystal Structures
Oxide structures
oxygen anions much larger than metal cations
close packed oxygen in a lattice (usually FCC)
cations in the holes of the oxygen lattice
The same ideas apply to all “ceramics”
Principles of Ceramic Architecture:
Size relationships Cation to Anion
Electrical Neutrality of the overall structure
Crystallographic Arrangements
Stoichiometry Must Match

5. Silica Glass A “Dense form” of amorphous silica
Charge imbalance corrected with “counter cations” such as Na+
Borosilicate glass is the pyrex glass used in labs
better temperature stability & less brittle than sodium glass

6. GLASSES – transparent and easily shaped
Noncrystalline Silicates + oxides (CaO, Na2O, K2O, Al2O3)
E.g. Soda lime glass = 70wt% SiO2 + 30% [Na2O (soda) and CaO(lime)
Table 13.1

7. GLASS PROPERTIES • Specific volume (1/r) vs Temperature (T):
• Crystalline materials:
--crystallize at melting temp, Tm
--have abrupt change in spec.
vol. at Tm
• Glasses:
--do not crystallize
--spec. vol. varies smoothly with T
--Glass transition temp, Tg
Adapted from Fig. 13.5, Callister, 6e.
• Viscosity:
--relates shear stress &
velocity gradient:
--has units of (Pa-s) 9

8. GLASS VISCOSITY VS T AND IMPURITIES
• Viscosity decreases with T increase
• Impurities lower Tdeform
from E.B. Shand, Engineering Glass, Modern Materials, Vol. 6, Academic Press, New York, 1968, p. 262. 10

9. Important Temperatures
Melting point = viscosity of 10 Pa.s
Working point= viscosity of 1000 Pa.s
Softening point= viscosity of 4x107Pa.s
Temperature above which glass cannot
be handled without altering dimensions)
Annealing point= viscosity of 1012 Pa.s.
Strain point = viscosity of 3x1013Pa.s
Fracture occurs before deformation
• Viscosity decreases with T
• Impurities lower Tdeform

10. Silicates
Combine SiO44- tetrahedra by having them share corners, edges, or faces
Cations such as Ca2+, Mg2+, & Al3+ act to neutralize & provide ionic bonding
Mg2SiO4
Ca2MgSi2O7

11. Layered Silicates Layered silicates (clay silicates) =
SiO4 tetrahedra connected together to form 2-D plane
(Si2O5)2-
So need cations to balance charge =

12. Layered Silicates
Kaolinite clay alternates (Si2O5)2- layer with Al2(OH)42+ layer
Adapted from Fig , Callister 7e.
Note: these sheets loosely bound by van der Waal’s forces

13. Layered Silicates Can change the counterions Micas: KAl3Si3O10(OH)2
this changes layer spacing
the layers also allow absorption of water
Micas: KAl3Si3O10(OH)2
Bentonite
used to seal wells
packaged dry
swells 2-3 fold in H2O
pump in to seal up well so no polluted ground water seeps in to contaminate the water supply.
Used in bonding Foundry Sands and Taconite pellets

14. Carbon Forms Carbon black – amorphous – surface area ca. 1000 m2/g
Diamond
tetrahedral carbon
hard – no good slip planes
brittle – can cleave (cut) it
large diamonds – jewelry
small diamonds
often man made - used for cutting tools and polishing
diamond films
hard surface coat – cutting tools, medical devices, etc.
(C likes to have covalent bonds & tetravalent)

15. Carbon Forms - Graphite
layer structure – aromatic layers
weak van der Waal’s forces between layers
planes slide easily, good lubricant
Like connected benzene rings

16. Carbon Forms – Fullerenes and Nanotubes
Fullerenes or carbon nanotubes
wrap the graphite sheet by curving into ball or tube
Buckminister fullerenes
Like a soccer ball C60 - also C70 + others
Adapted from Figs & 12.19, Callister 7e.

17. Defects in Ceramic Structures
• Frenkel Defect
--a cation is out of place.
• Shottky Defect
--a paired set of cation and anion vacancies.
Shottky
Defect:
Frenkel
Defect
Adapted from Fig , Callister 7e. (Fig is from W.G. Moffatt, G.W. Pearsall, and J. Wulff, The Structure and Properties of Materials, Vol. 1, Structure, John Wiley and Sons, Inc., p. 78.)
• Equilibrium concentration of defects

18. Mechanical Properties
We know that ceramics are more brittle than metals. Why?
Consider method of deformation
slippage along slip planes
in ionic solids this slippage is very difficult
too much energy needed to move one anion past another anion (like charges repel)

19. Measuring Elastic Modulus
• Room T behavior is usually elastic, with brittle failure.
• 3-Point Bend Testing often used.
--tensile tests are difficult for brittle materials! F
L/2
d = midpoint
deflection
cross section R b d
rect.
circ.
Adapted from Fig , Callister 7e.
• Determine elastic modulus according to: F x
linear-elastic behavior d
slope = E = L 3 4 bd 12 p R
rect.
cross
section
circ.

20. Measuring Strength s = 1.5Ff L bd 2 Ff L pR3 x F F
• 3-point bend test to measure room T strength. F
L/2
d = midpoint
deflection
cross section R b d
rect.
circ.
location of max tension
Adapted from Fig , Callister 7e.
• Flexural strength:
• Typ. values:
Data from Table 12.5, Callister 7e.
rect. s fs =
1.5Ff L
bd 2
Ff L
pR3
Si nitride
Si carbide
Al oxide
glass (soda) 69
304
345
393
Material
(MPa) E(GPa) x F Ff d

21. Mechanical Issues:
Properties are significantly dependent on processing – and as it relates to the level of Porosity:
E = E0(1-1.9P+0.9P2) – P is fraction porosity
fs = 0e-nP -- 0 & n are empirical values
Because the very unpredictable nature of ceramic defects, we do not simply add a factor of safety for tensile loading
We may add compressive surface loads
We often choose to avoid tensile loading at all – most ceramic loading of any significance is compressive (consider buildings, dams, brigdes and roads!)

22. Application: Refractories
• Need a material to use in high temperature furnaces.
• Consider the Silica (SiO2) - Alumina (Al2O3) system.
• Phase diagram shows:
mullite, alumina, and crystobalite as candidate refractories.
Composition (wt% alumina)
T(°C)
1400
1600
1800
2000
2200 20 40 60 80
100
alumina +
mullite
+ L
Liquid
(L)
crystobalite
alumina + L
3Al2O3-2SiO2
Adapted from Fig , Callister 7e. (Fig is adapted from F.J. Klug and R.H. Doremus, "Alumina Silica Phase Diagram in the Mullite Region", J. American Ceramic Society 70(10), p. 758, 1987.)

23. Application: Die Blanks
-- Need wear resistant properties!
tensile
force A o d
die
Adapted from Fig (d), Callister 7e.
Courtesy Martin Deakins, GE Superabrasives, Worthington, OH. Used with permission.
• Die surface:
-- 4 mm polycrystalline diamond
particles that are sintered onto a
cemented tungsten carbide
substrate.
-- polycrystalline diamond helps control
fracture and gives uniform hardness
in all directions.
Courtesy Martin Deakins, GE Superabrasives, Worthington, OH. Used with permission.

24. Application: Cutting Tools
-- for grinding glass, tungsten,
carbide, ceramics
-- for cutting Si wafers
-- for oil drilling
• Solutions:
oil drill bits
blades
-- manufactured single crystal or polycrystalline diamonds
in a metal or resin matrix.
coated single
crystal diamonds
-- optional coatings (e.g., Ti to help
diamonds bond to a Co matrix
via alloying)
polycrystalline
diamonds in a resin
matrix.
-- polycrystalline diamonds
resharpen by microfracturing
along crystalline planes.
Photos courtesy Martin Deakins,
GE Superabrasives, Worthington,
OH. Used with permission.

25. Application: Sensors • Example: Oxygen sensor ZrO22+
impurity
removes a Zr 4+
and a O 2 -
ion.
• Approach:
Add Ca impurity to ZrO2:
-- increases O2- vacancies
-- increases O2- diffusion rate
• Example: Oxygen sensor ZrO2
• Principle: Make diffusion of ions
fast for rapid response.
reference
gas at fixed
oxygen content O 2-
diffusion
gas with an
unknown, higher - +
voltage difference produced!
sensor
• Operation:
-- voltage difference
produced when
O2- ions diffuse
from the external
surface of the sensor
to the reference gas.

26. Alternative Energy – Titania Nano-Tubes
"This is an amazing material architecture for water photolysis," says Craig Grimes, professor of electrical engineering and materials science and engineering. Referring to some recent finds of his research group (G. K. Mor, K. Shankar, M. Paulose, O. K. Varghese, C. A. Grimes, Enhanced Photocleavage of Water Using Titania Nanotube-Arrays, Nano Letters, vol. 5, pp ), "Basically we are talking about taking sunlight and putting water on top of this material, and the sunlight turns the water into hydrogen and oxygen. With the highly-ordered titanium nanotube arrays, under UV illumination you have a photoconversion efficiency of 13.1%. Which means, in a nutshell, you get a lot of hydrogen out of the system per photon you put in. If we could successfully shift its bandgap into the visible spectrum we would have a commercially practical means of generating hydrogen by solar energy.

27. Ceramic Fabrication Methods-I
PARTICULATE FORMING
CEMENTATION
GLASS
FORMING
• Pressing:
plates, dishes, cheap glasses
--mold is steel with graphite lining
Gob
Parison
mold
Pressing
operation
• Fiber drawing:
wind up
• Blowing:
suspended
Parison
Finishing
mold
Compressed
air
Adapted from Fig. 13.8, Callister, 7e. (Fig is adapted from C.J. Phillips, Glass: The Miracle Maker, Pittman Publishing Ltd., London.)

28. Sheet Glass Forming Sheet forming – continuous draw
originally sheet glass was made by “floating” glass on a pool of mercury – or tin
Adapted from Fig. 13.9, Callister 7e.

29. Modern Plate/Sheet Glass making:
Image from Prof. JS Colton, Ga. Institute of Technology

30. Heat Treating Glass • Annealing: • Tempering:
--removes internal stress caused by uneven cooling.
• Tempering:
--puts surface of glass part into compression
--suppresses growth of cracks from surface scratches.
--sequence:
before cooling
hot
surface cooling
hot
cooler
further cooled
tension
compression
--Result: surface crack growth is suppressed.

31. Ceramic Fabrication Methods-IIA
GLASS FORMING
PARTICULATE
FORMING
CEMENTATION
• Milling and screening: desired particle size
• Mixing particles & water: produces a "slip"
ram
billet
container
force
die holder
die A o d
extrusion
--Hydroplastic forming:
extrude the slip (e.g., into a pipe)
Adapted from Fig (c), Callister 7e.
• Form a "green" component
solid component
--Slip casting:
Adapted from Fig , Callister 7e.
(Fig is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.)
hollow component
pour slip
into mold
drain
mold
“green
ceramic”
absorb water
• Dry and fire the component

32. Clay Composition A mixture of components used (50%) 1. Clay
(25%) 2. Filler – e.g. quartz (finely ground)
(25%) 3. Fluxing agent (Feldspar)
binds it together
aluminosilicates + K+, Na+, Ca+

33. Features of a Slip • Clay is inexpensive • Adding water to clay charge
weak van
der Waals
bonding
charge
neutral Si 4+ Al 3 + - OH O 2-
Shear
• Clay is inexpensive
• Adding water to clay
-- allows material to shear easily
along weak van der Waals bonds
-- enables extrusion
-- enables slip casting
• Structure of
Kaolinite Clay:
Adapted from Fig , Callister 7e.
(Fig is adapted from W.E. Hauth, "Crystal Chemistry of Ceramics", American Ceramic Society Bulletin, Vol. 30 (4), 1951, p. 140.)

34. Drying and Firing • Drying: layer size and spacing decrease. • Firing:
Adapted from Fig , Callister 7e.
(Fig is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.)
wet slip
partially dry
“green” ceramic
Drying too fast causes sample to warp or crack due to non-uniform shrinkage
• Firing:
--T raised to ( °C)
--vitrification: liquid glass forms from clay and flows between
SiO2 particles. Flux melts at lower T.
Adapted from Fig , Callister 7e.
(Fig is courtesy H.G. Brinkies, Swinburne University of Technology, Hawthorn Campus, Hawthorn, Victoria, Australia.)
Si02 particle
(quartz)
glass formed
around
the particle
micrograph of
porcelain
70 mm

35. Ceramic Fabrication Methods-IIB
GLASS FORMING
PARTICULATE
FORMING
CEMENTATION
Sintering: useful for both clay and non-clay compositions.
• Procedure:
-- produce ceramic and/or glass particles by grinding
-- place particles in mold
-- press at elevated T to reduce pore size.
• Aluminum oxide powder:
-- sintered at 1700°C
for 6 minutes.
15 m
Adapted from Fig , Callister 7e.
(Fig 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.)

36. Powder Pressing
Sintering - powder touches - forms neck & gradually neck thickens
add processing aids to help form neck
little or no plastic deformation
Uniaxial compression - compacted in single direction
Isostatic (hydrostatic) compression - pressure applied by fluid - powder in rubber envelope
Hot pressing - pressure + heat
Adapted from Fig , Callister 7e.

37. Tape Casting thin sheets of green ceramic cast as flexible tape
used for integrated circuits and capacitors
cast from liquid slip (ceramic + organic solvent)
Adapted from Fig , Callister 7e.

38. Ceramic Fabrication Methods-III
GLASS FORMING
PARTICULATE
FORMING
CEMENTATION
• Produced in extremely large quantities.
• Portland cement:
-- mix clay and lime bearing materials
-- calcinate (heat to 1400°C)
-- primary constituents:
tri-calcium silicate
di-calcium silicate
• Adding water
-- produces a paste which hardens
-- hardening occurs due to hydration (chemical reactions
with the water).
• Forming: done usually minutes after hydration begins.

39. Applications: Advanced Ceramics
Disadvantages:
Brittle
Too easy to have voids- weaken the engine
Difficult to machine
Heat Engines
Advantages:
Run at higher temperature
Excellent wear & corrosion resistance
Low frictional losses
Ability to operate without a cooling system
Low density
Possible parts – engine block, piston coatings, jet engines
Ex: Si3N4, SiC, & ZrO2

40. Applications: Advanced Ceramics
Ceramic Armor
Al2O3, B4C, SiC & TiB2
Extremely hard materials
shatter the incoming projectile
energy absorbent material underneath

41. Applications: Advanced Ceramics
Electronic Packaging
Chosen to securely hold microelectronics & provide heat transfer
Must match the thermal expansion coefficient of the microelectronic chip & the electronic packaging material. Additional requirements include:
good heat transfer coefficient
poor electrical conductivity
Materials currently used include:
Boron nitride (BN)
Silicon Carbide (SiC)
Aluminum nitride (AlN)
thermal conductivity 10x that for Alumina
good expansion match with Si