Bahan Kualih ceramic and composites

1. Chapter 12 -

2. Chapter 12 -
Introduction
References
The course will be presented mainly with help of overheads.
PDF versions of the overheads and additional course material will be available on our internet home
page.
Textbook
The Chemistry of Ceramics
Hiroaki Yanagida, Kunihiko Koumoto, Masaru Miyayama
John Wiley and Suns 1996
Additional References
Barsoum Michael
Fundamentals of Ceramics
McGraw Hill, 1997 ISBN: 0071141847
W.D., Kingery, H.K. Bowen, and D.R., Uhlmann
Introduction to Ceramics
2nd ed., John Wiley and Sons, New York, 1976
Y.M., Chiang, D., Birnie III, and W.D., Kingery
Physical Ceramics
John Wiley and Sons, New York, 1997

3. Chapter 12 -
Entymology
Introduction
The term "ceramic" is derivated from greek "keramos" meaning "clay"
or "brick", but also "the one who went through the fire". The last
meaning is connected with greek mythology and the heroe Keramos.
Keramos was the result of a quick affair between Dyonisos, the god of
wine, and Ariadne on the isle of Naxos. Since his youth, Keramos was
responsible for the replacement of the drinking cups, which got broken
during his father's binges.
Examples of greek ceramic ware, 1500 B.C.

4. Chapter 12 -
Definition: Ceramics can be defined as inorganic, nonmetallic materials. They are typically
crystalline in nature and are compounds formed between metallic and nonmetallic elements such
as aluminum and oxygen (alumina-Al2O3) or silicon and nitrogen (silicon nitride-Si3N4).
Type of ceramic materials based on composition:
- Silicate ceramics: compounds containing the anionic complex (SiO4) e.g. the silicate group.
- Advanced ceramics:
Oxide ceramics: alumina, zirconia etc.
Non-oxide ceramics: carbides and nitrides are the most important compounds of this group.
Product groups:
Ceramic materials
Introduction
Ceramics

5. Chapter 12 -
Properties of Ceramic Materials I
Introduction
high values
low values
Ceramics Metals
Melting point
LT mechanical resistance
HT mechanical resistance
Thermal expansion
Ductility
Corrosion resistance
Abrasion resistance
Electrical conductivity
Density
Thermal conductivity
Thermal shock resistance

6. Chapter 12 -
The most remarkable property of ceramic materials is their very high melting,
sublimation or dissociation temperatures. Typical ceramic materials and melting
points
MgO 2800 °C HfC 3890 °C
Al2O3 2030 °C HfTa4C5 3940 °C
ZrO2 (stab. Y) 2550 °C WC 2600 °C
TiO2 1840 °C SiC 2250 °C (diss.
elements)
SiO2 1710 °C BN 2400 °C (subl.)
Mg2SiO4 1810 °C TiN 2950 °C
Al2SiO5 1810 °C AlN 2500 °C (subl.)
CaSiO3 1540 °C Si3N4 1900 °C (subl.)
C 3750 °C
Si 1421 °C
Properties of Ceramic Materials II
Introduction

7. Chapter 12 -
7000 BC. First bricks made of dried clay
4000 BC Frist fired bricks (Mesopotamia)
Appearance of potter's wheel and firing
kilns (Egypt)
2600 BC First bricks with sumeric cuneiform
writings
2300 BC Ziggourat build par Our-Nammon
(„The tower of Babylone“)
600 BC Ishtar portal in Babylone
build by king Nabuchodonosor (photo)
800 AC Developement of porcellaine in China
1600 AC Introduction of porcellaine manufacturing in
Europe (Saxony)
1900 AC First application of non-silicate ceramics,
refractories MgO and SiC
1960 AC Introduction of the Bayer process for the
manufacturing of alumina
1986 AC Discovery of supraconductivity in cuprate
ceramics (Müller and Bednorz, IBM Rüschlikon)
History of Ceramic Materials
Introduction

8. Chapter 12 -
Early Ming Dynasty Bowl 14th century
http://www.dadums.50megs.com/chinese/fish.html
Brick wall, Oxford St. Berkeley
http://www.ma.huji.ac.il
Tile pattern, Alhambra, Granada Spain
http://www.ma.huji.ac.il
Application of silicate ceramics
Introduction
Electric fuses
http://www.littelfuse.com

9. Chapter 12 -
Kryocera Si3N4 gas turbine rotor
BORIDE Inc WC blast nozzle
Kundan MgO refractory bricks
(furnace liners)
Application of advanced ceramics
Introduction
Structural Al2 O3
parts (Reed, 1995)

10. Chapter 12 - 10
Structures & Properties of Ceramics
ISSUES TO ADDRESS...
• How do the crystal structures of ceramic materials
differ from those for metals?
• How do point defects in ceramics differ from those
defects found in metals?
• How are impurities accommodated in the ceramic lattice?
• How are the mechanical properties of ceramics
measured, and how do they differ from those for metals?
• In what ways are ceramic phase diagrams different from
phase diagrams for metals?

11. Chapter 12 - 11
• Bonding:
-- Can be ionic and/or covalent in character.
-- % ionic character increases with difference in
electronegativity of atoms.
Adapted from Fig. 2.7, Callister & Rethwisch 8e. (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.)
• Degree of ionic character may be large or small:
Atomic Bonding in Ceramics
SiC: small
CaF2: large

12. Chapter 12 - 12
Ceramic Crystal Structures
Oxide structures
– oxygen anions larger than metal cations
– close packed oxygen in a lattice (usually FCC)
– cations fit into interstitial sites among oxygen ions

13. Chapter 12 - 13
Factors that Determine Crystal Structure
1. Relative sizes of ions – Formation of stable structures:
--maximize the # of oppositely charged ion neighbors.
Adapted from Fig. 12.1,
Callister & Rethwisch 8e.
- -
- -
+
unstable
- -
- -
+
stable
- -
- -
+
stable
2. Maintenance of
Charge Neutrality :
--Net charge in ceramic
should be zero.
--Reflected in chemical
formula:
CaF2: Ca2+
cation
F-
F-
anions
+
AmXp
m, p values to achieve charge neutrality
Charge
C. G.

14. Chapter 12 - 14
• Coordination # increases with
Coordination # and Ionic Radii
Adapted from Table 12.2,
Callister & Rethwisch 8e.
2
rcation
ranion
Coord
#
< 0.155
0.155 - 0.225
0.225 - 0.414
0.414 - 0.732
0.732 - 1.0
3
4
6
8
linear
triangular
tetrahedral
octahedral
cubic
Adapted from Fig. 12.2,
Callister & Rethwisch 8e.
Adapted from Fig. 12.3,
Callister & Rethwisch 8e.
Adapted from Fig. 12.4,
Callister & Rethwisch 8e.
ZnS
(zinc blende)
NaCl
(sodium
chloride)
CsCl
(cesium
chloride)
rcation
ranion
To form a stable structure, how many anions can
surround around a cation?
UNIT CELL-
ATOM RATIO
ION
LOCATIONS

15. Chapter 12 - 15
Computation of Minimum Cation-Anion
Radius Ratio
• Determine minimum rcation/ranion for an octahedral site
(C.N. = 6)
a = 2ranion
2ranion  2rcation = 2 2ranion

ranion  rcation = 2ranion

rcation = ( 2 1)ranion
a
r
r 2
2
2 cation
anion =

414
.
0
1
2
anion
cation =

=
r
r

16. Markets
Products 1990 1995 2000
Tiles 16.5 25.0 33.0
Dish ware 13.0 18.0 22.0
White ware 7.0 9.5 11.5
Refractories 26.0 21.0 19.0
Bricks 24.0 35.0 43.0
Advanced
ceramics
20.0 25.0 33.0
Total 106.5 133.5 161.5
Worldwide turnover for
ceramic products in billion $.
The 2000 numbers are
projected.
(Reh, 1998) -
Annual production numbers (1994)
China 723 billions of bricks de briques
67 billions of roof tiles
Switzerland
1‘100‘000 tons of bricks
240‘000 tons of roof tiles
Introduction

17. Manufacturing of ceramic materials I
Introduction
Material
Product
Design
Simulation
Manufacturing
Marketing
Economy
Manufacturing
System

18. Classification of ceramics by function
Introduction
Function Class
electrical insulation -Al2O3 , MgO, procelain
ferroelectrics BaTiO3, SrTiO3
piezoelectrics PbZr0.5Ti0.5O3
conductors MoSi2, SiC
fast ionic conductors -Al2O3 , doped ZrO2
superconductors Ba2YCu3O7-x
magnetic soft ferrites Mn0.4 Zn0.6Fe2O4
hard ferrites BaFe12O19, SrFe12O19
nuclear fuel UO2, UO2 - PuO2
shielding SiC, BC4
optical transparent envelopes -Al2O3, MgAl2O4
light memory doped PbZr0.5Ti0.5O3 , LiNbO3
colors doped ZrSiO4, doped ZrO2 , doped Al2O3
mechanical structural refractory -Al2O3 , MgO, Si3N4 , SiC
wear resistance -Al2O3, ZrO2 , Si3N4 , SiC
cutting -Al2O3, ZrO2 , Si3N4 , SiC, WC, SiAlON
abrasive -Al2O3 , MgO, SiC
construction CaO - Al2O3 - SiO2 , porcelain
thermal insulation -Al2O3, ZrO2 , Al6Si2O13 , SiO2
radiator ZrO2, TiO2, AlN
chemical gas sensor ZnO, ZrO2, SnO2, Fe2O3
catalyst carrier Mg2Al4Si5O18, Al2O3
electrodes TiO2 , SnO2, ZnO, TiB2
filters SiO2, Al2O3
coatings NaO - CaO - Al2O3 - SiO2
biological structural protheses -Al2O3, procelain
cements CaHPO4 - H2O

19. Manufacturing of ceramic materials II
Introduction
raw material
properties
microstructure
final product
properties
powder processing
forming, shaping
drying
firing
finishing
application

20. Introduction
General ceramic processing flow chart
(Reed, 1995)
Ceramic materials cannot be
formed by the manufacturing
processes known from metallic or
organic materials. The energy to
melt and cast ceramic raw
materials would be far too costly.
The process used to form ceramic
materials is a heat treatment of
very fine powders of the raw
material(s) called sintering. The
brittle nature of ceramic
endproducts demands as little as
possible machining after sintering.
The ceramic parts have,
therefore, to be shaped before
sintering.
Manufacturing of ceramic materials III

21. Chapter 12 - 21
Bond Hybridization
Bond Hybridization is possible when there is significant
covalent bonding
– hybrid electron orbitals form
– For example for SiC
• XSi = 1.8 and XC = 2.5
% ionic character = 100 {1-exp[-0.25(XSi XC)2
]} =11.5%
• ~ 89% covalent bonding
• Both Si and C prefer sp3 hybridization
• Therefore, for SiC, Si atoms occupy tetrahedral sites

22. Chapter 12 - 22
• On the basis of ionic radii, what crystal structure
would you predict for FeO?
• Answer:
550
0
140
0
077
0
anion
cation
.
.
.
r
r
=
=
based on this ratio,
-- coord # = 6 because
0.414 < 0.550 < 0.732
-- crystal structure is NaCl
Data from Table 12.3,
Callister & Rethwisch 8e.
Example Problem: Predicting the Crystal
Structure of FeO
Ionic radius (nm)
0.053
0.077
0.069
0.100
0.140
0.181
0.133
Cation
Anion
Al3+
Fe2+
Fe3+
Ca2+
O2-
Cl-
F-

23. Chapter 12 - 23
Rock Salt Structure
Same concepts can be applied to ionic solids in general.
Example: NaCl (rock salt) structure
rNa = 0.102 nm
rNa/rCl = 0.564
 cations (Na+) prefer octahedral sites
Adapted from Fig. 12.2,
Callister & Rethwisch 8e.
rCl = 0.181 nm

24. Chapter 12 - 24
MgO and FeO
O2- rO = 0.140 nm
Mg2+ rMg = 0.072 nm
rMg/rO = 0.514
 cations prefer octahedral sites
So each Mg2+ (or Fe2+) has 6 neighbor oxygen atoms
Adapted from Fig. 12.2,
Callister & Rethwisch 8e.
MgO and FeO also have the NaCl structure

25. Chapter 12 - 25
AX Crystal Structures
939
.
0
181
.
0
170
.
0
Cl
Cs =
=


r
r
Adapted from Fig. 12.3,
Callister & Rethwisch 8e.
Cesium Chloride structure:
 Since 0.732 < 0.939 < 1.0,
cubic sites preferred
So each Cs+ has 8 neighbor Cl-
AX–Type Crystal Structures include NaCl, CsCl, and zinc blende

26. Chapter 12 - 26
AX2 Crystal Structures
• Calcium Fluorite (CaF2)
• Cations in cubic sites
• UO2, ThO2, ZrO2, CeO2
• Antifluorite structure –
positions of cations and
anions reversed
Adapted from Fig. 12.5,
Callister & Rethwisch 8e.
Fluorite structure UNIT CELL –TWO
DIAGONALS

27. Chapter 12 - 27
ABX3 Crystal Structures
Adapted from Fig. 12.6,
Callister & Rethwisch 8e.
• Perovskite structure
Ex: complex oxide
BaTiO3
CHARGE C.G. SEPARATE
AT GEOMETRICAL
CENTER

28. Chapter 12 -
VMSE: Ceramic Crystal Structures
28

29. Chapter 12 - 29
Density Computations for Ceramics
A
A
C )
(
N
V
A
A
n
C




=

Number of formula units/unit cell
Volume of unit cell
Avogadro’s number
= sum of atomic weights of all anions in formula unit

AA

AC = sum of atomic weights of all cations in formula unit
NUMBER
OF CAT
AND
ANION
WITHIN AN
UNIT CELL

30. Chapter 12 - 30
Silicate Ceramics
Most common elements on earth are Si & O
• SiO2 (silica) polymorphic forms are quartz,
crystobalite, & tridymite
• The strong Si-O bonds lead to a high melting
temperature (1710ºC) for this material
Si4+
O2-
Adapted from Figs.
12.9-10, Callister &
Rethwisch 8e
crystobalite
TETRAHEDRON

31. Chapter 12 - 31
Bonding of adjacent SiO4
4- accomplished by the
sharing of common corners, edges, or faces
Silicates
Mg2SiO4 Ca2MgSi2O7
Adapted from Fig.
12.12, Callister &
Rethwisch 8e.
Presence of cations such as Ca2+, Mg2+, & Al3+
1. maintain charge neutrality, and
2. ionically bond SiO4
4- to one another
VARIOUS
COMBINATIONS

32. Chapter 12 - 32
• 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)
Adapted from Fig. 12.11,
Callister & Rethwisch 8e.
Glass Structure
Si04 tetrahedron
4-
Si4+
O2-
Si4+
Na+
O2-

33. Chapter 12 - 33
Layered Silicates
• Layered silicates (e.g., clays, mica, talc)
– SiO4 tetrahedra connected
together to form 2-D plane
• A net negative charge is
associated with each (Si2O5)2- unit
• Negative charge balanced by
adjacent plane rich in positively
charged cations
Adapted from Fig.
12.13, Callister &
Rethwisch 8e.

34. Chapter 12 - 34
• Kaolinite clay alternates (Si2O5)2- layer with Al2(OH)4
2+
layer
Layered Silicates (cont.)
Note: Adjacent sheets of this type are loosely bound to
one another by van der Waal’s forces.
Adapted from Fig. 12.14,
Callister & Rethwisch 8e.

35. Chapter 12 - 35
Polymorphic Forms of Carbon
Diamond
– tetrahedral bonding of
carbon
• hardest material known
• very high thermal
conductivity
– large single crystals –
gem stones
– small crystals – used to
grind/cut other materials
– diamond thin films
• hard surface coatings –
used for cutting tools,
medical devices, etc.
Adapted from Fig. 12.15,
Callister & Rethwisch 8e.
TWO DIAGONAL LINES ZnS

36. Chapter 12 - 36
Polymorphic Forms of Carbon (cont)
Graphite
– layered structure – parallel hexagonal arrays of
carbon atoms
– weak van der Waal’s forces between layers
– planes slide easily over one another -- good
lubricant
Adapted from Fig.
12.17, Callister &
Rethwisch 8e.
BENZENE STR
DOUBLE
BONDS

37. Chapter 12 - 37
Polymorphic Forms of Carbon (cont)
Fullerenes and Nanotubes
• Fullerenes – spherical cluster of 60 carbon atoms, C60
– Like a soccer ball
• Carbon nanotubes – sheet of graphite rolled into a
tube
– Ends capped with fullerene hemispheres
Adapted from Figs.
12.18 & 12.19, Callister
& Rethwisch 8e.

38. Chapter 12 - 38
• Vacancies
-- vacancies exist in ceramics for both cations and anions
• Interstitials
-- interstitials exist for cations
-- interstitials are not normally observed for anions because anions
are large relative to the interstitial sites
Adapted from Fig. 12.20, Callister
& Rethwisch 8e. (Fig. 12.20 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.)
Point Defects in Ceramics (i)
Cation
Interstitial
Cation
Vacancy
Anion
Vacancy

39. Chapter 12 - 39
• Frenkel Defect
-- a cation vacancy-cation interstitial pair.
• Shottky Defect
-- a paired set of cation and anion vacancies.
• Equilibrium concentration of defects
Adapted from Fig.12.21, Callister
& Rethwisch 8e. (Fig. 12.21 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.)
Point Defects in Ceramics (ii)
Shottky
Defect:
Frenkel
Defect
/kT
QD
e


40. Chapter 12 - 40
• Electroneutrality (charge balance) must be maintained
when impurities are present
• Ex: NaCl
Imperfections in Ceramics
Na+ Cl-
• Substitutional cation impurity
without impurity Ca2+ impurity with impurity
Ca2+
Na+
Na+
Ca2+
cation
vacancy
• Substitutional anion impurity
without impurity O2- impurity
O2-
Cl-
anion vacancy
Cl-
with impurity

41. Chapter 12 - 41
Ceramic Phase Diagrams
MgO-Al2O3 diagram:
Adapted from Fig.
12.25, Callister &
Rethwisch 8e.


42. Chapter 12 - 42
Mechanical Properties
Ceramic materials are more brittle than metals.
Why is this so?
• Consider mechanism of deformation
– In crystalline, by dislocation motion
– In highly ionic solids, dislocation motion is difficult
• few slip systems
• resistance to motion of ions of like charge (e.g., anions)
past one another

43. Chapter 12 - 43
• Room T behavior is usually elastic, with brittle failure.
• 3-Point Bend Testing often used.
-- tensile tests are difficult for brittle materials.
Adapted from Fig. 12.32,
Callister & Rethwisch 8e.
Flexural Tests – Measurement of Elastic
Modulus
F
L/2 L/2
d = midpoint
deflection
cross section
R
b
d
rect. circ.
• Determine elastic modulus according to:
F
x
linear-elastic behavior
d
F
d
slope =
3
3
4bd
L
F
E
d
= (rect. cross section)
4
3
12 R
L
F
E

d
= (circ. cross section)

44. Chapter 12 - 44
• 3-point bend test to measure room-T flexural strength.
Adapted from Fig. 12.32,
Callister & Rethwisch 8e.
Flexural Tests – Measurement of Flexural
Strength
F
L/2 L/2
d = midpoint
deflection
cross section
R
b
d
rect. circ.
location of max tension
• Flexural strength: • Typical values:
Data from Table 12.5, Callister & Rethwisch 8e.
Si nitride
Si carbide
Al oxide
glass (soda-lime)
250-1000
100-820
275-700
69
304
345
393
69
Material sfs(MPa) E(GPa)
2
2
3
bd
L
Ff
fs =
s (rect. cross section)
(circ. cross section)
3
R
L
Ff
fs

=
s

45. Chapter 12 - 45
SUMMARY
• Interatomic bonding in ceramics is ionic and/or covalent.
• Ceramic crystal structures are based on:
-- maintaining charge neutrality
-- cation-anion radii ratios.
• Imperfections
-- Atomic point: vacancy, interstitial (cation), Frenkel, Schottky
-- Impurities: substitutional, interstitial
-- Maintenance of charge neutrality
• Room-temperature mechanical behavior – flexural tests
-- linear-elastic; measurement of elastic modulus
-- brittle fracture; measurement of flexural modulus