Structure and Properties of Ceramics

1. Ceramics
• Mostly compounds between metallic and nonmetallic elements (ionic
bonding)
– Example: Sodium Chloride
• Bonding between nonmetallic elements (covalent bonding)
– Example: Diamond
• Ceramic comes from the Greek word keramikos which means ‘burnt stuff’
• Traditional ceramic products: china, porcelain, bricks, tiles, glasses
• Advanced ceramic products: silicon chips and optical fibers
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2. Properties and applications of
advanced ceramics
Property
Type
Property Applications and Examples
Thermal Insulation High-temperature furnace linings for
insulation (silica, alumina, zirconia)
Thermal Conductivity Heat sinks for electronic packages (AlN)
Mechanical Hardness Cutting tools (SiC reinforced)
High temperature strength
retention
Turbine clades (Si3N4)
Wear resistance Bearings (Si3N4)
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Fundamentals of Ceramics, Michael Baroum

3. Many Ceramics are CrystallineMany Ceramics are Crystalline
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This is an image of
the rock salt (sodium
chloride) crystal
structure.

4. Focus of Module
• Understanding crystal structures found in ceramic materials.
• For the crystal structures that are predominately ionic bonding, the
structures are composed to cation and anions.
• Factors influencing crystal structures:
– Magnitude of electrical charge of ions
– Relative sizes of cation and anion
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5. Factors for Crystal Structures
• Crystal structures must be electrically neutral to be stable
– Charge from cations must balance charge from anions
• Ratio of cation radius (rc) to anion radius (ra) determines the ideal number
of nearest neighbors
– Cation would like to have largest number of anion nearest neighbors
– Anion would like to have largest number of cation nearest neighbors
– Stable crystal structures are when the anions surrounding the cation are in contact with
the cation
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6. Coordination number determined
by rc/ra ratio
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7. AX- Type Crystal Structures
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Rock Salt Structure Cesium Chloride Structure Zinc Blende

8. Sodium Chloride Structure
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• Interchangeable Names:
• Sodium Chloride (NaCl) Structure
• Rock Salt Structure
• rc/ra is between 0.414 and 0.732
• Coordination number = 6
• The image to the right it the entire unit cell.
• 4 cations within the unit cell
• 4 anions within the unit cell
• FCC arrangement of anions
• Ions ‘touch’ along the unit cell edges

9. Cesium Chloride Structure
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• Name:
• Cesium Chloride (CeCl) Structure
• rc/ra is between 0.732 and 1.0
• Coordination number= 8
• The image to the right it the entire unit cell.
• 1 cations within the unit cell
• 1 anions within the unit cell
• SC arrangement of anions
• Ions ‘touch’ along the unit cell diagonal

10. Zinc Blende Structure
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• Interchangeable Names:
• Zinc Blende Structure
• Sphalerite Structure
• rc/ra is between 0.225-0.414
• Coordination number= 4
• The image to the right it the entire unit cell.
• 4 cations within the unit cell
• Sit in tetrahedral positions
• 4 anions within the unit cell
• Sit in FCC arrangement

11. Summary
Adapted from Table 12.2,
Callister 7e.
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
TD
OH
cubic
Adapted from Fig.
12.2, Callister 7e.
Adapted from Fig.
12.3, Callister 7e.
Adapted from Fig.
12.4, Callister 7e.
ZnS
(zincblende)
NaCl
(sodium
chloride)
CsCl
(cesium
chloride)
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12. On the basis of ionic radii, what crystal
structure would you predict for FeO?
Data from Table 12.3,
Callister 7e.
Ionic radius (nm)
0.053
0.077
0.069
0.100
0.140
0.181
0.133
Cation
Anion
Al 3+
Fe 2 +
Fe 3+
Ca 2+
O 2-
Cl -
F -
a) Zinc Blend
b) Rock Salt
c) Cesium Chloride
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13. There are other ratios of A and X
• There are other compound ceramic structures that have unequal numbers of
cations and anions.
• Some also combine different types of cations and anions
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14. 14
Calculating Density

15. Densities of Material Classes
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Data from Table B1, Callister 7e.
r(g/cm)3
1
2
20
30
Based on data in Table B1, Callister
*GFRE, CFRE, & AFRE are Glass,
Carbon, & Aramid Fiber-Reinforced
Epoxy composites (values based on
60% volume fraction of aligned fibers
in an epoxy matrix).10
3
4
5
0.3
0.4
0.5
Magnesium
Aluminum
Steels
Titanium
Cu,Ni
Tin, Zinc
Silver, Mo
Tantalum
Gold, W
Platinum
Graphite
Silicon
Glass -soda
Concrete
Si nitride
Diamond
Al oxide
Zirconia
HDPE, PS
PP, LDPE
PC
PTFE
PET
PVC
Silicone
Wood
AFRE*
CFRE *
GFRE*
Glass fibers
Carbon fibers
Aramid fibers

16. Covalent Structures: Diamond
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17. Silicates
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Composed primarily of
silicon and oxygen
Crystalline: Crystobalite Amorphous: Sodium Silicate Glass

18. The End
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