Chapter 10 Ceramics 2022-R's MacBook Air
Chapter 10 Ceramics 2022-R's MacBook Air
Chapter 10 Ceramics 2022-R's MacBook Air
Chapter 10
Ceramic Materials
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WHY STUDY Structures and Properties of Ceramics?
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Learning objectives
After this lesson you should be able to do the following:
1. Sketch/describe unit cells for sodium chloride, cesium chloride, zinc blende, diamond cubic, fluorite, and
perovskite crystal structures. Do likewise for the atomic structures of graphite and a silica glass.
2. Given the chemical formula for a ceramic compound, calculate the ionic radii of its component ions,
3. Predict the crystal structure. How
many
4. Calculate the theoretical density of a compound given that it has a crystal structure.
5. Name and describe two different ionic point defects that are found in ceramic compounds.
6. Briefly explain why there is normally significant scatter in the fracture strength for identical specimens of
the same ceramic material.
7. Compute the flexural strength of ceramic rod specimens that have been bent to fracture in three-point
loading.
8. On the basis of slip considerations, explain why crystalline ceramic materials are normally brittle.
Totiperient t.ie's ñi
brittleness How it made
ductile Suhar
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electronegativity
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 4
Cornell University.
Ionic Bonding & Structure
1. Size - Stable structures:
--maximize the # of nearest oppositely charged neighbors.
- - - - - -
+ + +
Adapted from Fig. 12.1,
Callister 7e.
- - - - - -
unstable stable stable
• Charge Neutrality:
--Net charge in the F-
structure should CaF 2 : Ca 2+ +
cation anions
be zero.
F-
--General form: A m Xp
m, p determined by charge neutrality 5
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Coordination # and Ionic Radii mayhem
r cation
• Coordination # increases with r
anion
Zinc
r cation ZnS
r anion
Coord struiture (zincblende)
#
Adapted from Fig.
< 0.155 2 linear 12.4, Callister 7e.
IF
Adapted from Fig.
12.2, Callister 7e.
rCl = 0.181 nm
rNa/rCl = 0.564
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AX Crystal Structures
AX–Type Crystal Structures include NaCl, CsCl, and zinc blende
rCs 0.170
0.939
rCl 0.181
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Ceramic Density Computation
Number of formula units/unit cell
n(AC AA )
VC N A
mass / unitcell
volume / unitcell
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Example 1
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Silicate Ceramics
Most common elements on earth are Si & O
Si4+
O2-
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Silicate Ceramics
Silica Glass
Noncrystalline solid, having a high degree of atomic
randomness
Eg: Containers, Windows
Silica glass added with other Oxides such as CaO and Na2O
Cations are incorporated within and modify the SiO44-
Borosilicate glass is the pyrex glass used in labs
better temperature stability & less brittle than
sodium glass
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Silicate Ceramics
The Silicates-simple silicates
Combine SiO44- tetrahedra by having them share
corners, edges, or faces
Al2 (Si2O5)(OH)4
brittle
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Carbon Forms - Graphite
layer structure – aromatic layers
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Impurities
• Impurities must also satisfy charge balance = Electroneutrality
• Ex: NaCl Na + Cl -
cation
• Substitutional cation impurity vacancy
Ca 2+
Na +
Na +
Ca 2+
initial geometry Ca 2+ impurity resulting geometry
Cl - Cl -
initial geometry O2- impurity resulting geometry 22
Ceramic Phase Diagrams
MgO-Al2O3 diagram:
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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
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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.
cross section F
L/2 L/2 Adapted from Fig. 12.32,
Callister 7e.
d R
b d = midpoint
rect. circ.
deflection
• Determine elastic modulus according to:
F F L3 F L3
x E= =
F d 4bd 3 d 12 p R4
slope =
d rect. circ.
cross cross
d section section
linear-elastic behavior 25
Measuring Strength
• 3-point bend test to measure room T strength.
cross section F
L/2 L/2 Adapted from Fig. 12.32,
Callister 7e.
d R
b d = midpoint
rect. circ.
deflection
location of max tension
d 26
dfs
Measuring Strength
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Application-Classification of Ceramics
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Group activities
Tape Casting
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Group activities
1. Describe the process that is used to produce glass–ceramics.
2. Name the two types of clay products, and then give two examples of each.
4. Name and briefly describe four forming methods that are used to fabricate
glass pieces.
6. Briefly describe and explain the procedure by which glass pieces are
thermally tempered.
7. Briefly describe processes that occur during the drying and firing of clay-
based ceramic ware.
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