Chapter 5 - Imperfections in Solids
• Point Defects
ƒMetals
ƒCeramics
•
Impurities
• Composition Calculations
•
Dislocations
•
Interfacial Defects
Chapter 5 (continued)
Qualitative Questions
23 Describe the different kinds of point defects that exist in
solids. Include the specific differences that exist in
ceramic crystal structures.
24 Define the term solution. Describe the two kinds of solid
solutions and the kinds of atoms that are involved in each.
25 Describe edge and screw dislocations. Include the
appearance of the dislocation and the orientation of the
distortion relative to the dislocation.
Quantitative Questions
6 Be able to convert atomic percent to weight percent and viceversa
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Chapter 5 (continued)
Introduction
• Solids are never _______________________________.
• Many properties are ____________________________.
• Often the imperfections are _______________________
_________.
• A defect is defined as anything that _________________
_______________ of the solid.
Chapter 5 (continued)
Defects are usually classified by their dimensionality
• __________________ (vacancies, interstitialcies,
impurities, etc)
• __________________
(dislocations)
• __________________ (surfaces, grain boundary, phase
boundaries, etc)
2
Chapter 5 (continued)
Point Defects
There are several types of point defects
___________
definition - a ________________
• rarely more than _____________ atoms missing
• there is a tendency for vacancies to cluster
• vacancies can move
This is caused by atomic movement
Chapter 5 (continued)
Figure 5.1
3
Chapter 5 (continued)
• The concentration of vacancies ( #/volume) is a function of
temperature
where
Nv = the number of vacancies / volume
N = the total number of atomic sites
Qv = the energy required to form a vacancy
k = the Boltzmann constant
= 1.38x10-23 J/(atom K)
T = the absolute temperature
Chapter 5 (continued)
Point Defects
(cont.)
___________ - ___________________________________
• could be a ________________, but not common due to the
stress involved
(This topic will return in the impurity section)
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Chapter 5 (continued)
Point Defects in Ceramics
• Both vacancies and interstitialcies are possible. Anion
interstitialcies are rare.
• _________________ must be maintained
ƒ _____________________________
ƒ _____________________________
Chapter 5 (continued)
Point Defects in Ceramics
(cont.)
Figure 5.2
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Chapter 5 (continued)
Point Defects in Ceramics
(cont.)
• Ceramic point defects can categorized based on the
_______________________________
ƒ ___________ ______ - the species ______ given by
the
______________ is maintained
with the defects
ƒ _____________________ - a deviation from the
formula ratio is needed to
________________
Chapter 5 (continued)
Point Defects in Ceramics
(cont.)
ex. - if (2) Fe+3 replace (2) Fe+2 another Fe+2 must be
removed
Figure 5.4
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Chapter 5 (continued)
Impurities in Solids
• There are always _____________ in any metallic crystal
• These can show up as point defects
• Most familiar metals are ________. The impurity atoms are
added ______________.
• This ______________________. For example, improved
mechanical strength and corrosion resistance
Chapter 5 (continued)
Impurities in Solids
(cont)
• Alloys can have two _________________________
(multiphase), or be a ______________________.
Definitions
• ______ - the element or compound present in the
____________ (the base lattice structure)
• ______ - the element or compound present in the
__________ amount (the "impurity")
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Chapter 5 (continued)
Impurities in Solids
Definitions
(cont)
(cont)
• _____ - a _______________________ of a material with
____________________________________
• _____________ - two or more elements ____________
_____________________________
__________________________________________________________________________________________
ƒ There are 2 types of solid solutions - ______________
___________
Chapter 5 (continued)
Impurities in Solids (cont.)
Figure 5.5
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Chapter 5 (continued)
Substitutional Solid Solution
• solute atoms ___________ for solvent atoms in the lattice
• The solvent crystal structure is ______________________
• The fraction of substitution can range from 0 to 100%
Chapter 5 (continued)
Substitutional Solid Solution
(cont.)
For ________________________.
(In order of importance)
• ______________ must not differ by more than 15%
• __________________________ must be the same
• small difference in ___________________
• ____________. More solubility of solute if it has a higher
valence than the solvent
( see front cover for copper / nickel )
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Chapter 5 (continued)
Interstitial Solid Solutions
• The solute atoms ________________________ (spaces) in
the lattice
• Occurs when one atom is much larger than the other
( typically occurs with ____________ )
• Even small atoms (except for H) are ________________
______________ .
• Therefore, the ___________________________ (< 10%)
(ex. - about 2% for C in Fe)
Chapter 5 (continued)
Impurities in Ceramics
• Either substitutional or interstitial impurities are possible
• Remember _______________. All interstitial impurities
and some substitution impurities require a ____________.
Substitutions of the same charge do not require another
change.
• If not another change must be made, it could be a
__________________________________________
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Chapter 5 (continued)
• Impurities in Ceramics
(cont.)
• Example Problem 5.2
Assume a Ca+2 substitutes for an Na+1 in an NaCl structure
Possible second changes:
• _________________________________
• _________________________________
• _________________________________
Chapter 5 (continued)
Composition Conversion
• I don’t like the presentation in the book. This is more
general.
_____________________________________________________________________________________
• Procedure
ƒ choose a basis of what you know
ƒ use the atomic weight to change to the desired basis
ƒ calculate percentages in new basis
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Chapter 5 (continued)
Composition Conversion
(cont.)
example - mole percent to weight percent
An alloy consists of 20 mole % Cu, 30 mole % Sn and
50 mole % Pb. What is the composition on a weight
percent basis?
• assume 100 moles total
• convert to mass units
• calculate weight percents
Chapter 5 (continued)
Composition Conversion
(cont.)
20 mole Cu * 63.5 g/mole = 1270 g Cu
30 mole Sn * 118.7 g/mole = 3561 g Sn
50 mole Pb * 207.2 g/mole = 10360 g Pb
15191 g total
1270 / 15191 = 0.084 g Cu / g tot or 8.4 wt % Cu
3561 / 15191 = 0.234 g Sn / g tot or 23.4 wt % Sn
10360 / 15191 = 0.682 g Pb / g tot or 68.2 wt % Pb
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Chapter 5 (continued)
Composition Conversion
(cont.)
example - weight percent to mole percent
A mixture consists of 10 wt % hydrogen (H),
30 wt % nitrogen (N), and 60 wt % chlorine (Cl).
What is the composition on a mole percent basis?
• assume 100 grams total
• convert to mole units
• calculate mole percents
Chapter 5 (continued)
Composition Conversion
(cont.)
10 g H / 1.008 g/mole = 9.92 mole H
30 g N / 14 g/mole
= 2.14 mole N
60 g Cl / 35.4 g/mole = 1.69 mole Cl
13.75 mole total
9.92 / 13.75 = 0.721 mol H / mol tot or 72.1 mol % H
2.14 / 13.75 = 0.156 mol N / mol tot or 15.6 mol % N
1.69 / 13.75 = 0.123 mol Cl / mol tot or 12.3 mol % Cl
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Chapter 5 (continued)
Linear Defects - (aka Dislocations)
• A _________________ defect around which the ________
______________ .
• There are two types of dislocations, plus combinations
ƒ ________________
ƒ ________________
Chapter 5 (continued)
Linear Defects
(cont.)
Edge dislocation
• A _______________ which terminates within the crystal.
• There is _______________________________________.
Compression on one side, tension on the other.
• The distortion is _______________ to the dislocation line.
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Chapter 5 (continued)
Edge dislocation (cont.)
Figure 5.7
Chapter 5 (continued)
Linear Defects
(cont.)
Screw dislocation
• Caused by a ______________. A portion of the crystal is
shifted by one atom.
• Looks like a _____________.
• The distortion is ___________ to the dislocation line
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Chapter 5 (continued)
Figure 5.8
Screw dislocation
Chapter 5 (continued)
Linear Defects
(cont.)
Mixed Dislocation
• Often dislocations
show features of
both
Figure 5.9
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Chapter 5 (continued)
Interfacial Defects
• ________________defects.
• Anything that deviates from perfect crystal packing
_____________________________________________
External surfaces
• The external atoms are not surrounded by all possible
nearest neighbors, therefore they are at a higher energy.
Chapter 5 (continued)
Interfacial Defects
(cont)
Grain boundaries
• There is an ________________ where the grains meet
• These can be low angle or high angle
• The atoms are less tightly packed, __________________
___________________ .
• Grain boundaries are more chemically reactive
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Chapter 5 (continued)
Interfacial Defects
(cont)
Figure 5.11
Chapter 5 (continued)
Interfacial Defects
(cont)
Tilt Boundaries
• ________________ can
_______ themselves.
• This extends the defect
into a second dimension.
Figure 5.12
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Chapter 5 (continued)
Interfacial Defects
(cont)
Twin Boundaries
• A __________ lattice
symmetry
• Occurs along specific
crystal planes.
Figure 5.13
Chapter 5 (continued)
Interfacial Defects
(cont)
Miscellaneous interfacial defects
• _______ faults from a break in the _______ pattern in FCC
crystals or __________ pattern in HCP crystals
• Phase boundaries
(see Chapter 10)
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