Chapter 5 - Imperfections in Solids Point Defects Metals Ceramics Impurities Composition...

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Chapter 5 - Imperfections in Solids

• Point DefectsMetalsCeramics

• 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 vice-versa

Introduction

• Solids are never _______________________________.

• Many properties are ____________________________.

• Often the imperfections are _______________________ _________.

• A defect is defined as anything that _________________ _______________ of the solid.

Defects are usually classified by their dimensionality

• __________________ (vacancies, interstitialcies, impurities, etc)

• __________________ (dislocations)

• __________________ (surfaces, grain boundary, phase boundaries, etc)

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

Figure 5.1

• 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

Point Defects (cont.)

___________ - ___________________________________

• could be a ________________, but not common due to the stress involved

(This topic will return in the impurity section)

Point Defects in Ceramics

• Both vacancies and interstitialcies are possible. Anion interstitialcies are rare.

• _________________ must be maintained

_____________________________

Point Defects in Ceramics (cont.)

Figure 5.2

• Ceramic point defects can categorized based on the _______________________________

___________ ______ - the species ______ given by the ______________ is

maintained with the defects

_____________________ - a deviation from the formula ratio is

needed to ________________

ex. - if (2) Fe+3 replace (2) Fe+2 another Fe+2 must be removed

Figure 5.4

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

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")

Impurities in Solids (cont)

Definitions (cont)

• _____ - a _______________________ of a material with ____________________________________

• _____________ - two or more elements ____________ _______________________________________________________________________________________________________________________

There are 2 types of solid solutions - ______________ ___________

Impurities in Solids (cont.)

Figure 5.5

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%

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 )

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)

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 __________________________________________

• Impurities in Ceramics (cont.)

• Example Problem 5.2

Assume a Ca+2 substitutes for an Na+1 in an NaCl structure

Possible second changes:

• _________________________________

Composition Conversion

• I don’t like the presentation in the book. This is more general.

_____________________________________________________________________________________

• Procedure

choose a basis of what you know

use the atomic weight to change to the desired basis

calculate percentages in new basis

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

20 mole Cu * 63.5 g/mole = 1270 g Cu30 mole Sn * 118.7 g/mole = 3561 g Sn50 mole Pb * 207.2 g/mole = 10360 g Pb

15191 g total

1270 / 15191 = 0.084 g Cu / g tot or 8.4 wt % Cu3561 / 15191 = 0.234 g Sn / g tot or 23.4 wt % Sn10360 / 15191 = 0.682 g Pb / g tot or 68.2 wt % Pb

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

10 g H / 1.008 g/mole = 9.92 mole H30 g N / 14 g/mole = 2.14 mole N60 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

Linear Defects - (aka Dislocations)

• A _________________ defect around which the ________ ______________ .

• There are two types of dislocations, plus combinations

________________ ________________

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.

Edge dislocation (cont.)

Figure 5.7

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

Figure 5.8Screw dislocation

Mixed Dislocation

• Often dislocations show features of both

Figure 5.9

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.

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

Figure 5.11

Tilt Boundaries

• ________________ can _______ themselves.

• This extends the defect into a second dimension.

Figure 5.12

Twin Boundaries

• A __________ lattice symmetry

• Occurs along specific crystal planes.

Figure 5.13

Miscellaneous interfacial defects

• _______ faults from a break in the _______ pattern in FCC crystals or __________ pattern in HCP crystals

• Phase boundaries (see Chapter 10)

Chapter 5 - Imperfections in Solids Point Defects Metals Ceramics Impurities Composition...

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