MSE 170: Introduction to Materials Science and Engineering...Atomic structure and interatomic...
Transcript of MSE 170: Introduction to Materials Science and Engineering...Atomic structure and interatomic...
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MSE 170: Introduction to Materials Science and Engineering
Instructor Prof. Christine Luscombe
Email [email protected]
Office 302B Roberts Hall
Office hours 10:00am – 12:00pm, Monday, or by appointment Course website http://courses.washington.edu/mse170
Lab TAs:Peter Kazarinoff [email protected] Mueller 168
Omid Veiseh [email protected] Mueller 168 M 1:30-2:30pm
Steven Hau [email protected] Mueller 168 T 10:30-11:30am
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What is Materials Science and Engineering?
An interdisciplinary field thataddresses the fundamentalrelationships between theProcessing, Structure and Propertiesof materials and develops them forthe desired technological application(Performance).
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Materials through the ages
Stone Age (beginning of life – 3000 BC)
Feature: Using naturally occurring materials with only changes in shape
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Materials through the ages
Bronze Age (3000 BC – 1200 BC)Copper and Tin alloy
Ability to modify materials byrefining (using heat), chemicalmodifications (alloying) andmechanical deformation (coldworking)
Imperfection (Ch. 4)Diffusion (Ch. 5)Phase diagram (Ch. 9)Metal Processing (Ch. 11)
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Materials through the ages
Iron Age (1200 BC – Present)
Casting and alloying wasn’t perfected until16th century
Mastery of Steel (Iron alloy) technologyenables Industrial Revolution in the 18th
and 19th century
Ability to heat treat at high temperature, controlmicrostructure at different length scale and abilityto design specific microstructures for specificproperties
Phase transformation (Ch. 10)
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Materials through the ages
Plastic Age (1940 - Present)Discovery of polymers, and the ability tosynthesize and process polymers.
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Materials through the ages
Silicon Age (1950 - Present)Commercialization of silicon technology(integrated circuits, electronic devices, etc…)leads to the information age, which givesboost to human productivity
Ability to control alloying accurately,ability to make thin films
Electronic Prop. (Ch.18)Thermal Prop. (Ch.19)Magnetic Prop. (Ch.20)Optical Prop. (Ch.21)
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Future
1. Nanotechnology- Synthesis and characterizations of nanomaterials and nanostructure
2. Biotechnology- biomimetics and biomaterials
3. Energy/Environmental- Next generation energy conversion
4. Information Technology- Materials informatics
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What is Materials Science and Engineering?
An interdisciplinary field thataddresses the fundamentalrelationships between theProcessing, Structure and Propertiesof materials and develops them forthe desired technological application(Performance).
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Two Forms of Carbon
GraphiteDiamond
• A structure of carbon only produced at high temperature andpressure.
• The hardest known material.
• A structure of carbon that is inequilibrium (it is stable and will notchange form over time).
• It is soft.
Atomic structure and interatomic bonding (Ch.2) Crystallography (Ch. 3), Imperfection (Ch. 4)
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CeramicsCh. 12
PolymersCh.14 and 15
MetalsCh. 11
Materials
CompositeCh. 16
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Atomic structure
Quarks GluonsNeutronNucleus
ElectronProtons
orbital electrons:n = principalquantum number
n=3 2 1
BOHR ATOM
Nucleus: Z =
= 1 for hydrogen to 94 for plutonium
Atomic mass A ≈
# protons
N = # neutronsZ + N
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Electronic structure
Valence electrons determine all of the following properties:
Electrons have wavelike and particulate properties.• This means that electrons are in orbitals defined by a probability.• Each orbital at discrete energy level determined by quantum numbers.
Quantum # Designation
• Chemical• Electrical • Thermal• Optical
n = principal (energy level-shell) K, L, M, N, O (1, 2, 3, etc.)
l = subsidiary (orbitals) s, p, d, f (0, 1, 2, 3,…, n -1)
ml = magnetic 1, 3, 5, 7 (-l to +l)
ms = spin ½, -½
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Electronic structure
147f
105d
63p
3221sN4
105d
63p
1821sM3
63p
821sL2
221sK1
Per shellPer subshell
Number of electronsNo. ofstatesSubshellsShell
designationPrincipal
quantum no.
1 2 3 4 5s
sp
sp
d sp
d
f
sp
d
f
g
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Electron energy states
1s
2s2p
K-shell n = 1
L-shell n = 2
3s3p M-shell n = 3
3d
4s
4p4d
Energy
N-shell n = 4
• have discrete energy states• tend to occupy lowest available energy state.
Electrons...
Adapted from Fig. 2.4,Callister 7e.
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Electronic configuration
ex: Fe - atomic # = 26
Adapted from Fig. 2.4,Callister 7e.
1s
2s2p
K-shell n = 1
L-shell n = 2
3s3p M-shell n = 3
3d
4s
4p4d
Energy
N-shell n = 4
1s2 2s2 2p6 3s2 3p6 3d 6 4s2
valence electrons
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Survey of elements
• Why? Valence (outer) shell usually not filled completely.
• Most elements: Electron configuration not stable.
Electron configuration
(stable)
...
...
1s 2 2s 2 2p 6 3s 2 3p 6 (stable)...
1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable)
Atomic #
18...
36
Element1s 1 1Hydrogen1s 22Helium1s 2 2s 1 3Lithium1s 2 2s 24Beryllium1s 2 2s 2 2p 15Boron1s 2 2s 2 2p 26Carbon
...
1s 2 2s 2 2p 6 (stable)10Neon1s 2 2s 2 2p 6 3s 111Sodium1s 2 2s 2 2p 6 3s 2 12Magnesium1s 2 2s 2 2p 6 3s 2 3p 113Aluminum
...
Argon...
Krypton
Adapted from Table 2.2,Callister 7e.
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The periodic table
• Columns: Similar Valence Structure
Adapted from Fig.2.6, Callister 7e.
Electropositive elements:Readily give up electronsto become + ions.
Electronegative elements:Readily acquire electronsto become - ions.
give
up
1e
give
up
2e
give
up
3e
iner
t gas
es
acce
pt 1
e
acce
pt 2
e
O
Se
Te
Po At
I
Br
He
Ne
Ar
Kr
Xe
Rn
F
ClS
Li Be
H
Na Mg
BaCs
RaFr
CaK Sc
SrRb Y
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Electronegativity
• Ranges from 0.7 to 4.0,
Smaller electronegativity Larger electronegativity
• Large values: tendency to acquire electrons.
Adapted from Fig. 2.7, Callister 7e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the ChemicalBond, 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell University.
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Bonding forces and energies
r• Attractive force, FA
• Repulsive force, FR
Forc
e F
Rep
ulsi
onA
ttrac
tion
0
+
-
Attractive force, FA
Interatomic separation r
Repulsive force, FR
Net force, FN
!
E = Fdr"
!
EN
= FNdr
"
r
# = FAdr
"
r
# + FRdr
"
r
#
!
= EA
+ER
Attractive energy EA
Net energyEN
Repulsive energy ER
Interatomic separation r
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Properties from bonding
• Bond length, r
• Bond energy, Eo
• Melting Temperature, Tm
Tm is larger if Eo is larger.
ro r
Energy
r
larger Tm
smaller Tm
Eo =
“bond energy”
Energy
ro
r
unstretched length
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Properties from bonding: thermal expansion coefficient
• Coefficient of thermal expansion, α
• α ~ symmetry at ro
α is larger if Eo is smaller.
= α ( T2
- T1
)Δ L
L o
coeff. thermal expansion
Δ L
length, L o
unheated, T1
heated, T2
ro
r
larger α
smaller α
Energy
unstretched length
Eo
Eo
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Properties from bonding: modulus E
Forc
e F
Rep
ulsi
onA
ttrac
tion
0
+
F = kxr
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Types of bonding: ionic
• Occurs between + and - ions.
• Requires electron transfer.
• Large difference in electronegativity required.
• Example: NaCl
Na (metal)
unstable
Cl (nonmetal)
unstable
+ -
Coulombic
Attraction
Na (cation)
stable
Cl (anion)
stable
electron
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Examples of ionic bonding
• Predominant bonding in Ceramics
Adapted from Fig. 2.7, Callister 7e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the ChemicalBond, 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell University.
Give up electrons Acquire electrons
NaCl
MgO
CaF2
CsCl
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Covalent bonding
C: has 4 valence e-, needs 4 more
H: has 1 valence e-, needs 1 more
Electronegativities are comparable.
Adapted from Fig. 2.10, Callister 7e.
•similar electronegativity ∴ share electrons•bonds determined by valence – s & p orbitals dominate bonding
•Example: CH4
shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
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Metallic bonding
•Ions in a sea of electrons•Attraction between free electrons and metal ions
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Ionic-covalent mixed bonding
% ionic character =
where XA & XB are Pauling electronegativities
%)100( x
!
1"e"
(XA"XB)2
4
#
$
% % %
&
'
( ( (
ionic 70.2% (100%) x e1 characterionic % 4
)3.15.3(
2
=!!!
"
#
$$$
%
&
'=
''
Example: MgO XMg = 1.3XO = 3.5
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Secondary bonding
Arises from interaction between dipoles
• Permanent dipoles-molecule induced
• Fluctuating dipoles
-general case:
-example: liquid HCl
-example: polymer
Adapted from Fig. 2.13, Callister 7e.
Adapted from Fig. 2.14, Callister 7e.
asymmetric electron
clouds
+ - + -
secondary bonding
HH HH
H2 H2
secondary bonding
example: liquid H2
H Cl H Clsecondary
bonding
secondary bonding
+ - + -
secondary bondingsecondary bonding
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Summary
DirectionalInterchain (polymer)Intermolecular
SmallestSecondary
Non-directional (metals)VariableTungsten (large)Mercury (small)
Metallic
Directional(semiconductors, ceramics,polymer chains)
VariableDiamond (large)Bismuth (small)
Covalent
Non-directional (ceramics)Large!Ionic
CommentsBond EnergyType
Directional properties,Secondary bondingdominatesSmall Tm and E, large α
Polymers(Covalent & secondary)
Variable bond energyModerate Tm, E, and α
Metals(Metallic bonding)
Large bond energyLarge Tm and E, small α
Ceramics(Ionic & covalent bonding)
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Energy and packing
• Non dense, random packing
• Dense, ordered packing
Dense, ordered packed structures tend to have lower energies.
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
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Materials and packing
• atoms pack in periodic, 3D arraysCrystalline materials...
-metals-many ceramics-some polymers
• atoms have no periodic packingNoncrystalline materials...
-complex structures-rapid cooling
crystalline SiO2
noncrystalline SiO2"Amorphous" = NoncrystallineAdapted from Fig. 3.22(b), Callister 7e.
Adapted from Fig. 3.22(a), Callister 7e.
Si Oxygen
• typical of:
• occurs for:
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Crystals
7 crystal systems
14 crystal lattices
Fig. 3.4, Callister 7e.
Unit cell:
a, b, and c are the lattice constants
Lattice points: 3D array of points whichcoincides with atom positions.
smallest repetitive volume which contains the complete lattice pattern of acrystal.
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Simple cubic structure (SC)
• Rare due to low packing density (only Po has this structure)• Close-packed directions are cube edges.
• Coordination # = 6 (# nearest neighbors)
(Courtesy P.M. Anderson)
1 atoms/unit cell: 8 corners x 1/8
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Face centered cubic structure (FCC)
• Coordination # = 12
Adapted from Fig. 3.1, Callister 7e.
(Courtesy P.M. Anderson)
• Atoms touch each other along face diagonals.--Note: All atoms are identical; the face-centered atoms are shaded differently only for ease of viewing.
ex: Al, Cu, Au, Pb, Ni, Pt, Ag
4 atoms/unit cell: 6 face x 1/2 + 8 corners x 1/8
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Atomic packing factor (APF): FCC
• APF for a FCC structure = 0.74Maximum achievable APF
APF =
a 3
4
3π R
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atomsunit cell
atomvolume
unit cellvolume
APF = Volume of atoms in unit cell*
Volume of unit cell
*assume hard spheres
close-packed directions
contains 6 x 1/2 + 8 x 1/8 = 4 atoms/unit cell
a
2 a
Adapted fromFig. 3.1(a),Callister 7e.
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Theoretical density, ρ
where n = number of atoms/unit cell A = atomic weight VC = Volume of unit cell = a3 for cubic NA = Avogadro’s number = 6.023 x 1023 atoms/mol
VC NA
n Aρ =
Density = ρ =Total volume of unit cell
Mass of atoms in unit cell
Ex: Cu (FCC)A = 63.54 g/molR = 0.128 nm
n = 4
a = 2R 2
ρ = a 3
63.544atoms
unit cellmol
g
unit cellvolume atoms
mol
6.023 x 1023
ρtheoretical
ρactual
= 8.9 g/cm3
= 8.94 g/cm3
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Body centered cubic structure (BCC)
• Coordination # = 8
Adapted from Fig. 3.2, Callister 7e.
(Courtesy P.M. Anderson)
• Atoms touch each other along cube diagonals.--Note: All atoms are identical; the center atom is shaded differently only for ease of viewing.
ex: Cr, W, Fe (α), Tantalum, Molybdenum
2 atoms/unit cell: 1 center + 8 corners x 1/8
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Atomic packing factor (APF): BCC
• APF for a FCC structure = 0.68
APF =
a 3
4
3π (√ 3a/4)
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atomsunit cell
atomvolume
unit cellvolume
aR
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FCC stacking sequence
A sites
B B
B
BB
B B
C sites
C C
CA
B
B sites
• ABCABC... Stacking Sequence• 2D Projection
• FCC Unit Cell
B B
B
BB
B B
B sitesC C
CA
C C
CA
AB
C
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Hexagonal close-packed structure (hcp)
• Coordination # = 12
• ABAB... Stacking Sequence
• APF = 0.74
• 3D Projection • 2D Projection
Adapted from Fig. 3.3(a),
Callister 7e. 6 atoms/unit cell
ex: Cd, Mg, Ti, Zn
• c/a = 1.633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer