Ms115a principles of materials science fall 2012
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MS115a Principles of Materials Science Fall 2012. Instructor: Prof. Sossina M. Haile 307 Steele Laboratories, x2958, [email protected] http://addis.caltech.edu/teaching/MS115a/MS115a.html Class Meetings: MWF 11am-noon; 080 Moore; to 12:30pm?? Teaching Assistant:

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Ms115a principles of materials science fall 2012
MS115a Principles of Materials ScienceFall 2012

  • Instructor:

    • Prof. Sossina M. Haile

    • 307 Steele Laboratories, x2958, [email protected]

  • http://addis.caltech.edu/teaching/MS115a/MS115a.html

  • Class Meetings: MWF 11am-noon; 080 Moore; to 12:30pm??

  • Teaching Assistant:

    • Alex Zevalkink, 317 Steele, x4804, [email protected]

  • TA Office Hours: TBA (likely Tuesdays)

  • All recommended and reference texts on reserve in SFL

  • Recommended:

    • “Understanding Solids,” Tilley; “Intro to Mat Sci for Engineers,” Shackelford

  • Additional references:

    • “The Principles of Engineering Materials,” Barrett, Nix & Tetelman

    • “Phase Transformations in Metals and Alloys,” Porter & Easterling

    • “Quantum Chemistry,” Levine


What is materials science

Chemistry / Composition

Processing

+

Structure

Properties / Performance

What is Materials Science?

?

?

kinetics

thermodynamics

(MS 115b)

MS 115a


Course content
Course Content

  • Introduction to Materials Science

    • Chemistry + Processing  Structure  Properties

  • Structure

    • Review: Structure of the Atom & Chemical Bonding

    • Crystalline Structure

    • Structural Characterization (X-ray diffraction)

    • Amorphous Structure

    • Microstructure

  • Defects in Crystalline Solids, Connections to Properties

    • Point Defects (0-D) and Diffusion & Ionic Conductivity

    • Dislocations (1-D) and Mechanical Deformation

    • Surfaces and interfaces (2-D)

    • Volume Defects (3-D) and Fracture


Course content1
Course Content

  • Electrons in Solids

    • Chemical Bonding, Revisited

    • Band Structure

    • Electronic Conductivity: Metals vs. Insulators

  • Thermodynamics

    • 1st and 2nd Laws

    • Gibb’s Free Energy

    • Phase Diagrams

  • Some Other Properties Along the Way

    • Thermal: Thermal Expansion, Heat Capacity, Thermal Conductivity

    • Optical: Refraction, Reflection; Absorption, Transmission, Scattering, Color

  • Conceptual vs. Highly Mathematical


Course structure
Course Structure

  • Homework: weekly 50%

    • Assigned Wednesdays

    • Due following Wednesday, 5pm

    • Place in course mailbox, 3rd floor Steele

  • Midterm HW: Oct 31 - Nov 6 15%

    • Solo homework

  • Final: Dec 12 - 14 35%

    • Take home


Hw collaboration policy
HW Collaboration Policy

  • Students are encouraged to discuss and work on problems together.

    • During discussion, you may make/take notes

    • However, do not bring and/or exchange written solutions or attempted solutions you generated prior to the discussion.

    • If you’ve worked the problem out and you plan to help a friend, you should know the solution cold.

  • Do not consult old problem sets, exams or their solutions.

  • Solutions will be handed out on Friday, or possibly Monday. Assignments turned in late, but before solutions are available, will receive 2/3 credit. Assignments will not be accepted after solutions are handed out.


Midterm homework
Midterm Homework

  • In lieu of a midterm exam there will be homework to be performed on an individual basis. This homework must be completed without collaborative discussion.

  • The problem set will focus primarily on recent lectures, but material from early topics may also be included.

  • Similar to other homeworks, you will have one week to complete the assignment.

  • You are permitted to utilize all available resources, with the exception of previous solutions; this exception includes solutions from earlier in the year.


Structure of the atom
Structure of the Atom

  • “Electron in a box” – use quantum mechanics to solve electron wave functions

    • Electron quantum numbers: describe orbitals

    • Electrical properties

  • Qualitative description of chemical bonding

    • Electrons ‘orbit’ atomic nucleus

Chemical notation

K

L

1

M

2

K-shell: n = 1

 l = 0

 1s

 m = 0

s = ± ½

3

 2s, 2p

L-shell: n = 2

 l = {0, 1}

 px. py. pz

m = 0

m = {-1, 0, 1}


Structure of the atom1
Structure of the Atom

  • Electrons occupy these orbitals

  • Pauli exclusion principle

    • Only one electron with a given set of QNs

    • For a multi-electron atom, fill up orbitals beginning with lowest energy & go up

  • Order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s,..


Chemical bonding
Chemical Bonding

  • Atoms  Molecules  Solids

  • Bonds form so as to produce filled outer shells

  • Some atoms are a few electrons short

    • Electronegative: readily pick up a few electrons from other atoms, become negatively charged

  • Some atoms have a few electrons too many

    • Electropositive: readily give up a few electrons to other atoms, become positively charged

  • Noble gases: filled outer shell, limited chemistry



Types of chemical bonds

+

-

+

-

+

-

+

-

+

+

+

+

e-

e-

+

+

+

e-

+

+

+

Types of Chemical Bonds

  • Primary

    • Ionic

      • Electronegative/Electropositive

    • Metallic

      • Electropositive – give up electrons

    • Colavent

      • Electronegative – want electrons

      • Shared electrons along bond direction

  • Secondary

    • Fluctuating/instantaneous dipoles

    • Permanent dipoles (H-bonds)

Isotropic, filled outer shells


Chemical bonding1
Chemical Bonding

  • Covalent – between electronegative elements

  • Metallic – between electropositive elements

  • Ionic – between different elements with differing electronegativities

  • Clear distinction between metallic & non-metallic

  • Ionic & covalent – somewhat qualitative boundary

  • ‘% ionic chararacter”: 1 – exp( -¼ (xA – xB)2)

    • xA, xB = electronegativities

  • Some properties from “bond-energy” curve


Some properties
Some Properties

The bond energy curve

short range repulsion

E = ER + EA

E

R0

R (interatomic distance)

E0

long range attraction

R0 : interatomic distance that minimizes E

is the equilibrium bond distance

E0 : decrease in energy due to bond formationthis much energy is required to break the bond define as bond energy sets the melting temperature


More properties
More Properties

Heat the material

E = ER + EA

E

R (interatomic distance)

R0 as T 

T 

Ethermal = kbT

Asymmetry in E(R) sets thermal expansion coefficient


Some mechanical properties
Some Mechanical Properties

E

R (interatomic distance)

R0

E0

F = dE/dR

The bond force curve

Elastic constants relate stress to strain

Stress – related to force

Strain – related to displacement

at R0 no net force (equilibrium bond distance)

attractive

F = kDx

F

k

stress*area

strain*length

R0

stress k strain

R (interatomic distance)

repulsive

Elastic constants given by slope of B.F. curve at R0

given by curvature of B.E. curve at R0


Covalent bonds
Covalent Bonds

  • Locally well-defined orbitals

  • Elements with electrons up to 2p or 3p states

    • Filled outer shell  octet rule (s + p  8 states)

    • Rule: 8 – N bondingelectrons = n bonds

  • Example: carbon (C)

    • 6 electrons total: 1s22s22p2

    • 2s22p2N = 4 n = 4

how can carbon atoms fill px, py and pz orbitals if the other element is also electronegative?

bonds

bonding electrons

s orbital

p orbitals

  • solution: sp2 or sp3 hybrization

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/orbitals.gif


Hybridized bonds

diamond

Hybridized Bonds

  • Elemental carbon (no other elements)

sp3 hybridization

also methane: CH4

one s + three p orbitals  4 (x 2) electron states

(resulting orbital is a combination)


Summary
Summary

  • Nature of the bonds formed depends on the chemical nature of the elements (as given by placement on the periodic table)

  • Bond energy / bond force curve gives

    • Equilibrium bond distance

    • Melt temperature

    • Thermal expansion coefficient

    • Elastic constants

  • In general, there is not a direct correlation between type of bond and value of properties


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