ms115a principles of materials science fall 2010 instructor: –prof. sossina m. haile –307 steele...
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MS115a Principles of Materials ScienceFall 2010
• Instructor: – Prof. Sossina M. Haile
– 307 Steele Laboratories, x2958, [email protected]
• http://addis.caltech.edu/teaching/MS115a/MS115a.html• Class Meetings:MWF 9-10am, 214 Steele• Teaching Assistants:
– Nick Heinz, 303 Steele, x1711, [email protected]– Balaji Gopal (BG) Chiranjeevi, 302 Steele, x2777, [email protected]
• TA Office Hours: TBA (likely Tuesdays)• Required Text: None• Recommended Text: “Intro to Mat Sci for Engineers” Shackelford• Reserved Texts: SFL
– “The Principles of Engineering Materials,” Barrett, Nix & Tetelman
– “Phase Transformations in Metals and Alloys,” Porter & Easterling
– “Quantum Chemistry,” Levine
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Chemistry / Composition
What is Materials Science?
Processing+
Structure
Properties / Performance
??
MS 115a MS 115b
thermodynamics kinetics
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Course Content
• Introduction to Materials Science– Chemistry + Processing Structure Properties
• Structure– Structure of the Atom & Introduction to 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
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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
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Course Structure
• Homework: weekly 50%– Assigned Wednesdays– Due following Wednesday, 5pm– Place in TA mailbox, 3rd floor Steele
• Midterm HW: Oct 27 - Nov 2 15%– Solo homework
• Final: Dec 8 - 10 35% – Take home
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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.
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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, including ones from earlier in the year.
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Structure of the Atom• “Electron in a box” – use quantum mechanics to solve
electron wave functions– Electron quantum numbers, orbitals– Electrical properties
• Qualitative description of chemical bonding– Electrons ‘orbit’ atomic nucleus
K
ML
Q.N.
n K, L, M “shell” n = 1, 2, 3 radius
l s, p, d “orbital” l = 0, 1 …. n-1
m px, py, pz “orientation” m = -l, -l + 1, …0,...l - 1, l
s spin s = ± ½
K-shell: n = 1 l = 0
1
32
1s m = 0 s = ± ½
L-shell: n = 2 l = {0, 1} 2s, 2p
m = 0 m = {-1, 0, 1} px. py. pz
Chemical notation
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Structure of the Atom
• Electrons occupy these orbitals
• Pauling 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,..
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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
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electronegativity
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• 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)
Types of Chemical Bonds
Isotropic, filled outer shells
+ - +
- + -
+ - +
+ + +
+ + +
+ + +
e-
e-
e-
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Some Properties
E
R (interatomic distance)long range attraction
1~
R
short range repulsion1
~nR
E = ER + EA
E0
R0
E0 : decrease in energy due to bond formation
this much energy is required to break the bond define as bond energy sets the melting temperature
R0 : interatomic distance that minimizes E
is the equilibrium bond distance
The bond energy curve
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E
R (interatomic distance)
E = ER + EA
Heat the material
More Properties
Ethermal = kbTT
R0 as T
Asymmetry in E(R) sets thermal expansion coefficient
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ER (interatomic distance)
F = dE/dR
Some Mechanical Properties
E0
R0
Fattr
activ
ere
puls
ive
R (interatomic distance)
The bond force curve
at R0 no net force (equilibrium bond distance)
R0
Elastic constants relate stress to strain Stress – related to force Strain – related to displacement
F = k x
stress*area strain*length
stress k strain
k
Elastic constants given by slope of B.F. curve at R0
given by curvature of B.E. curve at R0
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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 correlation between the type of bond and the value of the property