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 11amnoon; 080 Moore; to 12:30pm?? Teaching Assistant:
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Processing
+
Structure
Properties / Performance
What is Materials Science?
?
?
kinetics
thermodynamics
(MS 115b)
MS 115a
Chemical notation
K
L
1
M
2
Kshell: n = 1
l = 0
1s
m = 0
s = ± ½
3
2s, 2p
Lshell: n = 2
l = {0, 1}
px. py. pz
m = 0
m = {1, 0, 1}

+

+

+

+
+
+
+
e
e
+
+
+
e
+
+
+
Types of Chemical BondsIsotropic, filled outer shells
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
Heat the material
E = ER + EA
E
R (interatomic distance)
R0 as T
T
Ethermal = kbT
Asymmetry in E(R) sets thermal expansion coefficient
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
how can carbon atoms fill px, py and pz orbitals if the other element is also electronegative?
bonds
bonding electrons
s orbital
p orbitals
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/orbitals.gif
Hybridized Bondssp3 hybridization
also methane: CH4
one s + three p orbitals 4 (x 2) electron states
(resulting orbital is a combination)