1. Coaches Meeting 2011: Materials Science
Wisconsin
Science
Olympiad
Coaches Meeting 2011: Materials Science
i s o
Illinois Science Olympiad

2. New Rules - Materials Performance and Nano focus
Structure and Performance Relationships
Students will perform laboratory based experiments designed to evaluate the relationship between the atomic/molecular structure and the performance characteristics of common materials.
Structure and Characteristics of: metals, ceramics, polymers, semi-conductors and composites. - Utilizing stress-strain curves to evaluate the Young’s modulus.

3. Nanomaterials - focus on nanoparticles and carbon nanotubes.
General introductory topics regarding the physical and chemical properties that arise within the nano size regime.
surface area to volume ratios
quantum effects
nanomaterials visualization.
Understand SEM, TEM, AFM micrographs scaling
Cubic crystal structures.
Formula, density, dimensions. Miller Indices, and use of x-ray data to determine unit cell dimensions. Internet based modeling and/or simulations may be incorporated into event tasks and questions.

6. Materials Characteristics

7. ρ ≡ Density

8. Materials Characteristics
Metals: low electronegativity metal cationic atoms in a “sea” of delocalized electrons. Metallic bonds from electrostatic interaction - different from ionic bonds.
Conducts electrons on the delocalaized valence level “sea” of electrons
malleable/ductile, hard, tough, can be brittle.
Iron

9. Ceramics
covalent and ionic bonding of inorganic non-metals. electrons are localized in bonds - poor conductors, brittle and very thermally stable.
The crystal structure of bulk ceramic compounds is determined by the amount and type of bonds. The percentage of ionic bonds can be estimated by using electronegativity determinations. Resistance to shear and high-energy slip is extremely high.
Atoms are bonded more strongly than metals: fewer ways for atoms to move or slip in relation to each other. Ductility of ceramic compounds is very low and are brittle. Fracture stresses that initiate a crack build up before there is any plastic deformation and, once started, a crack will grow spontaneously.
Alumina
Al2O3

10. Semi-conductors
Metalloid in composition (w/ exception). Covalently bonded. More elastic than ceramics.
characterized by the presence of a band gap where electrons can become delocalized within the framework.

11. Polymers
macromolecules containing carbon covalently bonded with itself and with elements of low atomic number
molecular chains have long linear structures and are held together through (weak) intermolecular (van der Waals) bonds. Low melting temp.

12. Materials Performance
Optical properties (Quantum Dots, LEDs)
Magnetic properties (ferrofluids)
Electronic Properties ( semiconductors)
Thermal and Mechanical Properities (plastics, metals, ceramics)
Left: Emission spectrum of green CdSe QD; Middle: Ferrofluid in magnetic field; Right: Silicon wafers used in the manufacturing of computing hardware and other microelectronics.

13. Mechanical Performance
Stress Vs. Strain relationship
Stress vs. Strain curve of Geopolymer Concrete made from the fly ash rice husk ash. Right: stress/strain testing of concrete cylinder

14. Linear Deformation - Stress and Strain
Stress - force applied over a given area. Units of lbs/in2 or Gigapascals
Strain - Deformation of material as a change in dimension from initial. *Unitless

15. Stress, Strain, and Young’s Modulus
- a measure of material “stiffness”
- E = σ/ε
= F/A
l/L
1: True elastic limit
2: Proportionality limit
3: Elastic limit - yield strength --> enter region of plasticity vs. elasticity
4: Offset yield strength
Hooke’s Law: F = k∗Δx spring constant: k = F/Δx

16. True elastic behavior vs. elastic region
Glass - very brittle, displays no real elasticity, very sharp slope and
Rubber
Glass
Vable, M. Mechanics of Materials: Mechanical properties of Materials. Sept. 2011

17. Relationship of E and materials characteristics:
Polymers
m = E

18. E, Young’s Modulus GPa psi Rubber 0.01-0.1 1500-15000 Teflon 0.5
75,000
Nylon
2 - 4
290, ,000
Aluminum 69
10,000,000
*Glass
n/a
Copper
117
17,000,000
Steel
200
29,000,000
Diamond
1220
million
depends on composition of SiO2 and other metal oxides

19. Example Question

20. A different application of Young’s Modulus
The deflection d of the mid-point of a centrally loaded simple beam of uniform rectangular cross section is given byd = (Wl3)/(4ab3Y) For a circular beam of radius r the expression becomesd = (Wl3)/(12πr4Y)
where Y is the Young’s Modulus

21. Nanomaterials - Nanoworld
The size regime of the nanoworld is 1 million times smaller than a millimeter.

23. SEM, TEM, AFM Images of CdSe Quantum Dots
200 nm
Picture: C.P. Garcia, V. Pellegrini , NEST (INFM), Pisa. Artwork: Lucia Covi

24. Surface area to volume ratio

25. As volume decreases, SA increases as does pressure
Consequences of Large Surface Area to Volume ratio
Gas law: P = nRT V
As volume decreases, SA increases as does pressure

26. Electron conducting & band gaps
- Conducting is flow of e- from VB through the C.B.
* In metals, CB is linked to VB directly
- Semiconductors require some energy input to overcome a gap between VB and CB
- Insulators have a band gap too large to overcome, thus they insulate against e- conduction.

27. Characteristics of Light
Wave-like properties:
Wavelength (λ) or Frequency (ν)
c = λν (c is the speed of light, 3.0x108 m/s)
Particle-like properties:
A photon is a packet of energy (E)
E = hν = h c/ λ (h= 6.6 x J s)
E = 2.0x10-25/ λ (hc= 2.0 x J m)

28. Band gap, quantum effects, color
As size decreases, the electrons of the nanoparticle become confined to a smaller space, and the band gap increases

29. CdSe Quantum dots, 1.5 - 2 nm in size
Calculate particle size based on UV-Vis spectroscopy - Particle in a Box
where r is the radius of the nanoparticle. The second term is the particle-in-a-box confinement energy for an electron-hole pair in a spherical quantum dot and the third term is the Coulomb attraction between an electron and hole modified by the screening of charges by the crystal.
CdSe Quantum dots, nm in size

30. Crystal Structure

32. The size and shape of a unit cell is described, in three dimensions, by the lengths of the three edges (a, b, and c) and the angles between the edges (α, β, and γ).
These quantities are referred to as the lattice parameters of the unit cell.

34. *Only Po has this structure
Simple Cubic
*Only Po has this structure

45. Example Questions

47. Characterizing a Crystal

48. X-ray Diffraction in Crystalline Solids
Interference in Scattered Waves
X-ray Diffraction in Crystalline Solids

50. Diffraction Patterns

53. X-Ray powder diffraction patterns

54. Miller Indices
- Understanding crystal orientation

58. Additional Great Resources