Coaches Meeting 2011: Materials Science

1. 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 http://mst-online.nsu.edu/mst/ceramics/ceramics3.htm

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)

13. Mechanical Performance • Stress Vs. Strain relationship http://www.yourbuilding.org/Article/NewsDetail.aspx?p=83&id=1570

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 • Young’s Modulus • - a measure of material “stiffness” • - E = σ/ε • = F/A • l/L Hooke’s Law: F = k∗Δx spring constant: k = F/Δx

16. True elastic behavior vs. elastic region Rubber Glass Vable, M. Mechanics of Materials: Mechanical properties of Materials. Sept. 2011

17. Relationship of E and materials characteristics: Polymers m = E http://www.nrc-cnrc.gc.ca/eng/ibp/irc/cbd/building-digest-157.html

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 http://blog.cencophysics.com/2009/08/beam-deflection-youngs-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 http://mrsec.wisc.edu/Edetc/SlideShow/slides/quantum_dot/QDCdSe.html http://www.jpk.com/quantum-dots-manipulation.207.en.html?image=adf24cc03b304a4df5c2ff5b4f70f4e9

24. Surface area to volume ratio Volume Surface Area

25. 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 10-34 J s) E = 2.0x10-25/ λ (hc= 2.0 x 10-25 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. Calculate particle size based on UV-Vis spectroscopy - Particle in a Box CdSe Quantum dots, 1.5 - 2 nm in size http://www.beilstein-journals.org/bjnano/single/articleFullText.htm?publicId=2190-4286-1-14#E1

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. Simple Cubic *Only Po has this structure

45. Example Questions

47. Characterizing a Crystal

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

50. Diffraction Patterns