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

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.

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.

Materials Characteristics

ρ ≡ Density

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

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

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.

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.

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.

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 http://www.yourbuilding.org/Article/NewsDetail.aspx?p=83&id=1570

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

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

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

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

E, Young’s Modulus GPa psi Rubber 0.01-0.1 1500-15000 Teflon 0.5 75,000 Nylon 2 - 4 290,000-580,000 Aluminum 69 10,000,000 *Glass 50 - 90 n/a Copper 117 17,000,000 Steel 200 29,000,000 Diamond 1220 150 -175 million depends on composition of SiO2 and other metal oxides

Example Question

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/

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

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

Surface area to volume ratio

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

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.

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)

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

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, 1.5 - 2 nm in size http://www.beilstein-journals.org/bjnano/single/articleFullText.htm?publicId=2190-4286-1-14#E1

Crystal Structure

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.

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

Example Questions

Characterizing a Crystal

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

Diffraction Patterns

X-Ray powder diffraction patterns

Miller Indices - Understanding crystal orientation

http://www.doitpoms.ac.uk/tlplib/miller_indices/printall.php

Additional Great Resources www.nano.gov www.mrsec.wisc.edu/nano http://www.terrificscience.org/lessonpdfs/PolymerLab06.pdf http://phet.colorado.edu/en/simulation/photoelectric http://phet.colorado.edu/en/simulation/semiconductor http://phet.colorado.edu/en/simulation/conductivity http://phet.colorado.edu/en/simulation/wave-interference