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This presentation was prepared using draft rules. There may be some changes in the final copy of the rules. The rules which will be in your Coaches Manual and Student Manuals will be the official rules
Electron conducting & band gapsElectron conducting & band gaps
- Conducting is flow - Conducting is flow of e- from VB of e- from VB through the C.B.through the C.B.* In metals, CB is * In metals, CB is linked to VB directlylinked to VB directly
- Semiconductors - Semiconductors require some energy require some energy input to overcome a gap input to overcome a gap between VB and CBbetween VB and CB
- Insulators have a band gap too large - Insulators have a band gap too large to overcome, thus they insulate to overcome, thus they insulate against e- conduction.against e- conduction.
Characteristics of LightCharacteristics 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, colorBand gap, quantum effects, color
As size decreases, As size decreases, the electrons of the the electrons of the nanoparticle become nanoparticle become confined to a smaller confined to a smaller space, and the band space, and the band gap increasesgap increases
Experiments
Given the picture of a droplet, a protractor and a ruler, the students should be able to measure the contact angle
Given a pan of water covered in chalk dust, the students should be able to measure the approximate thickness of a detergent molecule or Oleic Acid
Questions continued
Given a series of reagents students should be able to arrange the reagents from least to most hydrophobic based on the contact angle
Questions continued
a) What type of Cell is this?b) How many tungsten
atoms occupy a unit cell?c) What is the radius of a
tungsten atomd) Based on the unit cell
dimensions, what is the density of tungsten?
Questions Continued
Questions Continued
The deflection d of the mid-point of a centrally loaded simple beam of uniform rectangular cross section is given by d = (Wl3)/(4ab3Y) For a circular beam of radius r the expression becomes d = (Wl3)/(12πr4Y) where Y is the Young’s Modulus
Questions Continued
Which class generally has the highest young’s modulus, metals, polymers or ceramics?– -Ceramics
Amorphous microstructures are most prevalent in which materials class?- Polymers
What characteristic of metals makes members of the class such good conductors of electricity?– - Bonded Metallic atoms share electrons in a “sea of
electrons”
Questions Continued
The most prevalent element by mass in a material is C. What class is the material most likely to belong to?-Polymers
Aluminum is one of the most common elements in the Earth’s crust, but pure Al was extremely rare until the late 19th century. Why is this?-Refining Al requires a large amount of electricity, which was not available in sufficient quantities until the late 19th century
Questions Continued
AA
• What is the size of the grain labeled “A” above?
• 15 μm• If the average grain size in the
material were 5μm, would this material have a higher or lower yield strength?
- Higher• What material class is most this
material most likely to be in?- Metals
• What material is this?-A high-carbon steel alloy (specifically from the Titanic, if anyone is interested…)
• What is one technique that one might use to increase the average grain size in this material?
•- Annealing would be the most common, although there are other options
Questions Continued
What caused the lines in the image above– Scanning electron microscope image - Charging from
the electron beam – lack of conduction in the target sample
What does the machine below measure? The fatigue limit of materials (by repeatedly cycling a material
through stress and counting cycles)
Questions Continued
SAMPLE ONLY, NOT A REFERENCE MATERIALSOME DATA MAY NOT BE 100% ACCURATE For a real test I would use more materials and data
Which material would be Which material would be best suited for:best suited for:Spacecraft reentry tiles
-Low-density Alumina blocks (due to melting temp and density)
Ferris Wheel tie-rods
-Medium-carbon Steel (due to strength and price)
Tennis racket frame
-Ti6Al4V (due to strength and density)
Shampoo bottles
-HDPE
Questions Continued
Calculate particle size based on UV-Vis Calculate particle size based on UV-Vis spectroscopy - Particle in a Boxspectroscopy - Particle in a Box
CdSe Quantum CdSe Quantum dots, 1.5 - 2 nm in dots, 1.5 - 2 nm in sizesize
http://www.beilstein-journals.org/bjnano/single/articleFullText.htm?publicId=2190-4286-1-14#E1
Questions Continued
The spacing between principle {200} planes of NaCl is 0.282 nm. It is found that 1st order Bragg reflection for this spacing occurs at a 2θ angle of 30º.– What is the wavelength of x-ray
used?nλ = d(sinθ)
.282(sin(16º))=155 nm
Experiments Continued
Given a type of crystal packing structure, some toothpicks and marshmallows, the students should be able to model common crystal packing structures
Given a picture or model and a Miller index, students should be able to determine which atoms are being cut across.
Questions Continued
Stress, strain, density, deformation under load
