Materials Science (C) By Linda (Lin) Wozniewski and Mat

Disclaimer 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 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, 3.0x10 8 m/s) Particle-like properties : A photon is a packet of energy (E) E = h ν = h c/ λ (h= 6.6 x J s) E = 2.0x / λ (hc= 2.0 x 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

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 atom d)Based on the unit cell dimensions, what is the density of tungsten?

Questions Continued

The deflection d of the mid-point of a centrally loaded simple beam of uniform rectangular cross section is given by d = (Wl 3 )/(4ab 3 Y) For a circular beam of radius r the expression becomes d = (Wl 3 )/(12πr 4 Y) where Y is the Youngs Modulus

Questions Continued Which class generally has the highest youngs 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 Earths crust, but pure Al was extremely rare until the late 19 th century. Why is this? -Refining Al requires a large amount of electricity, which was not available in sufficient quantities until the late 19 th century

Questions Continued A What is the size of the grain labeledA 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 MATERIAL SOME DATA MAY NOT BE 100% ACCURATE For a real test I would use more materials and data Which material would be 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 spectroscopy - Particle in a Box Calculate particle size based on UV-Vis spectroscopy - Particle in a Box CdSe Quantum dots, nm in size

Questions Continued The spacing between principle {200} planes of NaCl is nm. It is found that 1 st 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