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Materials Science (C) (or Its All About Bonding!) By Linda (Lin) Wozniewski and Mat

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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

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Safety Students must wear: – Closed shoes – Slacks or skirts that come to the ankles – Lab coat or lab apron – Indirect vent or unvented chemical splash proof goggles. No impact glasses or visorgogs are permitted – Sleeved Shirt (if wearing a lab apron) – Gloves are encouraged

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What Students May Bring One 3 ring notebook any size containing resources in any non-electronic form. One 3 ring notebook any size containing resources in any non-electronic form. Each student may bring Each student may bring – One non-programmable, non-graphing Calculator per student – A writing instrument

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What Supervisors Will Supply Everything the student will need – This may include: Glassware Reagents Balances Hot plates Thermometers Probes Magnets Stirrers Models Toothpicks and marshmallows/gumdrops

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What is Materials Science? Take the paperclip we have given you Bend it so that the inner part is 180º from the outer part Does it break? Bend it back. Does it break? How many times does it take till it breaks? You have just done Materials Science

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Properties Why did the paper clip break? Why didn’t all of the paper clips break on the same number of bends? What is the difference between how these materials behave? What about these? What are properties of materials? – Density – Deformation under load – Stiffness – Fatigue – Surface area to volume – Crystal structure – Thermodynamics ITS ALL ABOUT BONDING!!!!!

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Materials Science Materials Science - a relatively new interdisciplinary field Materials Science - a relatively new interdisciplinary field It merges Metallurgy, Ceramics, and Polymers’ It merges Metallurgy, Ceramics, and Polymers’ It merges Chemistry, Physics, and Geology It merges Chemistry, Physics, and Geology Materials Science takes advantage of the fact that we can not make pure crystals of anything & the interesting effects of the impurities. Materials Science takes advantage of the fact that we can not make pure crystals of anything & the interesting effects of the impurities. Materials Science is a field where many of our students will find lucrative employment in the future. Materials Science is a field where many of our students will find lucrative employment in the future. Materials Science also incorporates the fascinating area of nano-technology Materials Science also incorporates the fascinating area of nano-technology

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Main Focus Material Performance and Atomic Structure 50% Intermolecular Forces and Surface Chemistry 50% How to prepare Students Experiment ideas Resources

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Materials Characteristics

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Metals 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

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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 Al 2 O 3 Al 2 O 3

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Semiconductors 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. Germanium

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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.

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Materials Performance Stress Vs. Strain relationship

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Linear Deformation–Stress & Strain Stress - force applied over a given area. Units of lbs/in 2 or Gigapascals Strain - Deformation of material as a change in dimension from initial. *Unitless

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Stress, Strain, & Young’s Modulus Young’s Modulus Young’s Modulus - a measure of material “stiffness” - a measure of material “stiffness” - E = σ/ε - E = σ/ε = F/A = F/A l/L l/L Hooke’s Law: F = k ∗ Δ x spring constant: k = F/ Δ x

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Young’s Modulus E = σ/ε= (F/A o )/(ΔL/L o ) Where E = Young’s Modulus σ = Stress ε = Strain F = Force A o = Initial cross section of material ΔL = Change in length of material L o = Initial length of material

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Yield Strength Vable, M. Mechanics of Materials: Mechanical properties of Materials. Sept Rubber Glass Polymers True Elastic Behavior vs. Elastic Region

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Surface area to volume ratio Surface Area Volume

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

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Surface Tension Depends on attractive forces in fluids Examples How to Measure – The force to break a known area free from the liquid is measured

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Contact Angle The relationship between the surface tension of the liquid and the attraction of the solid Important if you want ink to stick to film or if you don’t want water to stick to car or skis Measured by finding angle between surface and tangential line drawn from drop contact

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Surface Tension Tension on thin glass or Pt plate measured Equation – l is the wetted perimeter of the plate 2d + 2w – θ is the contact angle In practice θ is rarely measured. Either literature values are used or complete wetting is assumed (θ = 0)

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Crystal Structure Hexagonal Close Packing

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Materials Characteristics-Density ρ ≡ Density

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Viscosity A measure of resistance of a fluid to deformation or flow. Water has a low viscosity. It is thin and flows easily Honey has a high viscosity. It is thick and does not flow easily Viscosity is measured usually in one of two ways: – A given volume is timed to fall through a hole – Balls are timed falling through a given length

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Viscosity Mark a stop and start point on the side of the tester Fill the tester over the start line. Time how long it takes for same amount of each standard liquid to go from start to stop Keep in mind that event supervisors will only be giving the students between ml of the substance to test in the event Event supervisors will give standard curve if doing this activity.

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Creep Rate Creep is the movement of material under stress over time usually at higher temperatures Creep ends when the material breaks

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Fracture Toughness K1K1 is the fracture toughness σis the applied stress αis the crack length βis a crack length and component geometry factor that is different for each specimen and is dimensionless.

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Fatigue Limit Maximum fluctuating stress a material can endure for an infinite number of cycles Determined from a stress/cycles curve

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Shear Modulus

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Poisson’s Ratio ν = -ε trans /ε axial Where ν = Poisson’s Ratio ε trans = Transverse Strain ε axial = Axial Strain ε= ΔL/L o ΔL = Change in length of material L o = Initial length of material

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Resources For Event Supervisors – For Lesson Plans for classroom use – Miller Indices – Stress, Strain, etc. – ed.org/EducationResources/CommunityCollege/Materials/ Mechanical/Mechanical.htm

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Resources Continued YouTube. – LOTS of nice videos on stress, strain, Young’s Modulus, etc. Contact Angles – van/participantactivities/Kondratko.FengertHS.Co ntactAngleIFTWetting.pdf

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Workshop Test Form the Silly Putty into a cone. Place it on a piece of paper Gently draw a circle around the widest part of the cone Note the time and place it out of the way After doing each of the next events (~10 min), note the time, and draw a circle around the cone.

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Young’s Modulus Measure the length & width of the Parafilm strip Place a clamp on each end, & place a pencil through one clip so it hangs off the table. Fasten a ruler so it is hanging down measuring from the table top down toward the floor. Attach a TI calculator with a force sensor or a paper cup that you can put pennies in to the other clip Apply a force, noting the force & determine how much the parafilm stretches

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Young’s Modulus Continued Stress = Force/Area 0 – Determine difference in Force – Determine the initial area of the parafilm – Divide Strain = ΔL/L 0 – Determine the difference in the lengths – Divide the difference by the original length Young’s Modulus – Divide Stress by Strain

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Surface Tension Fill petri dish with water. Use Pasteur pipette to drops of water to slide until large enough drop to measure contact angle. Measure width of slide Attach dual force sensor with hook end to calculator Attach slide suspended from clamp to hook Determine Force Determine Force when slide just touches water Determine how far up water moves on slide

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Surface Tension Determine perimeter of water on slide Determine force difference Surface tension is – l is the perimeter – θ is the contact angle – F is the difference in the forces

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Thickness of a Molecule Fill the pie plate with water Sprinkle chalk dust on top Determine how many drops from the Pasteur pipette are required to make 1 ml. Add one drop of soap to the center of the pie plate. Determine the radius of the circle of soap Since the soap has a hydrophobic part, it will spread out 1 molecule thick on top of the water. Divide the volume of the drop by the area

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Hexagonal Close Packing Take 1 Marshmallow and put 6 short (broken) toothpicks around the circle evenly spaced. Put 1 marshmallow at the end of each toothpicks. – The 6 outer marshmallows should be touching each other Repeat for a second and a third layer. Place the layers so that the central marshmallows fit in the holes between the other layer. Toothpick together Repeat.

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Questions Continued Using CuK α radiation (λ=.154 nm), the 1 st order reflection for the spacing between the {200} planes of gold occurs at a 2θ angle of 44.5º – What is the spacing between the {200} planes? – What is the value of a? – What is the radius of gold? nλ = 2d(sinθ) a=.406 nm r=.203 nm

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Surface Area/Volume Relationship Using your Play-Doh, make a 1 cm cube, 2 cm cube, and 3 cm cube. Determine the surface area of each Determine the volume of each Divide the surface area by the volume What trend do you see?

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Creep Rate Retrieve the silly putty cone Note the time and draw the last circle around the bottom Without removing the circle lines, remove the kiss. Measure all of the diameters and match them to their times Using your calculator, make a spreadsheet of the times vs. the diameters. Subtract the original diameter from each diameter

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Creep Rate Divide the differences in the diameters by the original diameter and multiply by 100 to get the percent stress Plot the time on the x axis vs. the stress on the y axis. Determine the slope of the middle range by defining the area of interest and then finding the tangent. The creep rate is the slope

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Deflection Measure the length and diameter of a straightened paperclip. Suspend the paperclip across two tall containers so the paperclip is resting at its two ends. Place a ruler across the containers too. Attach a dual range force sensor with a hook to the calculator Pull down in the center of the paperclip until the clip is deflected down a measureable amount. Note the deflection and the Force difference.

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Deflection The formula for deflection is: – d = (Wl 3 )/(12πr 4 Y) Solving for Young’s Modulus (Y) we get: – Y = (WI 3 )/12πr 4 d) – W = force added – I = length of paperclip – d = deflection – r = radius of paperclip = diameter/2

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Viscosity Take one of the cups with the hole in the bottom. Place finger over hole and pour a liquid in cup until liquid is over start line on side of cup Remove finger and place cup on pipe Time how long it takes liquid to go from start line to stop line. Compare to standard curve to get viscosity.

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Classification of Pure Substances

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Types of Solids

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Materials Properties Optical properties (Quantum Dots, LEDs) Magnetic properties (ferrofluids) Electronic Properties ( semiconductors) Thermal and Mechanical Properities (plastics, metals, ceramics)

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Nano World The size regime of the nano world is 1 million times smaller than a millimeter.

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Units of length

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

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Characterizing a Crystal

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Wave Particle Interaction Interference in Scattered Waves X-ray Diffraction in Crystalline Solids

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Bragg’s Law

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Diffraction Patterns

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Common X-Ray Wavelengths

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X-Ray Powder Diffraction Patterns

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Miller Indices Understanding crystal orientation

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Space Lattice A lattice is an array of points repeated through space A translation from any point through a vector R lmn +la+mb+nc, where l, m, & n are integers, locates an exactly equivalent point. a, b, & c are known as lattice vectors.

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Cubic Crystal Lattices 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. 90º

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Simple Cubic

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Body Centered Cubic

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Face Centered Cubic

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