materials science (c) (or its all about bonding!) by linda (lin) wozniewski [email protected] and mat...
TRANSCRIPT
Materials Science (C)(or Its All About Bonding!)
By
Linda (Lin) Wozniewski
and
Mat Chalker
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
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
What Students May Bring
One 3 ring notebook any size containing resources in any non-electronic form.
Each student may bring– One non-programmable, non-graphing Calculator
per student– A writing instrument
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
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
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!!!!!
Materials Science
Materials Science - a relatively new interdisciplinary field It merges Metallurgy, Ceramics, and Polymers’ 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 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
Main Focus
Material Performance and Atomic Structure 50% Intermolecular Forces and Surface Chemistry
50% How to prepare Students Experiment ideas Resources
Materials Characteristics
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
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.
http://mst-online.nsu.edu/mst/ceramics/ceramics3.htm
Alumina Al2O3
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
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.
Linear Deformation–Stress & 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, & 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
Young’s Modulus
E = σ/ε= (F/Ao)/(ΔL/Lo) Where E = Young’s Modulus σ = Stress ε = Strain F = Force Ao= Initial cross section of material ΔL = Change in length of material Lo = Initial length of material
Yield Strength
Vable, M. Mechanics of Materials: Mechanical properties of Materials. Sept. 2011
Rubber
Glass
Polymers
True Elastic Behavior vs. Elastic Region
Surface area to volume ratio
Surface Area
Volume
Consequences of Large Surface Area to Volume ratio
Gas law: P = nRT
As volume decreases, SA increases as does pressure
V
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
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
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)
Crystal Structure
Hexagonal Close Packing
Materials Characteristics-Density
ρ ≡ Density
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
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 30-50 ml of the substance to test in the event
Event supervisors will give standard curve if doing this activity.
Creep Rate
Creep is the movement of material under stress over time usually at higher temperatures
Creep ends when the material breaks
Fracture Toughness
K1 is the fracture toughness
σ is the applied stress
α is the crack length
β is a crack length and component geometry factor that is different for each specimen and is dimensionless.
Fatigue Limit
Maximum fluctuating stress a material can endure for an infinite number of cycles
Determined from a stress/cycles curve
Shear Modulus
Poisson’s Ratio
• ν = -εtrans/εaxial
• Where• ν = Poisson’s Ratio• εtrans = Transverse Strain
• εaxial = Axial Strain
• ε= ΔL/Lo
• ΔL = Change in length of material
• Lo = Initial length of material
Resources
For Event Supervisors– http://mypage.iu.edu/~lwoz/socrime/index.htm
For Lesson Plans for classroom use– http://mypage.iu.edu/~lwoz/socrime/index.htm
Miller Indices– http://www.doitpoms.ac.uk/tlplib/miller_indices/printall.php
Stress, Strain, etc. – http://www.ndt-ed.org/EducationResources/
CommunityCollege/Materials/Mechanical/Mechanical.htm
Resources Continued
YouTube.– LOTS of nice videos on stress, strain, Young’s
Modulus, etc. Contact Angles
– http://www.csu.edu/chemistryandphysics/csuphysvan/participantactivities/Kondratko.FengertHS.ContactAngleIFTWetting.pdf
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.
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
Young’s Modulus Continued
Stress = Force/Area0
– Determine difference in Force– Determine the initial area of the parafilm– Divide
Strain = ΔL/L0
– Determine the difference in the lengths– Divide the difference by the original length
Young’s Modulus– Divide Stress by Strain
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
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
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
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.
Questions Continued
Using CuKα radiation (λ=.154 nm), the 1st 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
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?
y = 6x-1
R² = 102468
0 1 2 3 4
Su
rfa
ce
Are
a t
o V
olu
me
R
ati
o (
1/c
m)
Side (cm)
Surface Area/Volume Ratio to Side Relationship
y = 0.068x1.5
R² = 1
0
10
20
30
0 10 20 30 40 50 60Su
rfac
e A
rea
(cm
^2)
Volume (cm^3)
Surface Area to Volume Relationship
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
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
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.
Deflection
The formula for deflection is: – d = (Wl3)/(12πr4Y)
Solving for Young’s Modulus (Y) we get:– Y = (WI3)/12πr4d)– W = force added– I = length of paperclip– d = deflection– r = radius of paperclip = diameter/2
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.
Classification of Pure Substances
Types of Solids
Materials Properties
Optical properties (Quantum Dots, LEDs)
Magnetic properties (ferrofluids)
Electronic Properties ( semiconductors)
Thermal and Mechanical Properities (plastics,
metals, ceramics)
Nano World
The size regime of the nano world is 1 million times smaller than a millimeter.
Units of length
SEM, TEM, AFM Images of CdSe Quantum Dots
Picture: C.P. Garcia, V. Pellegrini , NEST (INFM), Pisa. Artwork: Lucia Covihttp://mrsec.wisc.edu/Edetc/SlideShow/slides/quantum_dot/QDCdSe.htmlhttp://www.jpk.com/quantum-dots-manipulation.207.en.html?image=adf24cc03b304a4df5c2ff5b4f70f4e9
Characterizing a Crystal
Wave Particle Interaction
Interference in Scattered Waves
X-ray Diffraction in Crystalline Solids
Bragg’s Law
Diffraction Patterns
Common X-Ray Wavelengths
X-Ray Powder Diffraction Patterns
Miller Indices
Understanding crystal orientation
http://www.doitpoms.ac.uk/tlplib/miller_indices/printall.php
Space Lattice
A lattice is an array of points repeated through space
A translation from any point through a vector Rlmn+la+mb+nc, where l, m, & n are integers, locates an exactly equivalent point. a, b, & c are known as lattice vectors.
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
Simple Cubic
Body Centered Cubic
Body Centered Cubic
Face Centered Cubic
Face Centered Cubic