materials science (c) (or its all about bonding!) by linda (lin) wozniewski lwoz@iun.edu and mat...

Materials Science (C)(or Its All About Bonding!)

By

Linda (Lin) Wozniewski

lwoz@iun.edu

and

Mat Chalker

chalker7@gmail.com

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.

Materials Performance

Stress Vs. Strain relationship

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