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Materials Science (C) (or Its All About Bonding!)
Original materials by
Linda (Lin) Wozniewski
and
Mat Chalker
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.
One non-programmable, non-graphing
Calculator
Each student may bring 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
Next year will
rotate out with
Polymers
Main Focus
Material Performance and Atomic Structure
50%
Intermolecular Forces and Surface Chemistry
50%
How to prepare Students
Experiment ideas
Resources
Materials Characteristics Properties depend on type of bonding
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 delocalized 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.
Force
F F
Cross
Sectional
Area, A
F/A
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
Can investigate using Playdoh party favors
Polymers
Yield Strength
Vable, M. Mechanics of Materials: Mechanical properties of Materials. Sept. 2011
Rubber
Glass
True Elastic
Behavior vs.
Elastic Region
Surface area to volume ratio
Surface Area
Volume
A good thing for students
to practice calculating
Consequences of Large Surface Area to Volume ratio
Gas law: P = nRT
As volume decreases, SA increases as does
pressure
V
Surface Tension
Particles in the bulk of the liquid
are pulled in all directions by
the intermolecular forces.
Particles on the surface are
pulled from below, but not from
above. This unbalanced force
is the surface tension.
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
Measure force to lift thin glass or Pt plate out
of liquid
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
Reference
materials
for binder.
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
Can use silly putty to
measure.
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.
State and
National Only
Fatigue Limit
Maximum fluctuating stress a material can
endure for an infinite number of cycles
Determined from a stress/cycles curve
State and
National Only
Shear Modulus
State and
National Only
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
State and
National Only
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/csuphys
van/participantactivities/Kondratko.FengertHS.Co
ntactAngleIFTWetting.pdf
Practice Lab - Creep
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?
Surface Area/Volume Ratio to Side
Relationship
y = 6x-1
R2 = 10
2
4
6
8
0 1 2 3 4
Side (cm)
Su
rfa
ce
Are
a t
o
Vo
lum
e R
ati
o
(1/c
m)
Surface Area to Volume Relationship
y = 0.068x1.5
R2 = 1
0
10
20
30
0 10 20 30 40 50 60
Volume (cm^3)
Su
rface A
rea
(cm
^2)
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.
Additional Resouces
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 Covi
http://mrsec.wisc.edu/Edetc/SlideShow/slides/quantum_dot/QDCdSe.html
http://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
