Unit Cell smallest repeating unit of a crystal structure Slip Planes surface along which layers of atoms can slide past one another plane of closely packed atoms Crystal System Terms Void or Interstice ID: 653279
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Slide1
Crystal SystemsSlide2
Crystal System Terms
Unit Cell
smallest repeating unit of a crystal structure
Slip Planes - surface along which layers of atoms can slide past one another
plane of closely packed atomsSlide3Slide4Slide5
Crystal System Terms
Void or Interstice-
empty space in a crystal Slide6
Crystal Packing – loosely packedSlide7
Crystal Packing – More Densely Packed
Most metals are
close packed
- that is, they fit as many atoms as possible into the available volumeSlide8
simple cubic
FCC
– Face Centered Cubic
BCC
- Body Centered Cubic
HCP
– Hexagonal
Close PackedSlide9
Slip Planes of FCC
Morton SchafferSlide10
Slip Planes
Morton Schaffer
1Slide11
Slip Planes
Morton Schaffer
2Slide12
Slip Planes
Morton Schaffer
3Slide13
Slip Planes
Morton Schaffer
4Slide14
Slip Planes
Morton Schaffer
5Slide15
Slip Planes
Morton Schaffer
6Slide16
Slip Planes
Morton Schaffer
7Slide17
Body-centered cubic (BCC)
Face-centered cubic (FCC)
Hexagonal close-packed (HCP)
center atom
Slip Planes
Morton Schaffer
12 Slip Planes
Up to 48 Slip Planes
3 Slip PlanesSlide18Slide19
STOP – Crystal Models LabSlide20
SIMPLE CUBIC
FACE CENTERED CUBIC
(FCC)
BODY CENTERED CUBIC
(BCC)
HEXAGONAL CLOSE PACKED
(HCP)Slide21Slide22
Why do Crystal Systems Matter?
Workability
changing the shape of a solid without breaking or cracking
Malleability
ability of being hammered into thin sheets
Ductility
ability of being drawn into wiresSlide23
Workability
Which crystal structure is more workable?
Many slip planes or few slip planes?
Tightly packed or loosely packed? Slide24
Models of Crystals Lab
*more tightly packed = more workable
*more slip planes = more workable
Type of crystal structure
Closely packed?
Many slip planes?
Workability
FCC
BCC
HCPSlide25
Models of Crystals Lab
*more tightly packed = more workable
*more slip planes = more workable
Type of crystal structure
Closely packed?
Many slip planes?
Workability
FCC
Yes
Yes
Highest
BCC
No
Yes
Medium
HCP
Yes
No
LowestSlide26
Crystal Structures & Metals
BCC
FCC
HCP
OtherSlide27
Crystal Structures & Metals
BCC
FCC
HCP
Other
Chromium
Aluminum
Cobalt
Manganese
Iron (<910°C)
Calcium
Magnesium
tin
Molybdenum
Copper
Titanium
Sodium
Gold
zinc
tungsten
Iron (>910°C)
Lead
Nickel
Platinum
silverSlide28
28
Sargent Welch Periodic Table
Crystal structures on the back.Slide29
Crystalline vs. Amorphous?
Orderly arrangement
Repeating pattern
Predictable
Opaque (not see through)
Random arrangement
No repeating pattern
Not predictable
ClearSlide30
Allotropes (review)
Different forms of the same element in the same physical state
Difference is in how the atoms are arranged
Also called polymorphism
Examples:
Carbon – diamond, graphite,
buckyballs
Oxygen – O
2
(atmospheric) and O
3
(ozone)
Sulfur – rhombic, monoclinic, amorphousSlide31
Allotropes of Carbon
buckyballSlide32
Allotropes of Sulfur
rhombic
amorphous
monoclinicSlide33
Solid State Phase Change
Change in crystal structure while remaining a solid.
Example:
Amorphous sulfur changing to crystalline sulfurSlide34
Milk Jug DemoWhat is happening when you heat the plastic to the crystal structure
?
Before heat
Crystalline b/c it was opaque
During heating Changing to amorphous, became clear
After heat atoms were able to go back to close to original states & went back to crystallineSlide35
Sulfur LabGrowing CrystalsSlide36
Sulfur MSDSSlide37
Sulfur MSDSSlide38
Sulfur MSDSSlide39
Sulfur MSDSSlide40
Monday, 9/19/16Review lab on Friday!Slide41
Part A – Rhombic Sulfur
Forming crystals from a solution
What did we do?
Heated
in mineral oil to dissolve
What did we see?
Crystals
formed in
solutionSlide42Slide43
Part B: Monoclinic Sulfur
Forming crystals from a melted substance
What did we do?
1
. Fill a test tube approximately
1/2
full with sulfur. Keep the sulfur powder off the sides of the test tube.
2
. Make a cone out of
filter paper
and place it in a funnel.
3. Heat the test tube of sulfur
very
slowly - passing it back and forth above the flame. Totally melt to a liquid. Use
Bunsen burner
and test tube clamp. Keep the sulfur
yellow
.
4. Pour liquid sulfur into filter paper cone. As soon as a crust forms, open the filter paper to original shape. Slide44Slide45Slide46
What did we see? Forming crystals from a melted substanceLong skinny pointy crystalsSlide47Slide48Slide49
Part C: Amorphous Sulfur
What did we do?
Heat
sulfur slowly. It will pass through
stages.
Pour
hot sulfur into beaker of cold water. (quench
)
What did we see?
melt to yellow liquid
individual rings of 8
red liquid
short chains of 8 – 16 sulfur atoms
dark reddish-brown thick syrup
longer chains of sulfur atoms that entangle
dark runny liquid
longer chains of sulfur atoms that have enough energy to flowSlide50
Ring of
8 sulfur atoms
Chain
of sulfur
atomsSlide51
Amorphous SulfurSlide52
Crystalline balls
of sulfurSlide53
What does crystalline mean?How easy is it to grow a perfect crystal?What types of defects are possible?
Crystal DefectsSlide54
CRYSTAL TERMS
Grains
individual crystals
They grow in different directions and meet up with each other
Grain Boundary
boundaries where grains meetSlide55Slide56
Crystal Grains
“Crystal grains
”
are regions of regularity. At the grain
boundaries,
atoms have become misaligned. Slide57
Crystal Defects and Imperfections
I
mpurities
and disruptions in the pattern of atoms
A
ffect
many physical properties
T
hree
main typesSlide58
1. Interfacial Defects
grain boundaries
affected by size of grainsSlide59Slide60
By cooling more quickly, a smaller grain size results and this has the effect of making the resulting solid stronger. Figure
2 and Figure 3 are examples of metals with different grain size – the one exhibited in Figure 3 will be significantly stronger than its counterpart in Figure 2.
Figure 2
Figure 3Slide61
Application in IndustryCreepHigh temperatures with less grain boundaries
(30-50% of melting temperature)
Stronger
Stretching
Low temperatures with more grain boundaries
Increases tensile strength – more stretch
Read Case Study on “Creep of Turbine Blades”Slide62
Phenyl Salicylate Demo
freezing a liquid to grow crystals
nucleation
site – location where a crystal starts growing
watch
for grains and grain boundariesSlide63
2. Dislocation – Line Defects
regions in crystals where atoms are not perfectly aligned – an extra partial plane
can
move
a small number make a metal more workable
a large number make a metal harder to work
dislocations can get “jammed” or “pinned”
makes the metal harder =
work-hardening
Becomes so strong it becomes brittle and breaksSlide64Slide65Slide66Slide67Slide68Slide69
Dislocation MovementSlide70
3. Point Defects
single atom
defectsSlide71
Substitutional
replace some of the original atoms with different atoms
used in making alloys
examples – brass and bronzeSlide72
Interstitial extra atoms inserted in the gaps between the regular atomsused in making alloys
example - steelSlide73
Vacancyatom is missing (void)move around in crystal by diffusionSlide74
Silver Nitrate onCopper Wire
Growing CrystalsSlide75
Growing Silver Crystals
Place a flattened 1” piece of Cu wire on a microscope slide.
Focus one end of wire under stereoscope.
Have the teacher drop AgNO
3
(silver nitrate) on the wire.
Make observations:
Low and high power
Light from above and belowSlide76
Crystal Definitions
Dendrites
crystal branches
crystal growth pattern – directional
grow until they eventually become large enough to impinge upon (interfere with) each other
spaces between the dendrite arms
crystallize to make a more regular
crystalSlide77
Once nucleated, the dendrites spread sideways and the secondary arms generate further tertiary arms and so on. When solidification is complete, all the dendrites that have formed knit together to form grains (or crystals).Slide78Slide79
Snow - IceSlide80
Dendritic copper crystals