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Engineering 45. Crystalline MicroStructure. Bruce Mayer, PE Registered Electrical & Mechanical Engineer BMayer@ChabotCollege.edu. Learning Goals. Learn How atoms assemble into solid structures Use metals as Prototypical Example - PowerPoint PPT Presentation
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BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt1
Bruce Mayer, PE Engineering-45: Materials of Engineering
Bruce Mayer, PERegistered Electrical & Mechanical Engineer
BMayer@ChabotCollege.edu
Engineering 45
CrystallineCrystallineMicroStructMicroStruct
ureure
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt2
Bruce Mayer, PE Engineering-45: Materials of Engineering
Learning GoalsLearning Goals
Learn How atoms assemble into solid structures• Use metals as Prototypical Example
Determine Relationship Between Material density and material MicroStructure
Understand how material properties vary with the sample (i.e., part) orientation
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt3
Bruce Mayer, PE Engineering-45: Materials of Engineering
Properties of Solid MaterialsProperties of Solid Materials
Mechanical: Characteristics of materials displayed when Forces and/or Moments are applied to them.
Physical: Characteristics of materials that relate to the interaction of materials with various forms of Energy.
Chemical: Material characteristics that relate to the e− structure of a material.
Dimensional: Size, shape, and finish
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt4
Bruce Mayer, PE Engineering-45: Materials of Engineering
Material PropertiesMaterial Properties Chemical Physical Mechanical Dimensional
Composition Melting Point Tensile properties Standard Shapes
Microstructure Thermal Toughness Standard Sizes
Phases Magnetic Ductility Surface Texture
Grain Size Electrical Fatigue Stability
Corrosion Optical Hardness Mfg. Tolerances
Crystallinity Acoustic Creep
Molecular Wt Gravimetric Compression
Flammability
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt5
Bruce Mayer, PE Engineering-45: Materials of Engineering
Energy and Atomic PackingEnergy and Atomic Packing NonDense, Random Packing
Dense Regular Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Regular Structures Tend to have LOWER Energy → Energetically Favored
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt6
Bruce Mayer, PE Engineering-45: Materials of Engineering
Materials and Atomic-PackingMaterials and Atomic-Packing
Si Oxygen
crystalline SiO2
noncrystalline SiO2
CRYSTALLINE Materials• atoms pack in periodic, 3D arrays
• typical of: Metals, many Ceramics, and some Polymers
NONcrystalline Materials• atoms have no periodic packing
• occurs for:– Complex structures
– Rapid Cooling
"Amorphous" Noncrystalline
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt7
Bruce Mayer, PE Engineering-45: Materials of Engineering
Crystal BasicsCrystal Basics Crystalline Material
• atomic arrangement in solid:– periodic and repeating
3D array
– Long Range Order
lattice
Unit Cell Smallest Repeating Entity Within a Lattice• Geometry
– Lattice Constants: a, b, c
– interaxial angles:
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt8
Bruce Mayer, PE Engineering-45: Materials of Engineering
Crystal StructureCrystal Structure
Crystal Structure geometry + atom-positions• i.e.; the spatial arrangement of Atoms,
Ions, or Molecules
Some Types
polymer
Crystal Type Typical Metal Typical CeramicsFace Centered Cubic (FCC) Cu, Al NaCl
Body Centered Cubic (CCC) Cr, W CsCl
Hexagonal Close Packed (HCP Ti, Zn ZnSB
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt9
Bruce Mayer, PE Engineering-45: Materials of Engineering
Example Crystal SystemsExample Crystal Systems Tab 3.2 In Text
Shows the 7 Most Common Crystal Systems• Some Examples
Cubic• a = b = c = = = 90°
Hexagonal• a = b c = = 90°, =
120°
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt10
Bruce Mayer, PE Engineering-45: Materials of Engineering
Simple Cubic Stucture (SC)Simple Cubic Stucture (SC) Rare due to poor
packing (only Po has this structure)
Close-packed directions are cube edges.
Coordination No. = 6• CoOrd No. (CN) = the
No. of Nearest Neighbors
Ro
tate
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt11
Bruce Mayer, PE Engineering-45: Materials of Engineering
Polonium, Z = 84, SC StructurePolonium, Z = 84, SC Structure HardSphere Model
a (pm) b (pm) c (pm) 335.9 335.9 335.9 90 90 90
Lattice Constants InterAxial 's
Reduced Sphere Mod
Note: 100 PicoMeters = 1 Å http://www.webelements.com/webelements/index.html
http://www.webelements.com/webelements/elements/text/Po/key.html
http://www.webelements.com/webelements/elements/text/Po/xtal.html
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt12
Bruce Mayer, PE Engineering-45: Materials of Engineering
Atomic Packing Factor, APFAtomic Packing Factor, APF Assuming HardSphere Model
APF For Simple Cubic Structure = 52%
Cell Unit of Volume TOTAL
Cell Unit aIn ATOMS of VolumeAPF
close-packed directions
a
R=0.5a
contains 8 x 1/8 = 1 atom/unit cell
APF = a3
4
3(0.5a)31
atoms
unit cellatom
volume
unit cellvolume
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt13
Bruce Mayer, PE Engineering-45: Materials of Engineering
Body Centered Cubic (BCC)Body Centered Cubic (BCC) HardSphere Model
Atoms per Unit Cell = 1 + (8 x 1/8) = 2
CoOrd No. = 8• 8 Atoms Touch the
“Center” Atom Rotate
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt14
Bruce Mayer, PE Engineering-45: Materials of Engineering
Atomic Packing Factor: BCC Atomic Packing Factor: BCC Find Radius, r, in
terms of Lattice Const, a
Thus r in Terms of a
Atoms Touch On Cube Diagonal, L• L = a3 = L = 4r
aarra 433.04
343
And Vsphere = (4/3)R3
So the BCC APF
cellma
atmacellat
APF33
3
3
43
34
2
%02.68BCCAPF
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt15
Bruce Mayer, PE Engineering-45: Materials of Engineering
Face Centered Cubic (FCC)Face Centered Cubic (FCC) HardSphere Model
Atoms per Unit Cell = 6x½ + (8 x 1/8) = 4
CoOrd No. = 12• CN = 4top + 4bot + 4midRotate
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt16
Bruce Mayer, PE Engineering-45: Materials of Engineering
Atomic Packing Factor: FCC Atomic Packing Factor: FCC Find Radius, r, in
terms of Lattice Const, a
Thus r in Terms of a
Atoms Touch on Face Diagonal, f• f = a2 = 4r
aarra 3536.022
142
And Vsphere = (4/3)R3
So the FCC APF
cellma
atmacellat
APF33
3
3
22
134
4
%05.74FCCAPF
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt17
Bruce Mayer, PE Engineering-45: Materials of Engineering
FCC Stacking SequenceFCC Stacking Sequence
An ABCABC... Stacking Sequence• The 2D
projection
A sites
B B
B
BB
B B
C sites
C C
CA
B
B sites B B
B
BB
B B
B sitesC C
CA
C C
CA
The FCCUnit Cell
AB
C
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt18
Bruce Mayer, PE Engineering-45: Materials of Engineering
Hexagonal Close Packed (HCP) Hexagonal Close Packed (HCP) Built Up in an A-B
Stacking Pattern Exhibits NonCubic
Symmetry on a & c axes• c:a Ratio 1.633
Atoms per Cell = 6• (12 x 1/6)corners +
(2 x ½)top/bot + 3mid = 6
APF and CN are the SAME as the FCC Structure• APF = 74.05%
– Close Packeda
c
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt19
Bruce Mayer, PE Engineering-45: Materials of Engineering
HCP CoOrdination NumberHCP CoOrdination Number For 3 Stacking
Planes Below, Consider the CENTER Atom
Observe The Center Atom’s Nearest Neighbors• 6 Surrounding in the
Center Plane
• 3 Touching From Below
• 3 Touching From Above
Thus
12363 HCPCN
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt20
Bruce Mayer, PE Engineering-45: Materials of Engineering
Structure of Compounds Structure of Compounds Compounds: Often
have similar close-packed structures
NaCl Structure• Ionic Radii
– Na+ = 116 pm
– Cl– = 167 pm
Expand Na+ ions to Reveal Close-Packed X-tal Structure
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt21
Bruce Mayer, PE Engineering-45: Materials of Engineering
Theoretical Density, Theoretical Density, Atomic Radii for Crystals are Measured by
X-Ray Diffraction • Can use The Data From XRD Measurements to
Calc Density for Crystals
On the Macro Scale Densities are Calc’d by Weight & Measure of Chunks of Crystals
n AVcNA
# atoms/unit cell Atomic weight (g/mol)
Volume/unit cell
(cm3/unit cell)Avogadro's number (6.023 x 1023 atoms/mol)
Fcn of Ratom
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt22
Bruce Mayer, PE Engineering-45: Materials of Engineering
Theoretical Density Example Theoretical Density Example For Copper
• Ratom = 128 pm
• Acu = 63.54 g/mol
• Xtal Structure = FCC
Recall From FCC APF Calc
FCC Cu has 4 atoms per Unit Cell; so
And The VC = a3
3330
233
kg/m8893g/pm10893.8
10023.6pm128216
54.634
AC
Cu
NV
nA
macro = 8940 kg•m-3
0.53% HIGHER than Theoretical Value
RaaR 2222
1
333 22822 RRa
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt23
Bruce Mayer, PE Engineering-45: Materials of Engineering 15
Element Aluminum Argon Barium Beryllium Boron Bromine Cadmium Calcium Carbon Cesium Chlorine Chromium Cobalt Copper Flourine Gallium Germanium Gold Helium Hydrogen
Symbol Al Ar Ba Be B Br Cd Ca C Cs Cl Cr Co Cu F Ga Ge Au He H
At. Weight (amu) 26.98 39.95 137.33 9.012 10.81 79.90 112.41 40.08 12.011 132.91 35.45 52.00 58.93 63.55 19.00 69.72 72.59 196.97 4.003 1.008
Atomic radius (nm) 0.143 ------ 0.217 0.114 ------ ------ 0.149 0.197 0.071 0.265 ------ 0.125 0.125 0.128 ------ 0.122 0.122 0.144 ------ ------
Density (g/cm3) 2.71 ------ 3.5 1.85 2.34 ------ 8.65 1.55 2.25 1.87 ------ 7.19 8.9 8.94 ------ 5.90 5.32 19.32 ------ ------
Crystal Structure FCC ------ BCC HCP Rhomb ------ HCP FCC Hex BCC ------ BCC HCP FCC ------ Ortho. Dia. cubic FCC ------ ------
Characteristics of Some Elements at 20 °CCharacteristics of Some Elements at 20 °C
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt24
Bruce Mayer, PE Engineering-45: Materials of Engineering
16
(g
/cm
3)
Graphite/ Ceramics/ Semicond
Metals/ Alloys
Composites/ fibersPolymers
1
2
20
30Based on data in Table B1, Callister *GFRE, CFRE, & AFRE are Glass,
Carbon, & Aramid Fiber-Reinforced Epoxy composites (values based on 60% volume fraction of aligned fibers
in an epoxy matrix). 10
3 4 5
0.3 0.4 0.5
Magnesium
Aluminum
Steels
Titanium
Cu,Ni
Tin, Zinc
Silver, Mo
Tantalum Gold, W Platinum
Graphite Silicon
Glass -soda Concrete
Si nitride Diamond Al oxide
Zirconia
HDPE, PS PP, LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE *
CFRE *
GFRE*
Glass fibers
Carbon fibers
Aramid fibers
Why? Metals have... • close-packing (metallic bonding) • large atomic mass Ceramics have... • less dense packing (covalent bonding) • often lighter elements Polymers have... • poor packing (often amorphous) • lighter elements (C,H,O) Composites have... • intermediate values
Data from Table B1, Callister 6e.
Densities Of Material ClassesDensities Of Material Classesmetals > ceramics > polymers
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt25
Bruce Mayer, PE Engineering-45: Materials of Engineering
SINGLE Crystal Applications SINGLE Crystal Applications Most Crystalline
Materials Are Composed of many Small Crystals• i.e., they are
POLYcrystalline and exhibit a GRAIN Structure
Grain Structure Introduces Weakness into the Material
But Making LARGE Single Crystals is Very Difficult; i.e., Expensive
Single Xtal Examples• SemiConductor
wafers
• Turbine Blades
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt26
Bruce Mayer, PE Engineering-45: Materials of Engineering
1-Material; Several Crystal Types1-Material; Several Crystal Types Polymorphism More Than One
Crystal Structure• Often Found in Compounds
Allotropy Polymorphism in ELEMENTAL Solids
Examples
• Carbon Allotropes– Graphite
– Diamond
– Bucky Balls/Tubes
• Iron Allotropes– BCC Ferrite (RT)
– FCC Austenite (> 912 °C)
– BCC Delta (~TMelt)
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt27
Bruce Mayer, PE Engineering-45: Materials of Engineering
Cabon Cabon Allotropes Allotropes Diamond - tetrahedral,
covalent bonds, Single-Element Form; the ZincBlende Crystal structure
Graphite – Layers of Hexagonally Bonded C-atoms
C60 Fullerenes
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt28
Bruce Mayer, PE Engineering-45: Materials of Engineering
WhiteBoard WorkWhiteBoard Work Example
similar to P3.15• Uranium
• Orthorhombic
• Lattice Constants– a = 286 pm
– b = 587 pm
– c = 495 pm
• ratom = 138.5 pm
= 19050 kg/m3
• AU = 238.03 g/mol
→ FIND APF
SR Case
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt29
Bruce Mayer, PE Engineering-45: Materials of Engineering
Uran
ium
Un
it Cell (B
CR
)U
raniu
m U
nit C
ell (BC
R)
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt30
Bruce Mayer, PE Engineering-45: Materials of Engineering
Uran
ium
Un
it Cell (B
C)
Uran
ium
Un
it Cell (B
C)
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt31
Bruce Mayer, PE Engineering-45: Materials of Engineering
Uran
ium
Un
it Cell (S
R)
Uran
ium
Un
it Cell (S
R)
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt32
Bruce Mayer, PE Engineering-45: Materials of Engineering
All Done for TodayAll Done for Today
Uranium hasthe Highest ZOf Any Natural
Element
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt33
Bruce Mayer, PE Engineering-45: Materials of Engineering
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt34
Bruce Mayer, PE Engineering-45: Materials of Engineering
P3-15P3-15
BMayer@ChabotCollege.edu • ENGR-45_Lec-03_Crystal_Structure.ppt35
Bruce Mayer, PE Engineering-45: Materials of Engineering