ce 336 material properties atomic structure determines: physical properties chemical properties...
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CE 336
Material Properties
Atomic Structure determines: Physical Properties Chemical Properties Biological Properties Electromagnetic Properties
CE 336
Physical Properties
Density
Mass
Structure
Permeability
Moisture content susceptibility
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Physical Properties
Specific gravity
Color
Texture
Shape
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Chemical Properties
Resistance to deterioration
Oxidation
Solubility
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Biological Properties
Bacterial growth
Hazard/exposure consideration
Resistance to infestation
Biodegradability
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Electromagnetic Properties
Conductance
Galvanic potential
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Material Selection
Strength ServiceabilityDeflectionsAdaptability to futureDurability
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Material and Testing Standards
ASTM /ASME StandardsAASHTO, State Highway, EPA, HUD, US-ArmyBOCA,ICBO, ICC, ISOAISC/ACI/AITC minimum quality standards, minimum application standards Some may be performance standards
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Primary Bonds
Types of primary bond 1. Ionic - transfer of electrons
Metallic and non metallic elements Sodium chloride salt
2. Covalent - sharing with adjacent atoms Polymeric materials Hydrogen gas
3. Metallic - mass sharing of electrons All metal
Na Cl
Metal ionsElectron cloud + + + +
+ + + +
+ + + ++ + +
+ + +
H H
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Ionic Bonds
Electrons transferred
Strong attractive forces between atoms
Solids at room temps
High melting temperature
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Ionic Bonds
Solution-good conductors
Solid-poor conductors
Soluble in polar solvents, water
Insoluble in nonpolar solvents, organic solvents.
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Ionic Bonds
Low energy metals bonding to high energy nonmetals
Ca+2 +O-2 = CaO
Exothermic in formation
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Attractive Forces
NaCl
MgO
131.0
81.195.
112
ccForce
951.0
40.165.
222
ccForce
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Covalent Bonds
Electrons are shared in joint orbital
Can lead to small molecules with polarity
No “bonding” between molecules, but some attraction and repulsion (secondary bonds).
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Covalent Bonds
Gases, liquids, (mech. weak substances)
Can lead to long extended networks
Ceramics, diamond (high binding energy)
Polymer chains (weak between chains)
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Metallic Bonds
Metal – “element with 1, 2, or 3, valence electrons”
No clearly defined molecules
Electron cloud & Electronic bond
Equilibrium of repulsive forces
+
+ + +
+ +
+ +
+ +
+
+ +
+ +
+
+
+ +
+ +
+ +
++ +
+ +
+
+
+ +
+ +
+ +
+
+ +
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Secondary Bonds - van der Waals Bonds
Weak compared to primary bondsResult from dipoles - electrostatic attraction Dipole occurs when have separation of
positive and negative portion of atom or molecule
Causes gasses to liquefy
Water also a dipole
Cl H
+ -
H
H
O105°
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Strengths of Different Types of BondsBonding Type Material Energy Melt
kJ/mole Temp.°C
Ionic NaCl 640 801
Covalent Si 4501410
Metallic Fe 4061538
Hydrogen H2O 51 0
van der Waals Cl 31 -101Source: Callister, Materials Science and Engineering
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Structure of Materials
Crystalline “Repeated pattern or arrangement of
atoms” Ordered systems not necessarily
crystalline Laminar or small ordered systems arranged
in disorganized manner
Amorphous Random molecular structure
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Material Classification
Metallic Solids Metallic bonding Steel, iron, aluminum, copper, other metals Crystalline
Organic Solids Primarily covalent and van der Waals bonding Asphalt, plastics, wood Largely amorphous (although not entirely)
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Material Classification
Inorganic Solids (ceramics) Primarily ionic and covalent bonding Portland cement, bricks, glass,
aggregates, minerals Largely crystalline (but not entirely)
*Note the change
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Bonding and Structure of Materials (Generally Speaking)
Material Bonding Structure
Steel Metallic Crystalline
Aggregates / Minerals
Ionic, Covalent Crystalline, Some Amorphous
Portland Cement
Ionic, Covalent, van der Waals
Amorphous, Crystalline
Asphalt Covalent, van der Waals
Amorphous
Polymers Covalent, van der Waals
Amorphous
Wood Covalent, van der Waals
Crystalline, Amorphous
Glass Covalent Amorphous (unaltered)
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Crystalline Structures
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Crystalline MaterialsAtoms arranged in repeating and regular arrayUnit cells individual crystals structural part Unit cell - smallest repeating unit
Body centered cubic (BCC)
Face centered cubic (FCC)
Hexagonal close-packed (HCP)
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Concepts of Crystalline Structure
Coordination numberNumber of “nearest neighbors”Here 8 for BCC
One at each corner
Atomic Packing Factor (APF)APF = Volume of atoms in cell
Total volume of cell
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Body Center Cubic Structure
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Face Centered Cubic Structure
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Hexagonally Close Packed
6 around 1 on top6 around 1 on bottom3 at mid-height
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Body Center Cubic Structure
Pure Iron
(600°C to 910°C)
Low Carbon Steel
(723°C to ~1400°C)
Some Aluminum Alloys
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Face Centered Cubic Structure
Pure aluminum
(-269°C to melting)
Pure iron
(910°C to 1403°C )
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Defects in Crystals
Point
Line
Area
Volume
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Point DefectsCrystal contains many - many unit cells Explain permanent (plastic) deformation in metals
Defects Interstitial
vacancy - missing interstitial - extra
Impurities Interstitial - extra
Carbon in iron Substitutional
Copper alloy in nickel
Source: Callister, Materials Science and Engineering
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Lattice Defects
Imperfections in arrangements of atoms
edge dislocation - line defect
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Arrangements of CrystalsGrain boundary
Types of Interfaces?
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Amorphous Structure