Material Properties
Atomic Structure determines:




Physical Properties
Chemical Properties
Biological Properties
Electromagnetic Properties
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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
Serviceability
Deflections
Adaptability to future
Durability
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Material and Testing
Standards
ASTM /ASME Standards
AASHTO, State Highway,
EPA, HUD, US-Army
BOCA,ICBO, ICC, ISO
AISC/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
Na


2. Covalent - sharing with adjacent atoms


Polymeric materials
Hydrogen gas Metal ions
Electron cloud
3. Metallic - mass sharing of electrons
 All metal
H H
+ + + +
+ + +
+ + + +
+ + +
+ + + +
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Cl

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
Force
 c


.
95
1


1
1 .
81

2
 c

0 .
131
MgO
Force
 c


.
65
2


2
1 .
40

2
 c

0 .
951
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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 bonds
Result from dipoles - electrostatic attraction

Dipole occurs when have separation of positive and negative portion of atom or molecule
Cl H
+ -
H
O

Causes gasses to liquefy
Water also a dipole
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H
105
°

Strengths of Different Types of
Bonds
Bonding Type Material Energy Melt kJ/mole Temp.°C
Ionic
Covalent
Metallic
Hydrogen van der Waals
NaCl
Si
Fe
H
2
O
Cl
640
450
406
51
31
801
1410
1538
0
-101
Source: 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
*Note the change
Inorganic Solids (ceramics)



Primarily ionic and covalent bonding
Portland cement, bricks, glass, aggregates, minerals
Largely crystalline (but not entirely)
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Bonding and Structure of
Materials
(Generally Speaking)
Material Bonding Structure
Steel Metallic Crystalline
Aggregates
/ Minerals
Portland
Cement
Asphalt
Polymers
Wood
Glass
Ionic, Covalent Crystalline, Some
Amorphous
Ionic, Covalent, van der
Waals
Amorphous,
Crystalline
Covalent, van der Waals Amorphous
Covalent, van der Waals Amorphous
Covalent, van der Waals Crystalline,
Amorphous
Covalent
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Amorphous
(unaltered)

Crystalline Structures
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Crystalline Materials
Atoms arranged in repeating and regular array
Unit 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 number
 Number 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 top
6 around 1 on bottom
3 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 Defects
Crystal 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
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Source: Callister, Materials Science and Engineering

Lattice Defects
Imperfections in arrangements of atoms
 edge dislocation - line defect
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Arrangements of Crystals
Grain boundary
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Types of Interfaces?

Amorphous Structure
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