Term
metals, ceramics, polymers
comparison |
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Definition
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Metals
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metalic elements or alloy
high thermal and electrical conductivity due to unbound valence electrons
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Ceramics
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both metallic and nonmetallic elements
cement, rock, glass, oxide
hard, brittle
thermal and electrical insulator
resistant to high temperature and severe environment
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Polymers
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low density
non-metallic macromolecules
poor thermal and electrical conductors due to shared valence electrons
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Term
| What do atomic bonds dictate? |
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Definition
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Term
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Definition
- electrons transfer from cation (metallic) (+) to anion (onometallic)
- cation is surrounded by anions to reduce repulsion
- highly ordered structure
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Term
Covalent bonding
forming x4
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Definition
- share four valence electrons
- equal tendencies to donate and accept electrons
- carbon, silicon
- every atom has four neighbors to fourm tetrahedra （四面体） or crystals
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Term
Ionic, covalent, metallic bonding
characteristics comparison |
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Definition
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Ionic Bonding
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Covalent Bonding
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Metallic Bonding
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Bond strength
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high
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high
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low
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directional bonding
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no
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yes
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no
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melting point
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high
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high
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moderate
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electrical & thermal conductivity
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low
(bound electrons can’t carry charge)
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low
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high
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Physical
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hard, stiff, brittle (breaks along bonding directions)
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hard, brittle or soft, elastic
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Transparent
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yes
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yes
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Others
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ductile（延展性）, luster（有光泽）
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Term
Metallic bonding
forming x3 |
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Definition
- ionizable atoms (transition metals)
- positive ions held together by electron cloud
- atoms switch spots easily
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Term
Comparison:
crystalline, amorphous, polycrystalline
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Definition
crystalline: ordered
amorphous: random
polycrystalline: many small randomly oriented crystal |
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Term
Polycrystalline
example x2
defects x3 |
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Definition
Most metals and ceramics
point
- addition of an extra atom (interstitial) or removal of an atom (vacancy)
line
- misalignment/movement of atoms in 1D (dislocation)
- introduced during solidification or when metal is deformed permanently
- lend ductility （延展性） to meltal
- dislocations impede movement of other dislocations
grain boundaries
- interface between crystals of identicle composition but different orientation
- small grains, more boundary surface area, more energy requred to break, tougher
- rapid cooling produces smaller grains
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Term
Microstructure
elements x6 |
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Definition
Grain structure
Grain size
Grain shape
Grain Orientation
Porosity
*substitute Chain for Grain if polymers |
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Term
| Definition of stress and strain |
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Definition
stress = force/area
strain = length change/original length
Yough's modulus = stress/strain |
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Term
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Definition
- test tension, compression, shear
- measure load and elongation
- calculate stress, strain and plot
- find Young's Modulus
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Term
elastic deformation x4
plastic deformation x4 |
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Definition
- small changes in atomic spacing and stretching of bonds
- sample return to original length and no permanent deformation
- elastic/proportional limit
- material breaks in elastic region (yield point) called brittle failure
- common for metals and polumers
- ultimate strength = maximum strength = breaking strength = rupture point
- toughness = area under elastic curve
- ductility = area under whole curve
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Term
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Definition
ceramics > metals > polymers
collagen > elastin |
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Term
stress relaxation
definition & plot |
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Definition
if under constant stress, the level of stress decreases over time
[image] |
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Term
| What does stiffness of a material depend on? |
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Definition
strain rate
faster rate gives stiffer material |
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Term
Isotropic & Anisotropic
definition |
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Definition
| Isotropic: material properties same in all directions |
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Term
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Definition
a constant stress is instantaneously applied to the material and the resulting strain is a function of time
[image]
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Term
what bond does metals have?
what bond does ceramics have? |
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Definition
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