Bonding Flashcards
3 primary bond types
Ionic
Covalent
Metallic
2 secondary bond types
Van see waals
Hydrogen
Main bonds in metals/alloys
Metallic
Main bonds in ceramics
Ionic/ covalent
Main bonds in polymers (2 aspects)
Covalent bonds between carbon atoms in chains
Van der waals or hydrogen bonds between chains
Elastic modulus and melting point are a function of
Bond energy
3 assumptions for materials structure
Atoms are close packed hard spheres
Atoms are packed two dimensionally in atomic planes
Planes are stacked to form crystals
3 arrangements of atoms are
Face centered cubic
Hexagonal close packed
Body centred cubic
Main features of FCC
Atom in each corner and on each face
Close packed
More slip directions so more ductile
Main features of BCC
Atom on each corner. 1 atom in centre
Non close pack structure
3 atom arrangements in order of ductility (best-worst)
FCC
BCC
HCP
3 atom arrangements in order of strength (best-worst)
HCP
BCC
FCC
What determines density( 3)
Which is most significant
Atomic weight ( most significant)
Size of atoms
Atom packing
What does crystalline mean
Regularly repeating pattern of structural units
Most materials are crystalline
FCC and HCP take up how much available space
74%
BCC takes up how much available space
68%
Ferrite (alpha) is iron at what temp with what packing
Room temp
BCC
Austenite is iron at what temp and with what packing
Above 912 c
FCC
Ferrite (delta)is iron at what temp and with what packing
Above 1394 c
BCC
Above what temp does iron become liquid
1538
Why do u quench iron
Stops carbon diffusion
Creates new structure which is harder to deform
What is another name for noncrystalline
Amorphous
Key feature of metallic crystal structure and 3 reasons why
Densely packed as
Only 1 element so atomic radii is constant
Metallic bonding is not directional
Electron clouds shield cores from each other
Atomic packing in glasses
Base often amorphous silica
Rapid cooling means the amorphous structure achieved by melting is maintained
Crystal structure of ceramics (?2 main facts)
Composed of at least 2 elements
Have cations and anions
Most materials are polycrystalline. Each crystal is called a …. with …. separating each one
Grain
Grain boundaries
4 crystalline imperfections
Vacancies
Solute atoms
Dislocations
Grain boundaries
Polymers are made up of….
they can be either …. or ….
Long chains of carbon atoms
Amorphous, crystalline or both
Polymorphism is
When materials change from one structure to another
Fullerenes are
Spherical cluster of 60 carbon atoms
Carbon nanotubes are
Sheet of graphite rolled into a tube. The ends are capped with fullerene hemispheres
Graphene is
A single atomic layer of graphite composer of hexagonally bonded carbon atoms
Diamond is only …. at
Meta stable
Room temp and pressure
Shape memory alloys are
Materials that show a memory when they are deformed /heated/ cooled due to reversible change in structure
