CHAPTER 2 -- light Flashcards
what are secondary bonds
dipolar electrostatic attraction. much weaker than primary bonds.
example of dipolar molecules and how they work.
H2O
one positive side while the other pole is negative
how are materials classified by bond type?
metals
inorganic solids
organic solids
metallic, covalent and ionic bonds and valence electrons : what about them?
metallic bonds b/n atoms w/ 1,2 or 3 valence electrons are for metals
covalent and ionic bonds b/n atoms w/ 5, 6 or 7 valence electrons are inorganic solids
what are organic solids
long molecules of covalent hydrogen carbon molecules w/ secondary bonds b/n chains
hydrocarbons
asphalt, plastics and wood
what is a crystal lattice structure
lattice repeating pattern of atoms
3D geometric pattern
unit cell (smallest repeating unit)
what is a body centered cubic?
- each corner
- center of lattice
- 9 atoms
what is a face centered cubic?
- each corner
- center of faces
- 14 atoms
what is a hexagonal close pack?
- each corner
- center top and bottom face
- center place
- 17 atoms
What are the 4 types of boundaries?
- coherent
- coherent strain
- semicoherent
- incoherent
The size and arrangement of crystal grains influence the material behaviour. This mainly depends on
- rate of cooling of the molten metal
- - smaller grains are formed by rapid cooling and increase toughness
What changes the structure of materials?
Heat treating and plastic strains during manufacturing change grain structure
What are alloys
one or more compounds dissolved in a metal
What alloy is steel?
alloy of iron and carbon but frequently contains chromium, copper, nickel, phosphorous, etc.
Alloys are possible only if the…
alloys are possible only if the different material have compatible crystal structures
What are interstitial atoms?
atoms that fit b/n the metal atoms
must have an atomic radius less than 60% of the host metal and can dissolve only about 6% into the host
what are substitutional atoms?
takes the place of a host atom in the lattice. if atoms are similar enough, compounds mix easily.
what are the three axis of a phase diagram?
x : temperature
y : pressure
z (sometimes) : brine composition (%)
what are binary phase diagrams?
phase diagram that displays relationship b/n percent of elements et transition temperatures
phase diagrams exist for what kind of mixtures?
soluble
partly soluble and
insoluble
Definition of Eutectic?
Sudden transition from liquid to solid w/out a 2phase region. On a phase diagram.
Define ceramics
- high strength
- high durability
- brittle due to bonding (covalent or ionic)
What are glasses?
based on silica and have a random or amorphous but very stable structure
What are vitreous ceramics?
Clay products like pottery, bricks, etc.
What are high-performance ceramics?
Expensive, highly refined materials specially developed to have very specific properties
2 other classes of inorganic solids?
cement and concrete
rocks and minerals
The mechanical properties of organic solids depend on
- polymer chain length
- extent of cross-linking (non-reversible)
- type of radical compounds linked to the H-C
What is a Mer?
repeating unit in a polymer chain
What is a monomer?
a single mer-unit (n=1)
What is a polymer?
Many mer-units along a chain (n=10^3 or more)
What is a degree of polymerization?
average number of mer-units in a chain
3 types of chain structures for polymers
linear
branched
cross-linked (e.g. PEX)
4 classes of organic compounds
thermoplastics
thermosets
elastomers or rubbers
natural polymers
describe thermoplastics + examples
transition from elastics to viscous plastic behavior when heated as the cross-link bonds b/n chains melt.
ex : asphalt PVC, polyethylene, polypropylene, polystyrene, teflon, etc.
describe thermosets + examples
chemical rxn to harden stable cross-links that don’t soften when heated
ex : epoxy, polyesters, phenol-formaldehyde, Formica.
describe + examples for elastomers or rubbers
limited cross-linking
flexible structure
ex : polyisoprene (natural rubber, silicone), polybutadiene (synthetic rubber) and polychloroprene (Neoprene)
what are natural polymers?
wood
2 other types of polymer chain structures?
ordered structure linear polymer
cross linked structure linear polymer
