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C5 - Microscopic Materials (Metals (Polycrystalline (Regular repeating…
C5 - Microscopic Materials
Size of an Atom
Rayleigh's Oil Drop Experiment
Measure diameter of oil drop (d)
Calculate radius (r)
Place on still water and observe spreading (use Talcum power to see more easily)
Measure diameter of patch of oil (D)
Calculate radius (R)
Metals
Positive ions surrounded by delocalised electrons
Polycrystalline
Regular repeating lattice of crystals/grains
Good conductors of heat and electricity
Electrostatic attraction between ions and electrons for non directional metallic bonds
Makes metals stiff
Strong bonded lattice makes metals tough
As ions are able to adjust to forces making the malleable and ductile
Expand
Alloying is when another element is added to the metal to pin the dislocations
Makes the metal stiffer, harder and more brittle
Ceramics
Giant rigid structures
Polycrystalline (similar to metals)
Some ceramics, like glass, are amorphous
This means there is no overall pattern
The quicker they are cooked, the more amorphous they are
Amorphous structure means there are no slip plains like metals
No mobile dislocations therefore they are very brittle
Atoms are either ionically or covalently bonded so they are very stiff
Polymers
Lots of monomers joined together
Can be natural or man made
Covalently bonded
Meaning even thin polymers are quite strong
Polymer chains are often entangled
These can untangle due to their rotational bonds
Makes Polymers very flexible
Cross-linking bonds link chains together
Makes the structure more stiff and brittle (e.g. Polystyrene cup)
