ceramics, composites, polymers Flashcards
whats a ceramic + type of bonding
combination of one or more metals with non-metallic element
- ionic or covalent bonding
mechanical prop. of ceramics 6/8
brittle
high hardness + compressive strength
low density
wear + chemical resistant
low thermal + electrical conductivity
high melting point
engineering ceramics
made to me more dense, hence stronger
- oxide ceramics
- non oxide ceramics
composite ceramics
carbon fibre reinforced silicon carbide used for braking systems in high performance cars
glass
soda lime, borosilicate, lead glasses
- basic ingredient is silica
- transparent to light
- brittle, shatters to impact loads
- weak tension
- strong compression
traditional clay ceramics
porcelains, earthenware, stoneware
p: fine tablewear, science equip
e: bricks
s: tiles
what is a composite + adv 3
combination of 2/+ different materials at a macroscopic level
- materials do not dissolve or blend into each other
- high strength + stiffness
- low weight ratio
- can be designed in addition to structure
fibre reinforcement
consist of matrix and fibres
- contribute to prop..
strength + stiffness, heat conductivity, chemical or electricity resistance
composite for brake lining
asbestos:
- resistant to high temp, good frictional prop
- asbestos fibres mixed with bronze particles bonded together with resin
sintered metal composites:
- metal particles pressed and bonded together with resin
- good heat dissipation
stable coeff of friction
what polymer + characteristics 3
material composed of long molecular chains formed by linking shorter chain molecules
- high strength and rigidity with low creep
- maintain over range of temps
addition polymerisation
process linking same monomers into larger polymer molecules
- NOT changing chemical composition NO by product
- most polymers made this way eg perspex
condensation polymerisation
two or more different monomers react together to produce a polymer WITH by product
- wide range of plastics eg nylon
thermosoftening/thermoplastic
- long molecules entangled together
- links between chains are strong primary covalent bonds, bonds btw links r weaker secondary bonds
- low temp: solid, molecules tgt
- heated, molecules move apart, seperate bonds, weaker chains, molecules move freely, reshape polymer
- cooling, bond reestablish and solidify new shape
thermosetting
similar to thermoplastic but with chemically active sites along chains
- sets off sites forming covalent bonds along n btwn chains forming 3d net like structure
- molecule not free, harden material
- non crystalline and stronger than thermoplastics
5 prop of polymers
low thermal conductivity
lower density
corrosion resistant
more ductiles
lower hardness + stiffness
higher creep value