C15 - Rusting Flashcards
corrosion
caused y chemical reactions between metal and substances in the environment
- destruction of material
- effects strength
rusting
corrosion of iron
-becomes soft, crumbly, flakes off
oxide layer of aluminium
-protects it from further corrosion
what is needed for iron to rust
both air and water
rust chemical formula
hydrated iron oxide
-water loosely bonded in structure
-iron + water + o2
prevention of rust
coat with:
- paint
-oil/grease
- plastic
-less/more reactive metal
sacrificial protection or electroplating elements
-zinc, mg, al for iron
sacrificial protection or electroplating process
-iron is galvanised (protected)
-reacts with water/o2 instead
why is zinc used in electroplating
zinc = more reactive and better reducing agent
electroplating used on
-equipment under sea
- where coating may be scratched
why are alloys harder than pure metals
- regular layers in a pure metal are distorted by differently sized atoms in alloy
bronze
alloy of copper + tin
-tough
-resists corrosion
-statues
brass
-alloy of copper + zinc
- musical instruments
aluminium alloys
- low density
- aircraft
why are pure metals alloyed
to make them harder
- pure iron = too soft to be useful
gold in jewellery
- alloy of silver,copper, zinc
carat
proportion of gold in alloy is measured in this
-24 = 100%
- 18 = 75%
steel
allows of iron and carbon and other metals
-added to change properties
carbon steels - high carbon properties
- strong but brittle
low carbon steel properties
softer
easily shaped
stainless steels
- contain chromium and nickel
- hard + resists corrosion
stainless steels eg
- cutlery
-pipework
nickel steel alloy eg
bridges
-bicycle chains
properties of polymer depends on
monomers affect this
- changing reaction conditions
HD and LD poly(ethene)
made from ethene
thermosoftening polymers
-soften easily
- re set when cooled
- made from individual polymer chains that are tangled
-can be remoulded
thermosoftening polymers - soften easily?
weak intermolecular forces
thermosoftening polymers - re set when cooled?
- intermolecular forces bring polymer molecules back
Thermosetting polymers
-don’t melt
- fixed together by strong covalent bonds
-form cross links between polymer chains
-don’t separate
thermosetting polymers heated highly
will char not melt
soda lime glass
made by heating sand, sodium carbonate, limestone
-form random arrangement when cooled
Borosilicate glass
made from glass + boron trioxide
- higher melting point than soda lime
-use = ovenware
clay ceramics eg
-pottery and bricks
ceramics
made by shaping wet clay
-heating in furnace
-hard but brittle
Composites
made of 2 materials
-one as binder for other
composites - binder
binds fibres of other material
-reinforcement process
purpose of composites
improves desirable properties that neither original material could offer alone
ceramics + polymers prop
- tough
-flexible - eg fibreglass (kayak)
examples of composites
plywood - thin sheets glued together
concrete - hard and strong in compression
concrete materials
cement
sand
gravel
water
plywood pros
prevents splitting along grain
