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Corrosion
deterioration of a metal due to a chemical reaction in the environment
Rusting
corrosion of iron and its alloys due to reaction with oxygen and water
Rust chemical formula
hydrated iron (III) oxide, Fe₂O₃H₂O
What is the appearance of rust? [2]
- reddish-brown
- crumbly
Formation of rust symbol equation:
4Fe + 3O₂ + 12H₂O → 2Fe₂O₃.6H₂O
Formation of rust word equation:
iron + oxygen + water → hydrated iron (III) oxide
What does it mean if a substance is hydrated?
there is water loosely bonded in its structure
Methods to prevent rust [5]:
- paint
- oil/grease
- plastic
- a more reactive metal
- a less reactive metal
How do these methods prevent rust?
stop oxygen and water contacting the iron
Galvanised
iron or steel objects that have been protected from rusting by a thin layer of zinc metal at their surface
Sacrificial protection
using a more reactive metal to protect iron from rusting
How does galvanisation stop iron from rusting? [3]
- uses metals more reactive than iron
- water and oxygen react with them first, protecting the iron
- works even if the coating is scratched
Metals used for galvanisation of iron [3]
- zinc
- aluminium
- magnesium
Conditions for rusting [2]:
- exposure to oxygen (through liquid or air)
- exposure to water
What substance speeds up rusting?
salt
Alloy
mixture of multiple metals
Why are alloys more useful than pure metals?
alloys are harder due to their uneven layers of ions
Bronze is made from [2]
- copper
- tin
Brass is made from [2]
- copper
- zinc
What are the properties of bronze? [3]
- hard
- malleable and ductile
- resistant to corrosion
What are the properties of brass? [3]
- hard
- malleable and ductile
- resistant to corrosion
What is bronze used in? [3]
- statues
- decorative items
- ship's propellers
What is brass used in? [3]
- musical instruments
- door fittings
- taps
Useful property of all aluminium alloys
low density (lightweight)
What are aluminium alloys used in? [2]
- aircraft building
- armour plating on military vehicles
Why is gold often alloyed? [3]
- harder
- more resistant to wear
- different shades
Carats
measure of the purity of gold
How do carats work?
24 carats is 100% pure; the fraction of 24 defines the purity of the gold
Steel
alloy of iron with carbon and/or other elements
Carbon steel
alloy of iron containing controlled small amounts of carbon
High carbon steel vs. low carbon steel [2]
- high carbon steel is stronger, but more brittle
- low carbon steel is weaker, but more malleable and ductile
What is nickel-steel used for? Why? [4]
- long-span bridges
- bicycle chains
- military armour plating
- because it is resistant to stretching forces
What is tungsten-steel used for? Why? [2]
- high speed tools such as drill bits
- operates well in high temperatures
What is stainless steel?
steel containing chromium and nickel
What is stainless steel/chromium-nickel-steel used for? Why? [3]
- cooking utensils
- cutlery
- because it is hard and corrosion-resistant (does not rust)
