Corrosion of metals
Introduced| English | Meaning |
|---|---|
| rust/rʌst/ | The mixture of hydrated iron oxides and related compounds formed when iron corrodes in the presence of water and oxygen. |
| corrosion/kəˈrəʊʒn/ | The gradual destruction of a material through chemical or electrochemical reactions with its surroundings. |
| rusting/ˈrʌstɪŋ/ | The corrosion of iron, forming hydrated iron(III) oxide (rust). |
| galvanising/ˈɡælvənaɪzɪŋ/ | Coating iron or steel with zinc to protect it from corrosion. |
| sacrificial protection/ˌsækrɪˈfɪʃl prəˈtekʃn/ | Protecting a metal by electrically connecting it to a more reactive metal, which oxidises preferentially. |
When metals are eaten away
- Leave iron out in the rain and it slowly turns to flaky brown rust 铁锈.
- This slow destruction of a metal is corrosion 腐蚀.
Rusting of iron requires which two things? (Select all that apply.)
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Both water and oxygen are needed.
The corrosion of iron specifically is called ______.
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Rust is hydrated iron(III) oxide.
Rusting 生锈 of iron
- Rusting is the corrosion of iron, forming hydrated iron(III) oxide (rust).
- It needs both water and oxygen — remove either and iron won't rust.
Corrosion slowly eats away unprotected metal
Rusting needs both water and oxygen — the nail rusts only in the tube that has both
Why iron rusts — and how to stop it
Step through rusting. Iron needs BOTH water and oxygen, and once it starts the rust flakes off to expose fresh metal — which is why we protect iron.
Painting iron prevents rust by:
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A barrier keeps out the water and oxygen.
Galvanising means coating iron with zinc.
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Zinc both forms a barrier and protects sacrificially.
Preventing corrosion
- Barrier methods: painting, oiling or coating to keep out water and oxygen.
- Galvanising 镀锌: coating iron with zinc.
In sacrificial protection, the iron is protected by a metal that is:
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The more reactive metal corrodes instead.
Sacrificial protection 牺牲保护
- A more reactive metal (like zinc) corrodes instead of the iron, protecting it.
- The zinc is the "sacrifice" — it reacts in preference to the iron.
The more reactive zinc corrodes and gives its electrons to the iron, so the iron is protected even where the surface is scratched
Rusting needs both water and oxygen. A famous experiment shows iron does not rust in boiled water (no oxygen) or in dry air (no water). Both must be present.
You've got it
- rusting is the corrosion of iron; it needs both water and oxygen
- prevent it with a barrier (paint, oil) or by galvanising (zinc coat)
- sacrificial protection: a more reactive metal corrodes instead of the iron