Corrosion and rusting
Corrosion is the destruction of a material by chemical reactions
with substances in the environment . Rusting is the corrosion
of ironBoth air (oxygen) and water are needed for iron to rust:
iron + oxygen + water → \rightarrow →
The rusting experiment: three test tubes each with an iron nail
Tube 1: nail in boiled water with a layer of oil on top (water,
no air): no rust
Tube 2: nail in air with anhydrous calcium chloride to absorb
water vapour (air, no water): no rust
Tube 3: nail in tap water open to the air (both): rusts
Only the nail with both air and water rusts, so both are necessary
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What iron needs in order to rust oil boiled water, with a layer of oil on top water but NO air no rust calcium chloride dry air, with calcium chloride to absorb water air but NO water no rust water, open to the air air AND water RUSTS Iron rusts only when BOTH water and oxygen are present. Rust is hydrated iron(III) oxide. Barrier methods — painting, greasing, or coating with plastic — keep the air and water out. Galvanising adds a layer of zinc, which is a barrier AND sacrificial protection: the zinc is more reactive, so it corrodes instead of the iron. The three-tube rusting experiment: boiled water under oil, dry air with calcium chloride, and water open to air, with only the third nail rusted
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In the full topic
• Corrosion and rusting• Preventing corrosion• Alloys as useful materialsRead the free chemistry topics →