Rust is the name of iron oxides of different colors, usually red or black, that form when iron or steel corrodes.
What causes rust is the reaction of iron with oxygen dissolved in an electrolyte, usually it's rainwater, condensing water from the atmosphere or freshwater.
The corrosion of iron and steel is an electrochemical reaction, it means that there is an exchange of electrons between the metal that is oxidized and corrodes and oxygen that is reduced.
There are always two different reactions in a corrosion process:
1) oxidation of Iron
2Fe ---> 2Fe2+ + 4e-
2) reduction of Oxygen
O2 + 4 e- + H2O ---> 4OH-
The overall reaction is:
2Fe2+ + 4OH- ----> 2Fe(OH)2
Fe(OH)2 reacts further with oxygen to form Iron oxides: Fe2O3 (hematite, red rust), Fe3O4 (magnetite, black)
Is possible to stop rusting of iron or steel by removing what causes rust, i.e. water. A metal placed in a dry environment corrodes less than a metal placed in a wet environment, like a marine atmosphere.
One of the most used method to stop rust, is to apply a coating that isolate the metal from the environment and prevent contact with water.
What is rust:
- iron oxides of different colors
What causes rust:
-oxygen dissolved in water reacts with iron
What is needed to rust iron:
-water must be in contact with metal surface
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