Corrosion + Prevention Methods `MK Based Answers

Define Corrosion

Corrosion is the oxidation of a metal by substances in the environment (H2O and O2)

What are the 4 prevention methods?

• Application of a surface layer

• Galvanising

• Sacrificial Anode

• Cathodic Protection

Application of a surface layer - MK Explained

• This is the coating of the iron with a protective nonmetal or a less reactive metal layer (1)

• This will prevent oxygen and water from coming in contact with the iron and reacting (1)

• However, if a less reactive metal is used as the coating, then any scratch on the irons surface will lead to an accelerated rate of corrosion on the iron (1)

Galvanising - MK Explained

• Coat iron with a protective layer of a more reactive metal

• This will prevent water and oxygen from making contact with the iron and reacting with it

• Even if the surface coating is scratched, the more reactive metal will be sacrificially oxidised instead of the iron being oxidised, thus preventing iron corrosion

• An example would be K, Ba, Sr, Ca, Zn

Sacrificial Anode - MK Explained

• This involves connecting the iron by a conducting wire to a more reactive metal (a metal with a higher standard oxidation potential) (1)

• The more reactive metal is therefore preferentially and sacrificially oxidised (1)

• The sacrificial anode can be replaced easily (1)

Cathodic Protection - MK Explained

• Scrap iron is used as the inert anode (1)

• A low voltage (DC current) is applied to make the iron structure a negative charge by making electrons flow there (1)

• This causes the iron to become the cathode (-) and thus the site of reduction

• For corrosion to occur, the iron must be the site of oxidation (1), thus making the iron the cathode prevents its oxidation