Question 7 - Corrosion and Rust

Question 1

Describe one approach for the limitation of corrosion on steel hulled ships.

Answer 1

Sacrificial cathode protection.

Question 2

What is sacrificial cathode protection?

Answer 2

A method of protecting metals from corrosion by connecting them to a more reactive metal such as zinc or magnesium (the sacrificial anode) that corrodes instead.
This is done through galvanisation, plating and the formation of alloys.

Question 3

How does sacrificial cathode protection work in terms of electrochemistry?

Answer 3

Zn or Mg are more electronegative and a much more anodic surface. The current flows from the Zn or Mg and the protected metal becomes cathodic, creating a galvanic cell. The oxidation reactions are transferred from the metal surface to the galvanic anode and will be sacrificed instead of the favoured metal.

Question 4

How does rust develop more quickly on mild steel than pure iron?

Answer 4

Mild steel is an alloy of non homogenous materials. Therefore there are variations in activity and any water in contact with the steel sets up microscopic concentration cells. Electrons circulating in these cells accelerate rusting.
Does not occur in iron, homogeonous.

Question 5

What is in mild steel?

Answer 5

Carbon (deliberately), impurities (eg. sulphur) due to manufacture.