YOUR AIMS

At the end of this lesson you should be able to:

• define the term corrosion
• describe corrosion by galvanic action
• identify the anode and cathode of corrosion cells formed by metals in contact
• define the term sacrificial anode
• describe, with examples, the use of sacrificial anodes in the prevention of corrosion
• describe the use of an external emf to control galvanic corrosion
• explain the use of mechanical barriers in the prevention of corrosion.

1. State two ways in which corrosion can be classified.

2. State three essential conditions for galvanic corrosion to occur.

3. How can hydroxyl ions, OH-, be formed around a cathode during corrosion in water containing dissolved oxygen?

4. Magnesium lies above copper in the E.C. series. What happens if a piece of magnesium ribbon is placed in a dilute solution of copper sulphate? Write an equation for the change.

5. Explain why there is no action when copper strip is placed in hydrochloric acid.

6. A strip of low carbon steel is placed in a solution of nickel sulphate. What would you expect to see?

7. How can the application of an external emf control galvanic corrosion?