Question

Part A

Cathodic protection of iron involves using another more reactive metal as a sacrificial anode. Classify each of the following metals by whether they would or would not act as a sacrificial anode to iron.

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Ag

Mg

Cu

Pb

Sn

Zn

Au

Will act as sacrificial anode for iron

Will not act as sacrificial anode for iron

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Part B

An old iron beam was coated with an unknown metal. There is a crack on the coating and it is observed that the iron is rusting at the fracture. The beam is in a structure that experiences high stress, resulting in frequent fractures to the coating.

What was the old metal coating likely made of and what metal you would use to repair the fractures to avoid further corrosion?

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gold

aluminum

tin

1. The old coating was likely made of .

2. would be a good choice for repairing the fracture.

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Answer 1

Ans part A;

Materials used for sacrificial anodes must be relatively pure active metals.

Or we can say any metal with more negative potential that that of iron ( +0.59) is used for sacrificial anode for iron

so from the above the following can be used as sacrificial anode for iron

Mg = +1.06

Al = +0.96

Zn = +0.7

The following will not be used as sacrificial anode for iron because their negative reduction potential is less than that of iron ( +0.59)

Ag = -0.76

Cu = -0.44

Pb = 0

Sn = +0.34

Au = -3.05

ANSWER PART B;

1 The old coating was made up of either gold or tin because these metals are not a ood sacrificial anode for iron as they have less negative reduction potention than that of iron (explained in ans of part a)

2 Aluminium would be a good choice for repairing the crack as aluminium is a good sacrificial material for iron