Corrosion of Metals

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Corrosion of Metals
Introduction
Have you ever had a bike that went rusty, figure 1? If the paint is scratched and the rust allowed to spread, it is very difficult to repair the frame so it looks as good as new again. Rusting costs us millions of pounds each year, either through replacing things or through trying to prevent it happening in the first place. Figure 1: Bike rusting.

In this booklet you learn about rusting and ways of stopping it, followed by a look at another metal, aluminium that is surprisingly resistant to corrosion. Rusting
Rust is the name we give to the substance formed when iron corrodes. The same applies to most types of steel, as they consist mainly of iron. We all know that things tend to go rusty if they are left in the rain. So is it water that causes iron to rust? 1

Look at the experiment below:
Q: Match the conditions to the tube in the experiment above. Air only Water only
Both air and water
Look at the results table below for the rusting experiment:
Tube Observations after several days
A no rust
B no rust
C water has turned orange, rust on nail and at bottom of test tube Q: Which conditions are needed for iron to rust? O water alone O both air and water
O air alone
2
Q: Which gas in the air do you think that iron reacts with as it rusts? O nitrogen O oxygen
O argon
Rust is a form of iron(III) oxide with water molecules loosely bonded in its structure. (For this reason, it is sometimes called hydrated iron(III) oxide). Preventing rust
Do you know where there are any painted iron gates or railings? Has the paint done a good job of protecting the iron underneath? Painting is one way of providing a barrier between the iron and the water and air waiting to attack it. Other barrier methods include coating the iron with: • oil

• grease
• plastic
• a less reactive metal (such as the tin used on steel food cans) These work well as long as the barrier remains intact. However, as soon as the barrier is broken, the...
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