Chem unit 5.4

Corrosion

When the metal forms a dull coating when exposed in the air

Corrosion word equation

Metal + oxygen → metal oxide

Which metals dont corrode?

Gold and platinum

Rusting

Special name given to the corrosion of iron and steel

What causes rusting

Presence of both air and water

How to make rusting faster?

By adding salts of acids

Rusting word equation

Iron + oxygen + water → hydrated iron oxide

Two main ways to prevent rusting

Physical barrier and sacrificial barrier

Physical barrier

This method tries to keep out air and water from iron or steel

Sacrificial barrier

Attaching a more reactive metal to the iron

Ways of protection by a physical barrier

1. Paint

2. Oil and grease

3. Plastic coatings

4. Tin plating

5. Electroplating

Explain tin-plating

Used to make the sheet metal for tin cans. Suitable for food containers as it is non-poisonous and prevents corrosion

Explain electroplating

Uses electricity to put a thin coating of an expensive metal onto iron. Cutlery and taps are often electroplated

What metals can be used for electroplating

Chromium and nickel

Main disadvantage of physical barrier?

The coating has to be maintained

How to do sacrificial protection

By adding blocks of zinc or magnesium to the metal

What is one way of sacrificial protection

Galvanizing

Galvanizing

Adding a zinc coating to iron or steel

Examples of when galvanizing is used

Girders for bridges and buildings

Car body panels

Motorway crash barriers

Buckets and roofing nails