In this work the words "" and "steel" are used interchangeably. Most steels have more than 99% , though steel contains about 18% chromium, 8% nickel and 74% iron.

Most react with moist air and this process is called "corrosion". is the name given to the corrosion of iron because of its colour. Rust forms when iron reacts with and . The chemical reaction is slow but it is very important to make the reaction even slower because the cost of repairing the damage that rust causes is very high. acts as a catalyst for the process, particularly noticeable where sea water attacks ironwork; also a very small increase in temperature also makes rusting take place much faster.

Many methods can be used to try to stop rusting.
1. Bridges, trains and ships and other large steel structures are often protected by . The work has to be checked regularly to see if there are any scratches because rusting will begin, forcing more and more away from the surface of the iron. is very cheap.


2. Most machinery has moving parts. If these were painted, the paint would rub off leaving the objects open to air and water vapour. Machinery is usually protected with or .


3. A thin layer of metal can be "plated" onto the surface of iron using an electric current. Often food cans are plated (and so are called "" even though they are mainly made of steel. plating is often used for steel that needs to look good because it gives a very bright, shiny surface and protects the object from rusting. Some bicycle parts and very many small objects such as umbrella tips, battery contacts and scissors are protected in this way.


4. is a process which places a thin layer of on the surface of steel. is more reactive than iron so if the object is scratched, the zinc instead of the iron. This method of protection is often used instead of painting where the object is likely to get damaged. Buckets and containers on building sites, as well as metal coverings for electrical wires and wire fences are usually .


5. Underground pipes and the parts of ships below the water line use a method known as "". It is like galvanising because the metal attached to the iron object is reactive than iron; it is usually zinc or magnesium, and the reactive metal corrodes of the iron. The reactive metal blocks can be inspected and replaced a lot more easily than mending a broken oil pipe or the bottom of a ship.


6. Coating a metal object in plastic is sometimes used for wire products, while many fridges and freezers are coated with a powder which is baked into the surface to give a very hard smooth white finish.


The method of protection chosen depends on how large the object is and how and where it will be used. List one more object for each different method of protection from rusting.