Have you ever seen a really old car that's been sitting abandoned for a number of years? If so, it was probably reddish-brown and flaking in many places. Those spots where the metal has corroded are called rust.

But what exactly is rust? Rust is usually used to refer to a very common, reddish-brown compound called iron oxide (Fe2O3). Iron oxide is formed when iron and oxygen react in the presence of water or moisture in the air.

Iron oxide is very common, because iron reacts easily with oxygen in the air. In fact, it reacts so readily with oxygen that it's actually very rare to find pure iron in nature.

Rust can also refer to the reaction of iron and chloride in an underwater environment. This can sometimes be seen on rebar used in underwater pillars. Over time, green rust will appear on these pillars as the iron reacts with chloride in the water.

Rust occurs when iron or its alloys, such as steel, corrode. The surface of a piece of iron will begin to corrode first in the presence of oxygen and water. Given enough time, any piece of iron will change entirely into rust and disintegrate.

The process of rusting is a combustion reaction, similar to fire. Left in contact with oxygen, iron will react with the oxygen to form rust. Unlike fire, though, the reaction is much slower and does not create a flame.

There are certain factors that can speed up the rusting process. For example, water speeds up the reaction. Other substances, such as salt, can also increase the speed of the rusting process.

To prevent rust, iron can be coated to prevent its reaction with oxygen and water. One such process is called galvanization. Galvanization usually involves coating an iron object with a protective layer of zinc. The layer of zinc helps to prevent the iron underneath from reacting with oxygen and water to form rust.

Another coating that's a popular means of preventing rust is much simpler and much more common. What is it? Paint! That's right. A simple coat of paint can also prevent iron from reacting with oxygen and water in the environment.

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