Iron and steel corrode after being exposed to oxygen or water. Corrosion is a huge trouble for ships, pipelines and oil rigs.
To prevent the troubles caused by rusting and protect the iron, another metal is used. Magnesium and zinc are often used for this purpose.
Magnesium is either attached with a cable or bolted to an object made of iron or steel. This method is known as sacrificial protection. As long as magnesium stays in contact with the steel or iron, the rust will form on the magnesium bar, since it reacts more strongly with oxygen and water than either of the other two metals. When the rust attacks the magnesium bar, it will be eaten away.
One magnesium bar must be replaced with another to protect iron or steel. Since magnesium is willingly allowed to be destroyed for the protection of iron or steel, this method is known as sacrificial protection.
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