Iron is one of the most useful metals that exist on earth. Because of its physical properties, like strength and high melting point, it is used to make several industrial machines and everyday commodities. Examples include bridges, iron sheets for roofs of houses, doors and vehicles’ bodies. However, iron suffers from rusting, which leads to loss of some properties such as strength. Rusting can be defined as the formation of hydrated iron (iii) oxide, a reddish brown compound which results from the reaction of iron with water and oxygen.
From the definition, we can conclude that rust forms when bare iron is exposed to air (oxygen) and moisture. Therefore, in order to prevent rust from forming, we have to isolate the iron from oxygen and moisture. One method is through painting of the iron metal surface. Paint contains oil which dries on the surface of iron and coats it from interaction with the air, thus keeping away air and moisture.
The second way of preventing rust is by anodizing. This involves the passing of electric current through the iron metal and forming a stable metal oxide on it. An example of a stable metal oxide is aluminum oxide. It is not easily disintegrated by chemical means and therefore it acts as an inactive layer protecting the iron.
The third method is through use of a ‘sacrificial metal.’ This incorporates the attachment of a more reactive metal, such as magnesium, to the iron. The more reactive metal is then earthed. Iron can be left to interact with air and moisture freely in this case. When oxygen or moisture tries to react with iron, magnesium sacrifices itself and reacts instead. This method is very effective and is commonly used when constructing steel bridges.
The last method to be discussed is galvanizing. It is simply the coating of iron with zinc which is more reactive than iron. This is a special method of sacrificial protection as the zinc provides a barrier by reacting with air to form zinc oxide which is a very stable compound. As a result, an inactive layer of zinc oxide prevents the iron from rusting. However, rusting may start occurring after several years due to the weakening of the layer with time or exposure to chemicals such as acids which can react and deplete the layer.
In conclusion, it is realized that as long as the agents of rusting, water and oxygen, are prevented from interacting with iron, rusting cannot occur.
