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Question
Give preventive methods by giving examples of corrosion?
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Solution
Corrosion can be prevented by the following methods:
- Galvanizing: Galvanizing is a process of giving a thin coating of zinc on iron or steel materials to protect them from corrosion. Zinc, being more electropositive than iron, undergoes corrosion first. Thus, it prevents corrosion of iron. However, if zinc layer goes away and the inner iron gets exposed, then the inner iron layer will start to rust.
- Tinning: Tinning is the process of giving a coating of tin over other metals. Cooking vessels, made of copper and brass get a greenish coating due to corrosion. This greenish coating is poisonous. If food is kept in such a vessel, it gets spoiled. Therefore, copper and brass vessels are coated with tin (kalhai) to prevent corrosion.
- Anodizing: The process of coating metals such as aluminium and copper with a thin and strong layer of their oxides by electrolysis is called anodizing process. For this, the copper or aluminium article is used as the anode. As this oxide layer is strong and uniform all over the surface, it is useful for the prevention of the corrosion of the metal.
- Electroplating: Electroplating is the process in which a less reactive metal is coated on a more reactive metal by electrolysis. It protects the object made of reactive metal from corrosion. For example, silver-plated spoons, gold plated ornaments, etc.
- Alloying: The homogenous mixture formed by mixing metal with other metals or nonmetals in a certain proportion is called an alloy Alloying helps to decrease the intensity of corrosion of metals. For example, stainless steel does not get stains with air or water and also does not rust. It is an alloy made from 74% iron, 18% chromium and 8% carbon.
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| A process of forming a thick oxide of aluminium when aluminium is exposed to air. This coat makes it resistant to corrosion. Resistance can be improved by making a layer of oxide thinker. In this technique, the aluminium article is the anode, and the electrolyte is sulphuric acid. The anode reaction results in the formation of a black-coloured film of aluminium oxide on the anode. By putting appropriate dyes in the electrolytic solution, both coloured surface with the decorative finish is achieved. Kitchen articles like anodised such as pressure cookers, pans and frames of sliding windows are applications of this technique. |
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