Corrosion

Has your cycle ever suffered from rust? You must have noticed a layer of rust on old swing chains, bike chains, or any other iron objects. Did you wonder how was it formed or why was it formed? There is a scientific phenomenon behind it known as corrosion. Let us learn more about this.

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What is corrosion?

Corrosion is a process where the metal corrodes. Corrosion is a natural process and in the presence of a moist atmosphere, chemically active metals get corroded. Contrary to popular belief, rusting and corrosion are not the same.

Rusting is the process where iron corrodes due to exposure to the atmosphere. Corrosion is a process where the water or the moisture on the surface of the metal oxidizes with the atmospheric oxygen, it is an oxidation reaction.  The main circumstance of corrosion occurs with iron because it is a structural material in construction, bridges, buildings, rail transport, ships, etc. Aluminum is also an important structural metal, but even aluminum goes under oxidation reactions. However, aluminum doesn’t corrode or oxidize as rapidly as its reactivity suggests. An alloy of aluminum or any other metal like magnesium can make aluminum stronger, stiffer and harder.

The alkali metals like sodium need to be stored in oil as they corrode quickly. Less reactive metals like lead and copper are used to roof situations. Copper (Cu) corrodes and forms a basic green carbonate and lead corrodes to form a white lead oxide or carbonate.

You what is Ionic Compounds?

Download Corrosion Cheat Sheet PDF

How to Prevent Corrosion of Metals

Covering the surface of the metal with enamel and lacquers helps to protect the metal against corrosion, parts of machines that move can be protected by coating layers of water repellent oil or grease. Another way of protecting iron and steel is by painting on them as it creates a barrier between the surface of the metal and moist air or water. Whereas, the other methods of protecting a metal are alloying, galvanizing, electroplating, etc.

Alloying

An alloy is a mixture of two or more metals. Alloying is a process where metals like iron or steel are mixed with a less reactive metal like chromium, magnesium, etc for protection against corrosion and to create non-rusting alloys. For e.g. Brass is an alloy which consists of copper is a cheap and non – reactive alloy. Another example of a non-rusting alloy is stainless steel, a mixture of iron and carbon.

Galvanizing

Coating iron or steel with Zinc to prevent corrosion is known as galvanizing. Dipping iron or steel in a liquid form of zinc and using it as the negative cathode zinc is coated on it, the layer is produced by electrolytic deposition.  Zinc oxides or corrodes to create a zinc oxide layer that does not flake off like iron oxide rust.

Electroplating

Electroplating is a process where a metal is coated by electrolytic deposition with chromium, silver, or another metal. This process is generally held at room temperature from aqueous electrolytes. It is one of the most popular and common methods to prevent corrosion.

Solved examples for you :

Q: Which of the following metals corrodes quickly?

1. Gold (Au)
2. Silver (Ag)
3. Copper (Cu)
4. Iron (Fe)

Ans: The correct answer is option ‘d’. Iron corrodes more quickly than most metals to form iron oxide. Corrosion or rusting of iron is accelerated in the presence of CO₂ and also in the presence of salt solution.