Question

What are corrosion and its prevention?

Answer 1

Corrosion: Corrosion is the process of slowly eating up metals by gas and water vapours present in the atmosphere due to the formation of certain compounds like oxide, sulphides, carbonate, etc.

Rust:

• Corrosion of iron is known as rusting.
• When Iron comes in contact with oxygen in presence of moisture(Water), a reddish-brown coating is formed on the surface of Iron which is called rust. .
• The chemical reaction can be represented as:
• $\underset{\mathrm{Iron}}{4\mathrm{Fe}\left(\mathrm{s}\right)}+\underset{\mathrm{Oxygen}}{3{\mathrm{O}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Water}}{2{\mathrm{xH}}_2\mathrm{O}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Rust}}{2{\mathrm{Fe}}_2{\mathrm{O}}_3.{\mathrm{xH}}_2\mathrm{O}\left(\mathrm{aq}\right)}$

Prevention of Rusting

Barrier Protection In this process, the metal is not allowed to come in contact with air, moisture, Oxygen and Carbon dioxide.
The methods used are
i) The metal surface is coated with paint.
ii) A film of oil or grease on the surface of iron tools and machinery.
iii) Coating the iron surface with non-corroding metals like Nickel, Chromium, Aluminium, etc., by the process of electroplating.
iv) Coating the iron surface with Phosphate or other chemicals gives protection from air and moisture.

Sacrificial protection: It involves covering the iron surface with a layer of metal that is more active i.e., electropositive than Iron. So, the more active metal will lose electrons, not Iron. When zinc is coated on the iron surface the process is called galvanization.

Using anti-rust solutions: Alkaline phosphate and alkaline chromate solutions due to their alkaline nature prevent the availability of H⁺ ions.
Phosphates provide a thick film of insoluble Iron phosphate which protects the Iron objects from rusting.