Corrosion

What is Corrosion?

Corrosion is the attack on a metal which is a result of chemical reactions between the metal and surrounding environment.

These substances may be moisture, acids, oxygen etc. 

In easy language, destruction of metal because of attack of moisture and acids is called corrosion.

Examples of Corrosion

Rusting of Iron

• Iron articles are shiny when new but they turn reddish-brown after some time due to formation of Iron Oxide (rust) .
  
  
• Chemical reactions of iron with atmospheric moisture and oxygen results in the formation of rust
  
  
  

Black Coating of Silver

• Black coating on silver coins is Silver Sulphide . 
• It is formed by the reaction of Silver with Hydrogen Sulphide in the atmosphere.

Green Coating on Copper

• Green coating on Copper is Copper Carbonate . 
• It is formed by the reaction of Copper with Carbon Dioxide, moisture and Oxygen in the atmosphere.

Note- Statue of Liberty has turned green over the years due to corrosion of the Copper metal it is made out of.

What are harmful effects of Corrosion?

It causes damage to cars, railways, bridges and all other structures that are made of iron.

Money is to be spent every year to replace them.

What is the chemical reaction for Rusting of Iron?

Iron reacts with Oxygen and Moisture (Water) to form Hydrated Iron Oxide

Iron + Oxygen + Water → Hydrated Iron Oxide

4Fe + 3O ₂ + 2xH ₂ O → 2Fe ₂ O ₃ .xH ₂ O

How to prevent corrosion?

1. Avoid exposure to Corrosive Agents
   This can be done storing the substances under safer conditions, away from moisture
   
   
2. By covering metal surfaces with paints
   Paint doesn't get oxidized, it acts as a barrier between the metal and the outer. environment. 
   
   
3. Electroplating
   Plating the surface of more reactive metal by a less reactive metal (like Zinc) can prevent it's oxidization.