Q1.
Have you noticed the formation of a green coating on the surface of copper objects or a black coating on the surface of silver objects?
Answer
Yes — an old copper lota left unused grows a dull green layer, and silver jewellery or a silver spoon slowly turns black.
| Metal | Coating that forms in the open | Name of the process |
|---|---|---|
| Iron | Brown deposit (rust) | Rusting — a kind of corrosion |
| Copper | Green coating | Corrosion |
| Silver | Black coating | Corrosion |
Gradual deterioration of metal surfaces caused by air, water or other substances is known as corrosion.
Why it matters: rusting is a serious problem for the country. Every year an enormous amount of money is spent to replace or repair iron structures — bridges, railway tracks, gates, pipes — damaged by rust. It is prevented by painting, oiling, greasing and galvanisation (a protective layer of zinc on the iron).
Did you know? The Iron Pillar of Delhi, made in the time of Chandragupta II more than 1600 years ago, is about 8 metres high and weighs more than 6000 kilograms — and after all those centuries of wind and rain it has barely any rust. It was made in a way that resists rusting, and it shows how advanced metal technology already was in India.