What is deposited on iron in the process of galvanisation?
Zinc
Understanding Galvanisation of Iron
Galvanisation is a widely used process to protect iron and steel from rusting. Rusting is a form of corrosion that occurs when iron reacts with oxygen and moisture in the presence of water, forming iron oxides (rust).
To prevent this corrosion, a protective layer is applied to the surface of the iron or steel. This protective layer acts as a barrier, preventing the iron from coming into contact with the elements that cause rust.
What is Deposited During Galvanisation?
In the process of galvanisation, the metal deposited on iron is zinc. The iron object, typically cleaned thoroughly, is dipped into a bath of molten zinc. The zinc adheres to the surface of the iron, forming a coating.
Why is Zinc Used in Galvanisation?
Zinc is chosen for galvanisation primarily for two reasons:
- Barrier Protection: The zinc coating acts as a physical barrier, preventing oxygen and water from reaching the iron surface.
- Sacrificial Protection: Zinc is more reactive than iron. This means that if the zinc coating is scratched and the iron is exposed, the zinc will corrode preferentially to the iron. The zinc sacrifices itself to protect the iron underneath. This is also known as sacrificial protection or cathodic protection.
This sacrificial nature of zinc makes galvanisation very effective, as the protection continues even if the coating is damaged.
Comparing Options for Iron Protection
Let's consider the given options in the context of protecting iron:
| Substance | Used for Protecting Iron? | Role |
|---|---|---|
| Tin | Yes (e.g., tin cans) | Barrier protection (less sacrificial than zinc). If scratched, iron rusts faster. |
| Zinc | Yes (Galvanisation) | Barrier and Sacrificial protection (more reactive than iron). Protects even if scratched. |
| Copper | Not typically used for galvanisation of iron | Copper is less reactive than iron and can even accelerate iron corrosion in some conditions (galvanic corrosion). |
| Aluminium | Yes (e.g., aluminizing) | Can provide protection through a durable oxide layer, but galvanisation specifically refers to zinc coating. Aluminium is also highly reactive but forms a tough oxide layer. |
Based on the definition and process of galvanisation, the substance deposited on iron is zinc.
Revision Table: Key Concepts of Galvanisation
| Term | Explanation | Importance |
|---|---|---|
| Galvanisation | Process of coating iron/steel with zinc. | Prevents rusting. |
| Rusting | Corrosion of iron (forms iron oxides). | Weakens structures. |
| Zinc Coating | The layer of zinc applied to iron. | Provides protection. |
| Sacrificial Protection | Zinc corrodes before iron does. | Protects iron even if the coating is damaged. |
Additional Information on Metal Protection
Besides galvanisation, there are other methods to protect metals from corrosion:
- Painting: Applying a layer of paint acts as a barrier. Requires regular maintenance.
- Plating: Coating with other metals like chromium or nickel for protection and aesthetics.
- Alloying: Mixing metals to create corrosion-resistant materials, like stainless steel (iron + chromium + nickel).
- Oiling/Greasing: Applying a layer of oil or grease to prevent contact with moisture and air, common for tools.
- Tinning: Coating iron with a thin layer of tin (like in food cans), provides barrier protection. However, if the tin layer is broken, the iron rusts quickly because tin is less reactive than iron.
Galvanisation using zinc remains one of the most effective and widely used methods for protecting iron and steel structures in various environments.
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