Galvanisation

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Chemistry Report – How does Galvanizing prevent Rusting?

Galvanization is the process of applying a protective zinc layer of coating to steel or iron to prevent rusting. The most common form of galvanization is hot-dip galvanization. Hot-dip galvanization is the process of coating iron or steel, which are less reactive, by passing the metal via a molten bath of zinc at high temperatures. Hence, when the solution gets exposed to the atmosphere, pure zinc reacts with oxygen to form zinc oxide. This further reacts with carbon dioxide to form zinc carbonate, a usually dull grey, fairly strong material that stops further corrosion. This is how the zinc coating protects the base metal. Galvanized steel is widely used in applications where resistance against rust is required.

Equations:
4Fe + 3O2=Fe2O3
(rusting)
Step 1 : 2 Zn+O2 =2 ZnO
(exposed to oxygen)
Step 2 : ZnO + CO2 = ZnC03
(reacts with carbon dioxide stops further corrosion)

Benefits of Galvanizing

Corrosion Resistance:
Zinc has a slow reaction with water, thus the coating generally has a very long life. Due to the nature of hot-dip galvanization, all areas of the galvanized object are covered, including regions that are generally inaccessible.

Cost:
The initial cost for galvanizing is very competitive; for many applications it is lower than the alternative coatings. It is more expensive than painting, which also prevents corrosion, but it is much more durable, and provides sacrificial (or cathodic) protection if the zinc coating is damaged.

Service:
A galvanized metal can go without servicing for up to 20-25 years and can last for more than 50 years in most rural environments.

Adhesion:
The process of galvanizing produces a coating, which, uniquely with metal finishing, bonds metallurgically with steel.

Coating toughness:
The alloy layers of the coating are considerably tougher than the base metal upon which they are formed. This gives outstanding resistance to...
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