Iron sheets are galvanised before use?

Answer 1

Iron [Fe] is a hard metal that can be rolled into sheets only a few millimetres thick and may be corrugated. These sheets are strong yet inexpensive to produce, so are often used as roofing materials. The main problem with untreated iron is that it reacts readily with water [H2O] and Oxygen [O2] - especially in the presence of a salt.

This chemical reaction - oxidation - results in the formation of a new compound Iron (III) Oxide [Fe2O3] or rust.

Iron must undergo a multi-staged oxidation reaction in order to form the "rust". Firstly, the stable Fe must lose 2 electrons [e-] to form the Iron (II) cation [Fe2+].

Fe(s) è Fe2+ + 2e-

The Ferrous provided by the initial oxidation undergoes further oxidation in the presence of water and Oxygen into Iron (III) cations [Fe3+].

2Fe2+(aq) è 2Fe3+(aq) + 2e-

The released electrons are accepted by Oxygen molecules from the air, reducing the Oxygen (in the presence of water) and forming basic Hydroxide ions.

O2(g) + 2H­2O(l) + 4e-­ è 4OH-(aq)

The Ferric ions [Fe3+] combine with free Oxygen molecules and water to form Iron (III) Oxide (rust).

2Fe3+(aq) + O2(g) + H2O è Fe2O3(s)

The degree and likelihood of metal corroding when exposed to water, oxygen (and salts) can be predicted by studying the electrochemical series. This is an ordered list of reactive metals, with the most electronegative at the top. The reactivity of the element with water decreases as the list continues. The alkaline metals (such as Lithium and Potassium) lead the series, with select stable transition metals like Gold bringing up the rear. Iron comes in around halfway down the list, not particularly reactive but it can readily corrode (rust). Just above Iron in the series is Zinc [Zn].

Iron sheets can be protected against rust in several ways, galvanisation being perhaps the most effective method. Galvanising involves "dipping" of the metal into molten zinc. This ensures complete coverage. This is not to be confused with electroplating, where the metal to be covered is submerged in an aqueous solution of ions and electrified - though the outcome may be the same this process is not called galvanising.

The Zinc coating will protect the sheet in two ways. Since the Iron has been fully coated with Zinc, it provides a barrier against moisture and the air - just as far less expensive painting would. However, the Zinc also offers effective "chemical" protection. Due to its increased electronegativity, Zinc will undergo corrosion (oxidation) more readily than the Iron. Since the oxidised form [Zn2+] dissolves readily in water, it will spread over any cracks in the coating, or other exposed Iron areas.

This aqueous Zinc will corrode in place of the iron, donating its own electrons and becoming oxidised but leaving the Iron reduced. This is known as "sacrificial protection". A lump of Zinc adhered to the centre of the Iron sheet should protect the entirety of the plate, it is an extremely effective method of preservation.

So, in short, the answer to your question is: To prevent rust.

Answer 2

iron reacts with moist air( water and oxygen) and gets rusted. to prevent this it is galvanised. it is the process of applying a layer of tin on the iron sheet

Answer 3

Primarily zinc metal with small addition of all or some of the following metals lead, bismuth, tin, aluminum, cadmium, nickel, vanadium,