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Zinc – Electrofer 4 Zinc |

Zinc

Zinc Plating is the galvanic electrodeposition of Zinc on a metal surface, usually steel.

The layer of Zinc deposited will form a barrier between the steel, easily oxidisable, and the oxidising agents such as atmospheric oxygen, chlorine salts, industrial sulphur dioxide, etc.

Due to the significant difference in electrochemical potential between Iron and Zinc, the Zinc layer will act as sacrificial material, oxidizing preferentially and thus delaying the oxidation of the base metal.

Obviously, the greater the deposited layer is, the greater the protection afforded. However, very thick layers of electrodeposited Zinc tend to blister and crack with the dilations and contractions caused by temperature changes, hence the thicknesses normally used may vary from a minimum of 3-4 microns to a maximum of 20-25 microns.

Nevertheless, the layer of electrodeposited Zinc is considerably more compact than the layers of Zinc obtained by other processes such as Hot Dip Galvanizing or by Plasma Metallization. Because of this the protection against corrosion obtained by a layer with 8 microns of Zinc Plating is equivalent to that obtained by layers 70-80 microns by other processes.
The fact that the layers of zinc obtained by electrodeposition are usually passivated contributes to the added protection.
Zinc is also a metal and, as such, it also oxidizes producing Zinc Oxide, a white powder (hence the phrase White Corrosion).
The passivation process is the chemical conversion of the upper Zinc layer’s surface which significantly delays the onset of oxidation of the Zinc layer, thereby delaying the onset of corrosion of the base metal (Red Corrosion due to the Iron Oxide’s colour).

The corrosion protection of these deposits can be further enhanced by the use of reactive Sealings or Top Coats.
The table below shows reference values of red corrosion resistance in Salt Spray Test for different combinations of coatings: