Hot Dip Galvanization
Unprotected Steel can be seriously damaged due to such environmental factors as rain & snow, wind, and extreme temperature. Corrosion transforms steel back to its natural state of iron, which is very fragile and can prove deadly in structures supporting heavy pressure (e.g. Towers).
The best way to avoid this phenomenon is through a process called "hot dip galvanization". It consists of dipping steel in melted zinc (450°C) at which an alloy is formed. The final product is a Steel surface protected with a zinc coating. The biggest factor in the appearance and gauge of galvanization is the contents of alloyable elements that are generally present in steel: carbon, magnesium, and silicon. If the content of these elements increase, the coating gauge also increases and it becomes matte gray. The greatest effect is produced by silicon in concentrations higher than 0.12%.
Due to the difference of electrochemical potential between zinc and steel (Cathode Protection), a zinc coating protects steel against vigorous forces such as cutting, scratching, piercing, and most importantly against corrosion.
Section through galvanized coating showing pure metal zinc and zinc-iron alloy layers which are the normal coating developments on rimmed or aluminum killed steels.
Section through galvanized coating on silicon containing steel; Coating is zinc-iron alloy which appears gray.
Section through brown stained galvanized coating which remains substantially intact under the brown stain. The uncolored material close to the galvanized surface is aluminum sheet used to assist in preparation of the section and to show the features of the coating more clearly.
For more information on the process:
A basic guide to hot dip galvanizing (.PDF - 176 Kb)
American Galvanizers Association (Official Website)