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Hot-dip galvanization

Hot-dip galvanization is the process of coating steel with zinc. in this process, the metal is immersed in molten zinc. the molten zinc will coat the metal and form a layer of zinc. when the steel is exposed to the atmosphere, the zinc coating will react with oxygen (O2) and form zinc oxide. furthermore, zinc oxide will react with carbon dioxide (CO2) to form zinc carbonate (ZnCO3). the zinc coating will have a dully grey appearance.  

Figure 1

The process of galvanization can be summarized into the following steps:

  • The steel will be cleaned with a caustic solution to remove oil/grease and dirts.the caustic solution should be removed after the completion of the cleaning process.
  • the next step is to pickle the steel in an acidic solution to remove the mill scale. the mill scale is the flaky surface of hot-rolled steel. the solution should be rinsed off after the completion of the pickling process.
  • A Zinc ammonium chloride is applied to the steel to inhibit oxidation of the cleaned surface upon exposure to air. This will be allowed to dry on the steel and aids in the process of the liquid zinc wetting and adhering to the steel.
  • then the steel will be dipped in molten zinc at a temperature of 449 C. the steel will be dipped until the temperature of steel equalized with the temperature of the bath.
  • the steel then will be cooled in a quench tank.
Galvanized steel will possess good resistance to corrosion. the zinc coating will offer a sacrificial protection from corrosion. structures that are constructed in coastal areas, where the concrete structures will be exposed to a harsh environment. this type of environment will result in accelerating the process of reinforcement corrosion. therefore, zinc-coated reinforcement can be used to resist the corrosion of reinforcement and extend the service life of structures. 


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