With forming a protective barrier, the zinc coatings act as a sacrificial anode. With doing that it makes a great protective barrier to the metal. It works by many chemicals interacting. It first starts as zinc and when it comes into contact with oxygen it then becomes zinc oxide. Then when the zinc oxide reacts with the water molecules in the air it then transforms into zinc hydroxide. And then finally when the zinc hydroxide reacts with the carbon dioxide it then produces a thin, air tight, strong and very insoluble dull grey layer of zinc carbonate.
This thin layer sticks very well to the underlying zinc and protects the metal from further corrosion. The zinc gives a very similar protection that you would get from aluminium, and also stainless steel.
When coating the body of a car it may need an extra coating because of additional rust. In this circumstance they would dip the parts in galvan. It is referred to as galvanizing. It gives an extra thick robust layer. Then a thin layer is applied by using electroplating. This process is called elecrtogalvanization. This process does not do well when the metal is exposed to salt water on a constant basis. When that is the case it is recommended to use stainless steel. Most of the nails that are made today are treated with this kind of process.
The traditional measure of a coating's effectiveness they test it's resistance to salt spray. The thin coatings cannot stay together when it is subjected to surface abrasion. A scratched or incomplete coating of chromium can actually aggravate corrosion to the underlying steel, because it is less electrochemically active than the substrate.
When you vary the number of particles that are added to the heterogeneous nucleation and you also control the rate of the cooling down process, you can make a more uniform coating. These type of variable crystallites are very rare in other types of engineering materials. The largest use of zinc is protective coatings for steel constitute.
The green process of galvanizing is thermal diffusion. It creates a zinc coating metallurgically similar to the hot dip galvanizing. Instead of dipping the metal parts in the molten zinc. The zinc is applied in a powder form with accelerator chemicals. The parts and the zinc compound are sealed in a drum which is then rotated in an oven.
Because the accelerator chemicals are added to the zinc powder, the zinc/iron diffusion it takes place at a lower temperature than the hot dip galvanizing, and this results in a more uniform and wear resistant coating. The reason that this process is more green is because it eliminates the need for hazardous caustic, acid, and flux baths.