What is corrosion?
From a chemical point of view, corrosion refers to an electrochemical reaction between two materials. In most cases, one of these materials is a type of metal, such as iron.
Ultimately, corrosion is an electric circuit. There is a flow of current between the cathodic and anodic site of the metal within an external conductive solution, also known as electrolyte. For instance, galvanic corrosion occurs when two different metals are located in an electrolyte, such as water. This leads to the more cathodic metal attracting the metal’s anodic molecules, resulting in the corrosion of the metal.
Preventing corrosion: Selection of Metal type
All ferritic metals corrode. However, not all metal types are equally susceptible. By analyzing and understanding the corrosive environment the material will be exposed to, one can choose the most fitting type of corrosion resistant metal or metal alloy.
For instance, stainless steels are generally more resistant towards corrosion than carbon steel. Due to alloys such as nickel, chromium and manganese, steel does not oxidize as fast. However, under some circumstances and harsh environments, such as high temperatures and humid environments, even stainless steel can corrode. To prevent this, engineers need to pick the most fitting metal type. You can learn more about choosing the right stainless steel grade here.
Preventing corrosion: Coatings
Cathodic coatings are also known as “sacrificial coating” because the coating metal reacts with the environment instead of the iron. A layer of zinc is a popular cathodic coating for steel (see galvanizing). Zinc is more reactive than iron, meaning that it will oxide in its stead, making the steel the cathode of a galvanic cell. Cathodic protection is used for steel applications that carry corrosive elements, such as water, fuel or oil.
Anodic coatings are the counterpart of cathodic coatings. Steel components are coated in less reactive metals that will not react with the oxygen in the environment. Tin is a popular metal for anodic coatings because it does not corrode. Steel becomes the anode of an electrochemical cell. This means that if steel becomes exposed to the electrolyte, it will corrode even faster. This is why anodic coatings have to be applied correctly, in order to act as a barrier rather than a catalyst for even faster corrosion.
A Protective coating, such as BoroCoat®, prevent corrosion of the underlying metal surface. They can harden the surface (as is the case with our boronizing technique), resulting in many additional beneficial material properties, such as improved hardness and strength.
Another type of protective layer are paint coatings, which prevent the metal from reacting with the environment. Protective coatings can also be applied as dry powder. The powder has to be heated afterward to embed the powder coating into the surface.
Improvement of environment
Essentially, corrosion is the chemical reaction between metal and the atoms in the environment. We have already established one option of corrosion prevention, which is to change the metal to reduce corrosion. The other option is, of course, changing the environment.
Removing materials from damaging environments, or improving the conditions, can significantly help to reduce corrosion.
If possible, the surrounding environment should be reducing its sulfur, chloride, sodium, acids and oxygen levels.