Corrosion in metals: what it is and why it occurs

Metal corrosion occurs by a chemical (or electrochemical) process by which the metal is transformed into an oxide or other compound. This corrosion occurs gradually, caused by different agents such as gases, acids, salts, substances that are in the atmosphere, substances of an organic nature, etc. Although determining the reason why metals corrode is complicated, various causes can be established.

If you want to know more about this topic, keep reading because we are going to explain what causes corrosion in metals and the methods to avoid it.

Corrosion is defined as “the gradual wear of metallic bodies by the action of external agents”, this means that it is the deterioration that is produced by the attack of oxygen, what we know as oxidation.

Metals can be more or less sensitive to corrosion depending on their oxidation potential, which is why they can be classified as basic (copper, lead, zinc, tin), ferrous (iron, manganese, molybdenum, chrome, titanium, cobalt, tungsten ), precious (silver, gold, platinum) and radioactive (plutonium, thorium, uranium, radium). Although they can all corrode, there are some metals like gold and platinum that have a very negative oxidation potential and are quite resistant to oxidation, so exposure to air does not affect them.

Iron, however, has a high potential for oxidation and although its cause is difficult to determine, some of the triggers are water and oxygen. When iron gets wet it rusts due to an electrochemical process.

uniform corrosion

This is the name given to corrosion in which the metal is destroyed equally over the entire surface. It usually occurs in pure metals and in homogeneous solid solution alloys.

local corrosion

This is what happens when the corrosion only affects some areas of the metal due to the breakage of the protection layer, so it is dispersed throughout the interior. Hits or scratches are the triggers for this type of corrosion.

intercrystalline corrosion

Also called intergranular corrosion, it is one in which the metal or alloy deteriorates along the edges of the vein. The biggest problem with this type of corrosion is that it is not usually visible to the naked eye, however, it spreads deep, which can cause serious damage and even disintegrate the vein.

galvanic corrosion

When a metal is in contact with another more noble metal in a humid environment, the movement of the metal ions causes the oxidation of the less noble metal.

pitting corrosion

It is the one that causes small holes in the metal, so it usually takes time to detect it, but it degrades the metal part at a great speed.

crevice corrosion

It occurs when there is a stagnant solution or liquid in contact with the metal.

Filiform corrosion

It usually happens on parts that are coated with paint and causes corrosion in the form of filaments.

Protection to prevent corrosion and oxidation in metals is a complex process for which universal solutions must be found. For this, different aspects must be taken into account, such as the type of metal to be protected, its composition and structure, the state in which it is found and the corrosive agents and all those aspects that influence its degradation.

To prevent corrosion in metals, various techniques can be used that provide excellent resistance to the agents that cause it.

Protection with protective materials

One of the most used methods due to its good results against oxidation and corrosion is the coating with a self-protective metal such as Zinc. This procedure is done by degreasing the surface to be treated with a solvent to make a pickling. The adhesion of the self-protective metal is done through electrolysis, this is the decomposition of a material using electric current.

Zinc is a very good protector in all kinds of metal parts, since it prevents the metal where it is applied from rusting. Zinc powder inhibits oxidation in a very effective way, since it offers what is called “sacrificial protection”, this means that it rusts before iron, so it “sacrifices” by degrading so that corrosive agents do not affect the metal.

To learn more about this technique, we recommend that you consult with experts in the field such as the professional team at Manuelrocasl.es, who knows very well the requirements of metals. In this company they are specialists in metal treatments and coatings of parts with Zinc: blue chromatized zinc, yellow chromatized zinc and nickel zinc. Thanks to their quality and experience, they offer great satisfaction to all their clients, exceeding their expectations.