Upon contact with oxygen, metals begin to corrode. This occurs when oxygen atoms break the bond of atoms in metals. The corrosion process begins when the metal comes into contact with the surrounding environment and begins to lose its structure and physical and chemical properties.
Can corrosion be prevented so that metals last much longer? Have you had or detected corrosion problems in your home, vehicle or workplace? In a COMO, we explain how to avoid corrosion and oxidation in metals such as galvanic, iron and steel. Go for it!
What are corrosion and oxidation?
Corrosion and oxidation are two processes that, although slightly different, damage metals and reduce the useful time of many of the objects we use on a day-to-day basis. In this section, we explain what is corrosion and oxidation, its causes and effects, as well as the types of environments that generate this process.
What is corrosion?
The corrosion phenomenon refers to the deterioration of a metal due to an external chemical or electrochemical attack. In this way, an evolution of electrons in the material is produced by being in the presence of an electrolyte or reactant such as water or oxygen. In technical terms, metals pass from an anodic region to a cathodic region. Corrosion of the metal occurs in the anodic region and its contamination and reduction occurs in the cathodic region.
Corrosion is not a phenomenon present exclusively in metals, as it also affects other materials such as ceramics and glass. It is also present in plastics, whose phenomenon is known as polymer degradation. In addition, these processes negatively affect the environment, both the atmosphere and water.
What is oxidation?
Oxidation, meanwhile, represents the phenomenon that produces corrosion of metals when the reactant is exclusively oxygen, which usually comes from water or air. Oxidation is the chemical reaction resulting from the combination of oxygen with other materials and substances, resulting in molecules of oxides that produce corrosion of the materials. Corrosion is caused by the loss of electrons in the atoms of the materials that remain positively charged.
Oxygen is called an oxidizing agent because it gains electrons, while the material that loses electrons is called a reducing agent. In this process, oxygen is reduced because it gains electrons and the material oxidizes because it loses electrons.
On some occasions, oxidation occurs intentionally in industries. For example, aluminum, which is found in nature as bauxite, is extracted from an electrolysis process in which aluminum oxide is separated from aluminum in its pure state.
Types of corrosive environments
There are different types of environments that produce corrosion. Among those we can mention are:
- Atmospheric : its main oxidizing agents are oxygen and water. It covers most corrosive environments, as it is present throughout the planet.
- Marine : it is characterized by the presence of salt water, as it happens in the seas or oceans. Saltwater contains chlorine, a highly corrosive agent.
- Industrial : this environment is highly corrosive due to its large amount of polluting and corrosive gases and liquids. Some of them are sulphurous, nitrous materials, among others.
- Galvanic : occurs when a metal comes into contact with another noble metal (metals that generate little chemical reaction and are not very susceptible to corrosion) and both are immersed in an electrolyte or humid medium.
How to avoid galvanic corrosion
The galvanic corrosion occurs between two metals of different nature that contact while immersed in an electrolyte such as saltwater. This results in an electrochemical process that produces corrosion.
An example of galvanic corrosion occurs, especially in marine environments or on the coast. Placing metals that are not very susceptible to corrosion next to highly susceptible metals accelerates the corrosion process of the susceptible metal. It usually occurs in corrugated steel sheets when the zinc that protects it is broken. It has also happened on some ships, when iron nails were used to fix the copper on the deck to the wood.The copper corrodes more quickly if they come into contact with the iron in seawater.
To avoid galvanic corrosion, you can follow the methods and techniques that we detail below:
- Insulate the contact points between metals using plastic or insulating rubber material.
- Place sacrificial electrodes such as zinc and magnesium so that they are the ones that suffer corrosion and are replaceable when worn. This process is known as cathodic protection.
- Avoid using materials that have different levels of electrochemical potential.
- Cover contact areas with insulating paint.
- Use the electroplating technique: coat the metal with an electrolyte such as silver or nickel.
How to avoid corrosion in iron
Iron represents the fourth most abundant element or material on Earth. Its symbol in the periodic table is Faith and is a ferromagnetic material. It is extracted directly from the mines and is treated in the steel companies. Like all metal, it is exposed to the phenomenon of oxidation.
Some of the objects we use daily and are made of iron are tools such as hammers, screws and nuts, as well as keys, doors, railings, window frames, chair frames, mechanical arms and gears. To prevent corrosion in iron, you can use the following methods:
- Cover iron with antioxidant aerosols that react to corrosive substances.
- Protect iron with active metals. Use alloys that modify it chemically, just as stainless steel can.
- Coat the iron with an impermeable layer of paint that prevents it from coming into contact with air and water.
How to prevent corrosion of steel
Steel is a metal that is produced from the combination of iron and carbon. However, steel also tends to oxidize. This process begins when the steel is exposed to oxygen, which forms ferric oxide. When this phenomenon occurs, the steel adopts a reddish color. Over time, this will cause deterioration in the surface of the steel, leaving it exposed and starting the corrosion process.
Some of the daily items that are made of steel include screws, nails, food utensils or auto parts. To prevent corrosion of steel, you can use the following antioxidant techniques or processes ideal for steel:
- Make cathodic protection with zinc anodes or cover it with zinc.
- Coat the steel with plastics.
- Cover or paint the steel with antioxidant paints.
- You can also use stainless steel, made of chrome, silicon and manganese.
- Perform a priming process. This consists of coating the steel with a kind of anticorrosive paint. If the steel is going to be used outdoors, you should use calcium plumbate, and if you are going to use it indoors, cover with zinc chromate.