- What is corrosion?
- Types of corrosion
- Examples of corrosion in everyday life
- How to avoid corrosion?
- Corrosion and oxidation
We explain what corrosion is and what types of corrosion exist. Examples and how to avoid it. In addition, the relationship between corrosion and oxidation.
What is corrosion?
Corrosion process degradation of certain materials, as a consequence of an electrochemical reaction, that is, of oxide-reduction, from its environment.
It's about a natural phenomenonspontaneous, affecting mainly (although not exclusively) the metals. The speed of the reaction depends on the temperature to which it occurs, as well as the properties of the elements involved, especially its salinity.
Corrosion is a chemical process in which three factors usually intervene: the corroded element, the environment and, generally, the Water. However, there are also corrosive substances, that is, capable of producing the corrosion of the materials with which they come in direct contact.
For its part, the metallurgical industry studies corrosion as an important enemy to be overcome by its products, especially those exposed to the environment, in architectural or construction pieces. In fact, it is estimated that every few seconds approximately five tons of steel are lost worldwide due to corrosion.
Types of corrosion
Broadly speaking, there are two types of corrosion: chemical and electrochemical, depending on the type of materials and reactions involved:
- Chemical corrosion. Occurs when a material reacts in a liquid or gas corrosive, until completely dissolved or until the liquid is saturated. This can happen in different ways:
- Liquid metal attack. It occurs when a solid metal and another liquid metal come into contact, and the former is corroded at its weak points by the latter.
- Selective leaching. It occurs when there is selective corrosion in alloys metallic.
- Chemical attack. It occurs with aggressive chemical reactions by solvents powerful, such as those that are capable of dissolving polymers, generally considered resistant to corrosion.
- Electrochemical corrosion. It generally occurs in metals, when their atoms lose electrons and they become ions. It can occur in different ways:
- Microbiological corrosion. When caused by microscopic living organisms capable of altering the chemistry of materials, such as bacteria, algae and mushrooms.
- Galvanic corrosion. It is the most intense of all and occurs when different metals interact with each other, and one acts as an anode and the other as a cathode, forming what is known as a galvanic battery.
- Corrosion by surface aeration. Known as the Evans Effect, it occurs on flat surfaces located in humid and dirty places, which promote electronegatively charged environments.
Examples of corrosion in everyday life
Some examples of corrosion in everyday life are:
- Corrosion of water pipes. It occurs especially in those metallic ones, which tend to break over time and contaminate the water with small doses of oxide, which give it a color blackish or brown.
- Rust on metals exposed to water. It occurs on the plate of an automatic washing machine, or the doors of cars left on the beach, where the saline environment accelerates the oxidative reaction and soon cracks and the typical brown spots of rust appear.
- The color of the Statue of Liberty. Its original tone should not be greenish, but color copper, material from which it is made. Being surrounded by water, the humidity of air It oxidizes and covers it with a greenish dust (copper oxide), a product of corrosion.
- Corrosion of tin cans. Cans that have been in the pantry too long are starting to show brown spots on some regions, an unequivocal sign that air corrosion has begun to affect them.
How to avoid corrosion?
The fight against corrosion is part of the metal industries, which have various mechanisms to avoid or slow down these metal-disintegrating processes, such as:
- Coatings. Many metals are coated with polymers or plastics, for example, to avoid or minimize environmental corrosion, isolating them from their environment in a substance more resistant to this type of reaction.
- Alloys. Many combinations of metals give the result greater resistance to corrosion, such as zinc-alloyed steels.
- Corrosion inhibitors. Is about chemical substances They have the property of slowing down or preventing the natural process of corrosion of certain materials, so it is enough to immerse them in a film of them to make them more resistant.
- Choice of materials. The simplest solution is to choose well which materials to leave exposed to the environment and which ones not, and which ones to use for works exposed to the elements or to the action of water, for example.
Corrosion and oxidation
Although it is not often called that way, oxidation is a corrosion reaction since an electronic exchange occurs in every act of oxidation, classifiable as electrochemical corrosion.
For this reason, metals left out in the open or submerged in water corrode, as they react with oxygen in the air or water and form oxide layers on their surface, which prevent corrosion. chemical reaction keep moving forward.
However, this oxide layer is mechanically removed and the deeper layers of the metal are again exposed to oxygen, resulting in the destruction of the material completely. This process is particularly fast in saline environments, since sodium chloride acts as a catalyst for the reaction, speeding it up.