We are surrounded by metals. All around us you can find metal constructions and their number is continuously rising. The main enemy of these construction is the phenomenon of degradation, which is called corrosion.
At first sight, when we talk about corrosion, we have in mind the image of rust that appears on ferrous metals.
And yet, what does the word "corrosion" mean?
Corrosion refers to the processes of metal deterioration and degradation, under the action of chemical agents in the environment. In brief, the degradation of a material as a result of its reaction with the environment to which it is exposed.
Any material corrodes, not just the metals:
- Stainless steel oxidizes when activated, or in certain environments;
- Wood - is rotting;
- Plastic - it decomposes (only very slowly, in thousands of years);
- People... are aging.
All these are forms of corrosion at a certain level.
The fact that many metals react with their surrounding neighbourhood is known for a long time. Thus, iron or steel are rusting, silver loses its gloss, copper gets a patina, aluminium is oxidizing (forming a very thin layer of oxide that prevents the reaction go further), zinc and lead gradually lose their metallic gloss.
The causes of these unwanted changes in metals are the chemical reactions, and especially, the electrochemical reactions, which start at the surface of the metal.
Considering the exception of so-called noble metals, all other metals are unstable in contact with the atmospheric environment. The way this instability happens, as well as the extent to which it occurs, depends both on the nature of the metal and its surrounding neighborhood.
The process consists in the gradual destruction of materials (usually metals) as a result of the chemical and / or electrochemical reaction with their environment. Corrosion degrades the useful properties of materials and structures, including strength, appearance and permeability to liquids and gases.
Many structural alloys corrode merely as a result of exposure to moisture in the air, but the process may be strongly affected by exposure to certain substances.
Corrosion may occur locally, forming a pit or crack, or spread over a larger area more or less uniformly, affecting a particular surface. Since corrosion is a diffusion-controlled process, it occurs on the exposed surfaces.
As a result, methods for reducing exposed surface activity, such as passivation, can increase resistance to corrosion for a material. However, certain corrosion-related mechanisms are less visible and therefore less predictable. Due to the need to prolong the life of the metallic surfaces to save money, the anti-corrosion protection services have emerged.
The US Army protects equipment (like helicopters) against corrosion, resulting in savings of millions of dollars. This is about increasing the operating life and savings. Who does not want this?
We will talk in a future article on anti-corrosion protection.