Electrochemical corrosion

Electrochemical corrosion is the most common type of violation of the integrity of the metal structure. It is not necessary to immerse the part in the electrolyte. It is often sufficient to have a thin film on the surface of the material.

Electrochemical corrosion of metals occurs, to a greater extent, as a result of the widespread application of technical and household salt (potassium chloride and sodium). Most often these substances are used in winter to quickly eliminate ice and snow from the streets of cities. Most, as practice shows, damage is thus applied to underground communications and ground transportation.

Electrochemical corrosion is observed on the details of machines, structures, instruments in soil, soil, water (sea or river), atmosphere, in technical solutions, under the influence of lubricating, cooling products.

Destruction can provoke stray currents that occur when a part of the current flows from the electrical circuit to the soil or water, and from there to the structural elements. Where there is a reverse exit (from metals to soil or water) there is a destruction of parts - electrochemical corrosion. Most often, wandering currents are formed in places where ground transport moves (trams, railway locomotives on electric traction). In this case, as studies show, 1 ampere per year can dissolve 33.4 kg of lead, 10.7 kg of zinc and 9.1 kg of iron.

Often in the development of destruction involves several factors.

Electrochemical corrosion is a special process. The alloy (or an independent material) loses some of the available atoms. They (the atoms) pass in the form of ions into the electrolytic solution. Instead of the particles lost by the metal, electrons appear that charge the material with a negative charge. In this case, the electrolyte has a positive charge. Thus, electrochemical corrosion forms a galvanic couple. The heterogeneity in the chemical structure of the material contributes to the oxidative-reduction reactions. The provoking factors in the formation of anodes and cathodes are the areas of permanent deformation, the lack of uniformity in protective films covering the metal .

You can observe the destruction of parts in the home. This requires three nails, three cups with saline solution (food salt dissolved in water), a small piece of zinc, copper wire (the insulation should be removed).

The first nail is lowered into a glass with a salt mixture. The second should be screwed on the wire and also placed in the solution (in the second glass). The third nail is lowered into the third container. Leave for two or three days. At the end of this period, all three nails will be rusted. However, in the worst condition there will be a nail with a wire, in the best - with zinc. This difference is due to the different ability of metals to give electrons.

To protect the material, a method of changing its potential is used. It should be noted that the technique is not related to insulation. As a protection, a cathodic (anodic) method is used.

In this case, the protected structure, which is in an unfavorable (for example, soil) environment, is connected to the cathode (charged negatively to the electrode) of the electric source. Thus, the part becomes a cathode. In the same environment, the old part is also placed, attaching it to the anode from an external source. Corrosive process leads to the destruction of the old metal, which becomes an anode.

There is also a protector type of protection. In contrast to the above, this option involves the use of a special anode - the protector. In its quality, a metal that is more active than that of the protected structure is used. In the process of corrosive destruction, the protector performs the task of the anode (positive electrode) and, failing, protects against integrity violation in the protected part.