Electrochemical corrosion is the most common type of violation of the integrity of a metal structure. It is not necessary to immerse the part in electrolyte. Often a thin film on the surface of the material is sufficient.
Electrochemical corrosion of metals occurs, to a greater extent, as a result of the widespread use of technical and household salts (potassium chloride and sodium). Most often, these substances are used in the winter to quickly remove ice and snow from city streets. Most of all, as practice shows, the damage is thus done to underground utilities and ground transport.
Electrochemical corrosion is observed on the details of machines, structures, devices located in soil, soil, water (sea or river), atmosphere, in technical solutions, under the influence of lubricating, cooling products.
Destruction can be caused by stray currents that occur when a part of the current leaks from an electric circuit to soil or water, and from there to structural elements. Where there is a return exit (from metals to soil or water), destruction of parts is noted - electrochemical corrosion. Most often, stray currents are formed in places where ground transport is moving (trams, electric locomotives). Moreover, studies show that 1 Ampere per year is able to dissolve 33.4 kg of lead, 10.7 kg of zinc and 9.1 kg of iron.
Often, several factors are involved in the development of destruction.
Electrochemical corrosion is a special process. Alloy (or an independent material) loses some of the available atoms. They (atoms) pass in the form of ions into an electrolytic solution. Instead of 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 pair. Redox reactions to a greater extent contribute to the heterogeneity in the chemical structure of the material. The provoking factors in the formation of anodes and cathodes are also areas of permanent deformation, lack of uniformity in the protective films covering the metal .
You can observe the destruction of parts at home. This will require three nails, three cups with saline (table salt dissolved in water), a small piece of zinc, copper wire (insulation should be removed).
The first nail is lowered into a glass with a salt mixture. The wire should be screwed to the second and also placed in the solution (in the second glass). The third nail is lowered into the third container. Leave on for two to three days. After this period, rust will be noted on all three nails. However, in the worst condition will be a nail with wire, in the best - with zinc. This difference is due to the different ability of metals to give electrons.
To protect the material, the method of changing its potential is used. It should be noted that the technique is not related to isolation. The cathodic (anodic) method is used as protection.
At the same time, the protected structure located in an unfavorable (for example, soil) environment is connected to the cathode (negatively charged electrode) of an electric source. Thus, the part becomes a cathode. The old part is also placed in the same medium, attaching it to the anode from an external source. The corrosion process leads to the destruction of the old metal, which becomes the anode.
There is also a tread type of protection. Unlike the one described above, this option provides for the use of a special anode - tread. In its quality, metal is used more active than that of the protected structure. In the process of corrosion damage, the tread performs the task of the anode (positive electrode) and, when destroyed, protects against integrity damage in the protected part.