Corrosion: types of corrosion, methods of protection

Corrosion is the destruction of metal, ceramic, wood and other materials as a result of chemical or physicochemical interactions. As for the causes of such an undesirable effect, they are different. In most cases, this is a structural instability to the thermodynamic effects of the environment. Let's take a closer look at what corrosion is. Types of corrosion, too, must be considered, and it will not be superfluous to talk about protection from it.

Some general information

We used to hear the term "rust", which is used in the case of corrosion of metal and alloys. There is still such a thing as "aging" - it is characteristic of polymers. In fact, it's the same thing. A vivid example is aging of rubber products due to active interaction with oxygen. In addition, some plastic elements are destroyed by the influence of atmospheric precipitation. The rate of corrosion depends directly on the conditions in which the object is located. So, rust on a metal product will spread the faster, the higher the temperature. Also affects the humidity: the higher it is, the faster the metal will become unsuitable for further use. It has been experimentally established that about 10 percent of metal products are irrevocably written off, and the fault is corrosion. Types of corrosion are different and are classified depending on the type of media, the nature of the leak and the like. Let's look at them in more detail.

Classification

Currently, there are more than two dozen rusting options. We give only the most basic types of corrosion. Conditionally they can be divided into the following groups:

• Chemical corrosion is the process of interaction with a corrosive medium, in which oxidation of the metal and reduction of the oxidant take place in one act. The metal and the oxidant are not spatially separated.
• Electrochemical corrosion is the process of interaction of a metal with an electrolyte solution. The ionization of atoms and the reduction of the oxidant take place in different acts, however, the speed largely depends on the electrode potential.
• Gas corrosion - chemical rusting of metal with a minimum moisture content (not more than 0.1 percent) and / or high temperatures in the gas environment. Most often this species is found in the chemical and oil refining industry.

In addition, there is still a huge number of rusting processes. All of them are corrosion. Types of corrosion, other than those described above, include biological, radioactive, atmospheric, contact, local, target rust, and others.

Electrochemical corrosion and its features

With this kind of destruction, the process proceeds when the metal contacts the electrolyte. The latter can be condensate or rainwater. The more salt and acids in the liquid, the higher the electrical conductivity, and, consequently, the speed of the process. As for the most corroded areas of the metal structure, these are rivets, welded joints, places of mechanical damage. If the structural properties of the iron alloy make it resistant to rusting, the process slows down somewhat, but still continues. A good example is galvanizing. The fact is that zinc has a more negative potential than iron. For this simple reason, the iron alloy is restored, and zinc rusts. However, the presence of an oxide film on the surface greatly slows down the process of destruction. Of course, all types of electrochemical corrosion are extremely dangerous and sometimes even impossible to fight with.

Chemical Corrosion

This change in the metal occurs quite often. A striking example is the appearance of scale as a result of the interaction of metal products with oxygen. High temperature in this case acts as an accelerator of the process, and liquids such as water, salts, acids, alkalis and salt solutions can participate in it. If we talk about materials such as copper or zinc, then their oxidation leads to the formation of a corrosion-resistant film. Steel products also form iron oxides. Further chemical processes lead to rust, which does not provide any protection against further destruction, but, on the contrary, contributes to this. Currently, all types of chemical corrosion are eliminated by galvanizing. Other means of protection may be used.

Types of corrosion of concrete

The change in the structure and increase in the embrittlement of concrete under the influence of the environment can be of three types:

• Destruction of parts of cement stone is one of the most common types of corrosion. It takes place if the concrete product undergoes systematic exposure to atmospheric precipitation and other liquids. As a result, the hydroxide of calcium oxide is washed away and the structure is broken.
• Interaction with acids. If the cement stone is in contact with acids, calcium bicarbonate is formed, an aggressive chemical element for the concrete product.
• Crystallization of hardly soluble substances. In fact, we mean biocorrosion. The bottom line is that microorganisms (spores, fungi) enter the pores and develop there, resulting in destruction.

Corrosion: types, ways of protection

Without a doubt, the billions of annual losses caused people to struggle with this harmful effect. It can be said with certainty that all types of corrosion lead to the loss not of the metal itself, but of valuable metal structures, the construction of which spends a lot of money. It is difficult to say whether it is possible to provide 100% protection. However, with proper preparation of the surface, which consists in abrasive blasting, you can achieve good results. From electrochemical corrosion reliably protects paintwork when properly applied. And from the destruction of metal under the earth, a special treatment of the surface will reliably protect.

Active and passive methods of struggle

The essence of the active methods is to change the structure of the double electric field. A direct current source is used for this. The voltage must be selected in such a way that the electrode potential of the product increases, which must be protected. Another extremely popular method is the "sacrificial" anode. It collapses, protecting the main material.

Passive protection means the use of paintwork. The main task is to completely prevent the ingress of moisture, as well as oxygen, to the surface to be protected. As already noted a little bit above, it makes sense to use zinc, copper or nickel sputtering. Even a partially destroyed layer will protect the metal from rusting. Of course, these types of protection against corrosion of metals are effective only when the surface will not have visible defects in the form of cracks, chips and the like.

Galvanizing in detail

We have already considered the main types of corrosion, and now I would like to talk about the best methods of protection. One such is galvanizing. Its essence lies in the fact that zinc or its alloy is applied to the surface to be treated, which gives the surface some physical and chemical properties. It is worth noting that this method is considered one of the most economical and effective, and this despite the fact that about 40 percent of the global extraction of this element is spent on zinc metallization. Steel sheets, fasteners, and also devices and other metal structures can be galvanized. It is interesting that with the help of metallization or spraying it is possible to protect the product of any size and shape. Zinc has no decorative purpose, although with the help of some special additives, it becomes possible to obtain shiny surfaces. In principle, this metal is able to provide maximum protection in aggressive environments.

Conclusion

So we told you about what corrosion is. Types of corrosion have also been considered. Now you know how to protect the surface from premature rusting. By and large, this is extremely simple, but of no small importance is where and how the product is operated. If it is constantly subjected to dynamic and vibrating loads, then there is a high probability of cracks in paint coatings, through which moisture will fall on the metal, as a result of which it will gradually break down. Nevertheless, the use of various rubber gaskets and sealants in the areas of interaction of metal products can somewhat extend the life of the coating.

Well, that's all for this topic. Remember that premature failure of the structure due to the effects of corrosion can lead to unforeseen consequences. At the enterprise, large material damage and human casualties are possible as a result of rusting of the bearing metal structure.