Corrosion is the destruction of metal, ceramic, wood and other materials as a result of chemical or physico-chemical interaction. As for the causes of such an undesirable effect, they are different. In most cases, this is structural instability to the thermodynamic effects of the environment. Let's take a closer look at what corrosion is. Types of corrosion must also be considered, and it will not be superfluous to talk about protection against it.
A bit of general information
We are used to hearing the term “rusting”, which is used in the case of corrosion of metal and alloys. There is such a thing as “aging” - it is characteristic of polymers. In fact, this is one and the same. A vivid example is the aging of rubber products due to the active interaction with oxygen. In addition, some plastic elements are destroyed by atmospheric precipitation. The corrosion rate directly depends on the conditions in which the object is located. So, rust on a metal product will spread the faster, the higher the temperature. Humidity also affects: the higher it is, the faster the metal will become unsuitable for further operation. It has been experimentally established that approximately 10 percent of metal products are irrevocably written off, and corrosion is to blame. Types of corrosion are different and are classified depending on the type of medium, the nature of the flow 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. They can be conditionally divided into the following groups:
- Chemical corrosion is a process of interaction with a corrosive environment in which the oxidation of a metal and the reduction of an oxidizing agent take place in one act. The metal and oxidizing agent are not spatially separated.
- Electrochemical corrosion is the process of interaction of a metal with an electrolyte solution. Ionization of atoms and reduction of an oxidizing agent occur in different events, however, the rate largely depends on the electrode potential.
- Gas corrosion - chemical rusting of a metal with a minimum moisture content (not more than 0.1 percent) and / or high temperatures in a gas environment. Most often, this species is found in the chemical and oil refining industries.
In addition, there are a huge number of rusting processes. All of them are corrosion. Types of corrosion, in addition to the above, include biological, radioactive, atmospheric, contact, local, target rusting, etc.
Electrochemical corrosion and its features
With this type of destruction, the process proceeds when the metal comes into contact with the electrolyte. Condensation or rainwater may be used as the latter. The more salts and acids are contained in the liquid, the higher the electrical conductivity, and hence the rate of the process. As for the most corroded places 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 rust, the process slows down somewhat, but still continues. A prime 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 corrodes. However, the presence of an oxide film on the surface greatly slows down the destruction process. Of course, all types of electrochemical corrosion are extremely dangerous and sometimes it is even impossible to fight them.
Chemical corrosion
Such a change in metal is quite common. A vivid example is the appearance of scale as a result of the interaction of metal products with oxygen. In this case, high temperature acts as an accelerator of the process, and such liquids 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 emergence of a film resistant to further corrosion. Steel products form iron oxides. Further chemical processes lead to the appearance of rust, which does not provide any protection against further destruction, but rather contributes to this. Currently, all types of chemical corrosion are eliminated by galvanizing. Other protective equipment may be used.
Types of concrete corrosion
Changing the structure and increasing the fragility 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 a concrete product is systematically exposed to precipitation and other liquids. As a result, calcium oxide hydrate is washed out and the structure is disturbed.
- Interaction with acids. If the cement stone is in contact with acids, then calcium bicarbonate is formed - an aggressive chemical element for a concrete product.
- Crystallization of sparingly soluble substances. In fact, biocorrosion is meant. The bottom line is that microorganisms (spores, fungi) enter the pores and develop there, resulting in destruction.
Corrosion: types, methods of protection
No doubt, billions of dollars in annual losses led to the fact that people began to deal with this harmful effect. It is safe to say that all types of corrosion do not lead to the loss of metal itself, but of valuable metal structures, for the construction of which huge amounts of money are spent. It is difficult to say whether it is possible to provide 100 percent protection. However, with proper surface preparation, which involves abrasive blasting, good results can be achieved. The paintwork reliably protects against electrochemical corrosion when applied correctly. And from the destruction of the metal underground, a special surface treatment will reliably protect it.
Active and passive methods of struggle
The essence of active methods is to change the structure of a double electric field. For this, a direct current source is used. The voltage must be selected so that the electrode potential of the product to be protected increases. Another extremely popular method is the “sacrificial” anode. It collapses, protecting the main material.
Passive protection involves the use of paintwork. The main task is to completely prevent the ingress of moisture, as well as oxygen, onto the surface to be protected. As noted above, it makes sense to use zinc, copper or nickel spraying. Even a partially destroyed layer will protect the metal from rust. Of course, these types of corrosion protection of metals are effective only when the surface will not have visible defects in the form of cracks, chips, and the like.
Galvanization in detail
We have already examined the main types of corrosion, and now I would like to talk about the best methods of protection. One of these 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 physico-chemical properties. It is worth noting that this method is considered one of the most economical and effective, and this despite the fact that approximately 40 percent of the global production 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 you can protect the product of any size and shape. Zinc does not have a decorative purpose, although with the help of some special additives it is possible to obtain shiny surfaces. In principle, this metal is able to provide maximum protection in aggressive environments.
Conclusion
So we told you what corrosion is. Types of corrosion were also considered. Now you know how to protect the surface from premature rusting. By and large, to do this is extremely simple, but where and how the product is operated is of no small importance. If it is constantly subjected to dynamic and vibrational stresses, then there is a high probability of cracks in the paintwork, through which moisture will fall on the metal, as a result of which it will gradually collapse. Nevertheless, the use of various rubber gaskets and sealants in the places where metal products interact can somewhat extend the life of the coating.
Well, that’s all about this topic. Remember that premature structural failure due to corrosion can lead to unintended consequences. At the enterprise, large material damage and loss of life are possible as a result of rusting of the supporting metal structure.