Methods of protecting metal from corrosion | Trainee
Research work:
Metal corrosion
1) Anodic protection - coating of metal with a more active metal. For example, in a galvanic couple Zn - Fe (galvanized iron) iron is protected, in a Zn - Cu couple copper is protected. Protectors are attached to the bottoms of ships - ingots of metal that are more active than the plating of the ship's bottom. Most often this is protective protection using zinc.
Cathodic protection - protection with a less active metal (tinned iron). For example, coating iron with tin (tinned iron).
2) Separation of metal from an aggressive environment (painting, lubricating, coating with varnishes, enamels). Scientists have created a new glass-crystalline coating that is durable and able to operate at higher temperatures than metals.
3) The use of corrosion inhibitors. More often these are organic substances or inorganic salts (sodium nitrate, strontium, lead, zinc chromates).
4) Electrical protection - neutralization of the current arising from corrosion by direct current passed in the opposite direction. The protected structure is connected to the cathode of an external current source, and the anode is grounded.
This is how oil and gas pipelines are usually protected; in no case should the poles of the current be mixed up; errors must be excluded.
5) Passivation of metals is the formation on the surface of the metal of a tightly adjacent oxide layer that protects against corrosion. For example, iron is passivated by immersing the product in concentrated nitric acid. Passivated iron stops interacting with acids and releasing hydrogen. Passivation can be eliminated by destroying the film.
6) Production of corrosion-resistant alloys. As a result of reducing the carbon content in stainless steel to 0.1%, it became possible to produce rolled sheets from it (corrosion-resistant steel).
Having studied the essence of corrosion and its basic properties, we decided to conduct several experiments to identify the causes and conditions for the appearance of rust, as well as to study methods of protection against the effects of corrosion.
Obtaining the effect of corrosion (experience with a nail)
The experiment was carried out in a well-ventilated area. To carry it out we needed metal (iron nail). Using a spray bottle, spray it with a significant amount of hydrogen peroxide. Then sprinkle the metal with salt.
This must be done while the peroxide is still wet. The rusting process begins almost immediately. After this, the nail needs to dry naturally, in the fresh air. Thus, with the help of artificial corrosion, we obtained a rusty nail. The result of the experiment is presented in Appendix 5.
Methods to protect metal from corrosion
The experiment was carried out with the aim of studying folk remedies for removing rust, which are safe and can be used in everyday life.
We took five rusty iron nails and the same number of plastic glasses. The glasses contained products that, in our opinion, could cope with metal corrosion. Glass No. 1 - with ketchup, No. 2 - with citric acid, No. 3 - with vinegar, No. 4 - rust remover, No. 5 - Coca-Cola. Place one nail in each glass and leave for a day.
According to the results of the experiment (Appendix 6), the most effective means were: rust remover (which contains various strong acids: hydrochloric, orthophosphoric, sulfuric, silicon and others), vinegar (due to the content of concentrated acetic acid in it, which corrodes rusty plaque ), ketchup (thanks to the diluted acetic acid included in its composition).
Conclusion
Thus, when carrying out research work, we found out that corrosion is a phenomenon that brings not only economic damage, but also negatively affects human health, causing material damage and negatively affecting the environment.
It was discovered that we encounter the process of corrosion, that is, the destruction of metal products, in everyday life. During the research, the hypothesis we put forward was confirmed - corrosion is truly controllable, knowing the processes and causes of its occurrence. Also, with the help of experiments, it was revealed that it is possible to protect metals from corrosion using affordable folk remedies. In the era of modern industry, the problem of corrosion still remains relevant.
Internet resources were used to write this work.
Appendix 6
Source: https://obuchonok.ru/node/4655
Protective protection against corrosion of metal products
Protective protection is one of the possible options for protecting pipeline structural materials from corrosion. It is used primarily on gas pipelines and other highways.
The essence of tread protection
Protective protection is the use of a special substance - an inhibitor, which is a metal with increased electronegative properties. When exposed to air, the protector dissolves, resulting in the base metal being preserved despite exposure to corrosive factors. Sacrificial protection is one of the varieties of the cathodic electrochemical method.
This option of anti-corrosion coatings is especially often used when an enterprise is limited in its ability to organize cathodic protection against corrosion processes of an electrochemical nature. For example, if the financial or technological capabilities of the enterprise do not allow the construction of power lines.
Pipeline protector scheme
An inhibitor protector is effective when the transition resistance between the protected object and the environment around it is not significant. High tread performance is possible only at a certain distance. To determine this distance, the radius of anti-corrosion action of the used protector is determined. This concept shows the maximum removal of the protecting metal from the protected surface.
The essence of corrosion processes comes down to the fact that the least active metal during the period of interaction attracts electrons of the more active metal to its own ions. Thus, two processes are carried out at the same time:
- reduction processes in metal with less activity (in the cathode);
- oxidation processes of the anode metal with minimal activity, due to which the pipeline (or other steel structure) is protected from corrosion.
After some time, the effectiveness of the protector decreases (due to loss of contact with the protected metal or due to dissolution of the protective component). For this reason, there is a need to replace the tread.
Features of the method
Protectors for protection against corrosion processes in acidic environments are meaningless. In such environments, tread dissolution occurs at a faster pace. The technique is recommended for use only in neutral environments.
Compared to steel, metals such as chromium, zinc, magnesium, cadmium, and some others are more active. In theory, it is the listed metals that should be used to protect pipelines and other metal structures. However, there are a number of features, knowing which, one can justify the technological pointlessness of using pure metals as protection.
For example, magnesium is characterized by a high rate of corrosion development, a thick oxide film quickly forms on aluminum, and zinc dissolves very unevenly due to its special coarse-grained structure. To negate such negative properties of pure metals, alloying elements are added to them. In other words, the protection of gas pipelines and other metal structures is carried out through the use of various alloys.
Magnesium alloys are often used. In addition to the main component - magnesium - they contain aluminum (5-7%) and zinc (2-5%). In addition, small amounts of nickel, copper and lead are added.
Magnesium alloys are relevant for corrosion protection in environments where the pH value does not exceed 10.5 units (traditional soil, fresh and slightly salted water bodies).
This limiting indicator is associated with the rapid solubility of magnesium at the first stage and the subsequent appearance of sparingly soluble compounds.
Note! Magnesium alloys often cause cracks in metal products and increase their hydrogen embrittlement.
For metal structures located in salt water (for example, an underwater offshore pipeline), protectors based on zinc should be used. Such alloys also contain:
- aluminum (up to 0.5%);
- cadmium (up to 0.15%);
- copper and lead (total up to 0.005%).
In a salty aquatic environment, protecting metals from corrosion using zinc-based alloys will be the best option. However, in fresh water bodies and on ordinary soil, such protectors very quickly become overgrown with oxides and hydroxides, as a result of which anti-corrosion measures become meaningless.
Zinc-based protectors are more often used to protect against corrosion those metal structures where technological conditions require the highest degree of fire safety and explosion safety. An example of the demand for such alloys are gas pipelines and pipelines for transporting flammable liquids.
In addition, zinc compounds, as a result of anodic dissolution, do not form pollutants. Therefore, such alloys have practically no alternative when it is necessary to protect a pipeline for transporting oil or metal structures in tanker ships.
In conditions of salty running water on the coastal shelf, aluminum alloys are often used. Such compositions include cadmium, thallium, indium, silicon (up to 0.02% in total), as well as magnesium (up to 5%) and zinc (up to 8%). The protective properties of aluminum compounds are close to those of magnesium alloys.
Combination of protectors and paints
Often there is a need to protect a gas pipeline from corrosion not only with a protector, but with paint and varnish material. Paint is considered a passive method of protection against corrosion processes and is truly effective only when combined with the use of a protector.
This combination technique allows:
- Reduce the negative impact of potential defects in the coating of metal structures (peeling, swelling, cracking, heaving, etc.). Such defects occur not only as a result of manufacturing defects, but also due to natural factors.
- Reduce (sometimes by a very significant amount) the consumption of expensive protectors, while increasing their service life.
- Make the distribution of the protective layer over the metal more uniform.
It is also worth noting that paint and varnish compositions are often not easy to apply to certain surfaces of an already operating gas pipeline, tanker or some other metal structure. In such cases, you will have to make do with only a protective protector.
Source: https://kraska.guru/specmaterialy/korroziya/protektornaya-zashhita-metallov.html
Is the Lada Vesta body galvanized or not?
A lot of controversy has been caused about the modern AVTOVAZ car, which is VESTA. Many do not believe our automobile industry and say that “modern generation” is nothing more than a continuation of the “folk” GRANT, KALINA, PRIOR on the one hand.
If we put aside everything else (technical and design), opponents of the brand, often entering into disputes, bring up the following facts - “ it will rot in a couple of years if not treated correctly ”! However, the manufacturer gives a guarantee “for 6 years” specifically on the body, that there will be no signs of through corrosion.
And now the concept of “galvanization” begins to blow, opponents will again say that it simply isn’t there (this is a LADA, NOT a MERCEDES), others say that it is there and that the parts are reliably protected. So where is the truth? Today we’ll break down whether it’s there or not
- Is VESTA galvanized?
- Four types of technologies
- How else to protect the body
- Why use a primer for galvanizing?
- About myths
- VIDEO VERSION
Starting the article, I would like to quote the words of one “mega-expert” from a specialized forum (I will not rewrite it verbatim), but this is the meaning. There used to be VAZ 2101s - the metal was of high quality, that’s why it didn’t rot! But now I don’t understand why, that’s why they cover it with all sorts of crap – “anti-corrosion”, “galvanization” and so on. I would like to immediately object to him, these methods are responses to modern road conditions.
Previously, when “KOPEYKA” appeared, there were very few cars, I remember the winters - the snow from the roads was practically not cleared (only the main highways), there were no reagents. And what now - the roads, even at minus 10, are somehow wet, all because they are simply covered in reagents that corrode snow and ice, respectively, the body, paint and even tires (and what can I say, sometimes even boots don’t work for the season).
Under such conditions, the entire “2101” would have rotted in a couple of years! So they protect modern cars, in a modern way, excuse the tautology.
Is VESTA galvanized?
YES there is a fairly decent layer. It’s hard to call it a reference, but to say that it simply isn’t there is IMPOSSIBLE!
In general, all external parts are processed, these are the doors, roof, hood, trunk lid, body pillar, etc. BUT INSIDE (in the cabin) there is NO treatment, only outside and only those parts that come into contact with the external environment.
The technology used by AVTOVAZ is the cheapest and far from the standard; it is powder coating by spraying.
Four types of technologies
A little about why zinc (Zn) protects steel - it is a non-ferrous metal, has a more negative potential and corrodes first (that is, when it collapses, it protects the coating underneath), and the protection works even when it is damaged or partially destroyed.
It becomes clear that the larger and thicker the zinc layer, the longer the car body is preserved and no corrosion occurs.
To apply particles of protective metal to the body, there are only four main technologies, I will list them from best to worst.
- Hot method. When the fully assembled body is dipped into a bath filled with zinc. Moreover, the temperature stays around 460 – 500 degrees Celsius. The method is very expensive and costly. Used by expensive brands on luxury cars - PORSHE, VOLVO, now on some premium HYUNDAI, etc.
- Galvanic method. The method consists in the process of deposition on the cathode (in our case, part of the body), positively charged particles (ions) of zinc from aqueous solutions (electrolytes). This technology works by passing a direct electric current through it. This is a less expensive and simpler technology, used by Mercedes, BMW, TOYOTA, Honda, Mitsubishi, KIA, etc.
- Zinc metal. It is used mainly by KIA, on cars from the “C” class. This is a kind of plastic coating that consists of two layers.
- Cold method. In essence, this is a kind of painting. A powder is applied to the body parts, which contains small particles of zinc powder. Used by many brands (Chevrolet, KIA, HYUNDAI, TOYOTA) including AVTOVAZ.
As you understand, VESTA is processed using the third technology; you choose where and in what volume to apply this layer.
This is where the disadvantages appear, namely the uniformity and thickness of the coating. It is also worth remembering that this layer is not 100% corrosion protection; it needs to be further strengthened.
How else to protect the body
If you leave only galvanization (which, by the way, is NOT inside the cabin), then such a body will not last long. After all, moisture, air, dust, etc. can also get into the cavity; all this can cause oxidation and then corrosion.
Therefore, to protect the inside (in cavities), a primer is used. Moreover, it is applied in two layers, and of course not with brushes, but with the help of technology - “CATAPHORESIS”. The body is lowered into the bath and soil particles settle onto the surface. Moreover, there are two such layers on the LADA VESTA!
Applying two layers of primer provides good protection - after all, the steel is “sealed”, and air access is practically excluded
Next, a layer of enamel is applied to the primed surface, followed by a finishing varnish. That is, it turns out to be a kind of multi-layer cake:
It should be noted that this is very good protection that will allow the body to operate even in difficult conditions for more than 6 years!
Why use a primer for galvanizing?
If everything is clear on the inside, there is no protective layer and primer is required - but why apply it to the outside, where there is galvanization?
If you remember, I wrote above that the larger the layer of this non-ferrous metal, the longer the body steel lasts. SO - the layer that is sprayed is not so large and it needs to be further strengthened.
According to materials science reference books, a ZINC layer 100 microns thick is enough for about 87 years. And the thickness of the “cold method” on the VESTA body is 10 microns
That is, ideally it should be enough for 8.7 years, that is, almost 9 years. However, AVTOVAZ does not provide a guarantee for such a period, due to several factors:
- Application is carried out by spraying, and there is no guarantee against defects (especially if painted by hand).
- As practice has shown, the layer is often about 8 microns
Thus, they extended a 6-year warranty on the body; by the way, when this model was launched, they wanted to give it 4–5 years. Now technology has improved a little.
Source: https://camaro-club.ru/vaz/kuzov-lady-vesty-otsinkovan-ili-net
What are the ways to protect metals from corrosion?
Corrosion has a destructive effect on metal products and alloys. When interacting with the environment, metal products become stained with rust. The more active the metal, the more susceptible it is to corrosion.
Corrosion has a destructive effect on cars, ships, communications and other metal products, which can lead to leakage of oil, gas and other negative consequences. It negatively affects human health, and oxidation products pollute the environment.
Corrosion is unacceptable in the aviation, chemical and nuclear industries. Sometimes the cost of repairing metal products exceeds the cost of the material that was used to manufacture them.
Main types of corrosion processes
Types of metal corrosion can be divided according to the following characteristics: nature of destruction, corrosive environment and mechanism of action.
Based on the nature of the damage, corrosion can be:
- solid. At the same time, it can be uniform and uneven. When uniform, the entire surface of the product is destroyed. When uneven, spots and pinpoint depressions appear;
- intercrystalline. In this case, it penetrates deep into the product along the grain boundaries of the metal;
- transgranular, in which the metal is cut through a grain by a crack;
- selective. One of the components of the alloy is destroyed. For example, zinc in brass can deteriorate.
- subsurface. It starts on the surface and gradually penetrates into the upper layers of the metal.
The following types of corrosive environments exist:
- atmosphere;
- gas;
- the soil;
- liquid (alkali, acid or saline solutions).
The mechanism of action divides corrosion into chemical and electrochemical.
Chemical corrosion is a process in which spontaneous destruction of metals occurs. It occurs when metal products interact with an actively corrosive environment, most often gas. These processes are accompanied by high temperatures.
As a result, simultaneous oxidation of the metal and restoration of the corrosive environment occurs. Chemical corrosion also occurs when interacting with organic liquids, for example, petroleum products, alcohol, etc.
Electrochemical corrosion occurs in electrolytes, for example, in aqueous solutions. The electrochemical reaction produces an electric current that causes the metal to break down. In this case, both chemical processes occur, in which electrons are released, and electrical processes, in which electrons move.
Fracture occurs when dissimilar metals come into contact. Therefore, metals containing many impurities are more susceptible to destruction.
The heterogeneity of the metal structure leads to the fact that during electrochemical corrosion, cathode-anode pairs are formed according to the laws of galvanics. If metal products differ from each other in chemical composition, then a layer of rust forms on the surface of the metal products.
This corrosion is most often the reason for the destruction of metals. Below are pictures showing the mechanism of action of electrochemical corrosion.
In the external environment, metal products are most actively affected by oxygen, high humidity, oxides of sulfur, nitrogen, carbon dioxide, and groundwater. Salt water accelerates the oxidation process, which is why sea vessels rust faster than river vessels.
It is impossible to stop this natural process; all that remains is to find ways to protect against corrosion. True, it is impossible to completely get rid of the corrosion process, but these methods help slow down the process itself.
Methods of resisting corrosion processes
The following methods exist to protect metals from corrosion:
- increasing the resistance of metals by increasing the chemical composition;
- insulation of metal coatings from aggressive environmental influences;
- reducing the aggressiveness of the environment in which metal products are used;
- electrochemical, which, thanks to the laws of galvanics, reduce corrosion processes.
These methods can be divided into two large groups. The first two methods are applied before metal products are used, that is, at the stage of their production. In this case, certain construction materials are selected for the production of the product, and various galvanic and protective coatings are applied.
The last two methods are used when operating metal products. In this case, for protection, current is passed through the product, the aggressiveness of the environment is reduced by adding various inhibitors, thus, the product itself is not pre-treated in any way before use.
Methods for increasing resistance
These protection methods are based on the creation of alloys that have anti-corrosion properties. Components are added to the metal to increase its corrosion resistance. An example is alloying steel with chromium.
Source: https://crast.ru/instrumenty/kakie-sushhestvujut-sposoby-zashhity-metallov-ot
