I decided to go ice skating this year. I took it out of the closet and saw that the blade of the skates was covered with some kind of red-brown coating. At first I was upset, because my skates were damaged and I probably couldn’t skate on them anymore.

In the evening, my mother came home from work, and I told her about my trouble. Mom calmed me down and explained that the blades of skates are made of iron. And it sometimes becomes covered with rust if moisture gets on the iron.

I was wondering:

-What is rust?

-Where does it come from?

-Do other materials besides iron also rust?

I thought perhaps rust is some kind of red-brown paint that covers all materials over time. To test my assumptions, I decided to conduct several experiments.

1. I took a piece of wood, iron, plastic, glass, fabric and wet them with water. Two days later, I discovered that the water had evaporated from pieces of fabric, wood, plastic, and glass and they were not covered with rust. And a red-brown coating appeared on the surface of the piece of iron.

So we can conclude:

Non-metallic objects - made of wood, plastic, glass, fabric - do not rust, but metal objects do.

Then I had another question:

-Do all metals tend to rust?

Dad brought me pieces of copper, aluminum, iron, cast iron.

I assumed that all metals rust. To test this hypothesis, I conducted the following experiment:

2. I took pieces of copper, aluminum, iron, cast iron, soaked them in water and watched them for several days. I saw that the surface of iron and cast iron was covered with rust, but the surface of copper and aluminum was not rusty.

Therefore, I came to this conclusion:

Not all metals rust. Iron and cast iron rust, but copper and aluminum do not rust.

I wonder if it’s only water that causes iron to rust, or could it be other liquids?

3. I assumed that it was not only from water. To confirm or refute my assumption, I took: cologne, acetone, vegetable oil, gasoline and four identical pieces of iron. I wet everything with the indicated liquids. I watched this process for several days.

As a result, I saw that the pieces lubricated with oil, gasoline, cologne, and acetone did not rust. This means that iron does not rust from other liquids.

So what is rust?

The chemistry teacher explained to me that rust is a guide iron oxide three. She told me that iron, when exposed to open air, quickly rusts. This happens even faster if it comes into contact with water. Iron and oxygen in the water begin to interact and form hydroxide, that is, rust. The water turns reddish and rust floats in the water in the form of small particles. When the water evaporates, rust remains on the surface of the iron, forming a reddish layer.

On the Internet, I learned about ways to combat rust, because it corrodes and destroys iron surfaces. To avoid this destructive process, iron surfaces are coated with paint, drying oil, enamel, varnish and other stainless metals (chrome, zinc).

And I decided to make sure of this.

4. I took three pieces of iron: I painted half of the first one, painted the second half with varnish, and cleaned the galvanized layer from half of the third. I wet them with water and began to observe. After a few days, I saw that those iron surfaces that were covered with varnish, paint, and zinc were not subject to rust, but the uncoated areas rusted. I am convinced that such methods of fighting rust help avoid the destruction of metal surfaces.

Therefore, the roofs of houses are covered with paint or stainless metals, bathrooms and metal utensils are covered with enamel, washing machines and refrigerators are made of stainless metals; Cars and trucks are painted with paint and varnish.

Conclusion:

As a result of research work, I learned what rust is, where it comes from, and what coating methods are used to avoid destruction and preserve the original appearance of iron surfaces.

My advice to adults and children: when winter is over, wipe your skates, lubricate the blades with machine oil, carefully wrap them in paper and put them in a closet. This way you can preserve your skate blades for a long time and enjoy the beauty of skating next year!

The concept of strength is often associated with metals. “Strong as steel,” - each of us has heard this phrase more than once. In fact, under the chemical influence of the external environment, metals can oxidize and destroy.

The term “corrosion” comes from the Latin “corrodere” - to corrode. But not only metals are susceptible to corrosion. Plastics, polymers, wood and even stones are also susceptible to corrosion.

Corrosion is the result of chemical exposure to the environment. As a result of corrosion, metals are destroyed spontaneously. Of course, metals can also be destroyed under the influence of physical impact. Such processes are called wear, aging, erosion.

Despite the fact that polymers, ceramics, and glass are widely used in industry and everyday life, the role of metals in human life continues to be very important.

We encounter metal corrosion very often. Rusty iron is the result of corrosion. It must be said that many metals can corrode. But only iron rusts.

What happens to metals during corrosion from a chemical point of view?

Chemical corrosion

The surface layer of the metal interacts with oxygen in the air. As a result, an oxide film is formed. Films of different strengths are formed on the surfaces of different metals. Thus, aluminum and zinc form a strong film when interacting with oxygen, which prevents further corrosion of these metals. The protective film of aluminum is aluminum oxide Al 2 O 3. Neither oxygen nor water can penetrate through it. For example, in an aluminum kettle, boiling water does not affect the metal.

But some metals and their compounds form loose films. If you cut off a piece of sodium metal, you can see a film with cracks appear on its surface. Such a film will freely allow air oxygen, water vapor and other substances to pass to the surface. Sodium corrosion will continue.

Chemical corrosion is a chemical interaction between a metal and the external environment, which results in a reaction of metal oxidation and restoration of the corrosive environment.

But the external environment contains not only oxygen and water vapor. Oxides of nitrogen, sulfur, and carbon are found in the air, and salts and dissolved gases can be found in water. And the corrosion process is a rather complex process. Different metals corrode differently. For example, bronze is coated with copper sulfate (CuOH) 2 SO 4, which looks like a green spider web.

Corrosion that occurs under the influence of electric current is not chemical. It is called electrochemical.

Why does iron rust?

Why does iron still rust?

During the corrosion process, the metal oxidizes and turns into an oxide.

A simplified equation for iron corrosion looks like this:

4Fe + 3O 2 + 2H 2 O = 2Fe 2 O 3 H 2 O

2Fe 2 O 3 ·H 2 O - hydrated iron oxide, or iron hydroxide. This is rust.

As can be seen from the reaction equation, rust forms on the surface of iron if it reacts with oxygen in water or humid air. Iron does not rust in a dry place. The surface of the rust does not protect the iron from further exposure to the environment, so eventually the iron will completely turn into rust. Rust is the name given to corrosion of iron and its alloys.

Chemical corrosion can be gas corrosion and corrosion in non-electrolyte liquids.

Types of chemical corrosion

Gas corrosion is the process of destruction of a metal surface under the influence of gases at high temperatures. Corrosion is best known when metal is exposed to oxygen.

Chemical corrosion of metals and their compounds can occur in non-electrolyte liquids. Non-electrolyte liquids - phenol, benzene, alcohols, kerosene, petroleum, gasoline, chloroform, molten sulfur, liquid bromine, and others. Such liquids do not conduct electricity. In their pure form, they do not contain impurities and do not react with metals. But if impurities get into them, then the metals in such liquids begin to undergo chemical corrosion.

To protect metal structures from chemical corrosion, coatings are applied to the surface, which will provide protection from the effects of a corrosive environment.

Metal corrosion is a widespread cause of deterioration of various metal parts. Metal corrosion (or rusting) is the destruction of metal under the influence of physical and chemical factors. Factors that cause corrosion include natural precipitation, water, temperature, air, various alkalis and acids, etc.

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Metal corrosion is becoming a serious problem in construction, at home and in production. Most often, designers provide protection for metal surfaces from rust, but sometimes rust occurs on unprotected surfaces and on specially treated parts.

Metal alloys form the basis of human life; they surround him almost everywhere: at home, at work, and during leisure. People don’t always notice metal things and parts, but they constantly accompany them. Various alloys and pure metals are the most produced substances on our planet. Modern industry produces various alloys 20 times more (by weight) than all other materials. Even though metals are considered to be some of the strongest substances on Earth, they can break down and lose their properties through rusting processes. Under the influence of water, air and other factors, the process of oxidation of metals occurs, which is called corrosion. Despite the fact that not only metal, but also rocks can corrode, processes associated specifically with metals will be discussed below. It is worth paying attention to the fact that some alloys or metals are more susceptible to corrosion than others. This is due to the speed of the oxidation process.

Metal oxidation process

The most common substance in alloys is iron. Corrosion of iron is described by the following chemical equation: 3O 2 +2H 2 O+4Fe=2Fe 2 O 3. H 2 O. The resulting iron oxide is that red rust that spoils objects. But let's look at the types of corrosion:

1. Hydrogen corrosion. It practically does not occur on metal surfaces (although theoretically possible). In this regard, it will not be described.
2. Oxygen corrosion. Similar to hydrogen.
3. Chemical. The reaction occurs due to the influence of the metal with some factor (for example, air 3O 2 +4Fe = 2Fe 2 O 3) and occurs without the formation of electrochemical processes. So, after exposure to oxygen, an oxide film appears on the surface. On some metals, such a film is quite strong and not only protects the element from destructive processes, but also increases its strength (for example, aluminum or zinc). On some metals, such a film peels off (destroys) very quickly, for example, sodium or potassium. And most metals deteriorate quite slowly (iron, cast iron, etc.). This is how, for example, corrosion occurs in cast iron. More often, rusting occurs when the alloy comes into contact with sulfur, oxygen, or chlorine. Due to chemical corrosion, nozzles, fittings, etc. rust.
4. Electrochemical corrosion of iron. This type of rusting occurs in environments that conduct electricity (conductors). The destruction time of different materials during electrochemical reactions is different. Electrochemical reactions are observed in cases of contact between metals that are located at a distance in a series of tensions. For example, a product made of steel has copper soldering/fastenings. When water hits the connections, the copper parts will be the cathodes and the steel will be the anode (each point has its own electrical potential). The speed of such processes depends on the amount and composition of the electrolyte. For reactions to occur, the presence of 2 different metals and an electrically conductive medium is required. In this case, the destruction of alloys is directly proportional to the current strength. The greater the current, the faster the reaction; the faster the reaction, the faster the destruction. In some cases, alloy impurities serve as cathodes.

Electrochemical corrosion of iron

It is also worth noting the subtypes that occur during rusting (we will not describe it, we will just list it): underground, atmospheric, gas, with different types of immersion, continuous, contact, caused by friction, etc. All subspecies can be classified as chemical or electrochemical rusting.

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Corrosion of reinforcement and welded structures often occurs during construction. Corrosion often occurs due to non-compliance with the rules for storing the material or failure to perform work on processing the rods. Corrosion of reinforcement is quite dangerous, since reinforcement is laid to strengthen structures, and as a result of the destruction of the rods, a collapse is possible. Corrosion of welds is no less dangerous than corrosion of reinforcement. This will also significantly weaken the seam and may lead to tearing. There are many examples where rust on power structures leads to the collapse of premises.

Other common cases of rusting in everyday life are damage to household tools (knives, cutlery, tools), damage to metal structures, damage to vehicles (both land, air and water), etc.

Perhaps the most common rusty things are keys, knives and tools. All these items are subject to rust due to the fact that friction removes the protective coating, which exposes the base.

The base is subject to destruction processes due to contact with aggressive environments (especially knives and tools).

Destruction due to contact with aggressive media

By the way, the destruction of things that are often used in everyday life can be observed almost everywhere and regularly, at the same time, some metal objects or structures can remain rusty for decades and will perform their functions properly. For example, a hacksaw, which was often used to cut logs and left for a month in a shed, will quickly rust and may break during the work, and a pole with a road sign can stand for ten or even more years rusty and not collapse.

Therefore, all metal items should be protected from corrosion. There are several methods of protection, but they are all chemical. The choice of such protection depends on the type of surface and the destructive factor acting on it.

To do this, the surface is thoroughly cleaned of dirt and dust in order to eliminate the possibility of the protective coating not getting on the surface. It is then degreased (for some types of alloy or metal and for some protective coatings this is necessary), after which a protective layer is applied. Most often, protection is provided by paints and varnishes. Depending on the metal and factors, different varnishes, paints and primers are used.

Another option is to apply a thin protective layer of another material. This method is usually practiced in production (for example, galvanizing). As a result, the consumer practically does not need to do anything after purchasing the item.

Applying a thin protective layer

Another option is to create special alloys that do not oxidize (for example, stainless steel), but they do not guarantee 100% protection; moreover, some things made from such materials oxidize.

Important parameters of protective layers are thickness, service life and rate of destruction under active adverse influences. When applying a protective coating, it is extremely important to accurately fit into the permissible layer thickness. Typically, manufacturers of paints and varnishes indicate it on the packaging. So, if the layer is larger than the maximum allowable, this will cause excessive consumption of varnish (paint), and the layer can be destroyed under strong mechanical stress, a thinner layer can wear off and shorten the protection period of the base.

A correctly selected protective material and correctly applied to the surface guarantees 80% that the part will not be subject to corrosion.

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Many people in everyday life do not think about how to protect their things from rye. And they get a problem in the form of a damaged item. How to properly solve this problem?

Removing rust from a part

In order to restore a thing or part from rust, the first step is to remove all the red plaque to a clean surface. It can be removed with sandpaper, files, or strong reagents (acids or alkalis), but drinks like Coca-Cola have earned particular fame for this. To do this, the item is completely immersed in a container with a miracle liquid and left for some time (from several hours to several days - the time depends on the item and the damaged area).

Red spots on steel products

According to the UN, each country loses from 0.5 to 7-8% of its gross national product per year due to corrosion. The paradox is that less developed countries lose less than developed countries. And 30% of all steel products produced on the planet are used to replace rusted ones. Therefore, it is highly recommended that you take this issue seriously.

What do a rusty nail, a rusty bridge or a leaky iron fence have in common? Why do iron structures and iron products rust in general? What is rust as such? We will try to answer these questions in our article. Let's look at the causes of rusting of metals and ways to protect against this natural phenomenon that is harmful to us.

Causes of rusting

It all starts with metal mining. Not only iron, but also, for example, magnesium, is initially mined in the form of ore. Aluminum, manganese, iron, magnesium ores do not contain pure metals, but their chemical compounds: carbonates, oxides, sulfides, hydroxides.

These are chemical compounds of metals with carbon, oxygen, sulfur, water, etc. There are one or two pure metals in nature - platinum, gold, silver - noble metals - they are found in the form of metals in a free state, and do not tend very much to formation of chemical compounds.

However, most metals under natural conditions are still not free, and in order to release them from their original compounds, it is necessary to smelt the ores, thus restoring pure metals.

But by smelting metal-containing ore, although we obtain the metal in its pure form, it is still an unstable state, far from natural. For this reason, pure metal under normal environmental conditions tends to return back to its original state, that is, to oxidize, and this is metal corrosion.

Thus, corrosion is a natural destruction process for metals that occurs under conditions of their interaction with the environment. In particular, rusting is the process of formation of iron hydroxide Fe(OH)3, which occurs in the presence of water.

But what plays into people’s hands is the natural fact that the oxidation reaction in the atmosphere we are accustomed to does not proceed particularly rapidly, it proceeds at a very low speed, so bridges and planes do not collapse instantly, and pots do not crumble into red powder before our eyes. In addition, corrosion can, in principle, be slowed down by resorting to some traditional tricks.

For example, stainless steel does not rust, although it consists of iron, which is prone to oxidation, it is nevertheless not coated with red hydroxide. But the point here is that stainless steel is not pure iron, stainless steel is an alloy of iron and other metals, mainly chromium.

In addition to chromium, steel may contain nickel, molybdenum, titanium, niobium, sulfur, phosphorus, etc. The addition of additional elements to the alloys, which are responsible for certain properties of the resulting alloys, is called alloying.

Ways to protect against corrosion

As we noted above, the main alloying element added to ordinary steel to give it anti-corrosion properties is chromium. Chromium oxidizes faster than iron, that is, it takes the blow. Thus, on the surface of stainless steel, a protective film of chromium oxide first appears, which is dark in color and not as loose as ordinary iron rust.

Chromium oxide does not allow aggressive ions from the environment that are harmful to iron to pass through, and the metal is protected from corrosion, as if by a durable, sealed protective suit. That is, the oxide film in this case has a protective function.

The amount of chromium in stainless steel, as a rule, is not lower than 13%, stainless steel contains slightly less nickel, and other alloying additives are present in much smaller quantities.

It is thanks to protective films, which are the first to absorb environmental influences, that many metals are resistant to corrosion in various environments. For example, a spoon, plate or pan made of aluminum never shines much; if you look closely, they have a whitish tint. This is precisely aluminum oxide, which is formed when pure aluminum comes into contact with air, and then protects the metal from corrosion.

The oxide film appears on its own, and if you clean an aluminum pan with sandpaper, after a few seconds of shine the surface will again become whitish - the aluminum on the cleaned surface will again oxidize under the influence of atmospheric oxygen.

Since the aluminum oxide film forms on it itself, without any special technological tricks, it is called a passive film. Such metals, on which an oxide film forms naturally, are called passivating. In particular, aluminum is a passivating metal.

Some metals are forcibly transferred into a passive state, for example, the highest iron oxide - Fe2O3 is able to protect iron and its alloys in air at high temperatures and even in water, which neither red hydroxide nor lower oxides of the same iron can boast of.

There are also nuances to the phenomenon of passivation. For example, in strong sulfuric acid, instantly passivated steel becomes resistant to corrosion, but in a weak solution of sulfuric acid, corrosion will immediately begin.

Why is this happening? The solution to the apparent paradox is that in a strong acid, a passivating film instantly forms on the surface of stainless steel, since a higher concentration of acid has pronounced oxidizing properties.

At the same time, a weak acid does not oxidize the steel quickly enough, and a protective film does not form; corrosion simply begins. In such cases, when the oxidizing environment is not aggressive enough, to achieve the passivation effect, they resort to special chemical additives (inhibitors, corrosion retarders) that help form a passive film on the metal surface.

Since not all metals are prone to the formation of passive films on their surface, even forcibly, the addition of moderators to an oxidizing environment simply leads to preventive retention of the metal under reduction conditions, when oxidation is energetically suppressed, that is, in the presence of an additive in an aggressive environment it turns out to be energetically unfavorable .

There is another way to retain the metal under recovery conditions, if it is not possible to use an inhibitor, - to use a more active coating: a galvanized bucket does not rust, since the zinc coating corrodes upon contact with the environment ahead of the iron, that is, it takes the blow, being a more active metal , zinc reacts more readily.

The bottom of a ship is often protected in a similar way: a piece of protector is attached to it, and then the protector is destroyed, but the bottom remains unharmed.

Electrochemical anti-corrosion protection of underground communications is also a very common way to combat the formation of rust on them. Reduction conditions are created by applying a negative cathode potential to the metal, and in this mode the process of metal oxidation can no longer proceed simply energetically.

Someone might ask why surfaces at risk of corrosion are not simply painted; why not just enamel the part that is vulnerable to corrosion every time? Why exactly are different methods needed?

The answer is simple. The enamel can be damaged, for example, car paint can chip off in an inconspicuous place, and the body will gradually but continuously rust, as sulfur compounds, salts, water, and oxygen from the air begin to flow to this place, and eventually the body will collapse.

To prevent such a development of events, they resort to additional anti-corrosion treatment of the body. A car is not an enamel plate, which you can simply throw away if the enamel is damaged and buy a new one..

Current state of affairs

Despite the apparent knowledge and elaboration of the phenomenon of corrosion, despite the versatile methods of protection used, corrosion still poses a certain danger to this day. Pipelines are destroyed and this leads to releases of oil and gas, planes crash, and trains crash. Nature is more complex than it might seem at first glance, and humanity still has many aspects of corrosion to study.

Thus, even corrosion-resistant alloys are resistant only under certain predictable conditions for which they were originally designed. For example, stainless steels do not tolerate chlorides and are affected by them - pitting, pitting and intercrystalline corrosion occurs.

Externally, without a hint of rust, the structure may suddenly collapse if small but very deep lesions have formed inside. Microcracks penetrating the thickness of the metal are invisible from the outside.

Even an alloy that is not subject to corrosion can suddenly crack when subjected to prolonged mechanical load - just a huge crack will suddenly destroy the structure. This has already happened all over the world with metal building structures, machinery, and even airplanes and helicopters.

Andrey Povny

Why does iron rust?

If you leave an iron object in a damp and damp place for several days, it will become covered with rust, as if it had been painted with reddish paint.

What is rust? Why does it form on iron and steel objects? Rust is iron oxide. It is formed as a result of the “combustion” of iron when combined with oxygen dissolved in water.

This means that in the absence of moisture and water in the air, there is no oxygen dissolved in the water at all and rust does not form.

If a drop of rain hits a shiny iron surface, it remains transparent for a short period of time. The iron and oxygen in the water begin to interact and form an oxide, that is, rust, inside the drop. The water turns reddish and rust floats in the water in the form of small particles. When the drop evaporates, the rust remains, forming a reddish layer on the surface of the iron.

If rust has already appeared, it will grow in dry air. This happens because the porous rust stain absorbs moisture in the air - it attracts and holds it. This is why it is easier to prevent rust than to stop it once it appears. The problem of preventing rust is very important, since iron and steel products must be stored for a long time. Sometimes they are covered with a layer of paint or plastic. What would you do to keep warships from rusting when not in use? This problem is solved with the help of moisture absorbers. Such mechanisms replace moist air in the compartments with dry air. Rust cannot appear in such conditions!