Steel repairs itself and kills bacteria: how the simplest material was reinvented

Steel that heals itself

In sci-fi movies, damage to robots heals itself.

yourself.Self-healing scratches on the car body are the dream of many car owners. And such steel already exists. But it is difficult to produce, it is expensive, so this steel is still used mainly in construction - for facade panels and roofing materials that will not rust. For example, when it is impossible to allow damage to the roof of a warehouse where goods are stored that do not tolerate contact with water.

Self-healing coatings are specialpaints. They are based on microcapsules with a special polymeric material. Under any mechanical impact, for example, during a scratch, the capsules are destroyed and the material is released from them, which covers the injured area, and a polymer layer is formed on the surface. It “heals” the damage by reacting with the edges of the undamaged coating and causing it to close the scratch, as well as isolating the area from the air, preventing metal from corroding.

The difficulty in producing steel with such a coating lies both in the creation of paint with microcapsules and in its application.

Paint is a colloidal solution of polymersmodifiers and microcapsules several micrometers in size. Modifiers, that is, binders, are needed to ensure that the polymers are inside the microcapsules in a liquid state. The composition of the mixture itself is classified, and only a few companies around the world are engaged in its production - the technology is new and is still in the pilot stage.

"Self-healing coatings are special paints"

The composition in the liquid state is applied to steel, andthen the binders are removed using a drying oven, leaving a continuous polymer layer with microcapsules. It is important that the coating is evenly distributed and that the capsules themselves are not damaged, otherwise the properties of the steel will differ in different areas.

If the market appreciates the properties of the material, its production becomes larger, and the unit price of the product falls, then it can be predicted that such steel will become widespread.

Bacteria killer steel

Steel with antibacterial coating is used inmedicine. It is used to make instruments of doctors, elements of hospital buildings like railings or panels on walls, where harmful microorganisms usually accumulate. Moreover, during the pandemic, many manufacturers of equipment, especially smartphones and laptops, began to make gadget cases out of it.

There are several variations on how steelacquires antibacterial properties. More often, a polymer coating is applied to the surface of the material, which includes silver and copper ions. These metals are very effective in the fight against microbes: upon contact, they destroy their shells, killing 99% of microorganisms.

But there are other developments as well.For example, if steel is immersed in an electrolyte solution and a voltage is applied in a special way, nanostructures are formed on the surface: microscopic pits, spikes and needles. They, like metal ions, damage the membranes of bacteria and kill them. At the same time, the technological process during which such steel is obtained does not differ from those already used in the processing of the material - in a similar way, the metal is polished or given anti-corrosion properties.

Both approaches are safe for animal and plant cells: their size greatly exceeds the size of microbes, a person has nothing to fear.

Promising areas of application for steel with antibacterial coatings today are the manufacture of ventilation and cladding panels - for example, interior decoration in transport and premises.

"Metallurgists are looking for ways to create both strong and lightweight steel to make light parts"

Heavy Duty Steel - For Heavy Duty Machines

Metallurgists are looking for ways to create simultaneouslystrong and light steel to make light parts. In the production of cars, this will increase their speed and driver safety. And in the production of special equipment, durable and lightweight hulls will reduce fuel consumption.

To achieve the desired parameters, metallurgists form a metal structure with a combination of various phases, some of which provide an increase in strength, while others are responsible for maintaining ductility.

In total, several phases of steel are distinguished in metallurgy:ferrite, followed by perlite, sorbite, troostite, bainites and martensite. Ferrite is characterized by low strength, while it is ductile and easily stretched. The farther from the ferrite is the phase, the higher its strength and the lower the ductility.

If we add to the plastic ferrite matrixinclusions of stronger phases (for example, martensite), you get a "pie" that will be both plastic and strong - due to the properties of each of the phases. At the same time, it is more difficult to obtain steel consisting of a combination of different phases if they are far from each other.

Ferrite-pearlitic steel learned to get a long time ago,today it is one of the standard tasks of metallurgy. Ferrite-troostite and ferrite-bainitic steel is much more difficult to obtain, but large metallurgical companies have mastered it. But a strong ferrite-martensite is already the result of a complex technological process that requires special equipment and a certain level of technology development.

Steel "hearts" of electrical appliances

One of the areas of application of steel aselectromagnetic material - the manufacture of cores of transformers, generators and electric motors. Iron is a unique material that can create its own magnetic field. This is due to its atomic structure.

The iron atom has four non-closed3d shell and instead of ten electrons, it has only six. In the case of some elements (in addition to iron, for example, nickel and cobalt), it becomes energetically favorable to fill two electrons in the 4s shell, which is the furthest from the nucleus, than to complete the 3d shell. So there are a few electrons left, in which the orbital and spin magnetic moments are not compensated, they orbit around the nucleus and create their own magnetic field.

Some metals (gold, aluminum) have electronson the shells compensate each other, due to which the materials do not create a magnetic field. There are many other metals with unfinished d-shells that can be magnetized, but only iron, nickel, and cobalt exhibit these properties at room temperature, not just cooled.

Steel in electronics must be well magnetizedin an external magnetic field and quickly remagnetize when changing its direction. For most industrial and residential networks, this happens 50 times per second. The main requirement in this process is precisely the ease of magnetization reversal, which will ensure minimal energy consumption during the operation of the finished product.

Iron as a material is a crystallinea structure in which the atoms are located at the tops of the edges and in the center of the cubes. Almost like in Lego. It turns out that the individual magnetic fields of each atom add up to a common field - due to it, parts made of iron can remagnetize, be attracted to magnets, or act in their role themselves.

“Iron is a unique material that can create its own magnetic field”

Unique steel for transformers

Transformer steel is one of the subspecieselectrical steels. It has a special structure, where the crystal lattice of each section of the steel is equally oriented in space, due to which it is possible to achieve minimal energy losses during the operation of the electrical appliance.

And now in simple words.Large volumes of steel are heterogeneous - they consist of small "grains" of metal in which atoms form a cubic crystal lattice. At the same time, in ordinary steel, different "grains" can be oriented differently relative to each other - their magnetic fields, respectively, also have different directions.

In transformer steel, metallurgists succeedto achieve a deviation between the lattices of different "grains" of just a couple of degrees. As a result of this orientation, a material is obtained that tends in structure to a single crystal, as if absolutely all atoms of the material were included in a single lattice, and not individual “grains”. Such a structure of the metal from the point of view of the classical theory of ferromagnetism is the most energetically advantageous, since the magnetic field passes through all the "grains" in one direction and provides a quick magnetization reversal of the core of the electrical unit with minimal power loss.

Technological production cycletransformer steel is the most difficult in all iron and steel industry. Steel is smelted using a certain chemical composition: for example, silicon is added to it, due to which the electrical resistance increases and surface currents do not disturb the magnetic field. Then there is hot rolling, pickling, cold rolling, decarburization annealing, second cold rolling, protective coating, high-temperature annealing, electrical insulating coating and, in some cases, laser surface treatment.

At each technological stage, decisions are madeseveral tasks, starting with obtaining the required strip geometry and ending with the formation of joints in the surface layers of the metal or over the entire section of the strip.

Nanostructured steel that looks like rubber

Nanostructured is called structuralsteel, in which the chemical composition is selected - manganese, carbon, chromium are added - and the processing parameters form a unique structure. It provides high strength and ductility.

Previously, to obtain such a material, they smeltedsteel with an unstable structure, due to which, during deformation, various phases of the metal passed from one to another, changing their properties. In other words, the steel became stronger under mechanical stress.

And nanostructured steel is a material, inin which each "grain" has a twin oriented in the opposite direction. It turns out a material that does not collapse during deformation, but stretches - in terms of properties, it is more like rubber. Nanostructured steel can elongate up to 50% of its original length without breaking and still withstand loads of 10 tons per square centimeter. For comparison, ordinary steel is 2.5 times less strong and can only elongate by 20-25%.

This material, despite the fact that so far itsproduced only in test mode and in small volumes, has great prospects in the automotive industry and mechanical engineering: nanostructured steel can be used to obtain strong parts of complex shape. But while production is not mass-produced due to complexity and high cost, because of this, the price of each sheet is too high. If the need for the material grows, production will take on a completely different scale, and then the price of each sheet will become acceptable - who knows, perhaps in the near future all machines will be made from such steel.

Metallurgy over the past few decadeshas taken a powerful step forward: materials that were considered science fiction half a century ago can now be obtained on an industrial scale. Many of them are not yet widespread, but it is not known how the market will behave: maybe very soon we will see new types of steel in smartphones, refrigerators and microwave ovens.

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