Methods of protection against corrosion. How to defeat rust: basic methods of protecting metal from corrosion Methods of protecting metal products from corrosion

Under influence external factors(liquids, gases, aggressive chemical compounds) destroy any materials. Metals are no exception. It is impossible to completely neutralize corrosive processes, but it is quite possible to reduce their intensity, thereby increasing the service life of metal structures or others that contain iron.

Methods of anti-corrosion protection

All methods of protection against corrosion can be conditionally classified as methods that are applicable either before the start of operation of the sample (group 1), or after its commissioning (group 2).

First

• Increased resistance to “chemical” effects.
• Avoid direct contact with aggressive substances (surface insulation).

Second

• Reducing the degree of aggressiveness environment(depending on operating conditions).
• Use of EM fields (for example, “superposition” of external electric currents, regulation of their density and a number of other techniques).

The use of one or another method of protection is determined individually for each design and depends on several factors:

• type of metal;
• conditions of its operation;
• the difficulty of carrying out anti-corrosion measures;
• production capabilities;
• economic expediency.

In turn, all methods are divided into active (implying constant “exposure” to the material), passive (which can be characterized as reusable) and technological (used at the stage of sample production).

Active

Cathodic protection

It is advisable to use if the medium with which the metal is in contact is electrically conductive. A large “minus” potential is applied to the material (systematically or constantly), which makes its oxidation in principle impossible.

Tread protection

It consists of cathodic polarization. The sample is bonded by contact with a material that is more susceptible to oxidation in a given conductive environment (protector). In fact, it is a kind of “lightning rod”, taking on all the “negativity” that aggressive substances create. But such a protector needs to be periodically replaced with a new one.

Polarization anodic

It is used extremely rarely and consists of maintaining the “inertness” of the material in relation to external influences.

Passive (surface treatment of metal)

Creating a protective film

One of the most common and low-cost methods of combating corrosion. To create the surface layer, substances are used that must meet the following basic requirements - to be inert towards aggressive chemical compounds, not conduct electricity and have increased adhesion (bond well with the base).

All substances used at the time of metal processing are in a liquid or “aerosol” state, which determines the method of their application - painting or spraying. For this purpose, paint and varnish compositions, various mastics and polymers are used.

Laying metal structures in protective “chutes”

This is typical for different types of pipelines and communications engineering systems. In this case, the role of an insulator is played by the air “gap” between the inner walls of the channel and the metal surface.

Phosphating

Metals are treated with special agents (oxidizing agents). They react with the base, resulting in the deposition of poorly soluble chemical compounds on its surface. Quite an effective way to protect against moisture.

Coating with more resistant materials

Examples of the use of this technique are products often found in everyday life with chrome plating (), silver plated, “galvanized” and the like.

As an option - protection with ceramics, glass, coating with concrete, cement mortars (coating) and so on.

Passivation

The idea is to sharply reduce the chemical activity of the metal. To do this, its surface is treated with appropriate special reagents.

Reducing environmental aggressiveness

• The use of substances that reduce the intensity of corrosion processes (inhibitors).
• Air drying.
• Its chemical purification (from harmful impurities) and a number of other techniques that can be used in everyday life.
• Hydrophobization of the soil (backfilling, introduction of special substances into it) in order to reduce the aggressiveness of the soil.

Treatment with pesticides

It is used in cases where there is a possibility of developing so-called “biocorrosion”.

Technological methods of protection

Alloying

The most famous way. The point is to create an alloy based on metal that is inert to aggressive influences. But it is implemented only on an industrial scale.

As follows from the information provided, not all anti-corrosion protection methods can be used in everyday life. In this regard, the possibilities of the “private owner” are significantly limited.

These methods can be divided into 2 groups. The first 2 methods are usually implemented before production operation metal products (selection of structural materials and their combinations at the stage of design and manufacture of the product, application of protective coatings to it). The last 2 methods, on the contrary, can only be carried out during the operation of the metal product (passing current to achieve a protective potential, introducing special inhibitor additives into the process environment) and are not associated with any pre-treatment before use.

The second group of methods allows, if necessary, to create new protection modes that ensure the least corrosion of the product. For example, in certain sections of the pipeline, depending on the aggressiveness of the soil, the cathode current density can be changed. Or use different inhibitors for different types of oil pumped through pipes.

Question: How are corrosion inhibitors used?

Answer: To combat metal corrosion, corrosion inhibitors are widely used, which are introduced in small quantities into an aggressive environment and create an adsorption film on the metal surface, inhibiting electrode processes and changing the electrochemical parameters of metals.

Question: What are the ways to protect metals from corrosion using paints and varnishes?

Answer: Depending on the composition of pigments and the film-forming base, paint and varnish coatings can serve as a barrier, passivator or protector.

Barrier protection is the mechanical insulation of a surface. Violation of the integrity of the coating, even at the level of the appearance of microcracks, predetermines the penetration of an aggressive environment to the base and the occurrence of under-film corrosion.

Passivation of a metal surface using paintwork is achieved through chemical interaction between the metal and the coating components. This group includes primers and enamels containing phosphoric acid (phosphating), as well as compositions with inhibitory pigments that slow down or prevent the corrosion process.

Protective protection of metal is achieved by adding powdered metals to the coating material, creating donor electron pairs with the protected metal. For steel these are zinc, magnesium, aluminum. Under the influence of an aggressive environment, the additive powder gradually dissolves, and the base material is not subject to corrosion.

Question: What determines the durability of metal protection against corrosion using paints and varnishes?

Answer: Firstly, the durability of metal protection from corrosion depends on the type (and type) of paint and varnish coating used. Secondly, the thoroughness of preparing the metal surface for painting plays a decisive role. The most labor-intensive process in this case is the removal of previously formed corrosion products. Special compounds are applied that destroy rust, followed by mechanical removal with metal brushes.

In some cases, rust removal is practically impossible, which requires the widespread use of materials that can be applied directly to surfaces damaged by corrosion - rust coating materials. This group includes some special primers and enamels used in multi-layer or independent coatings.

Question: What are high-fill two-component systems?

Answer: These are anti-corrosion paints and varnishes with a reduced solvent content (the percentage of volatile organic substances in them does not exceed 35%). The market for materials for home use mainly offers single-component materials. The main advantage of highly filled systems compared to conventional ones is significantly better corrosion resistance at a comparable layer thickness, lower material consumption and the possibility of applying a thicker layer, which ensures the required anti-corrosion protection in just 1-2 times.

Question: How to protect the surface of galvanized steel from destruction?

Answer: Anti-corrosion primer based on modified vinyl acrylic resins in the Galvaplast solvent is used for interior and exterior work on descaled ferrous metal substrates, galvanized steel, and galvanized iron. Solvent – ​​white spirit. Application – brush, roller, spray. Consumption 0.10-0.12 kg/sq.m; drying 24 hours.

Question: What is patina?

Answer: The word “patina” refers to a film of various shades that forms on the surface of copper and copper-containing alloys under the influence of atmospheric factors during natural or artificial aging. Sometimes patina refers to oxides on the surface of metals, as well as films that cause tarnish on the surface of stones, marble or wooden objects over time.

The appearance of patina is not a sign of corrosion, but rather a natural protective layer on the copper surface.

Question: Is it possible to artificially create a patina on the surface of copper products?

Answer: Under natural conditions, a green patina forms on the surface of copper within 5-25 years, depending on climate and the chemical composition of the atmosphere and precipitation. At the same time, copper carbonates are formed from copper and its two main alloys - bronze and brass: bright green malachite Cu 2 (CO 3) (OH) 2 and azure blue azurite Cu 2 (CO 3) 2 (OH) 2. For zinc-containing brass, the formation of green-blue rosasite with the composition (Cu,Zn) 2 (CO 3)(OH) 2 is possible. Basic copper carbonates can be easily synthesized at home by adding an aqueous solution of soda ash to an aqueous solution of a copper salt, such as copper sulfate. At the same time, at the beginning of the process, when there is an excess of copper salt, a product is formed that is closer in composition to azurite, and at the end of the process (with an excess of soda) - to malachite.

Saving coloring

Question: How to protect metal or reinforced concrete structures from the influence of aggressive environments - salts, acids, alkalis, solvents?

Answer: To create chemical-resistant coatings, there are several protective materials, each of which has its own area of ​​protection. The widest range of protection is provided by: enamels XC-759, “ELOCOR SB-022” varnish, FLC-2, primers, XC-010, etc. In each individual case, a specific painting scheme is selected, according to operating conditions. Tikkurilla Coatings Temabond, Temacoat and Temachlor paints.

Question: What compositions can be used when painting the internal surfaces of tanks for kerosene and other petroleum products?

Answer: Temaline LP is a two-component epoxy gloss paint with an amino adduct-based hardener. Application - brush, spray. Drying 7 hours.

EP-0215 ​​– primer for corrosion protection of the internal surface of caisson tanks operating in a fuel environment with an admixture of water. It is applied to surfaces made of steel, magnesium, aluminum and titanium alloys operated in various climatic zones, at elevated temperatures and exposure to polluted environments.

Suitable for use with BEP-0261 primer and BEP-610 enamel.

Question: What compounds can be used for protective coating of metal surfaces in marine and industrial environments?

Answer: Thick film paint based on chlorinated rubber is used for painting metal surfaces in marine and industrial environments exposed to moderate chemical exposure: bridges, cranes, conveyors, port equipment, tank exteriors.

Temacoat CB is a two-component modified epoxy paint used for priming and painting metal surfaces exposed to atmospheric, mechanical and chemical influences. Application - brush, spray. Drying 4 hours.

Question: What compositions should be used to coat difficult-to-clean metal surfaces, including those immersed in water?

Answer: Temabond ST-200 is a two-component modified epoxy paint with aluminum pigmentation and low solvent content. Used for painting bridges, tanks, steel structures and equipment. Application - brush, spray. Drying – 6 hours.

Temaline BL is a two-component epoxy coating that does not contain solvents. Used for painting steel surfaces exposed to wear, chemical and mechanical stress when immersed in water, containers for oil or gasoline, tanks and tanks, wastewater treatment facilities Wastewater. Application by airless spray.

Temazinc is a one-component zinc-rich epoxy paint with a polyamide-based hardener. Used as a primer in epoxy, polyurethane, acrylic, chlorinated rubber paint systems for steel and cast iron surfaces exposed to strong atmospheric and chemical influences. Suitable for painting bridges, cranes, steel frames, steel structures and equipment. Drying 1 hour.

Question: How to protect underground pipes from the formation of fistulas?

Answer: There can be two reasons for any pipe burst: mechanical damage or corrosion. If the first reason is the result of accident and carelessness - the pipe is caught in something or the weld has come apart, then corrosion cannot be avoided; this is a natural phenomenon caused by soil moisture.

In addition to the use of special coatings, there is protection that is widely used throughout the world - cathodic polarization. It represents the source direct current, providing a polar potential of min 0.85 V, max – 1.1 V. It consists only of a conventional AC voltage transformer and a diode rectifier.

Question: How much does cathodic polarization cost?

Answer: The cost of cathodic protection devices, depending on their design, ranges from 1000 to 14 thousand rubles. The repair team can easily check the polarization potential. Installing protection is also not expensive and does not involve labor-intensive excavation work.

Protection of galvanized surfaces

Question: Why can't galvanized metals be shot blasted?

Answer: Such preparation violates the natural corrosion resistance of the metal. Surfaces of this kind are treated with a special abrasive agent - round glass particles that do not destroy the protective layer of zinc on the surface. In most cases, it is enough to simply treat with an ammonia solution to remove grease stains and zinc corrosion products from the surface.

Question: How to restore damaged zinc coating?

Answer: Zinc-filled compositions ZincKOS, TsNK, “Vinikor-zinc”, etc., which are applied by cold galvanizing and provide anodic protection of the metal.

Question: How is metal protected using ZNC (zinc-filled compositions)?

Answer: Cold galvanizing technology using CNC guarantees absolute non-toxicity, fire safety, and heat resistance up to +800°C. Coating of metal with this composition is carried out by spraying, with a roller or even just with a brush and provides the product with, in fact, double protection: both cathodic and film. The validity period of such protection is 25-50 years.

Question: What are the main advantages of the cold galvanizing method over hot galvanizing?

Answer: This method has the following advantages:

1. Maintainability.
2. Possibility of application on a construction site.
3. There are no restrictions on the overall dimensions of protected structures.

Question: At what temperature is thermal diffusion coating applied?

Answer: Thermal diffusion zinc coating is applied at temperatures from 400 to 500°C.

Question: Are there any differences in the corrosion resistance of coatings obtained by thermal diffusion galvanizing compared to other types of zinc coatings?

Answer: The corrosion resistance of thermal diffusion zinc coating is 3-5 times higher than galvanic coating and 1.5-2 times higher than the corrosion resistance of hot zinc coating.

Question: What paint and varnish materials can be used for protective and decorative painting of galvanized iron?

Answer: For this, you can use both water-based ones - G-3 primer, G-4 paint, and organo-thinned ones - EP-140, "ELOCOR SB-022", etc. Tikkurila Coatings protective systems can be used: 1 Temakout GPLS-Primer + Temadur, 2 Temaprime EE+Temalak, Temalak and Temadur are tinted according to RAL and TVT.

Question: What paint can be used to paint galvanized drainage pipes?

Answer: Sockelfarg is a water-based latex paint in black and white. Designed for application to both new and previously painted outdoor surfaces. Resistant to weather conditions. Solvent – ​​water. Drying 3 hours.

Question: Why are water-based anti-corrosion agents rarely used?

Answer: There are 2 main reasons: the increased price compared to conventional materials and the prevailing opinion in certain circles that water systems have worse protective properties. However, as environmental legislation becomes stricter, both in Europe and throughout the world, the popularity of water systems is growing. Experts who tested high-quality water-based materials were able to verify that their protective properties are no worse than those of traditional materials containing solvents.

Question: What device is used to determine the thickness of the paint film on metal surfaces?

Answer: The “Constant MK” device is the easiest to use - it measures the thickness of paintwork on ferromagnetic metals. Much more functions are performed by the multifunctional thickness gauge "Constant K-5", which measures the thickness of conventional paintwork, galvanic and hot-zinc coatings on both ferromagnetic and non-ferromagnetic metals (aluminum, its alloys, etc.), and also measures surface roughness, temperature and air humidity, etc.

The rust is receding

Question: How can I treat items that are heavily corroded by rust?

Answer: First recipe: a mixture of 50 g of lactic acid and 100 ml of vaseline oil. The acid converts iron metahydroxide from rust into a salt soluble in petroleum jelly - iron lactate. Wipe the cleaned surface with a cloth moistened with petroleum jelly.

Second recipe: a solution of 5 g of zinc chloride and 0.5 g of potassium hydrogen tartrate, dissolved in 100 ml of water. Zinc chloride aqueous solution undergoes hydrolysis and creates an acidic environment. Iron metahydroxide dissolves due to the formation of soluble iron complexes with tartrate ions in an acidic environment.

Question: How to unscrew a rusty nut using improvised means?

Answer: A rusted nut can be moistened with kerosene, turpentine or oleic acid. After some time it is possible to unscrew it. If the nut “persists,” you can set fire to the kerosene or turpentine with which it was moistened. This is usually enough to separate the nut and bolt. The most radical method: apply a very heated soldering iron to the nut. The metal of the nut expands and the rust moves away from the thread; Now you can pour a few drops of kerosene, turpentine or oleic acid into the gap between the bolt and the nut. This time the nut will definitely come loose!

There is another way to remove rusty nuts and bolts. A “cup” of wax or plasticine is made around the rusted nut, the edge of which is 3-4 mm higher than the level of the nut. Dilute sulfuric acid is poured into it and a piece of zinc is placed. After a day, the nut can be easily unscrewed with a wrench. The fact is that a cup with acid and zinc metal on an iron base is a miniature galvanic cell. The acid dissolves the rust, and the resulting iron cations are reduced to the surface of the zinc. And the metal of the nut and bolt will not dissolve in the acid as long as it is in contact with zinc, since zinc is a more reactive metal than iron.

Question: What anti-rust compounds does our industry produce?

Answer: Domestic solvent-borne compounds applied “on rust” include well-known materials: primer (some manufacturers produce it under the name “Inkor”) and primer-enamel “Gramirust”. These two-part epoxy paints (base + hardener) contain corrosion inhibitors and targeted additives to cover tough rust up to 100 microns thick. The advantages of these primers: curing at room temperature, the possibility of application to a partially corroded surface, high adhesion, good physical and mechanical properties and chemical resistance, ensuring long-term operation of the coating.

Question: How can you paint old rusty metal?

Answer: For stubborn rust, it is possible to use several paints and varnishes containing rust converters:

• primer G-1, primer-paint G-2 (water-borne materials) – at temperatures up to +5°;
• primer-enamel XB-0278, primer-enamel AS-0332 – up to minus 5°;
• primer-enamel “ELOCOR SB-022” (materials based on organic solvents) – up to minus 15°C.
• Primer enamel Tikkurila Coatings, Temabond (tinted according to RAL and TVT)

Question: How to stop the rusting process of metal?

Answer: This can be done using stainless steel primer. The primer can be used both as an independent coating on steel, cast iron, aluminum, and in a coating system that includes 1 layer of primer and 2 layers of enamel. The product is also used for priming corroded surfaces.

“Nerzhamet-soil” works on the metal surface as a rust converter, binding it chemically, and the resulting polymer film reliably isolates the metal surface from atmospheric moisture. When using the composition, the total costs of repair and restoration work on repainting metal structures are reduced by 3-5 times. The primer is supplied ready for use. If necessary, it must be diluted to working viscosity with white spirit. The drug is applied to metal surfaces with remnants of tightly adhered rust and scale with a brush, roller, or spray gun. Drying time at a temperature of +20° is 24 hours.

Question: Roofing often fades. What paint can be used on galvanized roofs and gutters?

Answer: Stainless steel-cycron. The coating provides long-term protection from weather conditions, humidity, ultraviolet radiation, rain, snow, etc.

It has high hiding power and light fastness, does not fade. Significantly extends the service life of galvanized roofs. Also Tikkurila Coatings, Temadur and Temalak coatings.

Question: Can chlorinated rubber paints protect metal from rust?

Answer: These paints are made from chlorinated rubber dispersed in organic solvents. In terms of their composition, they are classified as volatile resin and have high water and chemical resistance. Therefore, it is possible to use them to protect metal and concrete surfaces, water pipes and tanks from corrosion. From Tikkuril Coatings materials, you can use the Temanil MS-Primer + Temachlor system.

Anticorrosive in the bathhouse, bathtub, pool

Question: What kind of coating can protect bath containers for cold drinking and hot wash water from corrosion?

Answer: For containers for cold drinking and washing water, we recommend paint KO-42; Epovin for hot water - compositions ZinkKOS and Teplokor PIGMA.

Question: What are enamel pipes?

Answer: In terms of chemical resistance, they are not inferior to copper, titanium and lead, and their cost is several times cheaper. The use of enameled carbon steel pipes instead of stainless steel pipes results in tenfold cost savings. The advantages of such products include greater mechanical strength, including in comparison with other types of coatings - epoxy, polyethylene, plastic, as well as higher abrasion resistance, which makes it possible to reduce the diameter of pipes without reducing their throughput.

Question: What are the features of re-enamelling bathtubs?

Answer: Enameling can be done by brush or spray with the participation of professionals, or by brushing yourself. Preliminary preparation of the bathtub surface involves removing old enamel and cleaning off rust. The whole process takes no more than 4-7 hours, another 48 hours for the bath to dry, and you can use it after 5-7 days.

Re-enamel bathtubs require special care. Such baths cannot be washed with powders such as Comet and Pemolux, or using products containing acid, such as Silit. It is unacceptable to get varnishes on the surface of the bathtub, including hair varnishes, or to use bleach when washing. Such bathtubs are usually cleaned with soap products: washing powders or dishwashing detergents applied to a sponge or soft rag.

Question: What paint materials can be used to re-enamel bathtubs?

Answer: The “Svetlana” composition includes enamel, oxalic acid, hardener, and tinting pastes. The bath is washed with water, etched with oxalic acid (stains, stones, dirt, rust are removed and a rough surface is created). Wash with washing powder. Chips are repaired in advance. Then the enamel should be applied within 25-30 minutes. When working with enamel and hardener, contact with water is not allowed. Solvent – ​​acetone. Bath consumption – 0.6 kg; drying – 24 hours. Fully gains properties after 7 days.

You can also use two-component epoxy-based paint Tikkurila “Reaflex-50”. When using glossy bathtub enamel (white, tinted), either washing powders or laundry soap are used for cleaning. Fully gains properties after 5 days. Bath consumption – 0.6 kg. Solvent – ​​industrial alcohol.

B-EP-5297V is used to restore the enamel coating of bathtubs. This paint is glossy, white, tinting is possible. The coating is smooth, even, durable. Do not use “Sanitary” type abrasive powders for cleaning. Fully gains properties after 7 days. Solvents – a mixture of alcohol and acetone; R-4, No. 646.

Question: How to ensure protection against breakage of steel reinforcement in the bowl of a swimming pool?

Answer: If the condition of the pool's ring drainage is unsatisfactory, softening and suffusion of the soil is possible. Penetration of water under the bottom of the tank can cause subsidence of the soil and the formation of cracks in concrete structures. In these cases, the reinforcement in the cracks can corrode to the point of breaking.

In such difficult cases, the reconstruction of damaged reinforced concrete tank structures should include the implementation of a protective sacrificial layer of shotcrete on the surfaces of reinforced concrete structures exposed to the leaching action of water.

Obstacles to biodegradation

Question: What external conditions determine the development of wood-decaying fungi?

Answer: The most favorable conditions for the development of wood-decaying fungi are considered to be: the presence of air nutrients, sufficient wood moisture and favorable temperature. The absence of any of these conditions will retard the development of the fungus, even if it is firmly established in the wood. Most mushrooms develop well only at high relative humidity (80-95%). When wood moisture content is below 18%, the development of fungi practically does not occur.

Question: What are the main sources of moisture in wood and what is their danger?

Answer: The main sources of wood moisture in the structures of various buildings and structures include ground (underground) and surface (storm and seasonal) water. They are especially dangerous for wooden elements of open structures located in the ground (poles, piles, power line and communication supports, sleepers, etc.). Atmospheric moisture in the form of rain and snow threatens the ground part of open structures, as well as the external wooden elements of buildings. Operating moisture in liquid or vapor form in residential premises is present in the form of household moisture released during cooking, washing, drying clothes, washing floors, etc.

A large amount of moisture is introduced into a building when laying raw wood, using masonry mortars, concreting, etc. For example, 1 sq.m of laid wood with a moisture content of up to 23% releases up to 10 liters of water when it dries to 10-12%.

The wood of buildings, which dries naturally, is at risk of rotting for a long time. If chemical protection measures have not been provided, it is usually affected by house fungus to such an extent that the structures become completely unusable.

Condensation moisture that occurs on the surface or in the thickness of structures is dangerous because it is detected, as a rule, already when irreversible changes have occurred in the enclosing wooden structure or its element, for example, internal rotting.

Question: Who are the “biological” enemies of the tree?

Answer: These are mold, algae, bacteria, fungi and antimycetes (this is a cross between fungi and algae). Almost all of them can be combated with antiseptics. The exception is fungi (saprophytes), since antiseptics only affect some of their species. But it is fungi that are the cause of such widespread rot, which is the most difficult to deal with. Professionals classify rot by color (red, white, gray, yellow, green and brown). Red rot affects coniferous trees, white and yellow rot affects oak and birch, green rot affects oak barrels, as well as wooden beams and cellar floors.

Question: Are there ways to neutralize porcini mushroom?

Answer: The white house mushroom is the most dangerous enemy of wooden structures. The speed at which wood is destroyed by porcini mushroom is such that in 1 month it completely “eats” a four-centimeter oak floor. Previously, in villages, if a hut was infected by this fungus, it was immediately burned to save all other buildings from infection. After that, the whole world built a new hut for the affected family in another place. Currently, in order to get rid of white house fungus, the affected area is dismantled and burned, and the rest is impregnated with 5% chromium (5% solution of potassium dichromate in 5% sulfuric acid), while it is recommended to treat the ground with 0.5 m depth.

Question: What are ways to protect wood from rotting in the early stages of this process?

Answer: If the rotting process has already begun, it can only be stopped by thoroughly drying and ventilating wooden structures. In the early stages, disinfectant solutions, for example, such as the “Wood Healer” antiseptic compositions, can help. They are available in three different versions.

Mark 1 is intended for the prevention of wooden materials immediately after their purchase or immediately after building a house. The composition protects against fungus and wood-boring beetles.

Brand 2 is used if fungus, mold or “blue stain” has already appeared on the walls of the house. This composition destroys existing diseases and protects against their future manifestations.

Mark 3 is the most powerful antiseptic; it completely stops the rotting process. More recently, a special composition (grade 4) was developed to combat insects - “anti-bug”.

SADOLIN Bio Clean is a disinfectant for surfaces contaminated with mold, moss, and algae, based on sodium hypochlorite.

DULUX WEATHERSHIELD FUNGICIDAL WASH is a highly effective neutralizer of mold, lichen and rot. These compositions are used both indoors and outdoors, but they are effective only in the early stages of combating rot. In case of serious damage to wooden structures, rotting can be stopped using special methods, but this is sufficient hard work, performed, as a rule, by professionals using restoration chemical compounds.

Question: What protective impregnations and preservative compositions presented on domestic market, prevent biocorrosion?

Answer: Of the Russian antiseptic drugs, it is necessary to mention metacid (100% dry antiseptic) or polysept (25% solution of the same substance). Such preservative compositions as “BIOSEPT”, “KSD” and “KSDA” have proven themselves well. They protect the wood from damage by mold, fungi, bacteria, and the last two, in addition, make the wood difficult to ignite. Textured coatings “AQUATEX”, “SOTEX” and “BIOX” eliminate the occurrence of fungus, mold and wood blue stains. They are breathable and have a durability of over 5 years.

A good domestic material for protecting wood is the glazing impregnation GLIMS-LecSil. This is a ready-to-use aqueous dispersion based on styrene-acrylate latex and reactive silane with modifying additives. Moreover, the composition does not contain organic solvents or plasticizers. Glazing sharply reduces the water absorption of wood, as a result of which it can even be washed, including with soap and water, protects against washing out of fireproofing impregnation, and thanks to its antiseptic properties destroys fungi and mold and prevents their further formation.

Of the imported antiseptic compositions for protecting wood, antiseptics from TIKKURILA have proven themselves well. Pinjasol Color is an antiseptic that forms a continuous water-repellent and weather-resistant coating.

Question: What are insecticides and how are they used?

Answer: To combat beetles and their larvae, toxic chemicals are used - contact and intestinal insecticides. Sodium fluoride and sodium fluoride are approved by the Ministry of Health and have been used since the beginning of the last century; When using them, safety precautions must be observed. To prevent damage to wood by the beetle, preventive treatment with silicofluoride compounds or a 7-10% solution of table salt is used. During historical periods of widespread wood construction, all wood was processed at the harvesting stage. Aniline dyes were added to the protective solution, which changed the color of the wood. In old houses you can still find red beams.

The material was prepared by L. RUDNITSKY, A. ZHUKOV, E. ABISHEV

The main condition for anti-corrosion protection of metals and alloys is to reduce the corrosion rate. The rate of corrosion can be reduced by using various methods of protecting metal structures from corrosion. The main ones are:

1 Protective coatings.

2 Treatment of corrosive media in order to reduce corrosive activity (especially with constant volumes of corrosive media).

3 Electrochemical protection.

4 Development and production of new structural materials with increased corrosion resistance.

5 Transition in a number of structures from metal to chemically resistant materials (plastic high-molecular materials, glass, ceramics, etc.).

6 Rational design and operation of metal structures and parts.

1. Protective coatings

The protective coating must be continuous, evenly distributed over the entire surface, impenetrable to the environment, have high adhesion (adhesion strength) to the metal, be hard and wear-resistant. The coefficient of thermal expansion must be close to the coefficient of thermal expansion of the metal of the protected product.

The classification of protective coatings is presented in Fig. 43

Protective coatings

Non-metallic Metallic coatings coatings

InorganicOrganicCathodeAnodic

Figure 43 - Classification scheme for protective coatings

1.1 Metal coatings

Application of protective metal coatings is one of the most common methods of combating corrosion. These coatings not only protect against corrosion, but also give their surface a number of valuable physical and mechanical properties: hardness, wear resistance, electrical conductivity, solderability, reflectivity, provide products with decorative finishing, etc.

According to the method of protective action, metal coatings are divided into cathodic and anodic.

Cathode coatings have more positive and anodic coatings have more electronegative electrode potentials compared to the potential of the metal on which they are deposited. So, for example, copper, nickel, silver, gold deposited on steel are cathode coatings, and zinc and cadmium in relation to the same steel are anodic coatings.

It should be noted that the type of coating depends not only on the nature of the metals, but also on the composition of the corrosive environment. In relation to iron in solutions of inorganic acids and salts, tin plays the role of a cathode coating, and in a number of organic acids (canned food) it serves as an anode. Under normal conditions, cathodic coatings protect the metal of the product mechanically, isolating it from the environment. The main requirement for cathode coatings is non-porous. Otherwise, when the product is immersed in an electrolyte or when a thin film of moisture condenses on its surface, the exposed (in pores or cracks) areas of the base metal become anodes, and the coating surface becomes a cathode. In places of discontinuities, corrosion of the base metal will begin, which can spread under the coating (Fig. 44 a).

Figure 11 Scheme of corrosion of iron with porous cathode (a) and anodic (b) coating

Anodic coatings protect the metal of the product not only mechanically, but mainly electrochemically. In the resulting galvanic cell, the coating metal becomes the anode and undergoes corrosion, and the exposed (in the pores) areas of the base metal act as cathodes and are not destroyed as long as the electrical contact of the coating with the protected metal is maintained and sufficient current passes through the system (Fig. 4 b). Therefore, the degree of porosity of anodic coatings, unlike cathodic ones, does not play a significant role.

In some cases, electrochemical protection may occur when applying cathodic coatings. This occurs if the coating metal is an effective cathode in relation to the product, and the base metal is prone to passivation. The resulting anodic polarization passivates the unprotected (in the pores) areas of the base metal and makes it difficult to destroy them. This type of anodic electrochemical protection appears for copper coatings on steels 12Х13 and 12Х18Н9Т in sulfuric acid solutions.

The main method of applying protective metal coatings is galvanic. Thermal diffusion and mechanothermal methods, metallization by spraying and immersion in the melt are also used. Let us examine each of the methods in more detail.

1.2 Galvanic coatings.

The galvanic method of deposition of protective metal coatings has become very widespread in industry. Compared to other methods of applying metal coatings, it has a number of serious advantages: high efficiency (protection of metal from corrosion is achieved by very thin coatings), the ability to obtain coatings of the same metal with different mechanical properties, easy controllability of the process (controlling the thickness and properties of metal deposits by changes in the electrolyte composition and electrolysis mode), the ability to obtain alloys of various compositions without the use of high temperatures, good adhesion to the base metal, etc.

The disadvantage of the galvanic method is the uneven thickness of the coating on products with complex profiles.

Electrochemical deposition of metals is carried out in a direct current galvanic bath (Figure 45). The product to be coated with metal is hung on the cathode. Plates made of deposited metal (soluble anodes) or of a material insoluble in the electrolyte (insoluble anodes) are used as anodes.

An essential component of the electrolyte is a metal ion deposited on the cathode. The composition of the electrolyte may also include substances that increase its electrical conductivity, regulate the course of the anodic process, ensure a constant pH, surfactants that increase the polarization of the cathodic process, brightening and leveling additives, etc.

Figure 5 Galvanic bath for electrodeposition of metals:

1 – body; 2 – ventilation casing; 3 – heating coil; 4 – insulators; 5 – anode rods; 6 – cathode rods; 7 – bubbler for mixing with compressed air

Depending on the form in which the discharging metal ion is in solution, all electrolytes are divided into complex and simple. The discharge of complex ions at the cathode occurs at a higher overvoltage than the discharge of simple ions. Therefore, deposits obtained from complex electrolytes are finer-grained and uniform in thickness. However, these electrolytes have lower metal current output and lower operating current densities, i.e. In terms of performance, they are inferior to simple electrolytes, in which the metal ion is in the form of simple hydrated ions.

The distribution of current over the surface of a product in a galvanic bath is never uniform. This leads to different deposition rates and, consequently, different coating thicknesses in individual areas of the cathode. A particularly strong variation in thickness is observed on products with complex profiles, which negatively affects the protective properties of the coating. The uniformity of the thickness of the deposited coating improves with an increase in the electrical conductivity of the electrolyte, an increase in polarization with an increase in current density, a decrease in the current efficiency of the metal with an increase in current density, and an increase in the distance between the cathode and anode.

The ability of a galvanic bath to produce coatings of uniform thickness on a relief surface is called dissipation ability. Complex electrolytes have the greatest dissipative ability.

To protect products from corrosion, galvanic deposition of many metals is used: zinc, cadmium, nickel, chromium, tin, lead, gold, silver, etc. Electrolytic alloys are also used, for example Cu – Zn, Cu – Sn, Sn – Bi and multilayer coatings.

Anodic coatings with zinc and cadmium protect ferrous metals from corrosion most effectively (electrochemically and mechanically).

Zinc coatings are used to protect machine parts, pipelines, and steel sheets from corrosion. Zinc is a cheap and accessible metal. It protects the main product by mechanical and electrochemical methods, since in the presence of pores or bare spots, zinc is destroyed, and the steel base does not corrode.

Zinc coatings occupy a dominant position. About 20% of all steel parts are protected from corrosion using zinc, and about 50% of the zinc produced in the world is spent on galvanic coatings.

In recent years, work has developed on the creation of protective galvanic coatings from zinc-based alloys: Zn – Ni (8 – 12% Ni), Zn – Fe, Zn – Co (0.6 – 0.8% Co). At the same time, it is possible to increase the corrosion resistance of the coating by 2-3 times.

Corrosion is the destruction of metal, ceramic, wood and other materials as a result of chemical or physical-chemical interaction. As for the reasons for the occurrence of such an undesirable effect, they are different. In most cases, this is structural instability to thermodynamic environmental influences. Let's take a closer look at what corrosion is. Types of corrosion also need to be considered, and it wouldn’t hurt to talk about protection against it.

Some general information

We are used to hearing the term “rusting”, which is used in the case of corrosion of metal and alloys. There is also such a thing as “aging,” which is characteristic of polymers. Essentially, it's the same thing. A striking example is the aging of rubber products due to active interaction with oxygen. In addition, some plastic elements are destroyed by exposure. The rate of corrosion directly depends on the conditions in which the object is located. Thus, rust on a metal product will spread faster the higher the temperature. Humidity also affects: the higher it is, the faster it becomes unsuitable for further use. It has been experimentally established that approximately 10 percent of metal products are irretrievably written off, and corrosion is to blame. Types of corrosion are different and are classified depending on the type of environment, the nature of the course, etc. Let's look at them in more detail.

Classification

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

• Chemical corrosion is a process of interaction with a corrosive environment, in which the reduction of the oxidizing agent occurs in one act. The metal and the oxidizing agent are not separated spatially.
• Electrochemical corrosion is the process of interaction of a metal with the ionization of atoms and the reduction of the oxidizing agent in different acts, but the rate largely depends on the electrode potential.
• Gas corrosion - chemical rusting of metal with a minimum moisture content (no more than 0.1 percent) and/or high temperatures in a gaseous environment. More often this type found in the chemical and oil refining industries.

In addition, there are still a huge number of rusting processes. All of them are corrosion. Types of corrosion, in addition to those described above, include biological, radioactive, atmospheric, contact, local, targeted rusting, etc.

Electrochemical corrosion and its features

With this type of destruction, the process occurs when the metal comes into contact with the electrolyte. The latter can be condensate or rainwater. The more salts and acids a liquid contains, the higher the electrical conductivity, and therefore the speed of the process. As for the places of metal structures most susceptible to corrosion, these are rivets, welded joints, and 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 striking example is galvanizing. The fact is that zinc has a more negative potential than iron. For this simple reason, the iron alloy is restored, but the zinc alloy is corroded. However, the presence of an oxide film on the surface greatly slows down the destruction process. Of course, all types of electrical chemical corrosion are extremely dangerous and sometimes it is even impossible to fight them.

Chemical corrosion

This change in metal is quite common. A striking example is the appearance of scale as a result of the interaction of metal products with oxygen. Heat in this case, it 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, their oxidation leads to the formation of a film that is resistant to further corrosion. Steel products form iron oxides. Further developments lead to the appearance of rust, which does not provide any protection against further destruction, but, on the contrary, contributes to it. Currently, all types of chemical corrosion are eliminated using galvanization. Other means of protection may also be used.

Types of concrete corrosion

Changes in the structure and increase in 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 occurs when a concrete product is systematically exposed to precipitation and other liquids. As a result, calcium oxide hydrate is washed out and the structure is disrupted.
• Interaction with acids. If cement stone comes into contact with acids, calcium bicarbonate is formed - an aggressive chemical element for a concrete product.
• Crystallization of sparingly soluble substances. In essence, this means biocorrosion. The bottom line is that microorganisms (spores, fungi) enter the pores and develop there, resulting in destruction.

Corrosion: types, methods of protection

Billions of dollars in annual losses have led people to fight against these harmful effects. We can say with confidence that all types of corrosion lead to the loss not of the metal itself, but of valuable metal structures, the construction of which costs a lot of money. It is difficult to say whether it is possible to provide 100% protection. However, with proper surface preparation, which consists of abrasive blasting, good results can be achieved. The paint coating reliably protects against electrochemical corrosion when applied correctly. And special surface treatment will reliably protect against metal destruction underground.

Active and passive methods of control

The essence of active methods is to change the structure of the double electric field. For this, a direct current source is used. The voltage must be selected in such a way that the product to be protected increases. Another extremely popular method is the “sacrificial” anode. It breaks down, protecting the base material.

Passive protection involves the use of paint and varnish. The main task is to completely prevent moisture and oxygen from entering the protected surface. As noted above, it makes sense to use zinc, copper or nickel plating. Even a partially destroyed layer will protect the metal from rusting. Of course, these types of protection against metal corrosion are effective only when the surface does not have visible defects in the form of cracks, chips, and the like.

Galvanizing in detail

We have already looked at 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 being 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 efficient, and this despite the fact that approximately 40 percent of the world's production of this element is spent on zinc metallization. Steel sheets, fasteners, as well as instruments and other metal structures can be galvanized. The interesting thing is that using metallization or spraying you can protect a 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 capable of providing maximum protection in aggressive environments.

Conclusion

So we told you about what corrosion is. Types of corrosion were also considered. Now you know how to protect the surface from premature rusting. By and large, this is extremely simple to do, but where and how the product is used is of considerable importance. If it is constantly subjected to dynamic and vibration loads, then there is a high probability of cracks in the paintwork, through which moisture will enter the metal, as a result of which it will gradually deteriorate. However, the use of various rubber gaskets and sealants in areas where metal products interact can slightly extend the life of the coating.

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

Depending on the nature of corrosion and the conditions under which it occurs, various protection methods are used. The choice of one method or another is determined by its effectiveness in a given particular case, as well as economic feasibility. Any method of protection changes the course of the corrosion process, either reducing the speed or stopping it completely. Corrosion diagrams, which most fully characterize the corrosion process, should also reflect those changes in the course of the process that are observed under protection conditions. Corrosion diagrams can be used so when designing possible ways protecting metals from corrosion. They serve as the basis for clarifying the fundamental features of a particular method. Such diagrams postulate a linear relationship between the density and potential of each particular reaction. This simplification turns out to be quite acceptable for a qualitative assessment of the features of most methods.

Is the effectiveness of protection expressed through the braking coefficient? or degree of protection Z. The braking coefficient shows how many times the corrosion rate decreases as a result of using this method of protection, where and is the corrosion rate before and after protection. The degree of protection indicates how completely corrosion was suppressed using this method:

corrosion chemical metal protection

Of all the protection methods based on changes in the electrochemical properties of a metal under the influence of a polarizing current, the most widespread is the protection of metals by applying cathodic polarization to them (cathodic protection). When the metal potential shifts toward more electronegative values ​​(compared to the value of the stationary corrosion potential), the rate of the cathodic reaction increases, and the rate of the anodic reaction decreases. If equality was observed at a stationary potential, then at a more negative value this equality is violated: moreover.

Metal protection cathodic polarization used to increase the resistance of metal structures under conditions of underground (soil) and sea corrosion, as well as when metals come into contact with aggressive chemical environments. It is economically justified in cases where the corrosive environment has sufficient electrical conductivity, and voltage losses (associated with the flow of protective current), and therefore, energy consumption is relatively small. Cathodic polarization of the protected metal is achieved either by applying a current from an external source (cathodic protection), or by creating a macrogalvanic couple with a less noble metal (aluminium, magnesium, zinc and their alloys are usually used). It plays the role of an anode here and dissolves at a speed sufficient to create the necessary force in the electric current system (protective protection). The soluble anode in sacrificial protection is often called a “sacrificial anode.”

Cathodic protection is usually associated with the protection of ferrous metals, since the vast majority of objects operating underground and when immersed in water are made from them, for example pipelines, pile foundations, piers, overpasses, ships, etc. As a material for consumable anode-protectors in all Magnesium is widely used around the world. It is typically used in the form of alloys containing 6% aluminum, 3% zinc and 0.2% manganese; these additives prevent the formation of films that reduce the rate of metal dissolution. The output of the protective current is always less than 100%, since magnesium corrodes and hydrogen is released on it. Aluminum alloyed with 5% zinc is also used, but the potential difference with iron for the alloy is significantly less than for a magnesium alloy. It is close to the potential difference for zinc metal, which is also used for protection, provided that film formation associated with iron contamination, which is common in zinc, is prevented by appropriate alloying on the anodes. The choice of material for anodes is a difficult task. In soils or other low conductivity environments, a large potential difference is necessary because the drop iR between the electrodes is very large, while in highly conductive environments a small potential difference, which is more economical to use, is possible. Important variables are the location of the electrodes, the dissipative ability of the medium, i.e. its ability to provide the same current density in all areas of the protected surface, as well as the polarization characteristics of the electrodes. If the electrodes are immersed in soil that is for some reason unacceptable, for example aggressive towards the anodes, then it is usually practiced to surround the latter with a bed of neutral porous conductive material called backfill.

In practice, cathodic protection is rarely used without additional measures. The current required for complete protection is usually excessively high, and in addition to the costly electrical installations to provide it, it must be borne in mind that such current will often cause harmful side effects, such as excessive alkalization. Therefore, cathodic protection is used in combination with certain types of coatings. The current required is small and serves only to protect exposed areas of the metal surface.

Anodic protection. Many metals are in a passive state in some aggressive environments. Chromium, nickel, titanium, zirconium easily pass into a passive state and maintain it stably. Often, alloying a metal that is less prone to passivation with a metal that passivates more easily leads to the formation of fairly well passivated alloys. An example is the varieties of FeCr alloys, which are various stainless and acid-resistant steels that are resistant, for example, to fresh water, atmosphere, nitric acid, etc. For practical use passivity requires such a combination of properties of the metal and the medium in which the latter provides the value of the stationary potential lying in the region. This use of passivity in corrosion protection technology has been known for a long time and has a huge impact. practical significance The use of anodic protection is advisable in highly aggressive environments, for example in the chemical industry. If there is a liquid-gas interface, it must be borne in mind that anodic protection cannot extend to the metal surface in a gaseous environment, which, however, is also typical for cathodic protection. If the gas phase is also aggressive or there is a restless interface, which leads to liquid splashing and settling of droplets on the metal above the interface, if periodic wetting of the product wall occurs in a certain zone, then the question of other methods of protecting the surface above a constant liquid level has to be raised.

Anodic protection is carried out by simply applying a constant emf. from an outside source electrical energy. The positive pole is connected to the protected product, and relatively small cathodes are placed near its surface. They are placed in such quantity and at such a distance from the protected surface to ensure as uniform anodic polarization of the product as possible. This method is used if it is large enough and there is no danger, with some inevitable uneven distribution of the anode potential, activation or repassivation, i.e. going beyond.

In this way, products made of titanium or zirconium can be protected in sulfuric acid. You just need to remember that for passivation you will first need to pass current greater strength, which is associated with the transfer of potential beyond. For the initial period, it is advisable to have an additional source of energy. One should also take into account the greater polarization of cathodes, the current density of which is high due to their small size. However, if the region of the passive state is large, then a change in the cathode potential even by a few tenths of a volt does not pose a danger.

Coatings as a method of protecting metals from corrosion. Protection of metals, based on changes in their properties, is carried out either by special treatment of their surface or by alloying. Treatment of the metal surface in order to reduce corrosion is carried out in one of the following ways: covering the metal with surface passivating films from its poorly soluble compounds (oxides, phosphates, sulfates, tungstates or combinations thereof), creating protective layers from lubricants, bitumen, paints, enamels, etc. P. and by applying coatings of other metals that are more resistant in these specific conditions than the metal being protected (tinning, galvanizing, copper plating, nickel plating, chrome plating, lead, rhodium plating, etc.).

The protective effect of most surface films can be attributed to the mechanical isolation of the metal from the environment they cause. According to the theory of local elements, their effect should be considered as a result of an increase in electrical resistance

The corrosion rate can also be reduced by changing the properties of the corrosive medium. This is achieved either by appropriate treatment of the environment, as a result of which its aggressiveness is reduced, or by introducing small additives of special substances, so-called corrosion retarders or inhibitors, into the corrosive environment.

Treatment of the environment includes all methods that reduce the concentration of its components, especially those that are corrosive. For example, in neutral salt environments and fresh water, one of the most aggressive components is oxygen. It is removed by deaeration (boiling, distillation, bubbling of inert gas) or lubricated with appropriate reagents (sulfites, hydrazine, etc.). A decrease in oxygen concentration should almost linearly reduce the limiting current of its reduction, and, consequently, the rate of metal corrosion. The aggressiveness of the medium also decreases when it is alkalized, the total salt content is reduced and more aggressive ions are replaced with less aggressive ones. When anti-corrosion treatment of water to reduce scale formation, its purification with ion-exchange resins is widely used.

Corrosion inhibitors are divided, depending on the conditions of their use, into liquid-phase and vapor-phase or volatile. Liquid-phase inhibitors are in turn divided into corrosion inhibitors in neutral, alkaline and acidic environments. Anionic inorganic substances are most often used as inhibitors for neutral solutions. Their inhibitory effect is apparently associated either with the oxidation of the metal surface (nitrites, chromates), or with the formation of a film of a sparingly soluble compound between the metal, this anion and, possibly, oxygen (phosphates, hydrophosphates). The exception in this regard is the salts of benzoic acid, the inhibitory effect of which is associated mainly with adsorption phenomena. All inhibitors for neutral media inhibit predominantly the anodic reaction, shifting the stationary potential in a positive direction. To date, it has not yet been possible to find effective inhibitors of metal corrosion in alkaline solutions. Only high molecular weight compounds have some inhibitory effect.

Almost exclusively organic substances containing nitrogen, sulfur or oxygen in the form of amino, imino, thio groups, as well as carboxyl, carbonyl and some other groups are used as acid corrosion inhibitors. According to the most common opinion, the effect of acid corrosion inhibitors is associated with their adsorption at the metal-acid interface. As a result of the adsorption of inhibitors, inhibition of the cathodic and anodic processes is observed, reducing the corrosion rate.