What is corrosion of metals in chemistry. What is chemical corrosion and how to eliminate it? Protective coatings. metal coatings

Corrosion of metals(corrosio - corrosion) - the physical and chemical reaction of metals and alloys with the environment, as a result of which they lose their properties. Corrosion is based on the reaction at the phase boundary between the material and the medium: 3Fe+2O2=Fe3O4.

According to the conditions of the course, corrosion is divided into: 1) contact; 2) slotted; 3) along the waterline; 4) in spray zones; 5) in zones of variable wetting; 6) flowing through the condensation of acid vapors; 7) radiation; 8) occurring during heat transfer; 9) formed by stray currents.

Types of corrosion:

Chemical or gas corrosion (metals and alloys are destroyed by interacting with oxygen, hydrogen and other gases in the absence of moisture).

Electrochemical corrosion (the occurrence of metal or alloy contact in an electrolyte solution).

Chemical corrosion. It is represented by the processes of metal oxidation and reduction of the corrosion agent (most often oxygen): 2Me + O2 = 2MeO.

An important role is played by gas corrosion - corrosion of metals at high temperatures in dry gases (fuel combustion products, etc.).

Factors affecting the rate of gas corrosion:

1) the nature of the metal (alloy);

2) the composition of the gaseous medium;

3) mechanical properties of the resulting corrosion products (oxide films);

4) temperature.

Electrochemical corrosion more common, includes the processes of metal oxidation and reduction of a corrosive agent, occurring separately in an electrolyte environment (solutions of salts, acids, soil, etc.).

The course of electrochemical corrosion is a combination of two conjugated reactions: the anodic reaction (oxidation) Me = Mez+ + ze- and the cathodic reaction (reduction) D + ze-+ (Dze-), where D- a depolarizer (oxidizing agent) that attaches metal electrons (oxygen, hydrogen ions and some metals) to itself.

Iron rusting process: 2Fe + 2H2O + O2 = 2Fe2++ 4OH-.

In carbon steels, galvanic cells "cathode-anode" often appear. This is due to the differentiation of steel surfaces into areas with different electronic potentials.

Electrochemical corrosion depending on the corrosive environment is divided into:

1) atmospheric; 2) soil; 3) microbiological; 4) liquid.

The intensity of corrosion depends on the chemical composition of the metal (its alloys), the content of impurities and the oxidizing agent itself, its concentration, and air humidity.

50. Protection of metals from corrosion

Protection of metals and alloys from corrosion in aggressive environments is based on:

1) increasing the corrosion resistance of the material itself; 2) reducing the aggressiveness of the environment; 3) prevention of contact of the material with the environment using an insulating coating; 4) regulation of the electrode potential of the protected product in a given environment.

There are methods used to protect against electrochemical corrosion:

1) the use of chemically resistant alloys; 2) protection by coating the surface of a metal or alloy; 3) decrease in the activity of the corrosive environment; 4) electrochemical methods.

Stainless (13% chromium) and acid-resistant (18% chromium, 8-10% nickel) steels are considered the most chemically resistant alloys.

For coating metals, various types of coatings are used - metallic, non-metallic, coatings formed during electrochemical and chemical surface treatment of metals. Metallic coatings- chromium, nickel, zinc, cadmium, aluminum, tin, etc. They are applied using electroplating methods.

Non-metallic coatings- varnishes, paints, enamels, phenol-formaldehyde resins, etc.

Coatings resulting from metal processing, - oxide or salt films (aluminum oxidation).

The method of reducing the aggressiveness of the environment is most effective for products used in a small amount of liquid. The most common aggressive media are water, aqueous solutions of alkalis and acids, soil and the atmosphere. The aggressiveness of aquatic environments depends on the concentration of dissolved oxygen and carbon dioxide. Physically, oxygen and carbon dioxide can be removed by heating water at reduced pressure, chemically by passing through a layer of steel or iron shavings or by treating it with a reducing agent. The aggressiveness of aqueous media is also removed using corrosion inhibitors. Anode inhibitors- hydroxide, carbonate, phosphates, nitrite and sodium benzoate. cathodic inhibitors- zinc sulfates, sodium bicarbonate.

The best effect is achieved in combination with cathodic inhibitors. In acidic environments, organic inhibitors are used. There are passivator inhibitors - they transfer the metal to a passive state (peroxide-type oxidizers, noble metal compounds).

The aggressiveness of the atmosphere depends on its humidity and area (industrial, rural, etc.). The influence of the atmosphere depends on the hygroscopicity of metal corrosion products and dust particles on the surface. The hygroscopicity of steel corrosion products is reduced by copper alloying in small quantities. The corrosive aggressiveness of the soil is determined by the content of O2 in it, humidity, electrical conductivity, and pH.

Company Logo Actualization of knowledge and motivation of educational activity Chemical dictation in 2 options (odd numbers - option 1, even numbers - option 2) 1. The ability of metals to conduct electricity well is due to the presence of .. 2. Metals have ... lattices of a metal depend on it… 4. The melting point of a metal depends on… 5. The lightest metal… 6. The heaviest metal…

Company Logo Actualization of knowledge and motivation of educational activity 7.Metals melting at temp. below C are called ... 8. Metals with a density less than 5 g / cm 3 are called ... 9. Temp. melting of refractory metals ... 10. With increasing temp. melting decreases ... 11. Metals, giving up electrons, play the role of ... 12. Ferrous metals include ...

Company Logo Actualization of knowledge and motivation of educational activity 13. Metals in technology are divided according to… 14. The most refractory metal is… Motivation: in ancient times people knew 7 metals. Their number corresponded to the number of planets then known: Saturn-lead, Mercury-mercury, Mars-iron, Moon-silver, Sun-gold, Venus-copper, Jupiter-tin. You know a lot more alchemists and today we will continue to study the properties of metals

Company Logo Metals 1. What do these elements have in common? 2. What properties of these elements do you know?

Company Logo Chemical properties of metals What properties of simple substances are shown on this slide?

Company Logo Chemical Properties of Metals What elements are metals? What is the main property of metals How does the activity of metals change in a period? Elements that have 1-2 electrons in their outer level. The main property is to donate valence electrons. With an increase in the charge of the nucleus, the activity of the metal in the period decreases.

Company Logo Activity series of metals Increasing reducing properties Consider the activity series of metals, draw a conclusion about the activity of various metals, and suggest what substances they can react with.

Company Logo Chemical properties of metals Interaction with non-metals: with oxygen with sulfur with halogens Li K Ca Na Mg Al Zn Cr Fe Ni Pb Cu Hg Ag Pt Au Under normal conditions M + O2 oxide Slowly or when heated M + O 2 oxide M + O 2

Company Logo Chemical Properties of Metals Write the reaction equations for the interaction of sodium with: oxygen, sulfur, chlorine 4Na + O2 = 2Na2O 2Na + S = Na2S 2 Na + CI2 = 2NaCI

Company Logo Interaction with complex substances: with water Li K Ca NaMg Al Zn Cr Fe Ni Pb (H 2) Cu Hg Ag Pt Au Under normal conditions M + H 2 O H 2 + alkali When heated M + H 2 OH 2 + oxide M + H2O

Company Logo Examples Complete the possible reaction equations: 1. Li + H2O = 2. AI + H2O = 3. Hg + H2O = 2Li + 2HOH = 2LiOH + H2 2AI +3H2O = Ai2O3 + 3H2 Hg + H2O

Company Logo Interaction with acid solutions Li K Ca Na Mg Al |Zn Cr Fe Ni Pb (H 2) Cu Hg Ag Pt Au Displace H 2 from acid solutions Do not displace H 2 from acid solutions

Company Logo Examples Write possible equations for reactions with dilute sulfuric acid: aluminium, zinc, sodium and copper

Company Logo Interaction with Salt Solutions Each metal displaces other metals to the right of it in the series of voltages from salt solutions, and can itself be displaced by metals to the left. Fe + CuSO4 = FeSO4 + Cu Zn + NiCI2 = ZnCI2 + Ni It is impossible to take active metals for this purpose, since they interact with water, forming alkalis.

Company Logo Reagents KCaFeCuAu O2 H2O HCl (solution) Pb(NO3)2 solution Exercises

Company Logo Verification Reactive substances NaCaFeCuAu O2O H2OH2O HCl (solution) Pb(NO 3) 2 solution +++--

Company Logo Corrosion Corrosion is a spontaneous process of destruction of materials and products from them under the chemical influence of the environment.

Company Logo Causes of corrosion A) gases (O2, SO2, H2S, Cl2, NH3, NO, NO2, H2O-steam, etc.); soot is an adsorbent of gases; B) electrolytes: alkalis, acids, salts; C) Cl- ions, air humidity; D) macro- and microorganisms; E) stray electric current; G) heterogeneity of metals.

Company Logo Types of Corrosion Corrosion Atmospheric Gas Chemical Electrochemical

Company Logo Atmospheric Atmospheric corrosion of metals occurs in moist air at ordinary temperatures.

Company Logo Chemical corrosion Chemical corrosion is the chemical destruction of metals by the action of oxygen, hydrogen sulfide and other gases in the absence of moisture.

Company Logo Gas Corrosion Gas corrosion is a type of chemical corrosion that affects furnace fittings, engine parts that operate at high temperatures.

Company Logo Electrochemical Corrosion Electrochemical corrosion is the breakdown of metal that is in contact with another metal and an electrolyte or water.

Company Logo Electrochemical corrosion On the surface of any metal, water condenses, in which atmospheric gases are dissolved, that is, an electrolyte is formed. If the metal contains impurities or comes into contact with another metal, electrochemical corrosion begins. In this case, the more active metal is destroyed first.

Company Logo Consequences of Corrosion Every year, direct losses from rust due to poor-quality protection of equipment, equipment and structures amount to about 10% of the total volume of metal produced in the world.

Company Logo Protecting metals from corrosion Protective coatings - applying protective coatings to the surface of a metal Alloying additives - adding chromium, nickel, titanium, cobalt Inhibitors - adding catalysts that slow down chemical reactions Protective protection - creating contact with a more active metal

Company Logo Consolidation of acquired knowledge What is called corrosion? What factors cause it? Destruction of metals and alloys under the influence of various external factors. Influence of atmospheric air, ground moisture, corrosive gases Aggressive chemical environment Electrolytes

Company Logo Consolidation of acquired knowledge Name the types of corrosion. What are the ways to protect metals from corrosion Atmospheric, chemical, gas and electrochemical. Protective coatings, alloying additives, inhibitors

"Methods of protecting metals from corrosion" - Galvanic sacrificial protection. chemical corrosion. mechanism of corrosion. Many metals corrode. The anode is destroyed. Corking rust. Phosphating. corrosion process. Defeat. Surfaces. corrosion cracking. electrochemical corrosion. Corrosion protection. Cold galvanized.

"Corrosion of metals and its types" - Classification of types of corrosion. cognitive tasks. Test tubes. Laboratory experience. Factors provoking the process of corrosion. Corrosion. processes occurring at the cathode. corrosion process. The intensity of corrosion. Corrosion protection methods. Examples of protection of metal products. inventive task. Tasks.

"Corrosion of metal" - Why do we need metals? The destruction of metals and alloys under the influence of the environment is called corrosion. Physical properties of metals. Corrosion of metals Methods for obtaining metals. Electrolysis. Metal connection. Of the two metals, the more active corrodes. General physical properties of metals. Chemical properties of metals.

"Types of corrosion of metals" - Electrochemical series of voltages of metals. electrochemical corrosion. Corrosion. Types of corrosion protection. chemical corrosion. Monuments. Rusty rat. Corrosion protection methods. Types of corrosion. Corrosion of metals. Danger.

"The process of corrosion of metals" - Metals of secondary subgroups. Corrosion of metals. Corrosion properties of metals. Corrosion - a red rat, gnaws on scrap metal. Spontaneous destruction of metals and alloys. Corrosion protection methods. electrochemical corrosion. Types of corrosion. chemical corrosion. Reducing agents are metals. Aluminum.

"Corrosion of metals" - Practical stage. Corrosion protection methods. Conditions conducive to electrochemical corrosion. Temperature increase. historical stage. Mechanism of electrochemical corrosion. The more active the metal, the more susceptible it is to corrosion. factors causing corrosion. Corrosion adversely affects the life and health of people.

In total there are 9 presentations in the topic

Chemical properties include the ability of metals to resist oxidation or enter into combinations with various substances: air oxygen, moisture (metals, when combined with oxygen and water, form bases (alkalis)), carbon dioxide, etc. The better the metal enters into compounds with other elements, the easier it is destroyed. The chemical destruction of metals under the action of the environment at ordinary temperature is called metal corrosion .

The chemical properties of metals include the ability to form scale when heated in an oxidizing atmosphere, as well as to dissolve in various chemically active liquids: acids, alkalis, etc. Metals that are resistant to oxidation at high temperatures are called heat resistant (scaling resistant).

The ability of metals to maintain their structure at high temperatures, not to soften or deform under the influence of a load is called heat resistance.

The resistance of metals to corrosion, scale formation and dissolution is determined by the change in the weight of the test samples per unit surface per unit of time.

Corrosion of metals. The word "corrosion" (in Latin - "corrosion") is used to denote the well-known phenomena, which consist in the rusting of iron, the coating of copper with a green oxide layer, and similar changes in metals.

As a result of corrosion, metals are partially or completely destroyed, the quality of products deteriorates, and they may be unsuitable for use.

Most metals occur in nature in the form of compounds with other elements, for example, iron - in the form of Fe 2 O 3, Fe 3 O 4, FeCO 3, copper - in the form of CuFeS 2, Cu 2 S, aluminum - in the form of Al 2 O 3 , etc. As a result of metallurgical processes, the stable bond between metals and substances, which existed in the natural state, is broken, but it is restored when metals combine with oxygen and other elements. This is the cause of corrosion.

The development of the theory of corrosion is the merit of Russian scientists V.A. Kistyakovsky, G.V. Akimov, N.A. Izgaryshev and others. According to researchers of corrosion phenomena, there are two types of corrosion: electrochemical and chemical corrosion.

electrochemical corrosion(Fig.13.) is the process of destruction of metals in contact with liquids that conduct electric current (electrolytes), i.e. with acids, alkalis, solutions of salts in water, water with air dissolved in it. The phenomena occurring here are similar to those that can be observed in a galvanic cell. In steel, for example, the galvanic cell forms iron carbide and ferrite. In electrolytes, carbide remains unchanged, while ferrite dissolves and gives rust with the electrolyte substance - a corrosion product.

The behavior of various metals in electrolytes can be judged by their place in a series of voltages: potassium, calcium, magnesium, aluminum, manganese, zinc, chromium, iron, cadmium, cobalt, nickel, tin, lead, hydrogen, antimony, bismuth, copper, mercury, silver, gold. In the above series, the metals are arranged according to the magnitude of the normal electric potential (i.e., obtained by immersing the metal in a normal solution of its salt) with respect to hydrogen. Each metal of this row, paired with another in electrolytes, forms a galvanic cell, and the metal that is located to the left in the row will be destroyed. So, in a pair of copper - zinc, zinc is destroyed. A number of voltages is of very great practical importance: it indicates the danger of having dissimilar metals in direct contact, since this creates conditions for the formation of a galvanic cell and the destruction of one of the metals to the left of the voltage series.

Fig.13. Scheme illustrating the process of electrochemical corrosion. Base metal dissolves (corrodes) at one pole, hydrogen is released at the other.

Chemical corrosion called the destruction of metals and alloys in dry gases at high temperatures and in liquids that do not have the properties of electrolytes, for example, in oil, gasoline, molten salts, etc. During chemical corrosion under the action of atmospheric oxygen, metals are covered with a thin layer of oxides. During chemical corrosion, the metal is not always only subjected to surface destruction, but corrosion also penetrates into the depth of the metal, forming foci or located along the grain boundaries. (example. Silver items darken over time, because the air contains gaseous sulfur compounds that react chemically with silver. The resulting silver sulfide remains on the surface of the items in the form of a brownish or black film.)

Some metals in nature can be found in the native state. These are mostly noble metals, such as gold. It is extracted by mechanical laundering from the surrounding rocks. However, the vast majority of metals (those on the left side of the voltage series) are found in nature in the form of compounds.

Natural minerals containing metals in their composition and suitable for the industrial production of metals are called ores. Upon receipt of any metal, you must:

1) to separate the ore from waste rock;

2) restore the metal from the compound.

Depending on the method of obtaining the metal, pyrometallurgy, hydrometallurgy and electrometallurgy are distinguished.

Pyrometallurgy covers methods for producing metals from their oxides. In cases where the ore is a salt, such as zinc sulfide, it is first converted into an oxide:

2ZnS + 3O 2 \u003d 2ZnO + 2SO 2

Carbon, carbon monoxide (II), hydrogen, methane are used as reducing agents of metals from their oxides:

Cu 2 O+C=2Cu+CO

Recovery with coal (coke) is usually carried out when the resulting metals do not form carbides at all or form fragile carbides; such are iron and many non-ferrous metals.

The reduction of metals from their compounds by other metals is called metallothermy. These processes also take place at high temperatures. Aluminum, magnesium, calcium, sodium, and silicon are used as reducing agents.

If aluminum is the reducing agent, then the process is called aluminothermy, if magnesium is magnesiumthermy:

Cr 2 O 3 + 2Al \u003d 2Cr + Al 2 O 3 TiCl 4 + 2Mg \u003d Ti + 2MgCl 2

Metalthermy usually produces those metals (and their alloys) which form carbides when their oxides are reduced with carbon. These are manganese, chromium, titanium, molybdenum, tungsten, etc.

Sometimes metals are reduced from oxides with hydrogen (hydrothermy):

MoO 3 + 3H 2 \u003d Mo + 3H 2 O

Hydrometallurgy covers methods for obtaining metals from their salts. In this case, the element of the metal that is part of the ore is first converted into a soluble salt with the help of an appropriate reagent, and only after that the metal is directly removed from the solution.

Currently, metals such as copper, silver, zinc, uranium, etc. are mined using the hydrometallurgical method. Many copper ores contain copper oxide. This ore is processed

dilute sulfuric acid and converted to copper sulfate, soluble in water:

CuO + H 2 SO 4 \u003d CuSO 4 + H 2 O

After that, copper is extracted from copper sulfate either by electrolysis or displaced with iron: CuSO 4 + Fe \u003d Cu + FeSO 4

Electrometallurgy covers methods of producing metals by electrolysis. In this way, mainly light metals - aluminum, sodium and others - are obtained from their molten oxides or chlorides.

The chemical and physical properties of metals are determined by the atomic structure and features of the metallic bond. All metals are distinguished by the ability to easily donate valence electrons. In this regard, metals exhibit pronounced reducing properties. The degree of reducing activity of metals reflects a number of stresses.

Knowing the position of the metal in this series, one can draw a conclusion about the comparative value of the energy expended on the detachment of valence electrons from the atom. The closer to the beginning of the row, the easier the metal oxidizes. The most active metals displace hydrogen from water under normal conditions with the formation of alkali:

2Na + 2Н 2 O \u003d 2NaOH + H 2

Less active metals displace hydrogen from water in the form of superheated steam and form oxides:

2Fe + 4H 2 O \u003d Fe 3 O 4 + 4H 2

React with dilute and anoxic acids, displacing hydrogen from them:

Zn + 2HCl \u003d ZnCl 2 + H 2

Metals that are in the series of voltages after hydrogen cannot displace it from water and from acids, but enter into redox reactions with oxidizing acids without displacing hydrogen:

Cu + 2H 2 SO 4 ( conc ) = CuSO 4 + SO 2 + H 2 O

All previous metals displace the stresses following them in a series of stresses from their salts: Fe + CuSO 4 \u003d FeSO 4 + Cu

In all cases, the reacting metals are oxidized. Oxidation of metals is also observed in the direct interaction of metals with non-metals:

2Na + S \u003d Na 2 S 2Fe + 3Cl 2 \u003d 2FeCl 3

Most metals actively react with oxygen, forming oxides of various compositions.

Oxidation of metals often leads to their destruction. The destruction of metals under the influence of the environment is called corrosion. There are two main types of corrosion: chemical and electrochemical.

Chemical corrosion is the destruction of a metal by its oxidation in the environment without the occurrence of an electric current in the system. In this case, the metal interacts with the constituent parts of the medium - with gases and non-electrolytes.

So, iron rusts in air - it is covered with a thin film of oxides (FeO, Fe 2 O 3 or Fe 3 O 4, depending on the conditions). The oxidation of iron occurs even more vigorously in the presence of water:

4Fe + 3O 2 + 6H 2 O \u003d 4Fe (OH) 3

As the temperature rises, chemical corrosion increases.

Corrosion under the action of substances at high temperatures in technology (in metallurgy, rocket engine nozzles, gas turbines) causes great harm to various structures. Some metals, such as aluminum, when exposed to oxygen or other oxidizing agents (concentrated HNO 3 ), form a protective film that prevents further contact of the metal with the oxidizing agent and thus protects the metal from further corrosion.

Electrochemical corrosion is the destruction of metal as a result of the occurrence of a galvanic couple and the appearance of an electric current inside the system. Electrochemical corrosion occurs when two metals come into contact through an electrolyte, while the metals themselves are the electrodes.

When a galvanic pair occurs, an electric current of greater strength appears, the farther the metals are from each other in a series of voltages. In this case, the flow of electrons goes from a more active metal to a less active one; the more active metal in this case is destroyed (corrodes).

For example, when a galvanic pair zinc - copper occurs, zinc corrodes.

Let's take zinc and copper plates and lower them into a solution of sulfuric acid, which is contained in the solution in the form of ions:

Zinc atoms, donating electrons in the form of ions, go into solution:

Zn°-2e - ®Zn +2

Electrons pass through the conductor to copper, and from copper to hydrogen ions:

H + +e - ®H°

Hydrogen in the form of neutral atoms is released on a copper plate, and zinc gradually dissolves. Thus, copper, as if pulling electrons from zinc, causes the latter to dissolve faster, i.e.

promotes oxidation (see Fig. 25).

Electrochemical corrosion occurs in the presence of both strong and weak electrolytes, however, in the presence of strong electrolytes, the corrosion rate is higher.

From the point of view of electrochemical corrosion, it becomes clear why corrosion increases if impurities are present in the metal. The metal and the impurity form a galvanic pair, as a result of which the metal is destroyed. It is in cases where a very high chemical resistance of metals is required that they achieve high purity.

Due to the fact that corrosion causes enormous damage to the national economy, various methods of corrosion protection are being developed. Currently, the following main methods of corrosion protection are used.

1. Surface coating of metals, which isolates the metal from the external environment.

Coatings can be metallic (zinc, copper, nickel, chromium) and non-metallic (varnishes, paints, enamels).

Burnishing is a process in which iron is exposed to strong oxidizing agents, as a result of which the metal is covered with an oxide film that is impervious to gases, protecting it from the effects of the external environment.

2. The creation of alloys resistant to corrosion, the introduction of chromium, manganese, nickel into the composition of steel makes it possible to obtain stainless steel, which is widely used in industry.

Substances that slow down corrosion, and sometimes almost completely stop it, are called inhibitors - retarders. The nature of the action of inhibitors is different. They either create a protective film on the metal surface or reduce the aggressiveness of the environment.

Alloys

Alloys are systems consisting of two or more metals, as well as metals and non-metals. The properties of the alloys are very diverse and differ from the original components. The chemical bond in alloys is metallic. Therefore, they have a metallic luster, electrical conductivity and other properties of metals.

Alloys are obtained by mixing metals in the molten state, they solidify during subsequent cooling. In this case, the following typical cases are possible.

1. Metals are mixed and melted, followed by solidification. In this case, the components that make up the alloy dissolve in each other to a limited or unlimited extent. This includes metals that crystallize in the same type of lattices and have atoms close in size, for example, Ag-Cu, Cu-Ni, Ag-Au and others. When such melts are cooled, solid solutions are obtained. The crystals of the latter contain atoms of both metals, which determines their complete homogeneity. Compared to true metals, solid solutions are characterized by higher strength, hardness, and chemical resistance; they are plastic and conduct electricity well.

2. Molten metals are mixed with each other in any ratio, however, when cooled, a solid solution is not formed. When such alloys solidify, a mass is obtained, consisting of the smallest crystals of each of the metals. This is typical for Pb-Sn, Bi-Cd, Ag-Pb, etc. alloys.

3. Molten metals, when mixed, interact with each other, forming intermetallic compounds. An example is the compounds of some metals with antimony: Na 3 Sb, Ca 3 Sb 2, NiSb, etc.

Currently, some alloys are prepared by powder metallurgy. A mixture of metals is taken in the form of powders, pressed under high pressure and sintered at high temperature.

perature in a reducing environment. In this way, superhard alloys are obtained.