Chemical reactions should be distinguished from nuclear reactions. As a result chemical reactions The total number of atoms of each chemical element and its isotopic composition do not change. Other business nuclear reactions - transformation processes atomic cereals As a result of their interaction with other nuclei or elementary particles, for example, the conversion of aluminum into magnesium:
27 13 Ал + 1 1 H \u003d 24 12 mg + 4 2
Classification of chemical reactions of multifaceted, that is, various signs can be laid in its foundation. But for any of such signs, reactions can be attributed both between the inorganic and between organic substances.
Consider the classification of chemical reactions on various features.
I. In terms of the number and composition of the reacting substances
Reactions going without changing the composition of substances.
In ne. organic chemistry Such reactions include the processes for obtaining allotropic modifications of one chemical element, for example:
C (graphite) ↔ C (diamond)
S (rhombic) ↔ s (monoclinic)
P (white) ↔ P (red)
SN (White Tin) ↔ SN (Gray Tin)
3O 2 (oxygen) ↔ 2O 3 (ozone)
In organic chemistry, the reactions of the reactions can be attributed to this type of reactions, which go unchanged not only by the qualitative, but also the quantitative composition of molecules of substances, for example:
1. Isomerization of alkanov.
The isomerization reaction of alkanans is of great practical importance, since the hydrocarbons of the isothing have a smaller point of detonation.
2. Isomerization of alkenes.
3. Isomerization of alkins (reaction of A. E. Favorsky).
CH 3 - CH 2 - C \u003d - CH ↔ CH 3 - C \u003d - C- 3
ethyl acetylene dimetnoxhetylene
4. Isomerization of halonens (A. E. Favorsky, 1907).
5. Isomerization of ammonium cyanite when heated.
For the first time, urea was synthesized by F. Weller in 1828. Isomerization of the ammonium cyanate during heating.
Reactions going with a change in the composition of the substance
Four types of such reactions can be distinguished: compounds, decomposition, substitution and exchange.
1. The reaction of the compound is such reactions in which one complex substance is formed from two or more substances.
In inorganic chemistry, the entire variety of compound reactions can be considered, for example, on the example of the reactions of obtaining sulfuric acid from sulfur:
1. Obtaining sulfur oxide (IV):
S + O 2 \u003d SO - one complicated two simple substances are formed.
2. Obtaining sulfur oxide (VI):
SO 2 + 0 2 → 2SO 3 - one complicated one is formed from simple and complex substances.
3. Preparation of sulfuric acid:
SO 3 + H 2 O \u003d H 2 SO 4 - from two complex substances is formed one complex.
An example of a compound reaction in which one complex substance is formed from more than two sources, a final stage of nitric acid production can be served:
4No 2 + O 2 + 2N 2 O \u003d 4NO 3
In organic chemistry, the connection reaction is called "reactions of attachment". All variety of such reactions can be considered on the example of a block of reactions that characterize the properties of unsaturated substances, such as ethylene:
1. Hydrogenation reaction - hydrogen attachment:
CH 2 \u003d CH 2 + H 2 → H 3 -CH 3
ethen → Ethan
2. Hydration reaction - water connection.
3. Polymerization reaction.
2. The decomposition reactions are such reactions in which several new substances are formed from one complex substance.
In inorganic chemistry, the variety of such reactions can be viewed on a block of reactions of oxygen production by laboratory methods:
1. Decomposition of mercury oxide (II) - from one complex substance are formed two simple.
2. The decomposition of potassium nitrate - one simple and one complex is formed from one complex substance.
3. The decomposition of potassium permanganate - from one complex substance two complex and one simple, that is, three new substances.
In organic chemistry, the decomposition reaction can be considered on the block of reactions of ethylene in the laboratory and in the industry:
1. Dehydration dehydration reaction (water cleaner) ethanol:
C 2 H 5 Oh → CH 2 \u003d CH 2 + H 2 O
2. Dehydrogenation reaction (hydrogen cleavage) of ethane:
CH 3 -CH 3 → CH 2 \u003d CH 2 + H 2
or CH 3 -CH 3 → 2C + ZN 2
3. Propane's cracking (splitting) reaction:
CH 3 -CH 2 -CH 3 → CH 2 \u003d CH 2 + CH 4
3. Replacement reactions are such reactions, as a result of which the atoms of a simple substance replace atoms of some element in a complex substance.
In inorganic chemistry, an example of such processes can serve as a block of reactions characterizing properties, such as metals:
1. The interaction of alkaline or alkaline earth metal with water:
2NA + 2N 2 O \u003d 2NOH + H 2
2. The interaction of metals with acids in the solution:
Zn + 2NSL \u003d ZNSL 2 + H 2
3. The interaction of metals with salts in solution:
FE + CUSO 4 \u003d FESO 4 + Cu
4. Metalothermia:
2Al + CR 2 O 3 → AL 2 O 3 + 2SR
The subject of studying organic chemistry is not simple substances, but only compounds. Therefore, as an example of reaction of substitution, we give the most characteristic property The limit compounds, in particular methane, is the ability of its hydrogen atoms to be replaced by halogen atoms. Another example is the bromination of aromatic compound (benzene, toluene, aniline).
C 6 H 6 + B 2 → C 6H 5 VR + HBR
benzole → Brombenzene.
Pay attention to the feature of reaction reaction from organic substances: As a result of such reactions, a simple and complex substance is formed as in inorganic chemistry, but two complex substances.
In organic chemistry, substitution reactions include some reactions between two complex substances, for example, benzene thread. It is formally a exchange reaction. The fact that this reaction of substitution becomes clear only when considering its mechanism.
4. Exchange reactions are such reactions in which two complex substances exchange their components
These reactions characterize the properties of electrolytes and in solutions proceed according to the rule of Bertoll, that is, only if the precipitate, gas or a slightly subsidiary (for example, H 2 O) is formed.
In inorganic chemistry, this may be a block of reactions characterizing, for example, alkali properties:
1. Neutralization reaction, which comes to the formation of salt and water.
2. The reaction between alkali and salt, which comes with the formation of gas.
3. The reaction between alkali and salt, which comes with the formation of a precipitate:
CUSO 4 + 2CON \u003d CU (OH) 2 + K 2 SO 4
or in ion form:
Cu 2+ + 2N - \u003d Cu (OH) 2
In organic chemistry, a block of reactions characterizing, for example, acetic properties, can be considered:
1. The reaction that comes with the formation of a weak electrolyte - H 2 O:
CH 3 coxy + NAON → NA (CH3SOO) + H 2 O
2. Reaction that comes with gas formation:
2SH 3 coam + saso 3 → 2 SO 3 SO + CA 2+ + CO 2 + H 2 O
3. Reaction that comes with the formation of a precipitate:
2 SOON 3 + K 2 SO 3 → 2K (CH 3 SO) + N 2 SO 3
2 SO 3 + SiO → 2 SIO 3 SIO + N 2 SiO 3
II. By changing oxidation degrees chemical elementsforming substances
This feature distinguishes the following reactions:
1. Reactions going with changes in the degrees of oxidation of elements, or oxidative reaction reactions.
These include many reactions, including all reactions of substitution, as well as the reactions of compound and decomposition, in which at least one simple substance is involved, for example:
1. Mg 0 + H + 2 SO 4 \u003d Mg +2 SO 4 + H 2
2. 2mg 0 + o 0 2 \u003d Mg +2 O -2
Complex oxidation reaction reactions are compiled using the electronic balance method.
2kmn +7 O 4 + 16hCl - \u003d 2KCL - + 2mn +2 Cl - 2 + 5Cl 0 2 + 8H 2 O
In organic chemistry, the prime example of redox reactions can be the properties of the aldehydes.
1. They are restored to the corresponding alcohols:
Aldekis are oxidized to the appropriate acids:
2. Reactions going without changing the oxidation of chemical elements.
These, for example, include all ion exchange reactions, as well as many compound reactions, many decomposition reactions, esterification reactions:
Nson + CHGOH \u003d NSOO 3 + H 2 O
III. On thermal effect
The thermal effect of the reaction is divided into exothermic and endothermic.
1. Exothermic reactions proceed with energy release.
These include almost all connection reactions. A rare exclusion is endothermic reactions of nitrogen oxide (II) from nitrogen and oxygen and the reaction of gaseous hydrogen with a solid iodine.
Exothermic reactions that occur with the release of light relate to burning reactions. Ethylene hydrogenation is an example of an exothermic reaction. It goes at room temperature.
2. Endothermic reactions proceed with energy absorption.
Obviously, they will relate to almost all reactions of decomposition, for example:
1. Limestone firing
2. Cracking Butane
The amount of energy isolated or absorbed as a result of the reaction is called the thermal effect of the reaction, and the equation of the chemical reaction with the indication of this effect is called the thermochemical equation:
H 2 (g) + C 12 (g) \u003d 2ns 1 (g) + 92.3 kJ
N 2 (g) + o 2 (g) \u003d 2no (g) - 90.4 kJ
IV. By aggregate state of reacting substances (phase composition)
According to the aggregative state of the reacting substances distinguish:
1. Heterogeneous reactions - reactions in which reacting substances and reaction products are in different aggregate states (in different phases).
2. Homogeneous reactions - reactions in which reacting substances and reaction products are in one aggregate state (in the same phase).
V. By the participation of the catalyst
By participation of the catalyst distinguish:
1. Necatelitic reactions going without the participation of the catalyst.
2. Catalytic reactions going with the participation of the catalyst. Since all biochemical reactions occurring in cells of living organisms, they go with the participation of special biological catalysts of protein nature - enzymes, they all relate to catalytic or, more precisely, enzymatic. It should be noted that more than 70% of chemical industries use catalysts.
Vi. Towards
In the direction distinguish:
1. Reassembled reactions proceed in these conditions only in one direction. These include all the exchange reactions, accompanied by the formation of precipitation, gas or a small substance (water) and all combustion reactions.
2. Reversible reactions under these conditions flow simultaneously in two opposite directions. Such reactions overwhelming majority.
In organic chemistry, a sign of reversibility reflects the names - antonyms of processes:
Hydrogenation - dehydrogenation,
Hydration - dehydration,
Polymerization - depolymerization.
Removed all esterification reactions (the opposite process, as you know, is called hydrolysis) and hydrolysis of proteins, esters, carbohydrates, polynucleotides. The reversibility of these processes underlies the most important property of a living organism - metabolism.
VII. By the flow mechanism distinguish:
1. Radical reactions go between the radicals and molecules during the reaction.
As you already know, with all reactions there is a breaking of old and the formation of new chemical ties. The method of breaking the bond in the molecules of the starting material determines the mechanism (path) of the reaction. If the substance is formed at the expense of a covalent bond, there may be two ways to break this connection: hemolytic and heterolytic. For example, for CL 2 molecules, CH 4, etc., a hemolytic bond break is realized, it will lead to the formation of particles with unpaired electrons, that is, free radicals.
Radicals are most often formed when bonds are broken, in which common electronic pairs are distributed between atoms of approximately the same (non-polar covalent bond), however, many polar bonds can also be torn in the same way, in particular when the reaction passes in the gas phase and under the action of light , such as in the case of the processes discussed above - interactions with 12 and CH 4 -. The radicals are very reactive, as they strive to complete their electronic layer, taking the electron in another atom or molecule. For example, when the chlorine radical faces hydrogen molecule, it causes a gap of a general electron pair that binds the hydrogen atoms, and forms a covalent bond with one of the hydrogen atoms. The second hydrogen atom, becoming a radical, forms a common electron pair with an unpaired electron of the chlorine atom from the collapsed CL 2 molecule, as a result of which the chlorine radical occurs, which attacks a new hydrogen molecule and so on
Reactions that are a circuit of successive transformations are called chain reactions. For the development of the theory of chain reactions, two outstanding chemist - our compatriot N. N. Semenov and the Englishman S. A. Khinshelwood were awarded Nobel Prize.
Similarly, the reaction of substitution between chlorine and methane proceeds:
According to the radical mechanism, most combustion reactions of organic and inorganic substances, water synthesis, ammonia, polymerization of ethylene, vinyl chloride, etc.
2. ionic reactions go between ions already available or formed during reaction.
Typical ionic reactions are interaction between electrolytes in solution. The ions are formed not only in the dissociation of electrolytes in solutions, but also under the action of electrical discharges, heating or radiation. γ-rays, for example, convert water and methane molecules to molecular ions.
On another ionic mechanism, the reactions of attachment to alkins of halogen gods, hydrogen, halogen, oxidation and dehydration of alcohols occur, the substitution of alcohol hydroxyl to halogen; Reactions characterizing the properties of aldehydes and acids. Ions in this case are formed during the heterolithic break of covalent polar bonds.
VIII. By type of energy,
by initiating the reaction, distinguish:
1. Photochemical reactions. They are initiated by light energy. In addition to the photochemical processes of the NCl synthesis or the reaction of methane with chlorine, they include obtaining ozone in the troposphere as a secondary atmospheric pollutant. In the role of primary in this case, nitrogen oxide (IV) performs, which, under the action of light, forms oxygen radicals. These radicals interact with oxygen molecules, resulting in ozone.
The formation of ozone is all the time, while there is enough light, since NO can interact with oxygen molecules to form the same NO 2. The accumulation of ozone and other secondary air pollutants can lead to the appearance of photochemical smog.
To this type of reactions belongs and the most important process flowing in vegetable cells - photosynthesis, whose name speaks for itself.
2. Radiation reactions. They are initiated by radiation of high energy - x-rays, nuclear radiation (γ-rays, and particles - not 2+, etc.). With the help of radiation reactions, it is carried out very fast radio andmerization, radioliz (radiation decomposition), and so on.
For example, instead of two-stage obtaining phenol from benzene, it can be obtained by reacting benzene with water under the action of radiation radiation. In this case, radicals are formed from water molecules [ON] and [H], with which benzene reacts with the formation of phenol:
From 6 H 6 + 2 [ON] → C 6 H 5 ON + H 2 O
Volcanization of rubber can be carried out without sulfur using radio tape, and the resulting rubber will be at all worse than the traditional.
3. Electrochemical reactions. They are initiated electricity. In addition to well-known electrolysis reactions, we also indicate the reactions of electrosynthesis, for example, the reaction of industrial production of inorganic oxidizers
4. Thermochemical reactions. They are initiated thermal energy. These include all endothermic reactions and many exothermic reactions, for the start of which the initial flow of heat is needed, that is, the initiation of the process.
The classification of chemical reactions discussed above is reflected in the diagram.
Classification of chemical reactions, like all other classifications, conditional. Scientists have agreed to divide the reactions to certain types of signs allocated by them. But most chemical transformations can be attributed to different types. For example, make a characteristic of the ammonia synthesis process.
This is a compound reaction, redox, exothermic, reversible, catalytic, heterogeneous (more precisely, heterogeneous-catalytic) flowing with a decrease in pressure in the system. For successful process management, you must consider all the information provided. A specific chemical reaction is always multi-city, it is characterized by different signs.
Chemical elements from which consists of a living and inanimate natureare in constant motion, because substances that consist of these elements are continuously changed.
Chemical reactions (from lat. Reaction - countering, rebuffing) is a response effect of substances to the effects of other substances and physical factors (temperature, pressure, radiation, etc.).
However, the definition also correspond to the physical changes taking place with substances - boiling, melting, condensation, etc. Therefore, it is necessary to clarify that chemical reactions are processes, as a result of which old chemical bonds are destroyed and new and, as a result, are destroyed. Source substances are formed new substances.
Chemical reactions are continuously occurring both inside our organism and in the world around us. Countless reactions are customary to classify on various features. Let's remember from the course of 8 class signs that you are already familiar. To do this, refer to the laboratory experience.
Laboratory experience number 3
Copper iron substitution in copper sulfate solution (II)
Pour 2 ml of copper sulfate solution (II) into the test tube and place the stationery or paper clips. What are you watching? Record the reaction equations in molecular and ionic forms. Consider the redox processes. On the basis of the molecular equation, take this reaction to a particular group of reactions based on the following features:
Now check yourself. Cuso 4 + Fe \u003d Feso 4 + Cu.
|
We approached a very important concept in chemistry - "chemical reaction speed". It is known that some chemical reactions proceed very quickly, others for considerable intervals. With the addition of silver nitrate solution to a solution of sodium chloride, a white cotton sediment is almost instantly falls:
AGNO 3 + NaCl \u003d Nano 3 + AgCl ↓.
With huge rates, reactions are accompanied by an explosion (Fig. 11, 1). On the contrary, stalactites and stalagmites are slowly growing in the stone caves (Fig. 11, 2), corrodes (rust) steel products (Fig. 11, 3) are destroyed under the action of acid rains Palaces and statues (Fig. 11, 4).
Fig. eleven.
Chemical reactions leaking with huge speeds (1) and very slowly (2-4)
| Under the speed of the chemical reaction, the change in the concentration of reacting substances per unit of time is understood: V p \u003d C 1 - C 2 / T. |
In turn, under a concentration understand the ratio of the number of substance (as you know, it is measured in a moles) to the volume it takes (in liters). From here it is not difficult to derive a unit of measuring the speed of the chemical reaction - 1 mol / (l c).
Reading the speed of the chemical reaction is a special section of chemistry, which is called chemical kinetics.
Knowledge of its patterns allows you to control a chemical reaction, forcing it to flow faster or slower.
What factors depends the rate of chemical reaction?
1. The nature of the reactant substances. Turn to the experiment.
Laboratory experience number 4
The dependence of the rate of chemical reaction from the nature of the reactant substances on the example of the interaction of acids with metals
| Pour into two tubes in 1-2 ml of hydrochloric acid and place: in the 1st - zinc granulus, in the 2nd - a piece of iron of the same size. The nature of which reagent affects the rate of interaction of acid with metal? Why? Record the equations of reactions in molecular and ionic forms. Consider them from the position of the reduction oxidation. Next, place in two other test tubes at the same zinc granule and pour acid solutions of the same concentration to them: in 1-hydrochloric acid, in the 2nd - acetic. The nature of which reagent affects the rate of interaction of acid with metal? Why? Record the equations of reactions in molecular and ionic forms. Consider them from the position of the reduction oxidation. |
2. Concentration of reactant substances. Turn to the experiment.
Laboratory experience number 5
The dependence of the speed of the chemical reaction from the concentration of reactant substances on the example of zinc interaction with hydrochloric acid Various concentrations
It is not difficult to conclude: the higher the concentration of reactants, the higher the interaction rate between them.
Concentration gaseous substances For homogeneous production processes increase, increasing pressure. For example, this is done in the production of sulfuric acid, ammonia, ethyl alcohol.
The dependence of the chemical reaction rate from the concentration of reactant substances is taken into account not only in production, but also in other areas of human life, such as medicine. Patients with light diseases, in which the interaction rate of blood hemoglobin with air oxygen is low, facilitate breathing with the help of oxygen pillows.
3. Square of contact of the reactant substances. An experiment illustrating the dependence of the chemical response speed from this factor can be performed using the following experience.
Laboratory experience number 6
The dependence of the chemical reaction rate from the area of \u200b\u200bcontact of the reactant substances
For heterogeneous reactions: the larger the area of \u200b\u200bcontact of the reactant substances, the higher the reaction rate.
In this you could make sure your personal experience. To ignite the fire, you put fine chips under firewood, and under them - a crumpled paper from which the entire fire closed. On the contrary, the fire extinguishing water is to reduce the area of \u200b\u200bcontact of burning items with air.
In production, this factor is taken into account specifically, use the so-called boiling layer. The solid substance to increase the reaction rate is crushed almost to the state of dust, and then the second substance is passed through it from below, usually gaseous. The passage of it through a small rude solid creates the boiling effect (hence the name of the method). The boiling layer is used, for example, in the production of sulfuric acid and petroleum products.
Laboratory experience number 7
Simulation of the "boiling layer"
4. Temperature. Turn to the experiment.
Laboratory experience number 8
The dependence of the rate of chemical reaction on the temperature of the reactant substances on the example of the interaction of copper oxide (II) with a solution of sulfuric acid of various temperatures
It is not difficult to conclude: the higher the temperature, the greater the reaction rate.
The first laureate of the Nobel Prize Dutch Chemist Ya. X. Want-Hoff formulated the rule:
In production, it is used, as a rule, high-temperature chemical processes: when smelting cast iron and steel, cooking glass and soap, paper production and petroleum products, etc. (Fig. 12).
Fig. 12.
High-temperature chemical processes: 1 - Cast iron smelting; 2 - Cooking glass; 3 - Production of petroleum products
The fifth factor on which the chemical reaction rate depends is catalysts. You will get acquainted with him in the next paragraph.
New words and concepts
- Chemical reactions and their classification.
- Signs of classification of chemical reactions.
- The speed of the chemical reaction and the factors from which it depends.
Tasks for independent work
- What is a chemical reaction? What is the essence of chemical processes?
- Give the full classification characteristic of the following chemical processes:
- a) combustion of phosphorus;
- b) the interaction of sulfuric acid solution with aluminum;
- c) neutralization reactions;
- d) the formation of nitrogen oxide (IV) from nitrogen oxide (II) and oxygen.
- Based personal experience Give examples of chemical reactions flowing at different speeds.
- What is the chemical reaction rate? What factors do it depends on?
- Give examples of the influence of various factors on biochemical and manufacturing chemical processes.
- Based on personal experience, bring examples of the influence of various factors for chemical reactions occurring in everyday life.
- Why are food stored in the refrigerator?
- The chemical reaction began to be carried out at a temperature of 100 ° C, then raised to 150 ° C. The temperature coefficient of this reaction is 2. How many times will the speed of the chemical reaction increase?
Chemical and technological process and its content
The chemical-technological process is a combination of operations to obtain a target product from the feedstock. All these operations are part of the three main stages characteristic practically for each chemical and technological process.
In the first stage, the operations are carried out necessary to prepare the initial reagents to carry out a chemical reaction. Reagents are translated, in particular, in the most reactive state. For example, it is known that the speed of chemical reactions is highly dependent on the temperature, so often the reagents are heated to the reaction. Gaseous raw materials to improve the efficiency of the process and reduce the size of the equipment are compressed up to a certain pressure. To eliminate side effects and obtain a high quality product, the feedstock is purified from extraneous impurities, using methods based on the difference in physical properties (solubility in various solvents, density, condensation temperature and crystallization, etc.). When cleaning raw materials and reaction mixtures, heat and mass transfer phenomena, hydromechanical processes are widely used. Can be used and chemical methods Cleaning based on chemical reactions, as a result of which unnecessary impurities turn into easily separable substances.
Appropriately prepared reagents at the next stage are subject to chemical interaction, which may consist of several stages. In the intervals between these stages, it is sometimes necessary to use heat-pasted and other physical processes. For example, in the production of sulfuric acid, sulfur dioxide is partially oxidized to trioxide, then the reaction mixture is cooled, removed from it by absorption of sulfur trioxide and again direct it to oxidation.
As a result of chemical reactions, a mixture of products (target, side, passing) and non-reacted reagents are obtained. The final operations of the last stage are associated with the separation of this mixture, for which hydromechanical, heat and mass exchange processes are used, for example: filtration, centrifugation, rectification, absorption, extraction, etc. The reaction products are sent to a warehouse of finished products or further recycling; Non-reacted raw materials are again used in the process, organizing his recycle.
At all stages, and especially on the final, the recovery of secondary material and energy resources is also carried out. The flows of gaseous and liquid substances falling into the environment are purified and neutralized from hazardous impurities. Solid waste either send further processing or placed for storage in safe for ambient Conditions.
Thus, the chemical-technological process as a whole is a complex system consisting of isolated interconnected processes (elements) and interacting with the environment.
The elements of the chemical-technological system are the above processes of heat and mass transfer, hydromechanical, chemical, etc. They are considered as a single process of chemical technology.
An important subsystem complex chemical and technological process is a chemical process.
The chemical process is one or more chemical reactions, accompanied by heat transfer phenomena, mass and pulse affecting both each other and on the flow of a chemical reaction.
Analysis of single processes, their mutual influence allows you to develop a technological mode.
The technological regime is called a combination of technological parameters (temperature, pressure, concentrations of reagents, etc.), which determine the conditions for the operation of the device or system of devices (technological scheme).
The optimal conditions for maintaining the process are a combination of basic parameters (temperature, pressure, composition of the original reaction mixture, etc.), which allows to obtain the largest yield of the product at high speed or to ensure the smallest cost, subject to the conditions of rational use of raw materials and energy and minimizing the possible damage to the surrounding Medium.
Single processes proceed in various devices - chemical reactors, absorption and distillation columns, heat exchangers, etc. Separate devices are connected to the process technological scheme.
Technological scheme - a rationally constructed system of single devices connected various species Relations (direct, reverse, consecutive parallel), which allows to obtain a given product of a given quality from natural raw materials or semi-finished products.
Technological schemes are open and closed, they may contain bypass (bypass) streams and recycles, which make it possible to increase the efficiency of the functioning of the chemical-technological system as a whole.
The development and construction of a rational technological scheme is an important task of chemical technology.
Classification of chemical reactions underlying industrial chemical-technological processes
In modern chemistry, a large number of different chemical reactions are known. Many of them are carried out in industrial chemical reactors and, therefore, become an object of studying chemical technology.
To facilitate the study of similar phenomena, in science, it is customary to classify them on general grounds. Depending on what features are taken as a basis, there are several types of classification of chemical reactions.
An important type of classification is the classification by mechanism for reaction.There are simple (single-sample) and complex (multistage) reactions, in particular parallel, serial and sequential-parallel.
Simples are called reactions, for the implementation of which only one energy barrier is overcomed (one stage) is required.
Complex reactions include several parallel or consecutive stages (simple reactions).
Real one-step reactions are extremely rare. However, some complex reactions passing through a number of intermediate stages are conveniently considered formally simple. This is possible in cases where intermediate reaction products in the conditions of the problem under consideration are not detected.
Classification of reactions by molecularitytakes into account how many molecules participate in the elementary act of the reaction; distinguish mono-, bi and trimolecular reactions.
The form of a kinetic equation (dependence of the reaction rate from reagent concentrations) allows you to classify in order of reaction.The procedure for reaction is called the sum of the degree indicators in the concentrations of reagents in the kinetic equation. There are reactions of the first, second, third, fractional order.
Chemical reactions are also distinguished on thermal effect.When exothermic reactions accompanied by heat release ( Q.\u003e 0), there is a decrease in the enthalpy of the reaction system ( Δh. < 0); при протекании эндотермических реакций, сопровождающихся поглощением теплоты (Q.< 0), an increase in the enthalpy of the reaction system ( Δh.> 0).
To select the design of a chemical reactor and process management methods, essential phase compositionreaction system.
Depending on how much (one or more) phases form the source reagents and reaction products, chemical reactions are divided into homofaznic and heterophase.
Homofaznos are called reactions in which the initial reagents, stable intermediates and reaction products are within the same phase.
Heterophase call reactions in which the initial reagents, stable intermediates and reaction products form more than one phase.
Depending on the zones of leakagereactions are divided into homogeneous and heterogeneous reactions.
The concepts of "homogeneous" and "heterogeneous" reactions do not coincide with the concepts of "homofhause" and "heterophase" processes. Homogeneity and heterogeneity of the reaction reflects to a certain extent its mechanism: whether the reaction in the volume of some single phase or on the surface of the phase partition. HomoPhasity and heterophasity of the process can only judge the phase composition of the participants in the reaction.
In the case of homogeneous reactions, reagents and products are located in one phase (liquid or gaseous) and the reaction proceeds in the amount of this phase. For example, the oxidation of nitrogen oxide oxygen in the production of nitric acid is a gas-phase reaction, and the esterification reactions (the production of esters from organic acids and alcohols) is liquid-phase.
When heterogeneous reactions occur, at least one of the reagents or products is in phase state, which differs from the phase state of the remaining participants, and when it is analyzed, the surface of the phase section must be taken into account. For example, the neutralization of acid alkali is a homo-phase homogeneous process. Catalytic ammonia synthesis is a homofhazic heterogeneous process. The oxidation of hydrocarbons in the liquid phase with gaseous oxygen is a heterophasic process, but the flowing chemical reaction is homogeneous. Changing the lime Cao + H 2 O (OH) 2, in which all three participants of the reaction form separate phases, and the reaction comes on the boundary of the water separation and calcium oxide, is a heterophase heterogeneous process.
Depending on whether or does not apply to change the reaction rate, special substances - catalysts are distinguished catalyticand noncatalithicreactions and, accordingly, chemical and technological processes. The overwhelming majority of chemical reactions on which industrial chemical-technological processes are based is catalytic reactions.
Chemical properties of substances are detected in a variety of chemical reactions.
Transformations of substances accompanied by a change in their composition and (or) structure are called chemical reactions. Often meets such a definition: chemical reaction The process of converting the initial substances (reagents) to the final substances (products) is called.
Chemical reactions are recorded by chemical equations and schemes containing formulas of the initial substances and reaction products. In chemical equations, in contrast to the schemes, the number of atoms of each element is equally in the left and right parts, which reflects the law of mass conservation.
In the left part of the equation, the formulas of the initial substances (reagents) are written, in the right-hand of substances obtained as a result of the flow of a chemical reaction (reaction products, finite substances). The sign of equality connecting the left and the right side indicates that total amount Atoms of substances involved in the reaction remain constant. This is achieved by aligning in front of the formulas of integer stoichiometric coefficients showing quantitative relations between reactants and reaction products.
Chemical equations may contain additional information about the peculiarities of the reaction. If the chemical reaction proceeds under the influence of external influences (temperature, pressure, radiation, etc.), this is indicated by the corresponding symbol, as a rule, over (or "under") a sign of equality.
A huge number of chemical reactions can be grouped into several types of reactions that are inherent in quite definite signs.
As classification signs The following can be selected:
1. The number and composition of the source substances and reaction products.
2. The aggregate state of reagents and reaction products.
3. The number of phases in which the response participants are located.
4. The nature of the portable particles.
5. The possibility of reaction is direct and reverse.
6. The heat effect sign shares all reactions to: exothermic Reactions flowing with expo effect - the release of energy in the form of heat (Q\u003e 0, ΔH<0):
C + O 2 \u003d CO 2 + Q
and endothermic Reactions flowing with endo-effect - energy absorption in the form of heat (q<0, ∆H >0):
N 2 + O 2 \u003d 2NO - Q.
Such reactions refer to thermochemical.
Consider in more detail each of the types of reactions.
Classification by the number and composition of reagents and finite substances
1. Connection reactions
With the reactions of the compound of several reacting substances relative to the simple composition, one substance is obtained by a more complex composition:
As a rule, these reactions are accompanied by heat release, i.e. lead to the formation of more stable and less rich energy connections.
The reaction of compounds of simple substances is always a redox character. The reactions of the compound flowing between complex substances can occur as without changing valence:
Saso 3 + CO 2 + H 2 O \u003d CA (NSO 3) 2,
so refer to the number of redox:
2fesl 2 + Sl 2 \u003d 2fesl 3.
2. Reaction decomposition
The decomposition reactions lead to the formation of several compounds from one complex substance:
A \u003d B + C + D.
Products decomposition of complex substances can be both simple and complex substances.
From the decomposition reactions occurring without changing valence conditions, the decomposition of crystallohydrates, bases, acids and salts of oxygen-containing acids should be noted:
| T O. | ||
| 4HNO 3. | = | 2H 2 O + 4NO 2 O + O 2 O. |
2AGNO 3 \u003d 2Ag + 2NO 2 + O 2,
(NH 4) 2Cr 2 O 7 \u003d CR 2 O 3 + N 2 + 4H 2 O.
Especially characterized by oxidation and reduction reactions of decomposition for nitric acid salts.
The reaction of decomposition in organic chemistry is called cracking:
From 18 h 38 \u003d s 9 h 18 + s 9 h 20,
or dehydrogenation
C 4 H 10 \u003d C 4 H 6 + 2H 2.
3. Replacement reactions
In reactions of substitution, usually a simple substance interacts with difficult, forming another simple substance and other complex:
A + Sun \u003d Av + \u200b\u200bS.
These reactions in the overwhelming majority belong to redox:
2Al + Fe 2 O 3 \u003d 2FE + AL 2 O 3,
Zn + 2NSL \u003d ZNCL 2 + H 2,
2Kvr + Sl 2 \u003d 2xl + in 2,
2xLO 3 + L 2 \u003d 2KLO 3 + SL 2.
Examples of reactions of substitution that are not accompanied by a change in valence states of atoms are extremely few. It should be noted a silica dioxide reaction with salts of oxygen-containing acids, which correspond to gaseous or volatile anhydrides:
Saso 3 + SiO 2 \u003d CaSio 3 + CO 2,
Ca 3 (PO 4) 2 + zsio 2 \u003d zsio 3 + p 2 o 5,
Sometimes these reactions are considered as a exchange reaction:
CH 4 + CL 2 \u003d CH 3 CL + HCl.
4. Exchange reactions
Exchange reactions They call the reactions between the two compounds that are exchanged with their composite parts:
AV + CD \u003d AD + SV.
If oxidative and reduction processes occur with reactions of substitution, the exchange reactions always occur without changing the valence state of atoms. This is the most common group of reactions between complex substances - oxides, bases, acids and salts:
Zno + H 2 SO 4 \u003d ZNSO 4 + H 2 O,
AGNO 3 + kVR \u003d AGVR + KNO 3,
CRCL 3 + ZNAON \u003d CR (OH) 3 + ZnaCl.
Private case of these exchange reactions - neutralization reactions:
Nsl + kon \u003d ksl + n 2 o.
Typically, these reactions are subject to the laws of chemical equilibrium and flow in the direction where at least one of the substances are removed from the sphere of reaction in the form of a gaseous, flying substance, sediment or a slightly subsorative (for solutions) of the compound:
NANCO 3 + HCL \u003d NASL + H 2 O + CO 2,
Sa (NSO 3) 2 + sa (it) 2 \u003d 2Souch 3 ↓ + 2N 2 o,
CH 3 + H 3 PO 4 \u003d CH 3 Soam + Nan 2 PO 4.
5. Transfer reactions.
With the transfer reactions, an atom or a group of atoms moves from one structural unit to the other:
Av + sun \u003d a + in 2 s,
A 2 V + 2SV 2 \u003d QA 2 + ASV 3.
For example:
2AgCl + SNCL 2 \u003d 2AG + SNCL 4,
H 2 O + 2NO 2 \u003d HNO 2 + HNO 3.
Classification of reactions by phase features
Depending on the aggregate state of reacting substances, the following reactions distinguish:
1. Gas reactions
| H 2 + Cl 2 | 2hcl. |
2. Reactions in solutions
Naone (p-p) + nsl (p - p) \u003d NaCl (P-P) + N 2 O (g)
3. Reactions between solids
| T O. | ||
| CAO (TV) + SiO 2 (TV) | = | SASIO 3 (TV) |
Classification of reactions by the number of phases.
Under the phase, they understand the combination of homogeneous parts of the system with the same physical and chemical properties and separated from each other by the surface of the section.
All variety of reactions from this point of view can be divided into two classes:
1. Homogeneous (single-phase) reaction. These include reactions occurring in the gas phase, and a number of reactions occurring in solutions.
2.Heterogeneous (multiphase) reactions. These include reactions in which reagents and reaction products are in different phases. For example:
gaze-phase reactions
CO 2 (g) + NaOH (P-P) \u003d NaHCO 3 (P-P).
phase phase reactions
CO 2 (g) + SAO (TV) \u003d SASO 3 (TV).
liquid fought-phase reactions
Na 2 SO 4 (p-p) + VasL 3 (P-P) \u003d VSO 4 (TV) ↓ + 2NAcl (P-P).
fluidium subsequent reactions
Ca (NSO 3) 2 (p-p) + H 2 SO 4 (p-p) \u003d CO 2 (R) + H 2 O (g) + SSO 4 (TV) ↓.
Classification of reactions by type of portable particles
1. Protolytic reactions.
TO protolytic reactionsbelieve chemical processes, the essence of which is to transfer the proton from some reacting substances to the other.
The basis of this classification is a protolytic theory of acids and bases, in accordance with which acid is considered to be any substance that gives the proton, and the base is a substance capable of attaching a proton, for example:
Protolytic reactions include neutralization and hydrolysis reactions.
2. Redox reactions.
These include reactions in which the reacting substances are exchanged by electrons by changing the degree of oxidation of the atoms of the elements that are part of the reacting substances. For example:
Zn + 2H + → Zn 2 + + H 2,
FES 2 + 8HNO 3 (conc.) \u003d Fe (NO 3) 3 + 5NO + 2H 2 SO 4 + 2H 2 O,
The overwhelming majority of chemical reactions refer to redox, they play an extremely important role.
3. Ligand-exchange reactions.
These include reactions, during which the electronic pair is transferred to the formation of a covalent bond on the donor-acceptor mechanism. For example:
Cu (NO 3) 2 + 4NH 3 \u003d (NO 3) 2,
Fe + 5Co \u003d
Al (OH) 3 + NaOH \u003d.
A characteristic feature of the ligand-exchange reactions is that the formation of new compounds called complex, occurs without changing the degree of oxidation.
4. Atomic molecular metabolism reactions.
This type of reaction includes many of the reactions studied in the organic chemistry flowing through a radical, electrical or nucleophilic mechanism.
Reversible and irreversible chemical reactions
Recognized such chemical processes whose products are capable of reacting with each other under the same conditions in which they are obtained by the formation of starting materials.
For reversible reactions, the equation is taken as follows:
Two oppositely directed arrows indicate that under the same conditions, both direct and reverse reaction take place simultaneously.
CH 3 Soam + C 2 H 5 It is CH 3 SOAP 2N 5 + H 2 O.
We irreversiblely called such chemical processes whose products are not able to react with each other to form the starting materials. Examples of irreversible reactions can be the decomposition of the bertolen salt when heated:
2xLo 3 → 2xl + ZO 2,
or oxidation of glucose oxygen by air:
C 6 H 12 O 6 + 6O 2 → 6SO 2 + 6N 2 O.
And classification steels
- quality;
- chemical composition;
- appointment;
- microstructure;
- strength.
Steel quality
By chemical composition
Carbon steel permanent impurities
Table 1.3.
Carbon steel
Alloying elements additivesor additives
Alloyed steel low alloy (up to 2.5 wt.%) alloyed (from 2.5 to 10 wt.%) and high-alloyed "Chrome"
By appointment of steel
Structural low- (or few-) and medium carbonistic.
Instrumental High carbon.
and (with special properties - ).
and
and Increased heat resistance filtering steel.
Ordinary quality
Structural steel,
Instrumental steel
6) bearing (ball bearings) become,
7) high-speed steel(high-alloy, high-quality instrumental steel with high tungsten content).
8) automatic, i.e.elevated (or high) workability, become.
An analysis of the composition of the historically established marking groups of steels shows that the applied marking systems allow you to encode five classification features, namely: quality, chemical composition, appointment, degree of dedication, as well as method of obtaining blanks (Automatic or, in rare cases, foundry). The connection of the marking groups and classes of steels is illustrated by the lower part of the flowchart in Fig. 1.
System of marking groups, labeling rules and examples of steel stamps
| Carbonistic | Ordinary quality | |||||||
| Panel Steel | Warranty supplies | Brands | ||||||
| BUT | By chemical composition | CT0. | St1 | ST2. | Stz | St4 | St5 | St6 |
| B. | by mechanical properties | BST0. | BST1 | BST2. | BSTZ. | BST4. | BST5 | BST6. |
| IN | on mechanical properties and chemical composition | East | Emb1 | EST2. | Jet | Emb.4 | Egg5 | Emb6 |
| Conditions of carbon, wt. % | 0,23 | 0,06-0,12 | 0,09-0,15 | 0,14-0,22 | 0,18-0,27 | 0,28-0,37 | 0,38-0,49 | |
| Quality high quality | Structural | Examples of Marks | ||||||
| Brand: two-digit number of hundredths of carbon percentage + indication of degree of dedication | 05 08kp 10 15 18kp 20a 25ps ZOA 35 40 45 50 55 ... 80 85 Notes: 1) The absence of a degree of dedication means "SP"; 2) "A" at the end of the brand shows that steel - high quality | |||||||
| Instrumental | Brands | |||||||
| Brand: symbol "y" + number Tenths of carbon percentage | U7 u7a u8 u10 y9 y10 u12 y12a | |||||||
| Alloyed | High quality high-quality high-quality | Structural | Examples of Marks | |||||
| Brand: two-digit number of hundredths of carbon percentage + symbol of the alloying element + integer | 09g2 10xst 18g2AFPS 20x 40g 45kn 65С2VA 110G13L Notes: 1) Digit "1" as a concentration pointer ≤ 1 wt.% The doping element is not installed; 2) brand 110g13l - one of the few, in which the number of hundredths of carbon percentage - three-digit | |||||||
| Instrumental | Examples of Marks | |||||||
| Brand: The number of tenths of carbon percentage + symbol of doping element+ integer | ZKH2N2MF 4xV2C 5HNM 7x3 9khvg x HP4 9x4mzf2Agst-w Notes: 1) The number "10" as a "ten tenths" index of wt.% Carbon is not put; 2) "-sh" at the end of the brand shows that steel is a special-quality, obtained, for example, by the method electroslakovoyinterpay (but not only) |
Carbon structural steel quality steel
Specific steel of this marking group are denoted by a two-letter combination "ST" which is key (system-forming) in the above marking group. The stamps of this group are immediately recognized on this symbol.
Behind the "Art" symbol without a space should be the number indicating numbermarks - OT «0» before "6".
The increase in the brand number corresponds to the growth of carbon content in steel, but does not indicate its specific value. The permissible limits of the carbon concentration in the steels of each brand are shown in Table. 1.5. Carbon content B. steels of carbonic ordinary quality does not exceed 0.5 wt.% Such steel are deepete-shaped in the structural criterion, and, it means structural on purpose.
After the figure follows one of three letters: "KP", "PS", "SP", - showing the degree of steel deoxidices.
In front of the "ST" symbol, capital letters "A", "B" or "B" or may not be any characters. In this way, information about the accessories of steel to one of the so-called "Supplies Groups": a, bor IN- Depending on which of the normalized indicators began to be guaranteed by the supplier.
Steel group BUTcomes with a guarantee of chemical composition, or given by GOST permissible values \u200b\u200bof carbon concentration and impurities. The letter "A" often in the brand is not put and its absence defaultmeans a guarantee of chemical composition. The steel consumer, without having information about the mechanical properties, can form them by appropriate heat treatment, the choice of modes of which requires knowledge of chemical composition.
Steel group B. Comes with a guarantee of the required mechanical properties. The consumer of steel can determine its optimal use in structures according to the known characteristics of mechanical properties without prior heat treatment.
Steel group INcomes with a guarantee of both chemical composition and mechanical properties. Used by the consumer, mainly to create welded structures. Knowledge of mechanical properties allows you to predict the behavior of a loaded design in zones far from the welds, and the knowledge of the chemical service makes it possible to predict and, if necessary, correct the heat treatment mechanical properties of the welds actually.
Examples of records of marks carbon steel of ordinary quality Look as follows: Embassy, BST6SP, St1kp .
Ball bearing steel
Steel for bearings have their own labeling, for their intended purpose make up a special group structural Steel, although in composition and properties they are close to instrumental stools. The term "ball bearings" defines their narrow destination area - rolling bearings (not only ball, but also roller and needle). For its labeling, an abbreviation "Shx" was proposed - ball bearing chromium- followed by the number tenths of interest middle concentration chromium. From previously well-known grades, SHX6, SHS9 and SHH15 was used in the use of the CHH15. The difference between ball bearings from a similar instrumental - in more stringent requirements for the number of non-metallic inclusions and uniformity of the distribution of carbides in the microstructure.
The improvement of steel SHH15 by introducing additional alloying additives (silicon and manganese) into it) peculiarly affected the labeling - distribution to specific The system of later rules for the designation of alloying elements in the composition of alloyed steels: SHCH15SG, SHH20SG.
Filter Steel
Film steels are specifically marked with the initial letter of the Russian alphabet "P" corresponding to the first sound in English Word rapid - fast, fast. Next follows an integer number of tungsten. As already mentioned, the most common brand of high-speed steel was P18.
In connection with the deficiency and high-cost tungsten, there was a transition to tolframolibdane steel P6M5 without nitrogen and P6AM5 with nitrogen. Similar to the bearing stools, a merger occurred (a kind of "hybridization") of two marking systems. Development and development of new high-speed steels with cobalt and vanadium enriched the arsenal of "hybrid" brands: P6AM5F3, R6M4K8, 11Р3AM3F2 - and also led to the appearance of generally blurred high-speed steels, which are marked and in a specific system (P0M5F1, P0M2F3), and fully in a new one - 9x6m3f3Agst-sh, 9x4m3f2Agst-sh.
Classification of castunov
Castings are called iron alloys with carbon, having more than 2.14 wt.% C.
The cast iron is paid to redistribute to steel (redistribution), to obtain ferroalloys playing the role of alloying additives, as well as high-tech alloys to obtain castings (foundries).
Carbon can be in cast iron in the form of two high carbon phases - cementite (Fe 3 C) and graphite, and sometimes simultaneously in the form of cementite and graphite. Cast iron, in which only cementite is present, gives a light brilliant flomb and is therefore called white. The presence of graphite gives a glow of iron gray. However, not all cast iron with graphite refers to the class of so-called graycastows. Between white and gray cast iron lies class half Castows.
Half Castings are called cast iron, in the structure of which, despite graphitization, at least partially preserved cementite aslant, and, it means, there is an actively icerite - having a specific appearance eutectic structural component.
TO graycastings are attracted in which cementitis of iceburita completely broke up, and the latter did not become in the structure. Gray cast iron consists of graphite inclusions and metal base. This metal base is a pearlite (eutectoid), ferrito-pearlite (dashetteidoid) or ferritic (small carbon) steel. The specified sequence of species of the metal base of gray iron corresponds to the increasing degree of cementite decay, which is part of the perlite.
Antifriction cast iron
Examples of brands: ACS-1, AHS-2, ACS-3.
Special alloyed heat-resistant, corrosion-resistant and heat resistant cast iron:
Examples of grades of special gray cast iron
Classification and marking
metal-ceramic solid alloys
Metal-ceramic solid alloys are called alloys manufactured by powder metallurgy (metal-ceramics) and consisting of carbides of refractory metals: WC, TIC, TAC, connected by a plastic metal bundle, most often with cobalt.
Currently, solid alloys of three groups are manufactured in Russia: tungsten, Titananolphram and TitanhatalolFram- containing as a bundle cobalt.
Due to the high cost of tungsten, solid alloys, not containing tungsten carbide, are developed. As a solid phase, they only contain titan's carbide or titan carbonitride - Ti (NC). The role of a plastic bundle performs nickel-molybdenum matrix. The classification of solid alloys is represented by a block diagram.
In accordance with the five classes of metal-ceramic solid alloys, existing marking rules forms five marking groups.
Tungsten (sometimes called tolframokobalt) solid alloys
Examples: VK3, VK6, VK8, VK10.
Titananovolframovy (sometimes called Titanovolframocobeal-Tova) Solid Alloys
Examples: T30K4, T15K6, T5K10, T5K12.
Titanhataloliframov (sometimes called Titananta-tungsten-turning) solid alloys
Examples: TT7K12, TT8K6, TT10K8, TT20K9.
Sometimes at the end of the brand through a hyphen, letters or lettering are added, characterizing the dispersion of particles of carbides in powder:
Classification of solid metal-ceramic alloys
Foreign analogs of some domestic grades of alloyed steels are shown in Table 1.1.
Table 1.1.
Foreign analogues of a number of domestic stamps of alloyed steels
| Russia, GOST | Germany, DIN * | USA, ASTM * | Japan, LS * |
| 15x | 15cr3. | SCR415 | |
| 40x | 41SG4. | SSG440. | |
| 30xm | 25Sgmo4 | SSM430, SSM2. | |
| 12HG3A | 14nicr10 ** | – | SNC815 |
| 20HMNM | 21NIsgm2. | SNSM220. | |
| 08x13. | X7cr1s ** | 410s. | SUS410S. |
| 20x13 | X20sg13 | SUS420J1 | |
| 12x17 | X8SG17 | 430 (51430 ***) | SUS430. |
| 12x18n9 | X12 sgni8 9. | SUS302. | |
| 08x18N10T. | X10CRNITI18 9. | .321 | SUS321. |
| 10x13Shu | X7cra133 ** | 405 ** (51405) *** | SUS405 ** |
| 20x25n20c2 | X15crnisi25 20. | 30314,314 | SS18, SUH310 ** |
* DIN (Deutsche Industrienorm), ASTM (American Societi for Testing Materials), Jis (Japanese Industrial Standart).
** steel close in composition; *** SAE standard
Characteristic of classification features
And classification steels
The modern classification features of steels include the following:
- quality;
- chemical composition;
- appointment;
- metallurgical features of production;
- microstructure;
- Traditional way of hardening;
- a traditional way to obtain billets or parts;
- strength.
Briefly describe each of them.
Steel qualityit is determined primarily in the content of harmful impurities - sulfur and phosphorus - and is characterized by 4 categories (see Table 1.2).
By chemical composition Steel conditionally divided into carbon (unalloyed) steel and alloyed.
Carbon steel Do not contain specially entered alloying elements. The elements contained in carbonaceous steel, except carbon, belong to the number of so-called permanent impurities. Their concentration should be within the limits determined by the relevant state standards (GOST). Table 1.3. The averaged limit values \u200b\u200bof the concentration of some elements are given, allowing these elements to the discharge of impurities, rather than alloying elements. Specific limits of impurities in carbon stools give GOST.
Table 1.3.
The limit concentrations of certain elements that allow them to be constant impurities
Carbon steel
Alloying elementssometimes called alloying additivesor additives, Especially entered into steel to obtain the desired structure and properties.
Alloyed steel divided by the total concentration of alloying elements except carbon on low alloy (up to 2.5 wt.%) alloyed (from 2.5 to 10 wt.%) and high-alloyed (more than 10 wt.%) When the content in the last iron is at least 45 wt.%. Typically, the injected doping element gives alloyed steel corresponding name: "Chrome" - doped with chromium, "silicon" - silicon, "chromocremary" - chrome and silicon at the same time, etc.
In addition, there are also alloys based on iron, when the composition of iron material is less than 45%, but its more than any other alloying element.
By appointment of steel divided into structural and instrumental.
Structuralsteel are considered to manufacture various parts of machines, mechanisms and structures in mechanical engineering, construction and instrument making. Must have the necessary strength and viscosity, as well as, if required, a complex of special properties (corrosion resistance, paramagnetism, etc.). As a rule, structural steel are low- (or few-) and medium carbonistic.Hardness is not a decisive mechanical characteristic for them.
Instrumentalcalled steel used for processing materials with cutting or pressure, as well as for the manufacture of the measuring instrument. Must have high hardness, wear resistance, durability and a number of other specific properties, such as heat resistance. A prerequisite for obtaining high hardness is the increased carbon content, so instrumental steel, with a rare exception, are always High carbon.
Inside each group, there is a more detailed division for its intended purpose. Structural steel are divided into construction, machine-building and steel special application (with special properties - heat resistant, heat-resistant, corrosion-resistant, non-magnetic).
Tools are divided into steel for cutting tools, stamped steeland steel for measuring tools.
The general operational property of the instrumental steels is high hardness, providing the resistance to the deformation tool and abrasion of its surface. At the same time, a specific requirement is presented to the steels for the cutting tool - to maintain high hardness at elevated temperatures (up to 500 ... 600ºС), which develop in the cutting edge at high cutting speeds. The indicated ability of steel is called it heat resistance (or redstomitivity). According to the specified criterion, steel for cutting tools are forces for non-flat, semi-resistant, heat-resistantand Increased heat resistance. The last two groups are known in the technique called filtering steel.
From stamping steels, in addition to high hardness, a high viscosity is required, since the stamping tool works under shock loading conditions. In addition, a hot stamping tool, in contact with the heated metal blanks, during long work can heal. Therefore, steel for hot stamping should be still heat-resistant.
Steel for a measuring tool In addition to high wear resistance, ensuring the size accuracy over a long service life, you must guarantee the stability of the size of the tools, regardless of the temperature conditions of operation. In other words, they must have a very slight value of the thermal expansion coefficient.