Oxidized form of iron. Iron - general characteristics of the element, chemical properties of iron and its compounds. Daily iron requirement

Iron is the main structural material. Metal is used literally everywhere - from rockets and submarines to cutlery and wrought iron grill decorations. To a large extent, this is facilitated by an element in nature. However, the real reason is its strength and durability.

In this article we will characterize iron as a metal, indicate its useful physical and Chemical properties. Separately, we tell you why iron is called ferrous metal and how it differs from other metals.

Oddly enough, the question of whether iron is a metal or a non-metal still sometimes arises. Iron is an element of group 8, period 4 of D.I. Mendeleev’s table. Molecular mass 55.8, which is quite a lot.

This is a silver-gray metal, quite soft, ductile, and has magnetic properties. In fact, pure iron is found and used extremely rarely, since the metal is chemically active and undergoes a variety of reactions.

This video will tell you what iron is:

Concept and features

Iron is usually called an alloy with a small proportion of impurities - up to 0.8%, which retains almost all the properties of the metal. It is not even this option that is widely used, but steel and cast iron. They got their name - ferrous metal, iron, or, more accurately, the same cast iron and steel - thanks to the color of the ore - black.

Today, iron alloys are called ferrous metals: steel, cast iron, ferrite, as well as manganese, and sometimes chromium.

Iron is a very common element. In terms of content in the earth's crust, it ranks 4th, inferior to oxygen, and. The Earth's core contains 86% of iron, and only 14% is in the mantle. Sea water contains very little of the substance - up to 0.02 mg/l; river water contains slightly more - up to 2 mg/l.

Iron is a typical metal, and also quite active. It reacts with dilute and concentrated acids, but under the influence of very strong oxidizing agents it can form salts of ferric acid. In air, iron quickly becomes covered with an oxide film, preventing further reaction.

However, in the presence of moisture, rust appears instead of an oxide film, which, due to its loose structure, does not prevent further oxidation. This feature, corrosion in the presence of moisture, is the main disadvantage of iron alloys. It is worth noting that impurities provoke corrosion, while chemically pure metal is resistant to water.

Important parameters

Pure metal iron is quite ductile, easily forged and difficult to cast. However, small impurities of carbon significantly increase its hardness and brittleness. This quality became one of the reasons for the displacement of bronze tools by iron ones.

• If we compare iron alloys and, from those that were known in the ancient world, it is obvious that, both in terms of corrosion resistance, and, therefore, in durability. However, the massive scale led to the depletion of tin mines. And, since it is significantly less than , the metallurgists of the past were faced with the question of replacement. And iron replaced bronze. The latter was completely supplanted when steel appeared: bronze does not provide such a combination of hardness and elasticity.
• Iron forms an iron triad with cobalt. The properties of the elements are very close, closer than those of their analogues with the same structure of the outer layer. All metals have excellent mechanical properties: they can be easily processed, rolled, drawn, and can be forged and stamped. Cobalt is both less reactive and more resistant to corrosion than iron. However, the lower abundance of these elements does not allow them to be used as widely as iron.
• The main “competitor” of hardware in terms of area of ​​use is. But in reality, both materials have completely different qualities. It is not nearly as strong as iron, it is less easily drawn out, and cannot be forged. On the other hand, metal is much lighter in weight, which makes the structure much lighter.

The electrical conductivity of iron is very average, while aluminum in this indicator is second only to silver and gold. Iron is ferromagnetic, that is, it retains magnetization in the absence of magnetic field, and is drawn into the magnetic field.

Such different properties lead to completely different areas of application, so construction materials “fight” very rarely, for example, in the production of furniture, where the lightness of an aluminum profile is contrasted with the strength of a steel one.

The advantages and disadvantages of iron are discussed below.

Advantages and disadvantages

The main advantage of iron compared to other structural metals is its abundance and relative ease of smelting. But, given the amount of iron used, this is a very important factor.

Advantages

The advantages of metal include other qualities.

• Strength and hardness while maintaining elasticity - we are not talking about chemically pure iron, but about alloys. Moreover, these qualities vary quite widely depending on the steel grade, heat treatment method, production method, and so on.
• The variety of steels and ferrites allows you to create and select a material for literally any task - from a bridge frame to a cutting tool. The ability to obtain specified properties by adding very minor impurities is an unusually great advantage.
• Ease of machining allows you to obtain products of the most different types: rods, pipes, shaped products, beams, sheet iron and so on.
• The magnetic properties of iron are such that the metal is the main material in the production of magnetic drives.
• The cost of alloys depends, of course, on the composition, but is still significantly lower than most non-ferrous alloys, albeit with higher strength characteristics.
• The malleability of iron provides the material with very high decorative capabilities.

Flaws

The disadvantages of iron alloys are significant.

• First of all, this is insufficient corrosion resistance. Special types steels - stainless, have this useful quality, but are also much more expensive. Much more often, metal is protected using a coating - metal or polymer.
• Iron is capable of storing electricity, so products made from its alloys are subject to electrochemical corrosion. The housings of instruments and machines, pipelines must be protected in some way - cathodic protection, sacrificial protection, and so on.
• Metal is heavy, so iron structures significantly weigh down the construction object - a building, a railway carriage, a sea vessel.

Composition and structure

Iron exists in 4 various modifications, differing from each other in lattice parameters and structure. The presence of phases is truly crucial for smelting, since it is phase transitions and their dependence on alloying elements that ensure the very flow of metallurgical processes in this world. So, we are talking about the following phases:

• The α phase is stable up to +769 C and has a body-centered cubic lattice. The α phase is ferromagnetic, that is, it retains magnetization in the absence of a magnetic field. A temperature of 769 C is the Curie point for the metal.
• The β-phase exists from +769 C to +917 C. The structure of the modification is the same, but the lattice parameters are somewhat different. In this case, almost all physical properties are preserved with the exception of magnetic ones: iron becomes paramagnetic.
• The γ phase appears in the range from +917 to +1394 C. It has a face-centered cubic lattice.
• The δ phase exists above a temperature of +1394 C and has a body-centered cubic lattice.

There is also an ε-modification, which appears at high pressure, as well as as a result of doping with certain elements. The ε phase has a close-packed hexagonal lattice.

This video will tell you about the physical and chemical properties of iron:

Properties and characteristics

Very much depend on its purity. The difference between the properties of chemically pure iron and ordinary technical, and even more so alloy steel, is very significant. Usually, physical characteristics given for technical iron with an impurity fraction of 0.8%.

It is necessary to distinguish harmful impurities from alloying additives. The first - sulfur and phosphorus, for example, impart brittleness to the alloy without increasing hardness or mechanical resistance. Carbon in steel increases these parameters, that is, it is a useful component.

• The density of iron (g/cm3) depends to some extent on the phase. Thus, α-Fe has a density of 7.87 g/cubic meter. cm at normal temperature and 7.67 g/cc. cm at +600 C. The density of the γ-phase is lower - 7.59 g/cubic. cm, and the δ-phase is even less - 7.409 g/cc.
• The melting point of the substance is +1539 C. Iron is a moderately refractory metal.
• Boiling point – +2862 C.
• Strength, that is, resistance to various types of loads - pressure, tension, bending, is regulated for each grade of steel, cast iron and ferrite, so it is difficult to talk about these indicators in general. Thus, high-speed steel has a bending strength of 2.5–2.8 GPa. And the same parameter of ordinary technical iron is 300 MPa.
• Hardness on the Mohs scale is 4–5. Special steels and chemically pure iron achieve much higher performance.
• Specific electrical resistance is 9.7·10-8 ohm·m. Iron conducts current much worse than copper or aluminum.
• Thermal conductivity is also lower than that of these metals and depends on the phase composition. At 25 C it is 74.04 W/(m K), at 1500 C it is 31.8 [W/(m K)].
• Iron is perfectly forged, both at normal and elevated temperatures. Cast iron and steel can be cast.
• A substance cannot be called biologically inert. However, its toxicity is very low. This is connected, however, not so much with the activity of the element, but with the inability human body absorb it well: the maximum is 20% of the dose received.

TO environmental substances iron cannot be included. However, the main harm environment It is not its waste that causes it, since iron rusts quite quickly, but production waste - slags and gases released.

Production

Iron is a very common element, so it does not require large expenses. Deposits are developed using both open-pit and mine methods. In fact, all mining ores contain iron, but only those where the proportion of metal is large enough are developed. These are rich ores - red, magnetic and brown iron ore with an iron share of up to 74%, ores with an average content - marcasite, for example, and low-grade ores with an iron share of at least 26% - siderite.

The rich ore is immediately sent to the plant. Rocks with medium and low content are enriched.

There are several methods for producing iron alloys. As a rule, the smelting of any steel involves the production of cast iron. It is smelted in a blast furnace at a temperature of 1600 C. The charge - agglomerate, pellets, is loaded together with flux into the furnace and blown with hot air. In this case, the metal melts and the coke burns, which allows you to burn out unwanted impurities and separate the slag.

To produce steel, white cast iron is usually used - in it, carbon is bound into a chemical compound with iron. The most common 3 methods:

• open hearth - molten cast iron with the addition of ore and scrap is smelted at 2000 C in order to reduce the carbon content. Additional ingredients, if any, are added at the end of the melt. This way the highest quality steel is obtained.
• oxygen converter is a more productive method. In the furnace, the thickness of the cast iron is blown with air under a pressure of 26 kg/sq. see. A mixture of oxygen and air or pure oxygen can be used to improve the properties of steel;
• electric melting – more often used to produce special alloy steels. Cast iron is fired in an electric furnace at a temperature of 2200 C.

Steel can also be obtained by the direct method. To do this, pellets with a high iron content are loaded into a shaft furnace and purged with hydrogen at a temperature of 1000 C. The latter reduces iron from the oxide without intermediate stages.

Due to the specific nature of ferrous metallurgy, either ore with a certain iron content or finished products– cast iron, steel, ferrite. Their prices vary greatly. The average cost of iron ore in 2016 – rich, with an element content of more than 60% – is $50 per ton.

The cost of steel depends on many factors, which sometimes makes price rises and falls completely unpredictable. In the fall of 2016, the cost of fittings and hot- and cold-rolled steel increased sharply due to an equally sharp rise in prices for coking coal, an indispensable participant in smelting. In November, European companies offer hot-rolled steel coils at 500 Euro per tonne.

Application area

The scope of use of iron and iron alloys is enormous. It is easier to indicate where metal is not used.

• Construction - the construction of all types of frames, from the load-bearing frame of a bridge to the frame of a decorative fireplace in an apartment, cannot do without steel different varieties. Fittings, rods, I-beams, channels, angles, pipes: absolutely all shaped and sectional products are used in construction. The same applies to sheet metal: roofing is made from it, and so on.
• Mechanical engineering - in terms of strength and wear resistance, there is very little that can compare with steel, so the body parts of the vast majority of machines are made of steel. Especially in cases where the equipment must operate under conditions of high temperatures and pressure.
• Tools – with the help of alloying elements and hardening, the metal can be given hardness and strength close to diamonds. High-speed steels are the basis of any machining tools.
• In electrical engineering, the use of iron is more limited, precisely because impurities noticeably worsen its electrical properties, which are already low. But metal is indispensable in the production of magnetic parts of electrical equipment.
• Pipeline - communications of any kind and type are made from steel and cast iron: heating, water pipelines, gas pipelines, including main lines, shells for power cables, oil pipelines and so on. Only steel can withstand such enormous loads and internal pressure.
• Household use – steel is used everywhere: from fittings and cutlery to iron doors and locks. The strength of the metal and wear resistance make it irreplaceable.

Iron and its alloys combine strength, durability and wear resistance. In addition, metal is relatively cheap to produce, which makes it an indispensable material for the modern national economy.

This video will tell you about iron alloys with non-ferrous and heavy ferrous metals:

IRON, Fe (a. iron; n. Eisen; f. fer; i. hierro), - chemical element Group VIII of the periodic table of elements, atomic number 26, atomic mass 55.847. Natural consists of 4 stable isotopes: 54 Fe (5.84%), 56 Fe (91.68%), 57 Fe (2.17%) and 58 Fe (0.31%). Radioactive isotopes 52 Fe, 53 Fe, 55 Fe, 59 Fe, 60 Fe were obtained. Iron has been known since prehistoric times. For the first time, man probably became acquainted with meteorite iron, because. The ancient Egyptian name for iron, beni-pet, means heavenly iron. In Hittite texts there is a mention of iron as a metal that fell from the sky.

Iron in nature

Iron is the only rock-forming element with variable valency. The ratio of iron oxide to ferrous iron steadily increases with increasing silicic acidity of the melts. Even greater growth occurs in alkaline systems, where a mineral containing ferric iron - (Na,Fe)Si 2 O 6 - becomes rock-forming. In the metamorphic process, iron apparently has little mobility. The iron content in modern oceanic sediments is close to that in ancient clayey rocks and clayey rocks. The main genetic types of deposits and enrichment schemes can be found in the article.

Getting iron

Pure iron is obtained by reduction from oxides (pyrophoric iron), electrolysis of aqueous solutions of its salts (electrolytic iron), and decomposition of iron pentacarbonyl Fe(CO) 5 when heated to 250°C. Particularly pure iron (99.99%) is obtained using zone melting. Technically pure iron (about 0.16% of impurities of carbon, sulfur, etc.) is smelted by oxidizing the components of cast iron in open-hearth steelmaking and in oxygen converters. Welding or brick iron is obtained by oxidizing the impurities of low-carbon steel with iron or by reducing ores with solid carbon. The bulk of iron is smelted in the form of steel (up to 2% carbon) or cast iron (over 2% carbon).

Application of iron

Iron-carbon alloys are the basis for the design of materials used in all industries. Technical iron is a material for the cores of electromagnets and armatures of electric machines, battery plates. Iron powder is used in large quantities in welding. Iron oxides - mineral paints; ferromagnetic Fe 3 O 4, g-Fe are used for the production of magnetic materials. FeSO 4 .7H 2 O sulfate is used in the textile industry, in the production of Prussian blue, ink; FeSO4 is a coagulant for . Iron is also used in printing and medicine (as an antianemic agent); artificial radioactive isotopes of iron - indicators in the study of chemical, technological and biological processes.

IRON, Fe, chemical element, atomic weight 55.84, atomic number 26; is located in VIII group periodic system on the same level as cobalt and nickel, melting point - 1529°C, boiling point - 2450°C; in the solid state it has a bluish-silver color. In its free form, iron is found only in meteorites, which, however, contain impurities of Ni, P, C and other elements. In nature, iron compounds are widespread everywhere (soil, minerals, animal hemoglobin, plant chlorophyll), ch. arr. in the form of oxides, hydrates of oxides and sulfur compounds, as well as iron carbonate, of which most iron ores consist.

Chemically pure iron is obtained by heating iron oxalate, which at 440°C first produces matte ferric oxide powder, which has the ability to ignite in air (the so-called pyrophoric iron); with the subsequent reduction of this nitrous oxide, the resulting powder acquires grey colour and loses its pyrophoric properties, turning into metallic iron. When ferrous oxide is reduced at 700°C, iron is released in the form of small crystals, which are then fused in a vacuum. Another way to obtain chemically pure iron is by electrolysis of a solution of iron salts, for example FeSO 4 or FeCl 3 in a mixture with MgSO 4, CaCl 2 or NH 4 Cl (at temperatures above 100°C). However, in this case, iron occludes a significant amount of electrolytic hydrogen, as a result of which it acquires hardness. When heated to 700°C, hydrogen is released, and the iron becomes soft and can be cut with a knife, like lead (hardness on the Mohs scale is 4.5). Very pure iron can be obtained aluminothermically from pure iron oxide. (see Aluminothermy). Well-formed iron crystals are rare. Octahedral-shaped crystals sometimes form in the cavities of large pieces of cast iron. A characteristic property of iron is its softness, ductility and malleability at a temperature significantly lower than its melting point. When strong nitric acid (which does not contain lower nitrogen oxides) acts on iron, the iron becomes covered with a coating of oxides and becomes insoluble in nitric acid.

Iron compounds

Easily combining with oxygen, iron forms several oxides: FeO - ferric oxide, Fe 2 O 3 - iron oxide, FeO 3 - ferric acid anhydride and FeO 4 - superglandular acid anhydride. In addition, iron also forms a mixed oxide Fe 3 O 4 - ferrous oxide, the so-called. iron oxide. In dry air, however, iron does not oxidize; Rust is aqueous iron oxides formed with the participation of air moisture and CO 2 . Ferrous oxide FeO corresponds to the hydrate Fe(OH) 2 and a number of divalent iron salts that can, upon oxidation, transform into iron oxide salts, Fe 2 O 3, in which iron manifests itself as a trivalent element; In air, ferric oxide hydrate, which has strong reducing properties, easily oxidizes, turning into iron oxide hydrate. Ferrous hydroxide is slightly soluble in water, and this solution has a clearly alkaline reaction, indicating the basic nature of divalent iron. Iron oxide is found in nature (see Red lead), but it can be artificially found. obtained in the form of a red powder by calcining iron powder and burning sulfur pyrites to produce sulfur dioxide. Anhydrous iron oxide, Fe 2 O 3, m.b. obtained in two modifications, and the transition of one of them to the other occurs when heated and is accompanied by a significant release of heat (self-heating). When strongly calcined, Fe 2 O 3 releases oxygen and turns into magnetic oxide-oxide, Fe 3 O 4. When alkalis act on solutions of ferric iron salts, a precipitate of hydrate Fe 4 O 9 H 6 (2Fe 2 O 3 · 3H 2 O) precipitates; when boiling it with water, the hydrate Fe 2 O 3 ·H 2 O is formed, which is difficult to dissolve in acids. Iron forms compounds with various metalloids: with C, P, S, with halogens, as well as with metals, for example with Mn, Cr, W, Cu, etc.

Iron salts are divided into ferrous salts - divalent iron (ferro-salts) and oxide - ferric iron (ferri-salts).

Ferrous salts . Ferric chloride, FeCl 2, is obtained by the action of dry chlorine on iron, in the form of colorless leaves; When iron is dissolved in HCl, ferric chloride is obtained in the form of FeCl 2 ·4H 2 O hydrate and is used in the form of aqueous or alcoholic solutions in medicine. Ferrous iodide, FeJ 2, is obtained from iron and iodine under water in the form of green leaves and is used in medicine (Sirupus ferri jodati); with further action of iodine, FeJ 3 (Liquor ferri sesquijodati) is formed.

Ferrous sulfate, iron sulfate, FeSO 4 ·7H 2 O (green crystals) is formed in nature as a result of the oxidation of pyrite and sulfur pyrites; this salt is also formed as a by-product during the production of alum; when weathered or heated to 300°C, it turns into white anhydrous salt - FeSO 4; also forms hydrates with 5, 4, 3, 2 and 1 water particles; easily dissolves in cold water(hot up to 300%); the solution is acidic due to hydrolysis; oxidizes in air, especially easily in the presence of another oxidizing substance, for example, oxalate salts, which FeSO 4 involves in a conjugate oxidation reaction, discolors KMnO 4; in this case, the process proceeds according to the following equation:

2KMnO 4 + 10FeSO 4 + 8H 2 SO 4 = 2MnSO 4 + K 2 SO 4 + 5Fe 2 (SO 4) 2 + 8H 2 O.

For this purpose, however, Mohr's double salt (NH 4) 2 Fe(SO 4) 2 6H 2 O, which is more constant in air, is used. Iron sulfate is used in gas analysis to determine nitrogen oxide absorbed by a solution of FeSO 4 with the formation of dark-colored -brown color of the (FeNO)SO 4 complex, and also for producing ink (with tannic acids), as a mordant for dyeing, for binding fetid gases (H 2 S, NH 3) in latrines, etc.

Iron oxide salts are used in photography due to their ability to restore silver compounds in the latent image captured on a photographic plate.

Iron carbonate, FeCO 3 , occurs naturally as siderite or iron spar; Iron carbonate, obtained by precipitation of aqueous solutions of ferrous salts of iron with carbonates, easily loses CO 2 and is oxidized in air to Fe 2 O 3.

Ferrous bicarbonate, H 2 Fe(CO 3) 2, is soluble in water and occurs naturally in ferruginous sources, from which, when oxidized, it is released on the surface of the earth in the form of iron oxide hydrate, Fe(OH) 3, which turns into brown iron ore.

Iron phosphate, Fe 3 (PO 4) 2 8H 2 O, white precipitate; found in nature slightly colored, due to the oxidation of iron, blue, in the form of vivianite.

Iron oxide salts . Ferric chloride, FeCl 3 (Fe 2 Cl 6), is obtained by the action of excess chlorine on iron in the form of hexagonal red tablets; ferric chloride dissolves in air; crystallizes from water in the form of FeCl 3 6H 2 O (yellow crystals); solutions are acidic; during dialysis it gradually hydrolyzes almost completely with the formation of a colloidal solution of Fe(OH) 3 hydrate. FeCl 3 dissolves in alcohol and in a mixture of alcohol and ether; when heated, FeCl 3 ·6H 2 O decomposes into HCl and Fe 2 O 3; used as a mordant and as a hemostatic agent (Liquor ferri sesquichlorati).

Iron sulfate oxide, Fe 2 (SO 4) 3, in the anhydrous state it has a yellowish color, it is strongly hydrolyzed in solution; when the solution is heated, basic salts precipitate; iron alum, MFe(SO 4) 2 12H 2 O, M - monovalent alkali metal; Ammonium alum, NH 4 Fe(SO 4) 2 12H 2 O, crystallizes best.

The oxide FeO 3 is ferric acid anhydride, as well as the hydrate of this oxide H 2 FeO 4 - iron acid- in a free state, not possible. obtained due to their extreme fragility; but in alkaline solutions there may be salts of iron acid, ferrates (for example, K 2 FeO 4), formed when iron powder is heated with nitrate or KClO 3. The poorly soluble barium salt of iron acid BaFeO 4 is also known; Thus, iron acid is in some respects very similar to sulfuric and chromic acids. In 1926, the Kyiv chemist Goralevich described compounds of octavalent iron oxide - supfereric anhydride FeO 4, obtained by fusing Fe 2 O 3 with nitrate or berthollet salt in the form of potassium salt of superglandular acid K 2 FeO 5; FeO 4 is a gaseous substance that does not form superglandular acid H 2 FeO 5 with water, which, however, may. isolated in a free state by the decomposition of the salt K 2 FeO 5 with acids. Barium salt BaFeO 5 ·7H 2 O, as well as calcium and strontium salts, were obtained by Goralevich in the form of non-decomposing white crystals, releasing water only at 250-300°C and turning green.

Iron gives compounds: with nitrogen - iron nitrous(nitride) Fe 2 N when iron powder is heated in a stream of NH 3, with carbon - Fe 3 C carbide when iron is saturated with coal in an electric furnace. In addition, a number of iron compounds with carbon monoxide have been studied - iron carbonyls, for example, pentacarbonyl Fe(CO) 5 is a slightly colored liquid with about 102.9 ° C (at 749 mm, specific gravity 1.4937), then an orange solid, Fe2(CO)9, insoluble in ether and chloroform, with a specific gravity of 2.085.

Are of great importance iron cyanide compounds. In addition to simple cyanides Fe(CN) 2 and Fe(CN) 3, iron forms a number of complex compounds with cyanide salts, such as salts of ferrous sulfur acid H 4 Fe(CN) 6 and salts of ferrous sulfur acid H 3 Fe(CN) 6, for example, red blood salt, which, in turn, enter into exchange decomposition reactions with ferrous and oxide iron salts, forming blue-colored compounds - Prussian blue and Turnbull blue. When replacing one CN group in the salts of ferrous sulfide acid H 4 Fe(CN) 6 with monovalent groups (NO, NO 2, NH 3, SO 3, CO), Prusso salts are formed, for example, sodium nitroprusside (sodium nitroferrous sulfide) Na 2 2H 2 O, obtained by the action of fuming HNO 3 on K 4 Fe(CN) 6, followed by neutralization with soda, in the form of ruby-red crystals, separated by crystallization from the simultaneously formed nitrate; the corresponding nitroferric acid H2 also crystallizes in the form of dark red crystals. Sodium nitroprusside is used as a sensitive reagent for hydrogen sulfide and sulfur metals, with which it gives a blood-red color that then turns blue. When in action copper sulfate sodium nitroprusside forms a pale green precipitate, insoluble in water and alcohol, used for testing essential oils.

Analytically, iron is detected by the action of its salt, in an alkaline solution, yellow blood salt. Ferric salts form a blue precipitate of Prussian blue. Ferrous salts form a blue precipitate of Turnbull's blue when exposed to red blood salt. With ammonium thiocyanate NH 4 CNS, ferric iron salts form rhodanic iron Fe(CNS) 3, soluble in water with a blood-red color; With tannin, iron oxide salts form ink. Copper salts of ferrous sulfide acid, which find application (Uvachrome method) in color photography, are also distinguished by their intense color. Of the iron compounds used in medicine, in addition to the mentioned iron halide compounds, the following are important: metallic iron (F. hydrogenio reductum), iron citrate (F. Citricum - 20% Fe), iron malate extract (Extractum ferri pomatum), iron albuminate ( Liquor ferri albuminatum), ferratin - a protein compound with 6% iron; ferratose - a solution of ferratin, carniferrin - a compound of iron with nuclein (30% Fe); ferratogen from yeast nuclein (1% Fe), hematogen - 70% solution of hemoglobin in glycerol, hemol - hemoglobin reduced with zinc dust.

Physical properties of iron

The numerical data available in the literature characterizing the various physical properties of iron fluctuate due to the difficulty of obtaining iron in a chemically pure state. Therefore, the most reliable data are those obtained for electrolytic iron, in which the total content of impurities (C, Si, Mn, S, P) does not exceed 0.01-0.03%. The data below in most cases refers to such hardware. For it, the melting point is 1528°C ± 3°C (Ruer and Klesper, 1914), and the boiling point is ≈ 2450°C. In the solid state, iron exists in four different modifications - α, β, γ and δ, for which the following temperature limits are quite accurately established:

The transition of iron from one modification to another is detected on the cooling and heating curves by critical points, for which the following designations are adopted:

These critical points are shown in Fig. 1 schematic heating and cooling curves. The existence of modifications δ-, γ- and α-Fe is currently considered indisputable, but the independent existence of β-Fe is disputed due to the insufficiently sharp difference between its properties and the properties of α-Fe. All modifications of iron crystallize in the form of a cube, with α, β and δ having a spatial lattice of a centered cube, and γ-Fe having a cube with centered faces. The most distinct crystallographic characteristics of iron modifications are obtained in x-ray spectra, as shown in Fig. 2 (Westgreen, 1929). From the given X-ray patterns it follows that for α-, β- and δ-Fe the lines of the X-ray spectrum are the same; they correspond to a lattice of a centered cube with parameters of 2.87, 2.90 and 2.93 A, and for γ-Fe the spectrum corresponds to a lattice of a cube with centered faces and parameters of 3.63-3.68 A.

The specific gravity of iron ranges from 7.855 to 7.864 (Cross and Gill, 1927). When heated, the specific gravity of iron falls due to thermal expansion, for which the coefficients increase with temperature, as the data in Table 1 show. 1 (Driesen, 1914).

The decrease in expansion coefficients in the ranges of 20-800°C, 20-900°C, 700-800°C and 800-900°C is explained by anomalies in expansion when passing through the critical points A C2 and A C3. This transition is accompanied by compression, especially pronounced at point A C3, as shown by the compression and expansion curves in Fig. 3. The melting of iron is accompanied by its expansion by 4.4% (Gonda and Enda, 1926). The heat capacity of iron is quite significant compared to other metals and is expressed for different temperature ranges in values ​​from 0.11 to 0.20 Cal, as shown in Table. 2 (Obergoffer and Grosse, 1927) and the curve constructed on their basis (Fig. 4).

In the given data, the transformations A 2 , A 3 , A 4 and the melting of iron are detected so clearly that thermal effects are easily calculated for them: A 3 ... + 6.765 Cal, A 4 ... + 2.531 Cal, iron melting ... - 64.38 Cal (according to S. Umino, 1926, - 69.20 Cal).

Iron is characterized by approximately 6-7 times less thermal conductivity than silver, and 2 times less than aluminum; namely, the thermal conductivity of iron is equal at 0°C - 0.2070, at 100°C - 0.1567, at 200°C - 0.1357 and at 275°C - 0.1120 Cal/cm·sec·°C. Most characteristic properties iron are magnetic, expressed by a number of magnetic constants obtained during the full cycle of magnetization of iron. These constants for electrolytic iron are expressed by the following values ​​in Gauss (Gumlich, 1909 and 1918):

When passing through point A c2, the ferromagnetic properties of iron almost disappear and may. discovered only with very precise magnetic measurements. In practice, β-, γ- and δ-modifications are considered non-magnetic. The electrical conductivity for iron at 20°C is equal to R -1 m m/mm 2 (where R is the electrical resistance of iron, equal to 0.099 Ω mm 2 /m). The temperature coefficient of electrical resistance a0-100° x10 5 ranges from 560 to 660, where

Cold working (rolling, forging, drawing, stamping) has a very noticeable effect on the physical properties of iron. Thus, their % change during cold rolling is expressed by the following figures (Gerens, 1911): coercive voltage +323%, magnetic hysteresis +222%, electrical resistance + 2%, specific gravity - 1%, magnetic permeability - 65%. The latter circumstance makes clear the significant fluctuations in physical properties that are observed among different researchers: the influence of impurities is often accompanied by the influence of cold mechanical processing.

Very little is known about the mechanical properties of pure iron. Electrolytic iron alloyed in a void revealed: tensile strength 25 kg/mm ​​2, elongation - 60%, compression cross section- 85%, Brinell hardness - from 60 to 70.

The structure of iron depends on the content of impurities in it (even in small quantities) and the pre-treatment of the material. The microstructure of iron, like other pure metals, consists of more or less large grains (crystallites), here called ferrite

The size and sharpness of their outlines depend on chap. arr. on the cooling rate of iron: the lower the latter, the more developed the grains and the sharper their contours. On the surface, grains are most often colored differently due to different crystallography, their orientation, and different etching effects of reagents in different directions in the crystal. Often grains are elongated in one direction as a result of mechanical processing. If the processing took place at low temperatures, then shear lines (Neumann lines) appear on the surface of the grains, as a result of the sliding of individual parts of the crystallites along their cleavage planes. These lines are one of the signs of hardening and those changes in properties that were mentioned above.

Iron in metallurgy

The term iron in modern metallurgy assigned only to wrought iron, i.e., a low-carbon product obtained in a dough-like state at a temperature not sufficient to melt the iron, but so high that its individual particles are well welded to each other, giving after forging a homogeneous soft product that does not accept hardening. Iron (in the indicated sense of the word) is obtained: 1) directly from ore in a dough-like state by the cheese-blowing process; 2) in the same way, but at a lower temperature, insufficient for welding iron particles; 3) redistribution of cast iron by a critical process; 4) redistribution of cast iron by puddling.

1) Cheese production process at present. time is used only by uncultured peoples and in areas where American or European iron obtained from in modern ways. The process is carried out in open cheese furnaces and ovens. The raw materials for it are iron ore(usually brown iron ore) and charcoal. Coal is poured into the forge in the half of it where the blast is supplied, while ore is poured into a heap on the opposite side. Carbon monoxide formed in a thick layer of burning coal passes through the entire thickness of the ore and, at a high temperature, reduces iron. The reduction of ore occurs gradually - from the surface of individual pieces to the core. Starting with upper parts heap, it accelerates as the ore moves into an area of ​​​​higher temperature; In this case, iron oxide first transforms into magnetic oxide, then into oxide, and finally, metallic iron appears on the surface of the ore pieces. At the same time, the earthy impurities of the ore (waste rock) combine with the not yet reduced ferrous oxide and form a fusible ferrous slag, which is melted through the cracks of the metal shell, which forms a kind of shell in each piece of ore. Being heated to white-hot heat, these shells weld together, forming a spongy mass of iron at the bottom of the furnace - kritsa, permeated with slag. To separate from the latter, the kritsa taken from the forge is cut into several parts, each of which is forged, boiled, after cooling in the same forge into strips or directly into products (household items, weapons). In India, the cheese-blowing process is now carried out in cheese-blowing ovens, which differ from forges only slightly greater height- about 1.5 m. The walls of the furnaces are made of clay mass (not brick) and serve only one heat. The blast is fed into the furnace through one tuyere by bellows driven by feet or hands. A certain amount of charcoal (“idle shell”) is loaded into an empty furnace, and then alternately, in separate layers, ore and coal, with the amount of the first gradually increasing until it reaches a ratio to coal determined by experience; the weight of all the filled ore is determined by the desired weight of the kritsa, which, generally speaking, is insignificant. The restoration process is the same as in the forge; iron is also not completely reduced, and the resulting kritsa on the flank contains a lot of ferrous slag. The kritsa is removed by breaking the stove and cut into pieces weighing 2-3 kg. Each of them is heated in a forge and processed under a hammer; the result is excellent soft iron, which, among other things, serves as a material for the manufacture of Indian steel “woots” (damask steel). Its composition is as follows (in%):

The insignificant content of elements - iron impurities - or their complete absence is explained by the purity of the ore, the incompleteness of the reduction of iron and the low temperature in the furnace. Due to the small size of the forges and furnaces and the frequency of their operation, the consumption of charcoal is very high. In Finland, Sweden and the Urals, iron was smelted in the Husgavel cheese furnace, in which it was possible to regulate the process of reduction and saturation of iron with carbon; the coal consumption in it was up to 1.1 per unit of iron, the yield of which reached 90% of its content in the ore.

2) In the future, we should expect the development of the production of iron directly from ore, not by using the cheese-blowing process, but by reducing iron at a temperature insufficient for the formation of slag and even for sintering waste ore (1000 ° C). The advantages of this process are the possibility of using low-grade fuels, eliminating flux and heat consumption for melting slag.

3) The production of wrought iron by the redistribution of cast iron by the furnace process is carried out in the furnaces of Ch. arr. in Sweden (in our country - in the Urals). For processing, special cast iron is smelted, the so-called. Lancashire, giving the least waste. It contains: 0.3-0.45% Si, 0.5-0.6% Mn, 0.02 P,<0,01% S. Такой чугун в изломе кажется белым или половинчатым. Горючим в кричных горнах может служить только древесный уголь.

The process is ongoing. arr.: the forge, freed from the crucible, but with the ripe slag of the end of the process remaining on the bottom board, is filled with coal, ch. arr. pine, on which cast iron heated by combustion products is placed in an amount of 165-175 kg (for 3/8 m 2 of the cross-section of the hearth there is 100 kg of cast iron). By turning the valve in the air duct, the blast is directed through pipes located in the under-arch space of the furnace, and is heated here to a temperature of 150-200 ° C, thus accelerating. melting cast iron. The smelting pig iron is constantly supported (with the help of crowbars) on the coal above the tuyeres. During such work, the entire mass of cast iron is subjected to the oxidative action of air oxygen and carbon dioxide, passing through the combustion zone in the form of drops. Their large surface contributes to the rapid oxidation of iron and its impurities - silicon, manganese and carbon. Depending on the content of these impurities, cast iron loses them to a greater or lesser extent before it collects at the bottom of the hearth. Since low-silicon and low-manganese cast iron is processed in a Swedish forge, when passing through the tuyere horizon, it loses all its Si and Mn (the oxides of which form the main slag with ferrous oxide) and a significant part of the carbon. Melting of cast iron lasts 20-25 minutes. At the end of this process, cold blast is released into the forge. The metal that has settled to the bottom of the hearth begins to react with the ripe slags located there, which contain a large excess (compared to the amount of silica) of iron oxides - Fe 3 O 4 and FeO, which oxidize carbon with the release of carbon monoxide, which causes the entire metal to boil. When the metal thickens (from loss of carbon) and “sits like a commodity,” the latter is lifted with crowbars above the tuyeres, hot blast is released again and the “commodity” is melted.

During secondary melting, the metal is oxidized by oxygen from both the blast and the slag that is melted from it. After the first rise, metal falls to the bottom of the forge, soft enough to collect kritsa from some of its ripest parts. But before, when using silicon grades of cast iron, it was necessary to resort to a second and even third lifting of the goods, which, of course, reduced the productivity of the forge, increased fuel consumption and iron waste. The results of the work were influenced by the distance of the tuyeres from the bottom board (the depth of the hearth) and the inclination of the tuyeres: the steeper the tuyere and the shallower the depth of the hearth, the greater the effect of the oxidizing atmosphere on the metal. A more gentle slope of the tuyeres, as well as a greater depth of the hearth, reduces the direct effect of oxygen in the blast, thus giving a greater role to the action of slag on iron impurities; oxidation by them is slower, but without iron waste. Under any given conditions, the most advantageous position of the tuyeres relative to the bottom board is determined by experience; in a modern Swedish forge, the tuyere eye is installed at a distance of 220 mm from the bottom board, and the inclination of the tuyeres varies within close limits - from 11 to 12°.

The resulting kritsa at the bottom of the furnace, unlike the cheese-blowing furnace, contains very little mechanically entrained slag; As for the chemical impurities of iron, then Si, Mn and C may be. completely removed (the negligible content of Si and Mn indicated by analysis is part of the mechanical impurity - slag), and sulfur is only partially removed, being oxidized by the blast during melting. At the same time, phosphorus is also oxidized, going into the slag in the form of phosphorus-iron salt, but the latter is then reduced by carbon, and the final metal can contain even relatively more phosphorus (from iron waste) than the original cast iron. That is why, in order to obtain first-class metal for export, Sweden only uses cast iron that is pure in terms of P. The finished kritsa taken out of the forge is cut into three parts (each 50-55 kg) and compressed under a hammer, giving the appearance of a parallelepiped.

The duration of the redistribution process in the Swedish forge is from 65 to 80 minutes; per day it turns out from 2.5 to 3.5 tons of compressed pieces “for fire”, with a consumption of charcoal of only 0.32-0.40 per unit of finished material and its yield is from 89 to 93.5% of the cast iron specified for processing. Most recently, in Sweden, successful experiments were carried out in the redistribution of liquid pig iron taken from blast furnaces, and in accelerating the boiling process by stirring the metal using mechanical rakes; at the same time, waste loss decreased to 7%, and coal consumption - to 0.25.

The following data (in%) give an idea of ​​the chemical composition of Swedish and South Ural iron:

Of all the types of iron produced industrially, Swedish iron is closest to chemically pure and, instead of the latter, is used in laboratory practice and research work. It differs from raw iron in its uniformity, and from the softest open-hearth metal (cast iron) in the absence of manganese; it is characterized by the highest degree of weldability, ductility and malleability. Swedish cast iron exhibits low tensile strength - only about 30 kg/mm ​​2, with an elongation of 40% and a reduction in cross-section of 75%. Currently, the annual production of cryogenic iron in Sweden has fallen to 50,000 tons, since after the war of 1914-18. The scope of industrial applications for this iron was greatly reduced. The largest amount of it is used for the production (in England and Germany) of the highest grades of tool and special steels; in Sweden itself, it is used to make special wire (“flower wire”), horseshoe nails, which are easily forged in a cold state, chains and strip blanks for welded pipes. For the last two purposes, the properties of cast iron are especially important: reliable weldability, and for pipes, in addition, the highest resistance to rust.

4) The development of iron production as a critical process entailed the destruction of forests; after the latter in various countries were taken under the protection of a law that limited their felling to annual growth, Sweden and then Russia - forested countries abounding in high-quality ores - became the main suppliers of iron on the international market throughout the 18th century. In 1784, the Englishman Cort invented puddling - the process of redividing cast iron on the hearth of a fiery furnace, in the firebox of which coal was burned. After Cort's death, Rogers and Gall introduced significant improvements in the design of the puddling furnace, which contributed to the rapid spread of puddling throughout all industrial countries and completely changed the nature and extent of their iron production during the first half of the 19th century. This process produced the mass of metal that was needed for the construction of iron ships, railways, locomotives, steam boilers and cars.

The fuel for puddling is long-flame coal, but where it is not available, we had to resort to brown coal, and here in the Urals - to firewood. Pine firewood produces a longer flame than coal; it heats well, but the moisture content in the wood should not exceed 12%. Subsequently, a Siemens regenerative furnace was used for puddling in the Urals. Finally, in the USA and here (in the Volga and Kama basins) puddling furnaces operated on oil sprayed directly into the working space of the furnace.

To speed up processing and reduce fuel consumption, it is advisable to have cold puddling cast iron; when smelting it on coke, however, the product produces a lot of sulfur (0.2 and even 0.3%), and with a high phosphorus content in the ore, phosphorus as well. For ordinary commercial grades of iron, such cast iron with a low silicon content (less than 1%), called pig iron, was previously smelted in large quantities. Charcoal cast iron, which was processed in the Urals and central Russia, did not contain sulfur and produced a product that was also used for the manufacture of roofing iron. Currently, puddling serves to produce high-quality metal according to special specifications, and therefore not ordinary pig iron is supplied to puddling furnaces, but high-quality pig iron, for example, manganese or “hematite” (low phosphorus), or, conversely, high phosphorus for the production of nut iron. Below is the content (in %) of the main elements in some types of cast iron used for puddling:

A puddling furnace, at the end of the previous operation, usually has a normal amount of slag on the hearth to work with the next charge. When processing highly siliceous cast iron, a lot of slag remains in the furnace, and it has to be drained; on the contrary, white cast iron leaves “dry” under the furnace, and work has to begin by throwing the required amount of slag onto the under, which is taken from under the hammer (“ripe”, the richest in magnetic oxide). A charge of cast iron, heated in a cast iron pot, is thrown onto the slag (250-300 kg in ordinary furnaces and 500-600 kg in double furnaces); then a fresh portion of fuel is thrown into the firebox, the grates are cleaned, and full draft is established in the furnace. Within 25-35 minutes. cast iron melts, undergoing b. or m. a significant change in its composition. Solid cast iron is oxidized by the oxygen of the flame, and iron, manganese and silicon produce double silicate, which flows down into the furnace; melting cast iron exposes more and more layers of solid cast iron, which also oxidizes and melts. At the end of the melting period, two liquid layers are obtained on the hearth - cast iron and slag, on the contact surface of which the process of carbon oxidation by magnetic iron oxide occurs, albeit to a weak extent, as evidenced by bubbles of carbon monoxide released from the bath. Depending on the content of silicon and manganese in cast iron, an unequal amount of them remains in the molten metal: in low-silicon charcoal cast iron or white cast iron - coke smelting - silicon in most cases burns out completely during melting; sometimes a certain amount of it remains in the metal (0.3-0.25%), as well as manganese. Phosphorus also oxidizes at this time, turning into iron phosphorus salt. Due to the decrease in the weight of the metal as the above-mentioned impurities burn out, the percentage content of carbon may even increase, although some of it is undoubtedly burned by the oxygen of the flame and slag covering the first portions of the molten metal.

To speed up the burnout of the remaining amounts of silicon, manganese and carbon, they resort to puddling, i.e. mixing cast iron with slag using a stick with the end bent at a right angle. If the metal is liquid (gray cast iron, highly carbonaceous), then stirring does not achieve the goal, and the bath is first made thick by throwing cold ripe slag into it, or by reducing the draft, incomplete combustion is established in the furnace, accompanied by a highly smoky flame (simmering). After a few minutes, during which continuous stirring is carried out, abundant bubbles of burning carbon monoxide appear on the surface of the bath - a product of the oxidation of cast iron carbon by the oxygen of magnetic oxide dissolved in the main ferrous slag. As the process progresses, the oxidation of C intensifies and turns into a violent “boiling” of the entire mass of metal, which is accompanied by swelling and such a significant increase in volume that part of the slag overflows the threshold of the working holes. As C burns out, the melting point of the metal increases, and in order for boiling to continue, the temperature in the furnace is continuously increased. Boiling completed at a low temperature produces a raw product, i.e., a high-carbon, spongy mass of iron that is incapable of welding; ripe goods “sit” in a hot oven. The process of oxidation of iron impurities in a puddling furnace begins due to the oxygen of the slag, which is an alloy of iron silica (Fe 2 SiO 4) with magnetic oxide and iron oxide of variable composition. In English furnaces, the composition of the oxide mixture is expressed by the formula 5Fe 3 O 4 5 FeO; at the end of boiling, the ratio of oxides in the depleted slag is expressed by the formula Fe 3 O 4 5FeO, i.e., 80% of the total magnetic oxide of the slag takes part in the oxidation process. Oxidation reactions may. represented by the following thermochemical equations:

As can be seen from these equations, the oxidation of Si, P and Mn is accompanied by the release of heat and, therefore, heats the bath, while the oxidation of C during the reduction of Fe 3 O 4 into FeO absorbs heat and therefore requires high temperature. This explains the procedure for removing iron impurities and the fact that carbon burnout ends more quickly in a hot furnace. The reduction of Fe 3 O 4 to metal does not occur, since this requires a higher temperature than the one at which “boiling” occurs.

The shriveled “product,” in order to become a well-welded iron, still needs steaming: the product is left for several minutes in the oven and from time to time turned over with crowbars, and its lower parts are placed on top; Under the combined action of the oxygen of the flame and the slags that permeate the entire mass of iron, the carbon continues to burn out at this time. As soon as a certain amount of well-welded metal is obtained, crits begin to be rolled out of it, avoiding unnecessary oxidation. In total, as the goods ripen, they roll from 5 to 10 krits (no more than 50 kg each); The grains are kept (steamed) at the threshold in the area of ​​​​the highest temperature and fed under the hammer for compression, which achieves the release of slag and gives them the shape of a piece (section from 10x10 to 15x15 cm), convenient for rolling in rolls. Those following them move forward to the place of the issued crits, until the last one. The duration of the process for the production of high-quality metal (fiber iron) from ripe (high-carbon) charcoal cast iron in the Urals was as follows: 1) cast iron planting - 5 minutes, 2) melting - 35 minutes, 3) simmering - 25 minutes, 4) puddling (mixing) - 20 min., 5) steaming the goods - 20 min., 6) rolling and steaming crits - 40 min., 7) dispensing crits (10-11 pcs.) - 20 min.; total - 165 min. When working on white cast iron, using ordinary commercial iron, the duration of the process was reduced (in Western Europe) to 100 and even 75 minutes.

As for the results of the work, they varied in different metallurgical regions depending on the type of fuel, the quality of the cast iron and the type of iron produced. Ural furnaces operating on wood gave the yield of usable iron per 1 m 3 of wood from 0.25 to 0.3 tons; Our oil consumption per unit of iron is 0.33, coal in European furnaces is from 0.75 to 1.1. The daily productivity of our large furnaces (600 kg of cast iron) when working on dried firewood was 4-5 tons; the yield of material suitable for the production of roofing iron was 95-93% of the amount of cast iron received for processing. In Europe, the daily productivity of ordinary furnaces (charge 250-300 kg) is about 3.5 tons with a waste of 9%, and for high-quality iron - 2.5 tons with a waste of 11%.

In terms of chemical composition and physical properties, puddling iron is a much worse product than cast iron, on the one hand, and cast open-hearth iron, on the other. The ordinary types of iron previously produced in Western Europe contained a lot of sulfur and phosphorus, since they were produced from unclean coke iron, and both of these harmful impurities only partially turn into slag; the amount of slag in puddling iron is 3-6%; in high-quality metal it does not exceed 2%. The presence of slag greatly reduces the results of mechanical tests of puddling iron. Below are some data in % characterizing puddling iron - ordinary Western European and good Ural:

The valuable property for which the production of puddling iron is now supported is its excellent weldability, which is sometimes of particular importance from a safety point of view. Railway specifications societies require the manufacture of coupling devices, rods for switches and bolts from puddling iron. Due to its better resistance to the corrosive effects of water, puddling iron is also used for the production of water pipes. It is also used to make nuts (a coarse-grained phosphorous metal) and high-quality fibrous iron for rivets and chains.

The structure of wrought iron, detectable under a microscope even at low magnification, is characterized by the presence of black and light components in the photographic image; the former belong to the slag, and the latter to grains or fibers of iron obtained by drawing the metal.

Trading iron

Metallurgical plants produce two main types of iron for industrial needs: 1) sheet and 2) sectional iron.

Sheet iron is currently rolled up to 3 m wide; with a thickness of 1-3 mm we call it thin-rolled; from 3 mm and above (usually up to 40 mm) - boiler, tank, ship, depending on the purpose to which the composition and mechanical properties of the material correspond. Boiler iron is the softest; it usually contains 0.10-0.12% C, 0.4-0.5% Mn, P and S - each no more than 0.05%; its temporary tensile strength is not valid. more than 41 kg/mm ​​2 (but not less than 34 kg/mm ​​2), elongation at break - about 28%. Reservoir iron is made harder and more durable; it contains 0.12-0.15% C; 0.5-0.7% Mn and no more than 0.06% of both P and S; tensile strength 41-49 kg/mm ​​2, elongation 25-28%. The length of the sheets of boiler and reservoir iron is set by order in accordance with the dimensions of the product riveted from the sheets (avoiding unnecessary seams and trimmings), but usually it does not exceed 8 m, since for thin sheets it is limited by their rapid cooling during the rolling process, and for thick sheets - by the weight of the ingot .

Sheet iron less than 1 mm thick is called black tin; it is used for the manufacture of tinplate and as a roofing material. For the latter purpose, in the USSR they roll sheets measuring 1422x711 mm, weighing 4-5 kg, with a thickness of 0.5-0.625 mm. Roofing iron is produced by factories in packs weighing 82 kg. Abroad, black tin is classified in trade according to special caliber numbers - from 20 to 30 (the normal thickness of German tin is from 0.875 to 0.22 mm, and that of English tin is from 1.0 to 0.31 mm). Tin is made from the softest cast iron containing 0.08-0.10% C, 0.3-0.35% Mn if it is made from charcoal cast iron (ours), and 0.4-0.5% Mn, if the starting material is coke iron; tensile strength - from 31 to 34 kg/mm ​​2, elongation - 28-30%. A type of sheet iron is corrugated iron. It is divided according to the nature of the waves into iron with low and high waves; in the first, the ratio of wave width to depth ranges from 3 to 4, in the second, 1-2. Corrugated iron is made with a thickness of 0.75-2.0 mm and a sheet width of 0.72-0.81 m (with low waves) and 0.4-0.6 m (with high waves). Corrugated iron is used for roofs, walls of light structures, blinds, and with high waves, in addition, it is used for the construction of rafterless floors.

Graded iron is divided into two classes according to its cross-sectional shape: ordinary graded iron and shaped iron.

The first class includes round iron (with a diameter of less than 10 mm called wire), square, flat or strip. The latter, in turn, is divided into: strip strip itself - from 10 to 200 mm wide and more than 5 mm thick; hoop - the same width, but thickness from 5 to 1 mm, indicated by the caliber number (from 3 to 19 normal German and from 6 to 20 new English caliber); tire - from 38 to 51 mm wide and up to 22 mm thick; universal - from 200 to 1000 mm wide and at least 6 mm thick (rolled in special rolls - universal). Both tire and hoop iron are produced by factories in rolls, rolled wire - in coils; other varieties are in the form of straight (straightened) strips, usually no more than 8 m long (normally - from 4.5 to 6 m), but by special order for concrete structures, strips are cut up to 18 mm long, and sometimes more.

The main types of shaped iron: corner (equal and unequal), box (channel), T-shaped, I-beam (beams), column (square) and zeta iron; There are also some other less common types of shaped iron. According to our normal metric assortment, the dimensions of shaped iron are indicated by the profile number (No. is the number, see the width of the shelf or the highest profile height). Angular unequal and T-iron have double No.; for example, No. 16/8 means corner with shelves of 16 and 8 cm or tee with a shelf of 16 cm and a tee height of 8 cm. The heaviest profiles of shaped iron rolled by us: No. 15 - corner, No. 30 - trough, No. 40 - I-beam.

The composition of ordinary weldable grade iron: 0.12% C, 0.4% Mn, less than 0.05% P and S - each; its tensile strength is 34-40 kg/mm ​​2; but round iron for rivets is made from a softer material of the composition: less than 0.10% C, 0.25-0.35% Mn, about 0.03% P and S each. Tensile strength is 32-35 kg/mm ​​2, and elongation is 28-32%. Shaped, non-welded, but riveted iron (“construction steel”) contains: 0.15 - 0.20% C, 0.5% Mn, up to 0.06% P and S - each; its tensile strength is 40-50 kg/mm ​​2, elongation 25-20%. To produce nuts, iron (Thomas iron) is made, containing about 0.1% C, but from 0.3 to 0.5% P (the larger the nuts, the more P). Abroad, to meet the needs of special rolling mills, a semi-product is used in trade - a square billet, usually 50 x 50 mm in cross section.

Iron is an element of the side subgroup of the eighth group of the fourth period of the periodic table of chemical elements with atomic number 26. It is designated by the symbol Fe (lat. Ferrum). One of the most common metals in the earth's crust (second place after aluminum).
The simple substance iron (CAS number: 7439-89-6) is a malleable silver-white metal with high chemical reactivity: iron corrodes quickly at high temperatures or when high humidity on air. Iron burns in pure oxygen, and in a finely dispersed state it spontaneously ignites in air.
In fact, iron is usually called its alloys with a low impurity content (up to 0.8%), which retain the softness and ductility of the pure metal. But in practice, alloys of iron with carbon are more often used: steel (up to 2.14 wt.% carbon) and cast iron (more than 2.14 wt.% carbon), as well as stainless (alloy) steel with additions of alloying metals (chrome, manganese, nickel, etc.). The combination of specific properties of iron and its alloys make it “metal No. 1” in importance for humans.
In nature, iron is rarely found in its pure form; most often it is found in iron-nickel meteorites. The abundance of iron in the earth's crust is 4.65% (4th place after O, Si, Al). Iron is also believed to make up most of the earth's core.

origin of name

There are several versions of the origin of the Slavic word “iron” (Belarusian zheleza, Ukrainian zalizo, Old Slavic zhelezo, Bulgarian zhelezo, Serbo-Croatian zhejezo, Polish żelazo, Czech železo, Slovenian železo).
One of the etymologies connects Praslav. *želězo with the Greek word χαλκός, which meant iron and copper, according to another version *želězo is cognate with the words *žely “turtle” and *glazъ “rock”, with a common seme “stone”. The third version suggests an ancient borrowing from an unknown language.
Romance languages ​​(Italian ferro, French fer, Spanish hierro, Port ferro, Roman fier) ​​continue Lat. ferrum. Latin ferrum (Germanic languages ​​borrowed the name of iron (Gothic eisarn, English iron, German Eisen, Dutch ijzer, Danish jern, Swedish järn) from Celtic.
The Proto-Celtic word *isarno- (> Old Irish iarn, Old Brett hoiarn) probably goes back to Proto-I.e. *h1esh2r-no- “bloody” with the semantic development “bloody” > “red” > “iron”. According to another hypothesis, this word goes back to the ancestral i.e. *(H)ish2ro- “strong, holy, possessing supernatural power.”
The ancient Greek word σίδηρος may have been borrowed from the same source as the Slavic, Germanic and Baltic words for silver.
The name of natural iron carbonate (siderite) comes from the Latin. sidereus - starry; Indeed, the first iron that fell into the hands of people was of meteorite origin. Perhaps this coincidence is not accidental. In particular, the ancient Greek word sideros (σίδηρος) for iron and the Latin sidus, meaning "star", probably have a common origin.

Receipt

In industry, iron is obtained from iron ore, mainly from hematite (Fe 2 O 3) and magnetite (FeO Fe 2 O 3).
Exist various ways extraction of iron from ores. The most common is the domain process.
The first stage of production is the reduction of iron with carbon in a blast furnace at a temperature of 2000 °C. In a blast furnace, carbon in the form of coke, iron ore in the form of agglomerate or pellets, and flux (such as limestone) are fed from above, and are met by a stream of forced hot air from below.
In the furnace, carbon in the form of coke is oxidized to carbon monoxide. This oxide is formed during combustion in a lack of oxygen. In turn, carbon monoxide reduces iron from the ore. To make this reaction go faster, heated carbon monoxide is passed through iron(III) oxide. Flux is added to get rid of unwanted impurities (primarily silicates; such as quartz) in the mined ore. A typical flux contains limestone (calcium carbonate) and dolomite (magnesium carbonate). To remove other impurities, other fluxes are used.
The effect of flux (in this case calcium carbonate) is that when it is heated, it decomposes into its oxide. Calcium oxide combines with silicon dioxide to form slag - calcium metasilicate. Slag, unlike silicon dioxide, is melted in a furnace. Slag, lighter than iron, floats on the surface - this property allows the slag to be separated from the metal. The slag can then be used in construction and agriculture. The molten iron produced in a blast furnace contains quite a lot of carbon (cast iron). Except in cases where cast iron is used directly, it requires further processing.
Excess carbon and other impurities (sulfur, phosphorus) are removed from cast iron by oxidation in open-hearth furnaces or converters. Electric ovens They are also used for smelting alloy steels.
In addition to the blast furnace process, the process of direct iron production is common. In this case, pre-crushed ore is mixed with special clay, forming pellets. The pellets are fired and treated in a shaft furnace with hot methane conversion products, which contain hydrogen. Hydrogen easily reduces iron without contaminating the iron with impurities such as sulfur and phosphorus, which are common impurities in coal. Iron is obtained in solid form and is subsequently melted in electric furnaces.
Chemically pure iron is obtained by electrolysis of solutions of its salts.

Iron is the eighth element of the fourth period in the periodic table. Its number in the table (also called atomic) is 26, which corresponds to the number of protons in the nucleus and electrons in the electron shell. It is designated by the first two letters of its Latin equivalent - Fe (Latin Ferrum - read as “ferrum”). Iron is the second most common element in the earth's crust, the percentage is 4.65% (the most common is aluminum, Al). This metal is quite rare in its native form; more often it is mined from mixed ore with nickel.

In contact with

What is the nature of this connection? Iron as an atom consists of a metallic crystal lattice, which ensures the hardness of compounds containing this element and molecular stability. It is for this reason that this metal is a typical solid unlike, for example, mercury.

Iron as a simple substance- a silver-colored metal with properties typical for this group of elements: malleability, metallic luster and ductility. In addition, iron is highly reactive. The latter property is evidenced by the fact that iron corrodes very quickly in the presence of high temperature and corresponding humidity. In pure oxygen, this metal burns well, but if you crush it into very small particles, they will not only burn, but spontaneously ignite.

Often we do not call pure metal iron, but its alloys containing carbon, for example, steel (<2,14% C) и чугун (>2.14% C). Also important industrial value have alloys to which alloying metals are added (nickel, manganese, chromium and others), due to which the steel becomes stainless, i.e. alloyed. Thus, based on this, it becomes clear what extensive industrial applications this metal has.

Characteristics of Fe

Chemical properties of iron

Let's take a closer look at the features of this element.

Properties of a simple substance

• Oxidation in air at high humidity (corrosive process):

4Fe+3O2+6H2O = 4Fe (OH)3 - iron (III) hydroxide (hydroxide)

• Combustion of iron wire in oxygen with the formation of a mixed oxide (it contains an element with both an oxidation state of +2 and an oxidation state of +3):

3Fe+2O2 = Fe3O4 (iron scale). The reaction is possible when heated to 160 ⁰C.

• Interaction with water at high temperatures (600−700 ⁰C):

3Fe+4H2O = Fe3O4+4H2

• Reactions with non-metals:

a) Reaction with halogens (Important! With this interaction, the oxidation state of the element becomes +3)

2Fe+3Cl2 = 2FeCl3 - ferric chloride

b) Reaction with sulfur (Important! With this interaction, the element has an oxidation state of +2)

Iron (III) sulfide - Fe2S3 can be obtained through another reaction:

Fe2O3+ 3H2S=Fe2S3+3H2O

c) Pyrite formation

Fe+2S = FeS2 - pyrite. Pay attention to the oxidation state of the elements that make up this compound: Fe (+2), S (-1).

• Interaction with metal salts located in the electrochemical series of metal activity to the right of Fe:

Fe+CuCl2 = FeCl2+Cu - iron (II) chloride

• Interaction with dilute acids (for example, hydrochloric and sulfuric):

Fe+HBr = FeBr2+H2

Fe+HCl = FeCl2+ H2

Please note that these reactions produce iron with an oxidation state of +2.

• In undiluted acids, which are strong oxidizing agents, the reaction is possible only when heated; in cold acids the metal is passivated:

Fe+H2SO4 (concentrated) = Fe2 (SO4)3+3SO2+6H2O

Fe+6HNO3 = Fe (NO3)3+3NO2+3H2O

• The amphoteric properties of iron appear only when interacting with concentrated alkalis:

Fe+2KOH+2H2O = K2+H2 - potassium tetrahydroxyferrate (II) precipitates.

The process of producing cast iron in a blast furnace

• Roasting and subsequent decomposition of sulfide and carbonate ores (release of metal oxides):

FeS2 —> Fe2O3 (O2, 850 ⁰C, -SO2). This reaction is also the first step in the industrial synthesis of sulfuric acid.

FeCO3 —> Fe2O3 (O2, 550−600 ⁰C, -CO2).

• Burning coke (in excess):

C (coke)+O2 (air) —> CO2 (600−700 ⁰C)

CO2+С (coke) —> 2CO (750−1000 ⁰C)

• Reduction of ore containing oxide with carbon monoxide:

Fe2O3 —> Fe3O4 (CO, -CO2)

Fe3O4 —> FeO (CO, -CO2)

FeO —> Fe (CO, -CO2)

• Carburization of iron (up to 6.7%) and melting of cast iron (melting temperature - 1145 ⁰C)

Fe (solid) + C (coke) -> cast iron. Reaction temperature - 900−1200 ⁰C.

Cast iron always contains cementite (Fe2C) and graphite in the form of grains.

Characteristics of compounds containing Fe

Let's study the features of each connection separately.

Fe3O4

Mixed or double iron oxide, containing an element with an oxidation state of both +2 and +3. Also called Fe3O4 iron oxide. This compound withstands high temperatures. Does not react with water or water vapor. Subject to decomposition by mineral acids. Can be reduced with hydrogen or iron at high temperatures. As you can understand from the above information, it is an intermediate product in the reaction chain industrial production cast iron

Iron scale is directly used in the production of mineral-based paints, colored cement and ceramic products. Fe3O4 is what is obtained when steel is blackened and blued. A mixed oxide is obtained by burning iron in air (the reaction is given above). The ore containing oxides is magnetite.

Fe2O3

Iron (III) oxide, trivial name - hematite, a red-brown compound. Resistant to high temperatures. It is not formed in its pure form by the oxidation of iron with atmospheric oxygen. Does not react with water, forms hydrates that precipitate. Reacts poorly with dilute alkalis and acids. It can alloy with oxides of other metals, forming spinels - double oxides.

Red iron ore is used as a raw material in the industrial production of cast iron using the blast furnace method. It also accelerates the reaction, that is, it acts as a catalyst, in the ammonia industry. Used in the same areas as iron oxide. Plus, it was used as a carrier of sound and pictures on magnetic tapes.

FeOH2

Iron(II) hydroxide, a compound that has both acidic and basic properties, the latter predominating, that is, it is amphoteric. A white substance that quickly oxidizes in air and “turns brown” to iron (III) hydroxide. Subject to decomposition when exposed to temperature. It also reacts with weak solutions acids and alkalis. We will not dissolve in water. In the reaction it acts as a reducing agent. It is an intermediate product in the corrosion reaction.

Detection of Fe2+ and Fe3+ ions (“qualitative” reactions)

Recognition of Fe2+ and Fe3+ ions in aqueous solutions is carried out using complex complex compounds - K3, red blood salt, and K4, yellow blood salt, respectively. In both reactions a precipitate of saturated of blue color with the same quantitative composition, but different position of iron with valency +2 and +3. This precipitate is also often called Prussian blue or Turnbull blue.

Reaction written in ionic form

Fe2++K++3-  K+1Fe+2

Fe3++K++4-  K+1Fe+3

A good reagent for detecting Fe3+ is thiocyanate ion (NCS-)

Fe3++ NCS-  3- - these compounds have a bright red (“bloody”) color.

This reagent, for example, potassium thiocyanate (formula - KNCS), allows you to determine even negligible concentrations of iron in solutions. Thus, when examining tap water, he is able to determine whether the pipes are rusty.