Chemical properties of iron 2 3. Chemical and physical properties of iron

IRON, Fe, chemical element, atomic weight 55.84, serial number 26; located in group VIII of the periodic table in the same row with cobalt and nickel, melting point - 1529 ° С, boiling point - 2450 ° С; in the solid state it has a bluish-silvery color. Free 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, oxides hydrates and sulfur compounds, as well as iron carbonate, of which most iron ores are composed.

Chemically pure iron is obtained by heating oxalic iron, and at 440 ° C, at first, a matte powder of iron oxide is obtained, 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 a gray color and loses its pyrophoric properties, passing into metallic iron. When iron 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 consists in the electrolysis of a solution of iron salts, for example FeSO 4 or FeCl 3 mixed with MgSO 4, CaCl 2 or NH 4 Cl (at temperatures above 100 ° C). However, in this case, the iron occludes a significant amount of electrolytic hydrogen, as a result of which it becomes hard. When calcined to 700 ° C, hydrogen is released, and the iron becomes soft and is cut with a knife, like lead (hardness on the Mohs scale - 4.5). Very pure iron can be obtained by the aluminothermic method from pure iron oxide. (see Aluminothermy). Well-formed iron crystals are rare. Octahedral crystals are sometimes formed in the cavities of large pieces of cast iron. The characteristic property of iron is its softening, ductility and malleability at a temperature significantly lower than the melting point. When strong nitric acid (which does not contain lower nitrogen oxides) acts on iron, iron becomes coated with oxides and becomes insoluble in nitric acid.

Iron compounds

Easily combining with oxygen, iron forms several oxides: FeO - ferrous oxide, Fe 2 O 3 - iron oxide, FeO 3 - ferric acid anhydride and FeO 4 - suprairon acid anhydride. In addition, iron also forms an oxide of the mixed type Fe 3 O 4 - iron oxide-oxide, the so-called. iron scale. In dry air, however, iron is not oxidized; rust is an aqueous iron oxide formed with the participation of air moisture and CO 2. Ferrous oxide FeO corresponds to hydrate Fe (OH) 2 and a number of ferrous salts, which are capable of converting during oxidation into ferrous oxide salts, Fe 2 O 3, in which iron manifests itself as a trivalent element; in air, ferrous oxide hydrate, which has strong reducing properties, is easily oxidized to form ferrous oxide hydrate. Ferrous oxide hydrate is slightly soluble in water, and this solution has a clearly alkaline reaction, indicating the basic nature of ferrous iron. Iron oxide is found in nature (see. Red lead), but artificially m. obtained in the form of a red powder by calcining iron powder and by calcining pyrite to obtain 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 upon heating and is accompanied by a significant release of heat (self-heating). When strongly calcined, Fe 2 O 3 releases oxygen and transforms into magnetic oxide-oxide, Fe 3 O 4. Under the action of alkalis on solutions of ferric salts, a precipitate of Fe 4 O 9 H 6 hydrate (2Fe 2 O 3 · 3H 2 O) precipitates; when boiled with water, 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 - ferrous 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 a hydrate FeCl 2 · 4H 2 O and is used in the form of aqueous or alcoholic solutions in medicine. Iron 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 sulphate, ferrous sulfate, FeSO 4 · 7H 2 O (green crystals) is formed in nature as a result of the oxidation of pyrite and sulfur pyrite; this salt is also formed as a by-product in the production of alum; when weathering or when heated to 300 ° C, it turns into a white anhydrous salt - FeSO 4; also forms hydrates with 5, 4, 3, 2 and 1 water particles; easily dissolves in cold water (up to 300% in hot water); the solution has an acidic reaction due to hydrolysis; it oxidizes in air, especially easily in the presence of another oxidizing substance, for example, oxalic acid salts, which FeSO 4 involves in a coupled oxidation reaction, discolors KMnO 4; 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 is used, which is more constant in air. Iron sulfate is used in gas analysis to determine nitrogen oxide absorbed by a FeSO 4 solution with the formation of a dark colored -brown color of the (FeNO) SO 4 complex, as well as for the production of ink (with tannic acids), as a mordant for dyeing, for binding fetid gases (H 2 S, NH 3) in latrines, etc.

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

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

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

Iron phosphate, Fe 3 (PO 4) 2 · 8H 2 O, white precipitate; occurs in nature slightly colored, due to oxidation of iron, in 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 plates; ferric chloride diffuses in the air; crystallizes from water in the form of FeCl 3 · 6H 2 O (yellow crystals); solutions are acidic; during dialysis, it gradually hydrolyzes almost to the end with the formation of a colloidal solution of Fe (OH) 3 hydrate. FeCl 3 dissolves in alcohol and in a mixture of alcohol with ether, when heated, FeCl 3 · 6H 2 O decomposes into HCl and Fe 2 O 3; it is used as a mordant and as a hemostatic agent (Liquor ferri sesquichlorati).

Iron sulfate, Fe 2 (SO 4) 3, in the anhydrous state has a yellowish color, in solution is highly hydrolyzed; 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 of all.

The oxide FeO 3 is an anhydride of iron acid, as well as the hydrate of this oxide is H 2 FeO 4 - iron acid- in a free state not m. b. obtained due to their extreme fragility; but in alkaline solutions there may be salts of iron acid, ferrates (for example, K 2 FeO 4), which are formed when the iron powder is heated with nitrate or KClO 3. Also known poorly soluble barium salt of iron acid BaFeO 4; Thus, the iron acid is in some respects very similar to sulfuric and chromic acids. In 1926, the Kiev chemist Goralevich described compounds of the oxide of octavalent iron - suprairon anhydride FeO 4 obtained by fusion of Fe 2 O 3 with nitrate or berthollet salt in the form of potassium salt of suprairon acid K 2 FeO 5; FeO 4 is a gaseous substance that does not form suprairon acid H 2 FeO 5 with water, which, however, can be used. isolated in a free state by acid decomposition of the K 2 FeO 5 salt. The barium salt BaFeO 5 · 7Н 2 О, as well as the calcium and strontium salts were obtained by Goralevich in the form of non-decomposable white crystals that release water only at 250-300 ° C and turn green at the same time.

Iron gives compounds: with nitrogen - nitrogenous iron(nitride) Fe 2 N when iron powder is heated in a stream of NH 3, with carbon - carbide Fe 3 C 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 - a slightly colored liquid with about 102.9 ° C (at 749 mm, specific gravity 1.4937), then an orange solid Fe 2 (CO) 9, insoluble in ether and chloroform, with specific gravity 2.085.

Are of great importance iron cyanide... 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 ferrocyanide acid H 4 Fe (CN) 6, and salts of ferrocyanide acid H 3 Fe (CN) 6, for example, red blood salt, which, in turn, enter into metabolic decomposition reactions with salts of ferrous and oxide iron, forming blue-colored compounds - Prussian blue and turnbull blue. When one CN group is replaced by monovalent groups (NO, NO 2, NH 3, SO 3, CO) in the salts of ferrous synergic acid H 4 Fe (CN) 6, prusso salts are formed, for example, sodium nitroprusside (nitro ferrous synergistic sodium) 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 nitrate formed at the same time; the corresponding nitro-iron cyanide acid H 2 also crystallizes in the form of dark red crystals. Sodium nitroprusside is used as a sensitive reagent for hydrogen sulfide and sulphide metals, with which it gives a blood-red, then turning into blue, coloration. When copper sulfate acts on sodium nitroprusside, a pale green precipitate, insoluble in water and alcohol, is formed, which is used to test essential oils.

Analytically, iron is detected by the action of yellow blood salt on its salts, in an alkaline solution. Ferric salts form a blue Prussian blue precipitate. Ferrous salts form a blue precipitate of turnbull blue when exposed to red blood salt. With ammonium thiocyanate NH 4 CNS, ferric salts form rhodane iron Fe (CNS) 3 soluble in water with a blood-red coloration; iron oxide salts form ink with tannin. Copper salts of ferruginous acid, which are used (uvachromic method) in color photography, also have an intense color. Of the iron compounds used in medicine, in addition to the aforementioned iron halide compounds, are important: metallic iron (F. hydrogenio reductum), citric acid iron (F. citricum - 20% Fe), extract of malic acid iron (Extractum ferri pomatum), iron albuminate ( Liquor ferri albuminatum), ferratin is a protein compound with 6% iron; ferratose - ferratin solution, carniferrin - a compound of iron with nuclein (30% Fe); ferratogen from yeast nuclein (1% Fe), hematogen - 70% solution of hemoglobin in glycerin, hemol - hemoglobin reduced by 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 are the data 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 and refer to such a gland. 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 with schematic heating and cooling curves. The existence of modifications δ-, γ- and α-Fe is currently considered indisputable, while the independent existence of β-Fe is disputed due to the insufficiently sharp difference between its properties and the properties of α-Fe. All iron modifications crystallize in the form of a cube, with α, β, and δ having a spatial lattice of a centered cube, and γ-Fe — a cube with centered faces. The most distinct crystallographic characteristics of iron modifications were obtained on X-ray spectra, as shown in Fig. 2 (Westgreen, 1929).

From the above X-ray diffraction patterns it follows that for α-, β- and δ-Fe, the lines of the X-ray spectrum are the same; they correspond to the lattice of a centered cube with parameters 2.87, 2.90 and 2.93 Ȧ, and for γ-Fe the spectrum corresponds to the lattice of a cube with centered faces and parameters 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 decreases due to thermal expansion, for which the coefficients increase with temperature, as shown in the data in table. 1 (Drizen, 1914).

The decrease in the expansion coefficients in the intervals 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 А С2 and А С3. This transition is accompanied by contraction, which is 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 in comparison with other metals and is expressed for different temperature ranges by values ​​from 0.11 to 0.20 Cal, as the data in Table 1 show. 2 (Obergoffer and Grosse, 1927) and a curve plotted on their basis (Fig. 4).

In the given data, the transformations А 2, А 3, А 4 and the melting of iron are revealed so clearly that the thermal effects are easily calculated for them: А 3 ... + 6.765 Сal, А 4 ... + 2.531 Сal, melting of iron ... - 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 - 0.11120 Cal / cm · s · ° C. The most characteristic properties of iron are magnetic, expressed by a number of magnetic constants obtained during a complete cycle of iron magnetization. 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 m. B. found only with very precise magnetic measurements. In practice, the β-, γ- and δ-modifications are considered non-magnetic. The electrical conductivity for iron at 20 ° C is equal to R -1 mo 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, broaching, stamping) has a very noticeable effect on the physical properties of iron. So, 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 those significant fluctuations in physical properties that are observed in different researchers: the influence of impurities is often joined 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: ultimate tensile strength 25 kg / mm 2, elongation - 60%, cross-sectional compression - 85%, Brinell hardness - from 60 to 70.

The structure of iron depends on the content of impurities in it (albeit in insignificant amounts) and the preliminary processing 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 Ch. arr. on the cooling rate of iron: the smaller the latter, the more developed the grains and the sharper their contours. From the surface, the grains are most often colored differently due to unequal crystallography, their orientation and unequal etching action of reagents in different directions in the crystal. Often, grains are elongated in one direction as a result of mechanical processing. If the treatment 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 work hardening and those changes in properties that were mentioned above.

Iron in metallurgy

The term iron in modern metallurgy is assigned only to wrought iron, that is, a low-carbon product obtained in a pasty state at a temperature not sufficient to melt iron, but high enough that its individual particles weld well together, giving a homogeneous soft product after forging. not taking hardening. Iron (in the indicated sense of the word) is obtained: 1) directly from ore in a pasty state by a raw-blown 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-blowing process at the present. time is used only by uncultured peoples and in areas where American or European iron, obtained by modern methods, cannot (due to the lack of convenient communication routes) penetrate. The process is carried out in open cheese-blowing forges 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 in a heap, from the opposite side. Formed in a thick layer of burning coal, carbon monoxide passes through the entire thickness of the ore and, having a high temperature, reduces iron. The ore is reduced gradually - from the surface of individual pieces to the core. Starting at the top of the heap, it accelerates as the ore moves to a higher temperature; At the same time, iron oxide passes first into magnetic oxide, then into nitrous oxide, and, finally, metallic iron appears on the surface of the pieces of ore. At the same time, earthy ore impurities (waste rock) combine with not yet reduced ferrous oxide and form a low-melting ferruginous slag, which is melted through the cracks of the metal shell, which forms, as it were, a shell in each piece of ore. When heated to white-hot heat, these shells are welded to each other, forming a spongy mass of iron at the bottom of the hearth - a kritsa permeated with slag. To separate from the latter, the kritsa taken out of 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 carried out even now in the cheese-blowing furnaces, which differ from the furnaces only by a slightly higher height - about 1.5 m. The walls of the furnaces are made of clay mass (not brick) and serve only one melting. The blast is fed into the kiln through one tuyere by bellows driven by legs or arms. A certain amount of charcoal ("blank ear") is loaded into an empty furnace, and then alternately, in separate layers, ore and coal, and the amount of the former gradually increases until it reaches a certain experience with regard to coal; the weight of the entire filled-in ore is determined by the desired weight of the rock, which, generally speaking, is insignificant. The recovery process is the same as in the forge; iron is also not completely reduced, and the resulting crumb on the bottom contains a lot of ferruginous slag. The chicken is removed by breaking the oven and cut into pieces, weighing 2-3 kg. Each of them is heated in a forge and processed under a hammer; the result is an excellent soft iron, which serves, among other things, as a material for the manufacture of Indian steel "wutz" (bulat). Its composition is as follows (in%):

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

2) In the future, it is necessary to expect the development of iron production directly from ore not by using a raw-blown process, but by reducing iron at a temperature insufficient for the formation of slag and even for sintering of waste ore rock (1000 ° C). The advantages of this process are the possibility of using low-grade fuels, elimination of flux and heat consumption for slag melting.

3) The production of wrought iron by the redistribution of cast iron by a critical process is carried out in the blast furnaces of Ch. arr. in Sweden (here - in the Urals). For redistribution, 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 underway. arr .: the forge, freed from the crumb, 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 laid in the amount of 165-175 kg (for 3/8 m 2 of the cross-section of the hearth there is 100 kg of cast iron cage). By turning the valve in the air duct, the blast is directed through the pipes located in the under-arch space of the hearth, and is heated here to a temperature of 150-200 ° C, thus accelerating. melting cast iron. The cast iron is supported all the time (with crowbars) on the coal above the tuyeres. During such work, the entire mass of cast iron is exposed to the oxidative action of atmospheric oxygen and carbon dioxide, passing through the combustion zone in the form of droplets. 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 accumulating at the bottom of the hearth. Since low-silicon and low-manganese cast iron is converted in the Swedish forge, then, passing the tuyere horizon, it loses all of its Si and Mn (whose oxides form the main slag with iron oxide) and a significant part of carbon. Cast iron melting lasts 20-25 minutes. At the end of this process, a cold blast is allowed into the furnace. The metal that has settled to the bottom of the hearth begins to react with ripe slags that are in the same place, containing a large excess (compared to the amount of silica) of iron oxides - Fe 3 O 4 and FeO, oxidizing carbon with the release of carbon monoxide, which brings the entire metal to boil. When the metal thickens (from the loss of carbon) and "shrinks as a commodity", the latter is lifted with crowbars above the tuyeres, hot blast is started again and the "commodity" is melted.

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

The resulting crumb at the bottom of the forge contains very little mechanically entrained slag, in contrast to the blowing-out one; as for the chemical impurities of iron, then Si, Mn and C m b. completely removed (the insignificant content of Si and Mn indicated by analyzes is part of the mechanical impurity - slag), and sulfur is only partially, oxidized by blowing during melting. At the same time, phosphorus is also oxidized, leaving in the slag in the form of a phosphorus-iron salt, but the latter is then reduced with 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 in Sweden, they take into redistribution exclusively pure in terms of P cast iron. The finished grill taken out of the forge is cut into three parts (each 50-55 kg) and squeezed under a hammer, giving the appearance of a parallelepiped.

The duration of the redistribution process in the Swedish churning furnace is from 65 to 80 minutes; per day we get from 2.5 to 3.5 tons of compressed pieces "on fire", with the consumption of charcoal only 0.32-0.40 per unit of finished material and its output from 89 to 93.5% of the cast iron specified for redistribution. Most recently, successful experiments have been carried out in Sweden to redistribute liquid iron taken from blast furnaces and to accelerate the boiling process by stirring the metal with the help of a mechanical rake; at the same time, the waste fell to 7%, and the coal consumption - to 0.25.

The chemical composition of the Swedish and South Ural iron is given by the following data (in%):

Of all the types of iron obtained by industrial methods, Swedish krynitsy is the closest to chemically pure and instead of the latter it is used in laboratory practice and research work. It differs from raw iron by its homogeneity, and from the softest open-hearth metal (cast iron) by the absence of manganese; it is characterized by the highest degree of weldability, ductility and ductility. Swedish crucible iron exhibits negligible ultimate 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 blast iron in Sweden has dropped to 50,000 tons, since after the war of 1914-18. the field of industrial applications for this iron has been greatly reduced. The largest amount of it goes to the manufacture (in England, main. Arr. And in Germany) of the highest grades of tool and special steels; in Sweden itself, it is used to make special wire ("flower"), horseshoe nails, well forged in the cold state, chains and a strip for welded pipes. For the last two purposes, the properties of blast iron are especially important: reliable weldability, and for pipes, moreover, the highest resistance to rusting.

4) The development of iron production by 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 - wooded countries abundant in high-quality ores - became the main suppliers of iron on the international market throughout the 18th century. In 1784 the Englishman Court invented puddling - the process of redistribution of cast iron on the hearth of a fiery furnace, in the furnace of which coal was burned. After the death of Cort, Rogers and Goll introduced significant improvements in the design of the puddling oven, which contributed to the rapid spread of puddling in all industrial countries and completely changed the nature and size of their iron production during the first half of the 19th century. By this process, they obtained the mass of metal that was needed for the construction of iron ships, railways, locomotives, steam boilers and machines.

Long-flame coal serves as fuel for puddling, but where it is not available, we had to resort to brown coal, and in our Urals - to firewood. Pine wood gives 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 applied to puddling in the Urals. Finally, in the USA and in our country (in the Volga and Kama basins), puddling furnaces operated on oil sprayed directly into the working space of the furnace.

For quick processing and reducing fuel consumption, it is desirable to have cold puddling iron; when smelting it on coke, however, a lot of sulfur is obtained in the product (0.2 and even 0.3%), and with a high content of phosphorus in the ore - and phosphorus. For ordinary commercial grades of iron, such cast iron with a low silicon content (less than 1%), called conversion iron, was previously smelted in large quantities. Charcoal cast iron, which was converted in the Urals and in central Russia, did not contain sulfur and gave a product that was also used to make roofing iron. At present, puddling is used for the production of high-quality metal according to special specifications, and therefore, not ordinary pig iron is supplied to puddling furnaces, but high-quality, for example, manganese or "hematite" (low-phosphorous), or, conversely, highly phosphorous for the production of nut iron. Below is the content (in%) of the main elements in some grades of cast iron used for pudding:

The puddling furnace, at the end of the previous operation, usually has a normal amount of slag in the hearth for 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 the work has to be started by throwing the required amount of slag onto the underside, which is taken from under the hammer ("ripe", the richest in magnetic oxide). A cast iron charge is thrown onto the slag, heated in a cast iron (250-300 kg in ordinary and 500-600 kg in double furnaces); then a fresh portion of fuel is thrown into the furnace, the grates are cleaned, and full draft is set in the furnace. Within 25-35 minutes. cast iron melts while undergoing b. or m. a significant change in its composition. Hard cast iron is oxidized by the oxygen of the flame, and iron, manganese and silicon give double silicate, which flows down to the furnace bottom; 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, albeit to a weak degree, the process of carbon oxidation by magnetic iron oxide occurs, as evidenced by the bubbles of carbon monoxide escaping 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 - coke smelting - silicon in most cases burns out completely during melting; sometimes some of it remains in the metal (0.3-0.25%), as well as manganese. Phosphorus is also oxidized at this time, passing into phosphorus-iron salt. From a decrease in the weight of the metal during the burnout of these impurities, the% carbon content may even increase, although a certain amount of it is undoubtedly burned by the oxygen of the flame and slag covering the first portions of the molten metal.

To accelerate the burnout of the remaining amounts of silicon, manganese and carbon, they resort to puddling, that is, mixing cast iron with slag using a club with an end bent at a right angle. If the metal is liquid (gray cast iron, strongly carbonaceous), then mixing does not achieve the goal, and the bath is preliminarily made thick by throwing cold ripe slag into it, or by reducing the thrust, incomplete combustion is set in the furnace, accompanied by the production of a highly smoky flame (languishing). After a few minutes, during which continuous stirring is carried out, abundant bubbles of burning carbon monoxide appear on the surface of the bath - the product of the oxidation of cast iron carbon by the oxygen of magnetic oxide dissolved in the main ferrous slag. As the process progresses, C oxidation 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 through the threshold of the working holes. As C burns out, the melting point of the metal rises, and in order for boiling to continue, the temperature in the furnace is continuously increased. The finished boil at a low temperature yields a raw product, that is, a high-carbon, spongy mass of iron, incapable of welding; in a hot oven ripe goods "sit down". The process of oxidation of iron impurities in the puddling furnace begins due to the oxygen of the slag, which is an alloy of silica iron (Fe 2 SiO 4) with magnetic oxide and ferrous oxide of variable composition. In English furnaces, the composition of the mixture of oxides 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, that is, 80% of the entire magnetic oxide of the slag takes part in the oxidation process. Oxidation reactions m. are 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 in FeO absorbs heat and therefore requires a high temperature. This explains the order of removal of iron impurities and the fact that carbon burnout ends rather in a hot furnace. The reduction of Fe 3 O 4 to metal does not occur, since this requires a higher temperature than that at which "boiling" occurs.

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

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

In terms of chemical composition and physical properties, puddling iron is a much worse product than blast iron, on the one hand, and cast open-hearth iron, on the other. Common grades of iron previously produced in Western Europe contained a lot of sulfur and phosphorus, since they were produced from unclean coke irons, and both of these harmful impurities only partly pass into the 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 on puddled iron. Below are some data in% characterizing puddling iron - common Western European and good Ural:

A 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 prescribe the manufacture of puddling iron couplings, rods for converting arrows and bolts. Due to its better resistance to the corrosive action of water, puddling iron is also used for the production of water pipes. It is also used for making nuts (phosphorous coarse-grained metal) and high-quality fibrous iron for rivets and chains.

The structure of wrought iron, visible 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 the grains or fibers of iron obtained by drawing the metal.

Iron, commercial

Metallurgical plants produce iron of two main types for the needs of industry: 1) sheet iron and 2) high-quality iron.

Sheet metal is currently rolled up to 3 m wide; with a thickness of 1-3 mm, we call it thin-rolled; from 3 mm and more (usually up to 40 mm) - boiler, tank, ship, depending on the purpose, which corresponds to the composition and mechanical properties of the material. The softest is boiler iron; it usually contains 0.10-0.12% C, 0.4-0.5% Mn, P and S - each not more than 0.05%; its temporary resistance to rupture is not d. b. more than 41 kg / mm 2 (but also 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 not more than 0.06% of both P and S; tensile strength 41-49 kg / mm 2, elongation 25-28%. The length of the boiler and tank iron sheets is set by order according to the dimensions of the product riveted from the sheets (avoiding unnecessary seams and scraps), 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 metal less than 1 mm thick is called black sheet; it is used for the production of tinplate and as a roofing material. For the latter purpose, in the USSR, sheets are rolled with dimensions of 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 by numbers of a special caliber - from 20 to 30 (the normal thickness of German tin is from 0.875 to 0.22 mm, and English - 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 of charcoal smelting cast iron (in our country), and 0.4-0.5% Mn, if the starting material is coke iron; tear resistance - from 31 to 34 kg / mm 2, elongation - 28-30%. A variety of sheet iron is corrugated (corrugated) iron. It is divided by the nature of the waves into iron with low and high waves; in the first - the ratio of the wavelength to the 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 ceilings.

Bar-shaped iron is divided into two classes according to the cross-sectional shape: ordinary bar 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: the actual strip - with a width of 10 to 200 mm and a thickness of more than 5 mm; hoop - the same width, but with a thickness of 5 to 1 mm, indicated by the number of caliber (from the 3rd to the 19th normal German and from the 6th to the 20th 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 ramps, rolled wire - in coils; other varieties are in the form of straight (straightened) strips, usually no more than 8 m in length (normally - from 4.5 to 6 m), but by special order for concrete structures, strips are cut to 18 mm in length, and sometimes even more.

The main types of shaped iron: angular (isosceles and unequal), box (channel), tee, I-beams (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 the shaped iron are indicated by the number of the profile (number - the number see the width of the shelf or the greatest height of the profile). Angular unequal and tee iron have a double No.; for example, No. 16/8 means angular with shelves of 16 and 8 cm or T-shaped with a shelf of 16 cm and a height of 8 cm. The heaviest profiles of shaped iron we rolled: No. 15 - corner, No. 30 - trough, No. 40 - I-beam.

The composition of ordinary welded high-quality 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 of a softer material of the composition: less than 0.10% C, 0.25-0.35% Mn, about 0.03% P and S - each. Tear resistance 32-35 kg / mm 2 and elongation 28-32%. Shaped not welded, but riveted iron ("building 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 is 25-20%. For the production of nuts, iron (Tomas') 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-finished product is circulated in trade - a square billet, usually 50 x 50 mm in cross section.

Iron (II) compounds

Iron compounds with an oxidation state of iron +2 are unstable and easily oxidized to iron (III) derivatives.

Fe 2 O 3 + CO = 2FeO + CO 2.

Iron (II) hydroxide Fe (OH) 2 freshly precipitated has a grayish-green color, does not dissolve in water, decomposes at temperatures above 150 ° C, quickly darkens due to oxidation:

4Fe (OH) 2 + O 2 + 2H 2 O = 4Fe (OH) 3.

Shows mild amphoteric properties with a predominance of basic, easily reacts with non-oxidizing acids:

Fe (OH) 2 + 2HCl = FeCl 2 + 2H 2 O.

Interacts with concentrated alkali solutions on heating to form tetrahydroxoferrate (II):

Fe (OH) 2 + 2NaOH = Na 2.

Shows reducing properties, when interacting with nitric or concentrated sulfuric acid, iron (III) salts are formed:

2Fe (OH) 2 + 4H 2 SO 4 = Fe 2 (SO 4) 3 + SO 2 + 6H 2 O.

It is obtained by the interaction of iron (II) salts with an alkali solution in the absence of atmospheric oxygen:

FeSO 4 + 2NaOH = Fe (OH) 2 + Na 2 SO 4.

Iron (II) salts. Iron (II) forms salts with almost all anions. Salts usually crystallize in the form of green crystalline hydrates: Fe (NO 3) 2 6H 2 O, FeSO 4 7H 2 O, FeBr 2 6H 2 O, (NH 4) 2 Fe (SO 4) 2 6H 2 O (salt Mora), etc. Salt solutions have a pale green color and, due to hydrolysis, an acidic environment:

Fe 2+ + H 2 O = FeOH + + H +.

Show all the properties of salts.

When standing in air, they are slowly oxidized by dissolved oxygen to iron (III) salts:

4FeCl 2 + O 2 + 2H 2 O = 4FeOHCl 2.

Qualitative reaction for cation Fe 2+ - interaction with potassium hexacyanoferrate (III) (red blood salt):

FeSO 4 + K 3 = KFe ↓ + K 2 SO 4

Fe 2+ + K + + 3- = KFe ↓

As a result of the reaction, a blue precipitate is formed - iron (III) - potassium hexacyanoferrate (II).

The oxidation state +3 is typical for iron.

Iron (III) oxide Fe 2 O 3 - brown substance, exists in three polymorphic modifications.

Shows mild amphoteric properties with a predominance of the main ones. Reacts easily with acids:

Fe 2 O 3 + 6HCl = 2FeCl 3 + 3H 2 O.

It does not react with alkali solutions, but upon fusion it forms ferrites:

Fe 2 O 3 + 2NaOH = 2NaFeO 2 + H 2 O.

Shows oxidizing and reducing properties. When heated, it is reduced with hydrogen or carbon monoxide (II), exhibiting oxidizing properties:

Fe 2 O 3 + H 2 = 2FeO + H 2 O,

Fe 2 O 3 + CO = 2FeO + CO 2.

In the presence of strong oxidants in an alkaline medium, it exhibits reducing properties and is oxidized to iron (VI) derivatives:

Fe 2 O 3 + 3KNO 3 + 4KOH = 2K 2 FeO 4 + 3KNO 2 + 2H 2 O.

At temperatures above 1400 ° C, decomposes:

6Fe 2 O 3 = 4Fe 3 O 4 + O 2.

It is obtained by thermal decomposition of iron (III) hydroxide:

2Fe (OH) 3 = Fe 2 O 3 + 3H 2 O

or by oxidation of pyrite:

4FeS 2 + 11O 2 = 2Fe 2 O 3 + 8SO 2.

FeCl 3 + 3KCNS = Fe (CNS) 3 + 3KCl,

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, nevertheless, its strength and durability.

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

Strange as it may seem, but still sometimes the question arises as to whether iron is a metal or a non-metal. Iron is an element of group 8, 4 periods of D.I.Mendeleev's table. The molecular weight is 55.8, which is quite a lot.

It is a silvery-gray metal, rather soft, ductile, and magnetic. In fact, pure iron is found and used extremely rarely, since the metal is chemically active and enters into 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 finds widespread use, but steel and cast iron. Its name - ferrous metal, iron, or rather, all the same cast iron and steel, got due to the color of the ore - black.

Today, ferrous metals are called iron alloys: 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 takes 4th place, yielding to oxygen, and. The Earth's core contains 86% of iron, and only 14% is in the mantle. In seawater, the substance contains very little - up to 0.02 mg / l, in river water a little more - up to 2 mg / l.

Iron is a typical metal, and it is also quite active. It interacts with dilute and concentrated acids, but under the action of very strong oxidants it can form ferric acid salts. In air, iron quickly becomes covered with an oxide film, which prevents further reaction.

However, in the presence of moisture, instead of an oxide film, rust appears, which, due to its loose structure, does not interfere with 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, it lends itself well to forging and poorly 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 of labor with iron ones.

• If we compare iron alloys and, of those that were known in the ancient world, it is obvious that, both in corrosion resistance, and, therefore, in durability. However, the massive depletion of the tin mines. And, since it is much less than that, the question of replacement remained before the metallurgists of the past. And iron replaced bronze. The latter was completely supplanted when steels appeared: bronze does not give such a combination of hardness and elasticity.
• Iron forms with cobalt and the iron triad. The properties of the elements are very close, closer than those of their counterparts with the same structure of the outer layer. All metals have excellent mechanical properties: they can be easily processed, rolled, stretched, they can be forged and stamped. Cobalt is both less reactive and more resistant to corrosion than iron. However, the lower prevalence of these elements does not allow them to be used as widely as iron.
• The main "competitor" for the use of hardware is. But in fact, both materials have completely different qualities. far not as strong as iron, it stretches worse, does not lend itself to forging. On the other hand, the metal is much lighter in weight, which makes the structure much lighter.

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

Such different properties determine completely different areas of application, so that construction materials very rarely "fight", for example, in furniture production, where the lightness of an aluminum profile is opposed to the strength of a steel one.

The advantages and disadvantages of iron are discussed below.

Pros and cons

The main advantage of iron over other structural metals is the prevalence and relative ease of smelting. But, considering how much iron is used, this is a very important factor.

Benefits

The pluses 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 within a fairly wide range, depending on the steel grade, the method of heat treatment, the method of production, and so on.
• A variety of steels and ferrites allow you to create and select material for literally any task - from the bridge frame to the cutting tool. The ability to obtain desired properties by adding very small impurities is an unusually great advantage.
• The ease of machining allows you to get products of a wide variety of types: rods, pipes, fittings, beams, sheet metal, 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 it is still much lower than that of most non-ferrous alloys, albeit with higher strength characteristics.
• The malleability of iron provides the material with very high decorative possibilities.

disadvantages

The disadvantages of iron alloys are significant.

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

Composition and structure

Iron exists in 4 different modifications, differing from each other in lattice parameters and structure. The presence of phases is really crucial for smelting, since it is the 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, has a body-centered cubic lattice. The α-phase is ferromagnetic, that is, it retains its magnetization in the absence of a magnetic field. A temperature of 769 C is the Curie point for 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. At the same time, almost all physical properties are retained with the exception of magnetic ones: iron becomes a paramagnet.
• The γ-phase appears in the range from +917 to +1394 C. For it, the character is a face-centered cubic lattice.
• The δ-phase exists above a temperature of +1394 С, has a body-centered cubic lattice.

The ε-modification is also distinguished, which appears at high pressure, as well as as a result of alloying with some 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 dependent on its purity. The difference between the properties of chemically pure iron and ordinary technical, and even more alloyed steel, is very significant. As a rule, physical characteristics are given for technical iron with an impurity fraction of 0.8%.

It is necessary to distinguish harmful impurities from alloying additives. The former, 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) is somewhat phase dependent. So, α-Fe has a density equal to 7.87 g / cc. cm at normal temperature and 7.67 g / cu. cm at +600 C. The density of the γ-phase is lower - 7.59 g / cu. see and the δ-phase is even less - 7.409 g / cc.
• The melting point of the substance is +1539 C. Iron belongs to moderately refractory metals.
• The boiling point is +2862 C.
• Strength, that is, resistance to loads of various kinds - pressure, tension, bending, is regulated for each grade of steel, cast iron and ferrite, so it's 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.
• The hardness on the Mohs scale is 4–5. Special steels and chemically pure iron achieve much higher rates.
• The 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 - 31.8 [W / (m.K)].
• Iron is perfectly forged, both at normal and elevated temperatures. Cast iron and steel lend themselves to casting.
• A substance cannot be called biologically inert. However, its toxicity is very low. This is due, however, not so much to the activity of the element as to the inability of the human body to assimilate it well: the maximum is 20% of the dose received.

Iron cannot be classified as an environmental substance. However, the main harm to the environment is not caused by its waste, since iron rusts rather quickly, and production waste - slags, emitted gases.

Production

Iron is one of the most common elements, so it does not require large expenditures. Deposits are developed both by open-pit and mining methods. In fact, all mountain ores include iron, but only those where the proportion of the metal is large enough are mined. These are rich ores - red, magnetic and brown iron ores with an iron content of up to 74%, ores with an average content - marcasite, for example, and poor ores with an iron content of at least 26% - siderite.

The rich ore is immediately sent to the plant. Medium and low grade breeds are enriched.

There are several methods for producing iron alloys. As a rule, the smelting of any steel includes the production of pig iron. It is smelted in a blast furnace at a temperature of 1600 C. The charge - agglomerate, pellets, is loaded together with the 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 obtain steel, white cast iron is usually used - in it, carbon is bonded to a chemical compound with iron. There are 3 most common ways:

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

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

Due to the specifics of ferrous metallurgy, either ore with a certain iron content or finished products - cast iron, steel, ferrite - gets on sale. Their price is very different. 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 the ups and downs of prices completely unpredictable. In the fall of 2016, the cost of rebar, hot and cold rolled steel rose sharply due to an equally sharp rise in prices for coking coal, an indispensable participant in the smelting process. In November, European companies are offering hot rolled steel coils at 500 Euros per ton.

Application area

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

• Construction - the construction of all types of frames, from the supporting frame of the bridge, to the box of the decorative fireplace in the apartment, cannot do without steel of different grades. Fittings, rods, I-beams, channels, angles, pipes: absolutely all shaped and high-quality 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 with steel there is very little that can be compared, so that the body parts of the vast majority of machines are made of steel. Especially in cases where the equipment must operate at high temperatures and pressures.
• Tools - with the help of alloying elements and hardening, the metal can be given the hardness and strength close to diamonds. High speed steels are the backbone of all machining tools.
• In electrical engineering, the use of iron is more limited, precisely because impurities significantly impair its electrical properties, and they are already small. But metal is indispensable in the production of magnetic parts for electrical equipment.
• Pipeline - communications of any kind and type are made of steel and cast iron: heating, water pipelines, gas pipelines, including trunk pipelines, sheaths for power cables, oil pipelines, and so on. Only steel is able to withstand such enormous loads and internal pressure.
• Domestic Use - Steel is used in everything 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, the metal is relatively cheap to manufacture, which makes it an indispensable material for the modern economy.

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

• Designation - Fe (Iron);
• Period - IV;
• Group - 8 (VIII);
• Atomic mass - 55.845;
• Atomic number - 26;
• Atom radius = 126 pm;
• Covalent radius = 117 pm;
• Distribution of electrons - 1s 2 2s 2 2p 6 3s 2 3p 6 3d 6 4s 2;
• melting point = 1535 ° C;
• boiling point = 2750 ° C;
• Electronegativity (Pauling / Alpred and Rohov) = 1.83 / 1.64;
• Oxidation state: +8, +6, +4, +3, +2, +1, 0;
• Density (n. At.) = 7.874 g / cm 3;
• Molar volume = 7.1 cm 3 / mol.

Iron compounds:

Iron is the most abundant metal in the earth's crust (5.1% by mass) after aluminum.

On Earth, iron in a free state is found in small quantities in the form of nuggets, as well as in fallen meteorites.

Iron is mined industrially at iron ore deposits, from iron-containing minerals: magnetic, red, brown iron ore.

It should be said that iron is a part of many natural minerals, causing their natural color. The color of minerals depends on the concentration and ratio of iron ions Fe 2+ / Fe 3+, as well as on the atoms surrounding these ions. For example, the presence of impurities of iron ions affects the color of many precious and semiprecious stones: topaz (from pale yellow to red), sapphires (from blue to dark blue), aquamarines (from light blue to greenish blue), etc.

Iron is found in the tissues of animals and plants, for example, in the body of an adult there is about 5 g of iron. Iron is a vital element, it is part of the protein hemoglobin, participating in the transport of oxygen from the lungs to tissues and cells. With a lack of iron in the human body, anemia develops (iron deficiency anemia).

Fig. The structure of the iron atom.

The electronic configuration of the iron atom is 1s 2 2s 2 2p 6 3s 2 3p 6 3d 6 4s 2 (see Electronic structure of atoms). In the formation of chemical bonds with other elements, 2 electrons can participate in the outer 4s-level + 6 electrons of the 3d-sublevel (a total of 8 electrons), therefore, in compounds, iron can take the oxidation states +8, +6, +4, +3, +2, +1, (the most common are +3, +2). Iron has an average chemical activity.

Fig. Iron oxidation states: +2, +3.

Physical properties of iron:

• silver-white metal;
• in its pure form, it is quite soft and plastic;
• possesses good heat and electrical conductivity.

Iron exists in the form of four modifications (differ in the structure of the crystal lattice): α-iron; β-iron; γ-iron; δ-iron.

Iron chemical properties

• reacts with oxygen, depending on the temperature and oxygen concentration, various products or a mixture of iron oxidation products (FeO, Fe 2 O 3, Fe 3 O 4) can be formed:
  3Fe + 2O 2 = Fe 3 O 4;
• iron oxidation at low temperatures:
  4Fe + 3O 2 = 2Fe 2 O 3;
• reacts with water vapor:
  3Fe + 4H 2 O = Fe 3 O 4 + 4H 2;
• finely crushed iron reacts when heated with sulfur and chlorine (ferrous sulfide and chloride):
  Fe + S = FeS; 2Fe + 3Cl 2 = 2FeCl 3;
• at high temperatures reacts with silicon, carbon, phosphorus:
  3Fe + C = Fe 3 C;
• with other metals and with non-metals, iron can form alloys;
• iron displaces less active metals from their salts:
  Fe + CuCl 2 = FeCl 2 + Cu;
• with dilute acids, iron acts as a reducing agent, forming salts:
  Fe + 2HCl = FeCl 2 + H 2;
• with dilute nitric acid, iron forms various acid reduction products, depending on its concentration (N 2, N 2 O, NO 2).

Getting and using iron

Industrial iron is obtained smelting cast iron and steel.

Cast iron is an alloy of iron with admixtures of silicon, manganese, sulfur, phosphorus, carbon. The carbon content in cast iron exceeds 2% (less than 2% in steel).

Pure iron is obtained:

• in oxygen converters made of cast iron;
• reduction of iron oxides with hydrogen and bivalent carbon monoxide;
• electrolysis of the corresponding salts.

Pig iron is obtained from iron ores by reduction of iron oxides. Pig iron is smelted in blast furnaces. The blast furnace uses coke as a heat source.

A blast furnace is a very complex technical structure with a height of several tens of meters. It is lined with refractory bricks and protected by an outer steel casing. As of 2013, the largest blast furnace was built in South Korea by the POSCO steel company at the Gwangyang steel plant (the furnace volume after modernization was 6,000 cubic meters with an annual capacity of 5,700,000 tons).

Fig. Blast furnace.

The process of smelting pig iron in a blast furnace goes on continuously for several decades until the furnace reaches its end of life.

Fig. The process of smelting pig iron in a blast furnace.

• beneficiated ores (magnetic, red, brown iron ore) and coke are poured through the top, located at the very top of the blast furnace;
• the processes of iron reduction from ore under the influence of carbon monoxide (II) occur in the middle part of a blast furnace (mine) at a temperature of 450-1100 ° C (iron oxides are reduced to metal):
  • 450-500 ° C - 3Fe 2 O 3 + CO = 2Fe 3 O 4 + CO 2;
  • 600 ° C - Fe 3 O 4 + CO = 3FeO + CO 2;
  • 800 ° C - FeO + CO = Fe + CO 2;
  • part of the bivalent iron oxide is reduced by coke: FeO + C = Fe + CO.
• in parallel, the process of reduction of silicon and manganese oxides is going on (they are included in iron ore in the form of impurities), silicon and manganese are part of the cast iron:
  • SiO 2 + 2C = Si + 2CO;
  • Mn 2 O 3 + 3C = 2Mn + 3CO.
• during thermal decomposition of limestone (introduced into a blast furnace), calcium oxide is formed, which reacts with silicon and aluminum oxides contained in the ore:
  • CaCO 3 = CaO + CO 2;
  • CaO + SiO 2 = CaSiO 3;
  • CaO + Al 2 O 3 = Ca (AlO 2) 2.
• at 1100 ° C, the iron reduction process stops;
• below the shaft is the steaming, the widest part of the blast furnace, below which follows a shoulder, in which the coke burns out and liquid products of smelting are formed - pig iron and slag, which accumulate at the very bottom of the furnace - the hearth;
• in the upper part of the hearth at a temperature of 1500 ° C in a stream of blown air, intensive combustion of coke occurs: C + O 2 = CO 2;
• passing through the red-hot coke, carbon monoxide (IV) is converted into carbon monoxide (II), which is a reducing agent for iron (see above): CO 2 + C = 2CO;
• slags formed by calcium silicates and aluminosilicates are located above the cast iron, protecting it from the action of oxygen;
• through special holes located at different levels of the hearth, cast iron and slag are discharged outside;
• Most of the pig iron goes for further processing - steel smelting.

Steel is smelted from cast iron and scrap metal by the converter method (open-hearth is already obsolete, although it is still used) or by electric melting (in electric furnaces, induction furnaces). The essence of the process (redistribution of cast iron) is to reduce the concentration of carbon and other impurities by oxidation with oxygen.

As mentioned above, the carbon concentration in steel does not exceed 2%. Due to this, steel, in contrast to cast iron, is quite easily forged and rolled, which makes it possible to manufacture various products from it with high hardness and strength.

The hardness of steel depends on the carbon content (the more carbon, the harder the steel) in a particular steel grade and heat treatment conditions. When tempered (slow cooling), the steel becomes soft; when quenched (quenched), the steel is very hard.

To give the steel the desired specific properties, ligating additives are added to it: chromium, nickel, silicon, molybdenum, vanadium, manganese, etc.

Cast iron and steel are the most important structural materials in the overwhelming majority of sectors of the national economy.

The biological role of iron:

• the body of an adult contains about 5 g of iron;
• iron plays an important role in the work of the hematopoietic organs;
• iron is a part of many complex protein complexes (hemoglobin, myoglobin, various enzymes).

68. Iron compounds

Iron (II) oxide FeO- a black crystalline substance, insoluble in water and alkalis. FeO corresponds to the base Fe (OH) 2.

Receiving. Iron oxide (II) can be obtained by incomplete reduction of magnetic iron ore with carbon monoxide (II):

Chemical properties. It is a basic oxide. Reacting with acids, forms salts:

Iron (II) hydroxide Fe (OH) 2- white crystalline substance.

Receiving. Iron (II) hydroxide is obtained from ferrous salts by the action of alkali solutions:

Chemical properties. Basic hydroxide. Reacts with acids:

In air, Fe (OH) 2 is oxidized to Fe (OH) 3:

Iron (III) oxide Fe2O3- a brown substance, occurs in nature in the form of red iron ore, insoluble in water.

Receiving... When firing pyrite:

Chemical properties. Shows weak amphoteric properties. When interacting with alkalis, forms salts:

Iron (III) hydroxide Fe (OH) 3- a substance of red-brown color, insoluble in water and excess alkali.

Receiving... Obtained by oxidation of iron (III) oxide and iron (II) hydroxide.

Chemical properties. It is an amphoteric compound (with a predominance of basic properties). Precipitates under the action of alkalis on ferric salts:

Ferrous salts are obtained by the interaction of metallic iron with appropriate acids. They are highly hydrolyzed, because their aqueous solutions are energetic reducing agents:

When heated above 480 ° C, it decomposes, forming oxides:

Under the action of alkalis on iron (II) sulfate, iron (II) hydroxide is formed:

Forms crystalline hydrate - FeSO4? 7H2O (ferrous sulfate). Iron (III) chloride FeCl3 - crystalline substance of dark brown color.

Chemical properties. Let's dissolve in water. FeCl3 exhibits oxidizing properties.

Reducing agents - magnesium, zinc, hydrogen sulfide, are oxidized without heating.