Meta iron acid. Physico-chemical properties of iron and its compounds

Iron(Latin ferrum), fe, a chemical element of group viii of Mendeleev's periodic system; atomic number 26, atomic mass 55.847; shiny silvery white metal. The element in nature consists of four stable isotopes: 54 fe (5.84%), 56 fe (91.68%), 57 fe (2.17%) and 58 fe (0.31%).

Historical reference. Iron was known in prehistoric times, but it found wide application much later, since it is extremely rare in nature in the free state, and its production from ores became possible only at a certain level of technological development. Probably, for the first time, a person became acquainted with meteoric iron, as evidenced by its names in the languages ​​of ancient peoples: the ancient Egyptian “beni-pet” means “heavenly iron”; the ancient Greek sideros is associated with the Latin sidus (genitive sideris) - a star, a celestial body. In Hittite texts of the 14th century. BC e. Zh. is mentioned as a metal that fell from the sky. In the Romance languages, the root of the name given by the Romans has been preserved (for example, French fer, Italian ferro).

The method of obtaining iron from ores was invented in the western part of Asia in the 2nd millennium BC. e.; after that, the use of Zh. spread in Babylon, Egypt, and Greece; for changing Bronze Age came iron age. Homer (in the 23rd canto of the Iliad) relates that Achilles awarded the winner of a discus-throwing competition with an iron cry discus. In Europe and Ancient Rus' for many centuries, Zh. received cheese process. Iron ore was reduced with charcoal in a furnace built in a pit; air was pumped into the furnace with bellows, the reduction product - kritsu was separated from the slag by hammer blows and various products were forged from it. As the methods of blowing were improved and the height of the hearth increased, the temperature of the process increased and part of the iron became carburized, i.e., it turned out cast iron; this relatively fragile product was considered a waste product. Hence the name pig iron, pig iron - English pig iron. Later, it was noticed that when not iron ore, but cast iron is loaded into the hearth, low-carbon iron bloom is also obtained, and such a two-stage process turned out to be more profitable than the raw blown one. In the 12th-13th centuries. the screaming method was already widespread. In the 14th century cast iron began to be smelted not only as a semi-finished product for further processing, but also as a material for casting various products. The reconstruction of the hearth into a shaft furnace (“domnitsa”), and then into a blast furnace, also dates back to the same time. In the middle of the 18th century in Europe, the crucible process for obtaining become, which was known on the territory of Syria in the early period of the Middle Ages, but later turned out to be forgotten. With this method, steel was obtained by melting metal mixtures in small vessels (crucibles) from a highly refractory mass. In the last quarter of the 18th century The puddling process of redistribution of cast iron into iron began to develop on the hearth of a fiery reverberatory furnace. The industrial revolution of the 18th and early 19th centuries, the invention of the steam engine, and the construction of railways, large bridges, and the steam fleet created an enormous need for iron and its alloys. However, all existing methods of producing iron could not meet the needs of the market. Mass production of steel began only in the middle of the 19th century, when the Bessemer, Thomas, and open-hearth processes were developed. In the 20th century the electric steelmaking process arose and became widespread, giving high-quality steel.

distribution in nature. In terms of content in the lithosphere (4.65% by weight), aluminum ranks second among metals (aluminum is in first place). It migrates vigorously in the earth's crust, forming about 300 minerals (oxides, sulfides, silicates, carbonates, titanates, phosphates, etc.). Zh. takes an active part in magmatic, hydrothermal, and supergene processes, which are associated with the formation of various types of its deposits. Zh. - metal of the earth's depths, it accumulates in the early stages of magma crystallization, in ultrabasic (9.85%) and basic (8.56%) rocks (in granites it is only 2.7%). In the biosphere, iron accumulates in many marine and continental sediments, forming sedimentary ores.

An important role in the geochemistry of iron is played by redox reactions—the transition of 2-valent iron to trivalent iron and vice versa. In the biosphere, in the presence of organic substances, fe 3+ is reduced to fe 2+ and easily migrates, and when it encounters atmospheric oxygen, fe 2+ is oxidized, forming accumulations of hydroxides of 3-valent iron. Widespread compounds of 3-valent iron have red, yellow, brown colors. This determines the color of many sedimentary rocks and their name - "red-colored formation" (red and brown loams and clays, yellow sands, etc.).

Physical and chemical properties. Zh.'s value in modern technology is determined not only by its wide distribution in nature, but also by a combination of very valuable properties. It is plastic, easily forged both in a cold and heated state, can be rolled, stamped and drawn. The ability to dissolve carbon and other elements serves as the basis for obtaining various iron alloys.

Zh. can exist in the form of two crystal lattices: a - and g - body-centered cubic (bcc) and face-centered cubic (fcc). Below 910 °C, a - fe is stable with a bcc lattice (a = 2.86645 å at 20 °C). Between 910°C and 1400°C, the g-modification with the fcc lattice is stable (a = 3.64 å). Above 1400°C, the bcc lattice d-fe (a = 2.94 å) is again formed, which is stable up to the melting point (1539°C). a - fe ferromagnetic up to 769°C (Curie point). Modification g -fe and d -fe are paramagnetic.

Polymorphic transformations of iron and steel during heating and cooling were discovered in 1868 by D.K. Chernov. Carbon forms with J. solid solutions interstitials, in which C atoms with a small atomic radius (0.77 å) are located in the interstices of the metal crystal lattice, which consists of larger atoms (atomic radius fe 1.26 å). A solid solution of carbon in g -fe called. austenite, and in (a -fe- ferrite. Saturated solid solution of carbon in g - fe contains 2.0% C by mass at 1130°C; a-fe dissolves only 0.02-0.04% C at 723°C, and less than 0.01% at room temperature. Therefore, when hardening austenite is formed martensite - supersaturated solid solution of carbon in a - fe, very hard and brittle. combination of hardening with vacation(by heating to relatively low temperatures to reduce internal stresses) allows you to give the steel the required combination of hardness and ductility.

The physical properties of zinc depend on its purity. As a rule, industrial iron materials are accompanied by impurities of carbon, nitrogen, oxygen, hydrogen, sulfur, and phosphorus. Even at very low concentrations, these impurities greatly change the properties of the metal. So, sulfur causes the so-called. red brittleness, phosphorus (even 10 -20% P) - cold brittleness; carbon and nitrogen reduce plastic, and hydrogen increases fragility Zh. (so-called hydrogen brittleness). Reducing the content of impurities to 10 -7 - 10 -9% leads to significant changes in the properties of the metal, in particular, to an increase in ductility.

The following are the physical properties of zinc, relating mainly to a metal with a total impurity content of less than 0.01% by weight:

Atomic radius 1.26 å

Ionic radii fe 2+ o.80 å, fe 3+ o.67 å

Density (20°C) 7.874 g/cm 3

t pl 1539°C

t kip about 3200 o C

Temperature coefficient of linear expansion (20°C) 11.7 10 -6

Thermal conductivity (25°C) 74.04 Tue/(m K)

The heat capacity of a liquid depends on its structure and varies with temperature in a complex way; average specific heat capacity (0-1000 o c) 640.57 j/(kg·TO) .

Electrical resistivity (20°C)

9.7 10 -8 ohm m

Temperature coefficient of electrical resistance

(0-100°C) 6.51 10 -3

Young's modulus 190-210 10 3 Mn/m 2

(19-21 10 3 kgf/mm 2)

Temperature coefficient of Young's modulus

Shear modulus 84.0 10 3 MN/m 2

Short term tensile strength

170-210 MN/m 2

Relative elongation 45-55%

Brinell hardness 350-450 MN/m 2

Yield strength 100 MN/m 2

Impact strength 300 MN/m 2

The configuration of the outer electron shell of the atom fe 3 d 6 4s 2 . Zh. exhibits variable valency (the most stable compounds are 2- and 3-valent Zh.). With oxygen, iron forms feo oxide, fe 2 o 3 oxide, and fe 3 o 4 oxide (feo compound with fe 2 o 3 , having the structure spinels) . In humid air at ordinary temperatures, iron becomes covered with loose rust (fe 2 o 3 n h2o). Due to its porosity, rust does not prevent the access of oxygen and moisture to the metal and therefore does not protect it from further oxidation. As a result of various types of corrosion, millions of tons of iron are lost every year. When iron is heated in dry air above 200°C, it is covered with a thin oxide film, which protects the metal from corrosion at ordinary temperatures; this is the basis of the technical method of protecting J. - bluing. When heated in water vapor, iron is oxidized to form fe 3 o 4 (below 570°C) or feo (above 570°C) and release hydrogen.

Hydroxide fe (oh) 2 is formed as a white precipitate by the action of caustic alkalis or ammonia on aqueous solutions of fe 2+ salts in an atmosphere of hydrogen or nitrogen. Upon contact with air, fe (oh) 2 first turns green, then blackens, and finally quickly turns into red-brown hydroxide fe (oh) 3 . Feo oxide exhibits basic properties. Oxide fe 2 o 3 amphoteric and has a weakly acidic function; reacting with more basic oxides (for example, with mgo), it forms ferrites - compounds of the type fe 2 o 3 n meo, which have ferromagnetic properties and are widely used in radio electronics. Acidic properties are also expressed in 6-valent iron, which exists in the form of ferrates, for example k 2 feo 4 , salts of iron acid not isolated in the free state.

Zh. easily reacts with halogens and hydrogen halides, giving salts, for example chlorides fecl 2 and fecl 3. When iron is heated with sulfur, sulfides fes and fes 2 are formed. Carbides Zh. - fe 3 c ( cementite) and fe 2 c (e-carbide) - precipitate from solid solutions of carbon in liquid upon cooling. fe 3 c is also released from solutions of carbon in liquid iron at high concentrations of carbon. Nitrogen, like carbon, gives interstitial solid solutions with iron; nitrides fe 4 n and fe 2 n stand out from them. With hydrogen, hydrogen gives only unstable hydrides, the composition of which has not been precisely established. When heated, iron reacts vigorously with silicon and phosphorus, forming silicides (for example, fe 3 si) and phosphides (for example, fe 3 p).

Zh. compounds with many elements (O, s, etc.), which form a crystal structure, have a variable composition (for example, the sulfur content in monosulfide can range from 50 to 53.3 at.%). This is due to defects in the crystal structure. For example, in iron oxide some of the fe 2+ ions at the lattice sites are replaced by fe 3+ ions; to maintain electrical neutrality, some lattice sites belonging to fe 2+ ions remain empty and the phase (wustite) under normal conditions has the formula fe 0.947 o.

Peculiarly, Zh.'s interaction with nitric acid. Concentrated hno 3 (density 1.45 g/cm 3) passivates iron due to the appearance of a protective oxide film on its surface; more dilute hno 3 dissolves iron with the formation of fe 2+ or fe 3+ ions, recovering to mh 3 or n 2 o and n 2 .

Solutions of salts of 2-valent iron are unstable in air - fe 2+ gradually oxidizes to fe 3+. Aqueous solutions of salts Zh. due to hydrolysis have an acid reaction. Adding thiocyanate ions scn - to solutions of fe 3+ salts gives a bright blood-red color due to the appearance of fe (scn) 3, which makes it possible to reveal the presence of 1 part of fe 3+ in about 10 6 parts of water. Zh. is characterized by education complex compounds.

Receipt and application. Pure iron is obtained in relatively small quantities by the electrolysis of aqueous solutions of its salts or by the reduction of its oxides with hydrogen. A method is being developed for the direct production of iron from ores by electrolysis of melts. The production of sufficiently pure iron is gradually increasing by means of its direct reduction from ore concentrates with hydrogen, natural gas, or coal at relatively low temperatures.

Zh. - the most important metal of modern technology. Iron is practically never used in its pure form because of its low strength, although in everyday life steel or cast iron products are often called “iron”. The bulk of iron is used in the form of alloys that are very different in composition and properties. Iron alloys account for approximately 95% of all metal products. Carbon-rich alloys (over 2% by weight) - cast iron, are smelted in blast furnaces from enriched iron ores. Steel of various grades (carbon content less than 2% by weight) is smelted from cast iron in open-hearth and electric furnaces and converters by oxidizing (burning out) excess carbon, removing harmful impurities (mainly s, P, O) and adding alloying elements. High-alloy steels (with a high content of nickel, chromium, tungsten, and other elements) are smelted in electric arc and induction furnaces. New processes such as vacuum remelting, electroslag remelting, plasma and electron beam melting, etc., are used for the production of steels and iron alloys of particular importance. Methods are being developed for smelting steel in continuously operating units that ensure high quality of the metal and process automation.

On the basis of iron, materials are created that can withstand the effects of high and low temperatures, vacuum and high pressures, aggressive media, high alternating voltages, nuclear radiation, etc. The production of iron and its alloys is constantly growing. In 1971, 89.3 million tons were smelted in the USSR. T pig iron and 121 mln. T become.

L. A. Shvartsman, L. V. Vanyukova.

Iron as an artistic material has been used since antiquity in Egypt (a headstand from the tomb of Tutankhamen near Thebes, mid-14th century BC, Ashmolean Museum, Oxford), Mesopotamia (daggers found near Carchemish, 500 BC, British Museum, London), India (iron column in Delhi, 415). Since the Middle Ages, numerous highly artistic items made of Zh. have been preserved in European countries (England, France, Italy, Russia, etc.) - forged fences, door hinges, wall brackets, weather vanes, chest fittings, and light fixtures. Forged through products made of twigs and products made of perforated sheet iron (often with a mica lining) are distinguished by planar forms, a clear linear graphic silhouette, and are effectively visible against a light-air background. In the 20th century Zh. is used for the manufacture of lattices, fences, openwork interior partitions, candlesticks, and monuments.

T. L.

Iron in the body. Zh. is present in the organisms of all animals and in plants (an average of about 0.02%); it is necessary mainly for oxygen exchange and oxidative processes. There are organisms (the so-called concentrators) that can accumulate it in large quantities (for example, iron bacteria - up to 17-20% W.). Almost all iron in animal and plant organisms is associated with proteins. Lack of Zh. causes a growth retardation and the phenomenon plant chlorosis, associated with lower education chlorophyll. Excess iron also has a harmful effect on the development of plants, causing, for example, sterility of rice flowers and chlorosis. In alkaline soils, iron compounds inaccessible to plant roots are formed, and the plants do not receive it in sufficient quantities; in acidic soils, iron passes into soluble compounds in excess. With a deficiency or excess of assimilable compounds in soils, plant diseases can be observed in large areas.

Zh. enters the body of animals and humans with food (liver, meat, eggs, legumes, bread, cereals, spinach, and beets are the richest in it). Normally, a person receives with a diet of 60-110 mg Zh., which significantly exceeds its daily requirement. Absorption of iron taken with food occurs in the upper part of the small intestines, from where it enters the blood in a protein-bound form and is carried with blood to various organs and tissues, where it is deposited in the form of iron - a protein complex - ferritin. The main depot of iron in the body is the liver and spleen. Due to G. ferritin, the synthesis of all iron-containing compounds of the body occurs: a respiratory pigment is synthesized in the bone marrow hemoglobin, in the muscles myoglobin, in various tissues cytochromes and other iron-containing enzymes. Zh. is excreted from the body mainly through the wall of the large intestine (in humans, about 6-10 mg per day) and to a small extent by the kidneys. The body's need for fat changes with age and physical condition. For 1 kg of weight, children need - 0.6, adults - 0.1 and pregnant women - 0.3 mg F. per day. In animals, the need for fat is approximately (per 1 kg dry matter of the ration): for dairy cows - at least 50 mg, for young animals - 30-50 mg, for piglets - up to 200 mg, for pregnant pigs - 60 mg.

V. V. Kovalsky.

In medicine, Zh. medicines (reconstituted Zh., lactate Zh., glycerophosphate Zh., sulfate of 2-valent Zh., Blo tablets, malic acid solution, feramid, hemostimulin, etc.) are used in the treatment of diseases accompanied by a lack of Zh. in the body (iron deficiency anemia), as well as general tonic (after infectious diseases, etc.). Zh. isotopes (52 fe, 55 fe, and 59 fe) are used as indicators in biomedical research and in the diagnosis of blood diseases (anemia, leukemia, polycythemia, etc.).

Lit.: General metallurgy, Moscow, 1967; Nekrasov B.V., Fundamentals of General Chemistry, vol. 3, M., 1970; Remi G., Course of inorganic chemistry, trans. from German, vol. 2, M., 1966; Brief chemical encyclopedia, v. 2, M., 1963; Levinson N. R., [Products from non-ferrous and ferrous metal], in the book: Russian decorative art, vol. 1-3, M., 1962-65; Vernadsky V.I., Biogeochemical essays. 1922-1932, M. - L., 1940; Granik S., Iron metabolism in animals and plants, in the collection: Trace elements, trans. from English, M., 1962; Dixon M., Webb F., enzymes, trans. from English, M., 1966; neogi p., iron in ancient india, calcutta, 1914; friend j. n., iron in antiquity, l., 1926; frank e. b., old french ironwork, camb. (mass.), 1950; lister r., decorative wrought ironwork in great britain, l., 1960.

download abstract

It has been known to people since antiquity: scientists attribute ancient household items made of this material to the 4th millennium BC.

Human life cannot be imagined without iron. It is believed that iron is used for industrial purposes more often than other metals. The most important structures are made from it. Iron is also found in small amounts in the blood. It is the content of the twenty-sixth element that colors the blood red.

Physical properties of iron

In oxygen, iron burns to form an oxide:

3Fe + 2O₂ = Fe₃O₄.

When heated, iron can react with non-metals:

Also, at a temperature of 700-900 ° C, it reacts with water vapor:

3Fe + 4H₂O = Fe₃O₄ + 4H₂.

Iron compounds

As you know, iron oxides have ions with two oxidation states: +2 and + 3. It is extremely important to know this, because completely different qualitative reactions will be carried out for different elements.

Qualitative reactions to iron

A qualitative reaction is needed in order to easily determine the presence of ions of one substance in solutions or impurities of another. Consider the qualitative reactions of ferrous and trivalent iron.

Qualitative reactions for iron (III)

The content of ferric ions in a solution can be determined using alkali. With a positive result, a base is formed - iron (III) hydroxide Fe (OH) ₃.

Iron(III) hydroxide Fe(OH)₃

The resulting substance is insoluble in water and has a brown color. It is the brown precipitate that may indicate the presence of ferric ions in the solution:

FeCl₃ + 3NaOH = Fe(OH)₃↓+ 3NaCl.

Fe(III) ions can also be determined using K₃.

A solution of ferric chloride is mixed with a yellowish blood salt solution. As a result, you can see a beautiful bluish precipitate, which will indicate that ferric ions are present in the solution. you will find spectacular experiments on the study of the properties of iron.

Qualitative reactions for iron (II)

Fe²⁺ ions react with the red blood salt K₄. If a bluish precipitate forms when the salt is added, then these ions are present in the solution.

Story

Iron as an instrumental material has been known since ancient times. The oldest iron products found during archaeological excavations date back to the 4th millennium BC. e. and belong to the ancient Sumerian and ancient Egyptian civilizations. These are made of meteoric iron, that is, an alloy of iron and nickel (the content of the latter ranges from 5 to 30%), jewelry from Egyptian tombs (about 3800 BC) and a dagger from the Sumerian city of Ur (about 3100 BC). e.). Apparently, one of the names of iron in Greek and Latin comes from the celestial origin of meteoric iron: “sider” (which means “starry”).

Products from iron obtained by smelting have been known since the time of the settlement of the Aryan tribes from Europe to Asia, the islands of the Mediterranean Sea, and beyond (the end of the 4th and 3rd millennium BC). The oldest known iron tools are steel blades found in the masonry of the pyramid of Cheops in Egypt (built around 2530 BC). As excavations in the Nubian desert have shown, already in those days the Egyptians, trying to separate the mined gold from heavy magnetite sand, calcined ore with bran and similar substances containing carbon. As a result, a layer of doughy iron floated on the surface of the gold melt, which was processed separately. Tools were forged from this iron, including those found in the pyramid of Cheops. However, after the grandson of Cheops Menkaur (2471-2465 BC), turmoil occurred in Egypt: the nobility, led by the priests of the god Ra, overthrew the ruling dynasty, and a leapfrog of usurpers began, ending with the accession of the pharaoh of the next dynasty, Userkar, whom the priests declared to be the son and incarnation the god Ra himself (since then this has become the official status of the pharaohs). During this turmoil, the cultural and technical knowledge of the Egyptians fell into decay, and, just as the art of building the pyramids degraded, the technology of iron production was lost, to the point that later, while exploring the Sinai Peninsula in search of copper ore, the Egyptians did not pay any attention to iron ore deposits there, but received iron from neighboring Hittites and Mitannians.

The first mastered the production of iron Hatt, this is indicated by the oldest (2nd millennium BC) mention of iron in the texts of the Hittites, who founded their empire on the territory of the Hatt (modern Anatolia in Turkey). So, in the text of the Hittite king Anitta (about 1800 BC) it says:

When I went on a campaign to the city of Puruskhanda, a man from the city of Puruskhanda came to bow to me (...?) and he presented me with 1 iron throne and 1 iron scepter (?) as a sign of humility (?) ...

(source: Giorgadze G. G.// Bulletin of ancient history. 1965. No. 4.)

In ancient times, khalibs were reputed to be masters of iron products. The legend of the Argonauts (their campaign to Colchis took place about 50 years before the Trojan War) tells that the king of Colchis, Eet, gave Jason an iron plow to plow the field of Ares, and his subjects, the halibers, are described:

They do not plow the land, do not plant fruit trees, do not graze herds in rich meadows; they extract ore and iron from the uncultivated land and barter food for them. The day does not begin for them without hard work, they spend in the darkness of the night and thick smoke, working all day ...

Aristotle described their method of obtaining steel: “the Khalibs washed the river sand of their country several times - thereby separating black concentrate (a heavy fraction consisting mainly of magnetite and hematite), and melted it in furnaces; the metal thus obtained had a silvery color and was stainless."

Magnetite sands, which are often found along the entire coast of the Black Sea, were used as raw materials for steel smelting: these magnetite sands consist of a mixture of fine grains of magnetite, titanium-magnetite or ilmenite, and fragments of other rocks, so that the steel smelted by the Khalibs was alloyed, and had excellent properties. Such a peculiar way of obtaining iron suggests that the Khalibs only spread iron as a technological material, but their method could not be a method for the widespread industrial production of iron products. However, their production served as an impetus for the further development of iron metallurgy.

In the deepest antiquity, iron was valued more than gold, and according to the description of Strabo, African tribes gave 10 pounds of gold for 1 pound of iron, and according to the studies of the historian G. Areshyan, the cost of copper, silver, gold and iron among the ancient Hittites was in the ratio 1: 160 : 1280: 6400. In those days, iron was used as a jewelry metal, thrones and other regalia of royal power were made from it: for example, in the biblical book Deuteronomy 3.11, an “iron bed” of the Rephaim king Og is described.

In the tomb of Tutankhamen (circa 1350 BC) was found a dagger made of iron in a gold frame - possibly a gift from the Hittites for diplomatic purposes. But the Hittites did not strive for the widespread dissemination of iron and its technologies, which is also evident from the correspondence of the Egyptian pharaoh Tutankhamun and his father-in-law Hattusil, the king of the Hittites, that has come down to us. The pharaoh asks to send more iron, and the king of the Hittites evasively answers that the iron reserves have run out, and the blacksmiths are busy with agricultural work, so he cannot fulfill the request of the royal son-in-law, and sends only one dagger from “good iron” (that is, steel). As you can see, the Hittites tried to use their knowledge to achieve military advantages, and did not give others the opportunity to catch up with them. Apparently, therefore, iron products became widespread only after the Trojan War and the fall of the Hittites, when, thanks to the trading activity of the Greeks, iron technology became known to many, and new iron deposits and mines were discovered. So the Bronze Age was replaced by the Iron Age.

According to Homer's descriptions, although during the Trojan War (circa 1250 BC) weapons were mostly made of copper and bronze, iron was already well known and in great demand, although more as a precious metal. For example, in the 23rd song of the Iliad, Homer says that Achilles awarded the winner in a discus throwing competition with an iron cry disc. The Achaeans mined this iron from the Trojans and neighboring peoples (Iliad 7.473), including from the Khalibs, who fought on the side of the Trojans:

“Other men of the Achaeans bought wine with me,
Those for ringing copper, for gray iron changed,
Those for ox-skins or high-horned oxen,
Those for their captives. And a merry feast is prepared ... "

Perhaps iron was one of the reasons that prompted the Achaean Greeks to move to Asia Minor, where they learned the secrets of its production. And excavations in Athens showed that already around 1100 BC. e. and later iron swords, spears, axes, and even iron nails were already widespread. The biblical book of Joshua 17:16 (cf. Judges 14:4) describes that the Philistines (biblical "PILISTIM", and these were proto-Greek tribes related to the later Hellenes, mainly Pelasgians) had many iron chariots, that is, in this iron has already become widely used in large quantities.

Homer in the Iliad and the Odyssey calls iron "a hard metal", and describes the hardening of tools:

“A quick forger, having made an ax or an ax,
Metal into the water, heating it up so that it doubles
He had a fortress, immerses ... "

Homer calls iron difficult, because in ancient times the main method of obtaining it was the raw-blowing process: alternating layers of iron ore and charcoal were calcined in special furnaces (forges - from the ancient "Horn" - a horn, a pipe, originally it was just a pipe dug in the ground , usually horizontally in the slope of a ravine). In the hearth, iron oxides are reduced to metal by hot coal, which takes away oxygen, oxidizing to carbon monoxide, and as a result of such calcination of ore with coal, doughy bloom (spongy) iron was obtained. Kritsu was cleaned of slag by forging, squeezing out impurities with strong hammer blows. The first hearths had a relatively low temperature - noticeably lower than the melting point of cast iron, so the iron turned out to be relatively low-carbon. In order to obtain strong steel, it was necessary to calcinate and forge the iron bar with coal many times, while the surface layer of the metal was additionally saturated with carbon and hardened. This was how “good iron” was obtained - and although it required a lot of work, the products obtained in this way were significantly stronger and harder than bronze ones.

Later, they learned how to make more efficient furnaces (in Russian - blast furnace, domnitsa) for steel production, and used furs to supply air to the furnace. Already the Romans were able to bring the temperature in the furnace to the melting of steel (about 1400 degrees, and pure iron melts at 1535 degrees). In this case, cast iron is formed with a melting point of 1100-1200 degrees, which is very brittle in the solid state (not even amenable to forging) and does not have the elasticity of steel. It was originally considered a harmful by-product. pig iron, in Russian, pig iron, ingots, where, in fact, the word cast iron comes from), but then it turned out that when remelted in a furnace with increased air blowing through it, cast iron turns into good quality steel, as excess carbon burns out. Such a two-stage process for the production of steel from cast iron turned out to be simpler and more profitable than bloomery, and this principle has been used without much change for many centuries, remaining to this day the main method for the production of iron materials.

Bibliography: Karl Bucks. Wealth of the earth's interior. M .: Progress, 1986, p. 244, chapter "Iron"

origin of name

There are several versions of the origin of the Slavic word "iron" (Belarusian zhalez, Ukrainian zalizo, old Slav. iron, bulg. iron, Serbohorv. zhezo, Polish. Zelazo, Czech železo, Slovenian zelezo).

One of the etymologies connects Praslav. *ZelEzo with the Greek word χαλκός , which meant iron and copper, according to another version *ZelEzo akin to words *zely"turtle" and *eye"rock", with the general seme "stone". The third version suggests an ancient borrowing from an unknown language.

The Germanic languages ​​borrowed the name iron (Gothic. eisarn, English iron, German Eisen, netherl. ijzer, dat. jern, swedish jarn) from Celtic.

Pra-Celtic word *isarno-(> OE iarn, OE Bret hoiarn), probably goes back to Proto-IE. *h 1 esh 2 r-no- "bloody" with the semantic development "bloody" > "red" > "iron". According to another hypothesis, this word goes back to pra-i.e. *(H)ish 2ro- "strong, holy, possessing supernatural power" .

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 lat. sidereus- stellar; indeed, the first iron that fell into the hands of people was of meteoric origin. Perhaps this coincidence is not accidental. In particular, the ancient Greek word sideros (σίδηρος) for iron and latin sidus, meaning "star", probably have a common origin.

isotopes

Natural iron consists of four stable isotopes: 54 Fe (isotopic abundance 5.845%), 56 Fe (91.754%), 57 Fe (2.119%) and 58 Fe (0.282%). More than 20 unstable iron isotopes with mass numbers from 45 to 72 are also known, the most stable of which are 60 Fe (half-life according to data updated in 2009 is 2.6 million years), 55 Fe (2.737 years), 59 Fe ( 44.495 days) and 52 Fe (8.275 hours); the remaining isotopes have half-lives of less than 10 minutes.

The iron isotope 56 Fe is among the most stable nuclei: all of the following elements can reduce the binding energy per nucleon by decay, and all previous elements, in principle, could reduce the binding energy per nucleon due to fusion. It is believed that a series of synthesis of elements in the cores of normal stars ends with iron (see Iron star), and all subsequent elements can be formed only as a result of supernova explosions.

Geochemistry of iron

Hydrothermal source with ferruginous water. Iron oxides turn water brown

Iron is one of the most common elements in the solar system, especially on the terrestrial planets, in particular on Earth. A significant part of the iron of the terrestrial planets is located in the cores of the planets, where its content is estimated to be about 90%. The content of iron in the earth's crust is 5%, and in the mantle about 12%. Of the metals, iron is second only to aluminum in terms of abundance in the crust. At the same time, about 86% of all iron is in the core, and 14% in the mantle. The content of iron increases significantly in the igneous rocks of the basic composition, where it is associated with pyroxene, amphibole, olivine and biotite. In industrial concentrations, iron accumulates during almost all exogenous and endogenous processes occurring in the earth's crust. In sea water, iron is contained in very small amounts of 0.002-0.02 mg / l. In river water, it is slightly higher - 2 mg / l.

Geochemical properties of iron

The most important geochemical feature of iron is that it has several oxidation states. Iron in a neutral form - metallic - composes the core of the earth, possibly present in the mantle and very rarely found in the earth's crust. Ferrous iron FeO is the main form of iron in the mantle and the earth's crust. Oxide iron Fe 2 O 3 is characteristic of the uppermost, most oxidized, parts of the earth's crust, in particular, sedimentary rocks.

In terms of crystal chemical properties, the Fe 2+ ion is close to the Mg 2+ and Ca 2+ ions, other main elements that make up a significant part of all terrestrial rocks. Due to their crystal chemical similarity, iron replaces magnesium and, in part, calcium in many silicates. The content of iron in minerals of variable composition usually increases with decreasing temperature.

iron minerals

A large number of ores and minerals containing iron are known. Of the greatest practical importance are red iron ore (hematite, Fe 2 O 3; contains up to 70% Fe), magnetic iron ore (magnetite, FeFe 2 O 4, Fe 3 O 4; contains 72.4% Fe), brown iron ore or limonite (goethite and hydrogoethite, FeOOH and FeOOH nH 2 O, respectively). Goethite and hydrogoethite are most often found in weathering crusts, forming the so-called "iron hats", the thickness of which reaches several hundred meters. They can also be of sedimentary origin, falling out of colloidal solutions in lakes or coastal areas of the seas. In this case, oolitic, or legume, iron ores are formed. Vivianite Fe 3 (PO 4) 2 8H 2 O is often found in them, forming black elongated crystals and radial-radiant aggregates.

Iron sulfides are also widespread in nature - pyrite FeS 2 (sulfur or iron pyrite) and pyrrhotite. They are not iron ore - pyrite is used to produce sulfuric acid, and pyrrhotite often contains nickel and cobalt.

In terms of iron ore reserves, Russia ranks first in the world. The content of iron in sea water is 1·10 −5 -1·10 −8%.

Other common iron minerals are:

• Siderite - FeCO 3 - contains approximately 35% iron. It has a yellowish-white (with a gray or brown tint in case of contamination) color. The density is 3 g / cm³ and the hardness is 3.5-4.5 on the Mohs scale.
• Marcasite - FeS 2 - contains 46.6% iron. It occurs in the form of yellow, like brass, bipyramidal rhombic crystals with a density of 4.6-4.9 g / cm³ and a hardness of 5-6 on the Mohs scale.
• Lollingite - FeAs 2 - contains 27.2% iron and occurs in the form of silver-white bipyramidal rhombic crystals. Density is 7-7.4 g / cm³, hardness is 5-5.5 on the Mohs scale.
• Mispikel - FeAsS - contains 34.3% iron. It occurs in the form of white monoclinic prisms with a density of 5.6-6.2 g / cm³ and a hardness of 5.5-6 on the Mohs scale.
• Melanterite - FeSO 4 7H 2 O - is less common in nature and is a green (or gray due to impurities) monoclinic crystals with a vitreous luster, fragile. The density is 1.8-1.9 g / cm³.
• Vivianite - Fe 3 (PO 4) 2 8H 2 O - occurs in the form of blue-gray or green-gray monoclinic crystals with a density of 2.95 g / cm³ and a hardness of 1.5-2 on the Mohs scale.

In addition to the above iron minerals, there are, for example:

Main deposits

According to the US Geological Survey (2011 estimate), the world's proven reserves of iron ore are about 178 billion tons. The main iron deposits are in Brazil (1st place), Australia, USA, Canada, Sweden, Venezuela, Liberia, Ukraine, France, India. In Russia, iron is mined at the Kursk Magnetic Anomaly (KMA), the Kola Peninsula, Karelia and Siberia. Recently, bottom oceanic deposits have acquired a significant role, in which iron, together with manganese and other valuable metals, is found in nodules.

Receipt

In industry, iron is obtained from iron ore, mainly from hematite (Fe 2 O 3) and magnetite (FeO Fe 2 O 3).

There are various ways to extract 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 sinter or pellets, and flux (such as limestone) are fed in from above and are met by a stream of injected 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 recovers iron from the ore. To make this reaction go faster, heated carbon monoxide is passed through iron (III) oxide:

Calcium oxide combines with silicon dioxide, forming a slag - calcium metasilicate:

Slag, unlike silicon dioxide, is melted in a furnace. Lighter than iron, slag floats on the surface - this property allows you to separate the slag from the metal. The slag can then be used in construction and agriculture. Iron melt obtained in a blast furnace contains quite a lot of carbon (cast iron). Except in such cases, when cast iron is used directly, it requires further processing.

Excess carbon and other impurities (sulphur, phosphorus) are removed from cast iron by oxidation in open-hearth furnaces or in converters. Electric furnaces are also used for smelting alloyed steels.

In addition to the blast furnace process, the process of direct production of iron is common. In this case, pre-crushed ore is mixed with special clay to form pellets. The pellets are roasted and treated in a shaft furnace with hot methane conversion products that contain hydrogen. Hydrogen easily reduces iron:

,

while there is no contamination of iron with impurities such as sulfur and phosphorus, which are common impurities in coal. Iron is obtained in solid form, and then melted down in electric furnaces.

Chemically pure iron is obtained by electrolysis of solutions of its salts.

Physical Properties

The phenomenon of polymorphism is extremely important for steel metallurgy. It is thanks to the α-γ transitions of the crystal lattice that the heat treatment of steel occurs. Without this phenomenon, iron as the basis of steel would not have received such widespread use.

Iron is a moderately refractory metal. In a series of standard electrode potentials, iron stands before hydrogen and easily reacts with dilute acids. Thus, iron belongs to the metals of medium activity.

The melting point of iron is 1539 °C, the boiling point is 2862 °C.

Chemical properties

Characteristic oxidation states

• Acid does not exist in its free form - only its salts have been obtained.

For iron, the oxidation states of iron are characteristic - +2 and +3.

The oxidation state +2 corresponds to black oxide FeO and green hydroxide Fe(OH) 2 . They are basic. In salts, Fe(+2) is present as a cation. Fe(+2) is a weak reducing agent.

+3 oxidation states correspond to red-brown Fe 2 O 3 oxide and brown Fe(OH) 3 hydroxide. They are amphoteric in nature, although their acidic and basic properties are weakly expressed. Thus, Fe 3+ ions are completely hydrolyzed even in an acidic environment. Fe (OH) 3 dissolves (and even then not completely), only in concentrated alkalis. Fe 2 O 3 reacts with alkalis only when fused, giving ferrites (formal salts of an acid that does not exist in a free form of acid HFeO 2):

Iron (+3) most often exhibits weak oxidizing properties.

The +2 and +3 oxidation states easily transition between themselves when the redox conditions change.

In addition, there is Fe 3 O 4 oxide, the formal oxidation state of iron in which is +8/3. However, this oxide can also be considered as iron (II) ferrite Fe +2 (Fe +3 O 2) 2 .

There is also an oxidation state of +6. The corresponding oxide and hydroxide do not exist in free form, but salts - ferrates (for example, K 2 FeO 4) have been obtained. Iron (+6) is in them in the form of an anion. Ferrates are strong oxidizing agents.

Properties of a simple substance

When stored in air at temperatures up to 200 ° C, iron is gradually covered with a dense film of oxide, which prevents further oxidation of the metal. In moist air, iron is covered with a loose layer of rust, which does not prevent the access of oxygen and moisture to the metal and its destruction. Rust does not have a constant chemical composition; approximately its chemical formula can be written as Fe 2 O 3 xH 2 O.

Iron(II) compounds

Iron oxide (II) FeO has basic properties, it corresponds to the base Fe (OH) 2. Salts of iron (II) have a light green color. When stored, especially in moist air, they turn brown due to oxidation to iron (III). The same process occurs during storage of aqueous solutions of iron(II) salts:

Of the iron (II) salts in aqueous solutions, Mohr's salt is stable - double ammonium and iron (II) sulfate (NH 4) 2 Fe (SO 4) 2 6H 2 O.

Potassium hexacyanoferrate (III) K 3 (red blood salt) can serve as a reagent for Fe 2+ ions in solution. When Fe 2+ and 3− ions interact, turnbull blue precipitates:

For the quantitative determination of iron (II) in solution, phenanthroline Phen is used, which forms a red FePhen 3 complex with iron (II) (light absorption maximum - 520 nm) in a wide pH range (4-9).

Iron(III) compounds

Iron(III) compounds in solutions are reduced by metallic iron:

Iron (III) is able to form double sulfates with singly charged alum-type cations, for example, KFe (SO 4) 2 - potassium iron alum, (NH 4) Fe (SO 4) 2 - iron ammonium alum, etc.

For qualitative detection of iron(III) compounds in solution, the qualitative reaction of Fe 3+ ions with thiocyanate ions SCN − is used. When Fe 3+ ions interact with SCN − anions, a mixture of bright red iron thiocyanate complexes 2+ , + , Fe(SCN) 3 , - is formed. The composition of the mixture (and hence the intensity of its color) depends on various factors, so this method is not applicable for the accurate qualitative determination of iron.

Another high-quality reagent for Fe 3+ ions is potassium hexacyanoferrate (II) K 4 (yellow blood salt). When Fe 3+ and 4− ions interact, a bright blue precipitate of Prussian blue precipitates:

Iron(VI) compounds

The oxidizing properties of ferrates are used to disinfect water.

Iron compounds VII and VIII

There are reports on the electrochemical preparation of iron(VIII) compounds. , , , however, there are no independent works confirming these results.

Application

Iron ore

Iron is one of the most used metals, accounting for up to 95% of the world's metallurgical production.

• Iron is the main component of steels and cast irons - the most important structural materials.
• Iron can be part of alloys based on other metals - for example, nickel.
• Magnetic iron oxide (magnetite) is an important material in the manufacture of long-term computer memory devices: hard drives, floppy disks, etc.
• Ultrafine magnetite powder is used in many black and white laser printers mixed with polymer granules as a toner. It uses both the black color of magnetite and its ability to adhere to a magnetized transfer roller.
• The unique ferromagnetic properties of a number of iron-based alloys contribute to their widespread use in electrical engineering for the magnetic circuits of transformers and electric motors.
• Iron (III) chloride (ferric chloride) is used in amateur radio practice for etching printed circuit boards.
• Ferrous sulfate (iron sulfate) mixed with copper sulphate is used to control harmful fungi in gardening and construction.
• Iron is used as an anode in iron-nickel batteries, iron-air batteries.
• Aqueous solutions of chlorides of divalent and ferric iron, as well as its sulfates, are used as coagulants in the purification of natural and waste water in the water treatment of industrial enterprises.

The biological significance of iron

In living organisms, iron is an important trace element that catalyzes the processes of oxygen exchange (respiration). The body of an adult contains about 3.5 grams of iron (about 0.02%), of which 78% are the main active element of blood hemoglobin, the rest is part of the enzymes of other cells, catalyzing the processes of respiration in cells. Iron deficiency manifests itself as a disease of the body (chlorosis in plants and anemia in animals).

Normally, iron enters enzymes as a complex called heme. In particular, this complex is present in hemoglobin, the most important protein that ensures the transport of oxygen with blood to all organs of humans and animals. And it is he who stains the blood in a characteristic red color.

Iron complexes other than heme are found, for example, in the enzyme methane monooxygenase, which oxidizes methane to methanol, in the important enzyme ribonucleotide reductase, which is involved in DNA synthesis.

Inorganic iron compounds are found in some bacteria and are sometimes used by them to bind atmospheric nitrogen.

Iron enters the body of animals and humans with food (liver, meat, eggs, legumes, bread, cereals, beets are the richest in it). Interestingly, once spinach was erroneously included in this list (due to a typo in the analysis results - the “extra” zero after the decimal point was lost).

An excess dose of iron (200 mg or more) can be toxic. An overdose of iron depresses the antioxidant system of the body, so it is not recommended to use iron preparations for healthy people.

Notes

1. Chemical Encyclopedia: in 5 volumes / Ed.: Knunyants I. L. (chief editor). - M .: Soviet Encyclopedia, 1990. - T. 2. - S. 140. - 671 p. - 100,000 copies.
2. Karapetyants M. Kh., Drakin S. I. General and inorganic chemistry: Textbook for universities. - 4th ed., erased. - M.: Chemistry, 2000, ISBN 5-7245-1130-4, p. 529
3. M. Vasmer. Etymological dictionary of the Russian language. - Progress. - 1986. - T. 2. - S. 42-43.
4. Trubachev O. N. Slavic etymologies. // Questions of Slavic linguistics, No. 2, 1957.
5. Borys W. Slownik etymologiczny języka polskiego. - Krakow: Wydawnictwo Literackie. - 2005. - S. 753-754.
6. Walde A. Lateinisches etymologisches Wörterbuch. - Carl Winter's Universitätsbuchhandlung. - 1906. - S. 285.
7. Meye A. The main features of the Germanic group of languages. - URSS. - 2010. - S. 141.
8. Matasovic R. Etymological Dictionary of Proto-Celtic. - Brill. - 2009. - S. 172.
9. Mallory, J. P., Adams, D. Q. Encyclopedia of Indo-European Culture. - Fitzroy-Dearborn. - 1997. - P. 314.
10. "New Measurement of the 60 Fe Half-Life". Physical Review Letters 103 : 72502. DOI: 10.1103/PhysRevLett.103.072502 .
11. G. Audi, O. Bersillon, J. Blachot and A. H. Wapstra (2003). "The NUBASE evaluation of nuclear and decay properties". Nuclear Physics A 729 : 3–128. DOI:10.1016/j.nuclphysa.2003.11.001 .
12. Yu. M. Shirokov, N. P. Yudin. Nuclear physics. Moscow: Nauka, 1972. Chapter Nuclear space physics.
13. R. Ripan, I. Chetyanu. Inorganic chemistry // Chemistry of non-metals = Chimia metalelor. - Moscow: Mir, 1972. - T. 2. - S. 482-483. - 871 p.
14. Gold and Precious Metals
15. Metal science and heat treatment of steel. Ref. ed. In 3 volumes / Ed. M. L. Bershtein, A. G. Rakhshtadt. - 4th ed., revised. and additional T. 2. Fundamentals of heat treatment. In 2 books. Book. 1. M.: Metallurgiya, 1995. 336 p.
16. T. Takahashi & W.A. Bassett, "High-Pressure Polymorph of Iron," Science, Vol. 145 #3631, 31 Jul 1964, p 483-486.
17. Schilt A. Analytical Application of 1,10-phenantroline and Related Compounds. Oxford, Pergamon Press, 1969.
18. Lurie Yu. Yu. Handbook of analytical chemistry. M., Chemistry, 1989. S. 297.
19. Lurie Yu. Yu. Handbook of analytical chemistry. M., Chemistry, 1989, S. 315.
20. Brower G. (ed.) Guide to inorganic synthesis. v. 5. M., Mir, 1985. S. 1757-1757.
21. Remy G. Course of inorganic chemistry. vol. 2. M., Mir, 1966. S. 309.
22. Kiselev Yu. M., Kopelev N. S., Spitsyn V. I., Martynenko L. I. Octal iron // Dokl. Academy of Sciences of the USSR. 1987. T.292. pp.628-631
23. Perfil'ev Yu. D., Kopelev N. S., Kiselev Yu. Academy of Sciences of the USSR. 1987. T.296. C.1406-1409
24. Kopelev N.S., Kiselev Yu.M., Perfiliev Yu.D. Mossbauer spectroscopy of the oxocomplexes iron in higher oxidation states // J. Radioanal. Nucl. Chem. 1992. V.157. R.401-411.
25. "Norms of physiological needs for energy and nutrients for various groups of the population of the Russian Federation" MR 2.3.1.2432-08

Sources (to the History section)

• G. G. Giorgadze."Text of Anitta" and some questions of the early history of the Hittites
• R. M. Abramishvili. On the issue of the development of iron in the territory of Eastern Georgia, VGMG, XXII-B, 1961.
• Khakhutayshvili D. A. On the history of ancient Colchian iron metallurgy. Questions of ancient history (Caucasian-Middle Eastern collection, issue 4). Tbilisi, 1973.
• Herodotus."History", 1:28.
• Homer. Iliad, Odyssey.
• Virgil."Aeneid", 3:105.
• Aristotle."On Incredible Rumors", II, 48. VDI, 1947, No. 2, p. 327.
• Lomonosov M.V. The first foundations of metallurgy.

see also

• Category: Iron compounds

Links

• Diseases caused by deficiency and excess of iron in the human body

Periodic system of chemical elements of D. I. Mendeleev

IRON (Ferrum, Fe) - an element of group VIII of the periodic system of D. I. Mendeleev; is part of the respiratory pigments, including hemoglobin, is involved in the process of binding and transporting oxygen to tissues in the body of animals and humans; stimulates the function of hematopoietic organs; It is used as a medicine for anemic and some other pathological conditions. The radioactive isotope 59 Fe is used as a radioactive indicator in a wedge, laboratory researches. Ordinal number 26, at. weight 55.847.

Four stable isotopes of iron have been found in nature, with mass numbers 54 (5.84%), 56 (91.68%), 57 (2.17%), and 58 (0.31%).

Iron is found everywhere, both on the Earth, especially in its core, and in meteorites. The earth's crust contains 4.2 weight percent, or 1.5 atomic percent iron. The content of iron in stony meteorites averages 23%, and sometimes reaches 90% (such meteorites are called iron meteorites). In the form of complex organic compounds, iron is a constituent of plant and animal organisms.

Zh. is a part of many minerals, which are iron oxides (red iron ore - Fe 2 O 3, magnetic iron ore - FeO-Fe 2 O 3, brown iron ore - 2Fe 2 O 3 -3H 2 O), or carbonates (siderite - FeCO 3), or sulfur compounds (iron pyrite, magnetic pyrite), or, finally, silicates (eg, olivine, etc.). Zh. is found in ground waters and waters of various reservoirs. Zh. is contained in sea water in a concentration of 5 10 -6%.

In the technique of zinc, it is used in the form of alloys with other elements that significantly change its properties. Iron alloys with carbon are of the greatest importance.

Physico-chemical properties of iron and its compounds

Pure Zh. - a brilliant white malleable metal with a grayish tint; t° pl 1539 ± 5°, t° boiling approx. 3200°; beats weight 7.874; possesses, in comparison with other pure metals, the highest ferromagnetic properties, i.e., the ability to acquire the properties of a magnet under the influence of an external magnetic field.

Two crystalline modifications of iron are known: alpha and gamma iron. The first, alpha modification, is stable below 911° and above 1392°, the second, gamma modification, in the temperature range from 911° to 1392°. At temperatures above 769°, alpha iron is non-magnetic, and below 769°, it is magnetic. Non-magnetic alpha iron is sometimes called beta iron, and high temperature alpha iron is sometimes called delta iron. Zh. easily interacts with diluted acids (for example, with hydrochloric, sulfuric, acetic) with the release of hydrogen and the formation of the corresponding ferrous salts of Zh., i.e., Fe (II) salts. Zh.'s interaction with highly diluted nitric acid occurs without hydrogen evolution with the formation of the ferrous nitrate salt of Zh. - Fe (NO 3) 2 and nitrogen ammonium salt - NH 4 NO 3. At interaction Zh. with konts. nitric acid forms an oxide salt Zh., i.e., a salt of Fe (III), - Fe (NO 3) 3, and nitrogen oxides are simultaneously released.

In dry air, iron is covered with a thin (3 nm thick) oxide film (Fe 2 O 3), but does not rust. At high temperatures, in the presence of air, iron is oxidized, forming iron scale - a mixture of oxide (FeO) and oxide (Fe 2 O 3) Zh. In the presence of moisture and air, iron corrodes; it oxidizes with the formation of rust, the edge is a mixture of hydrated iron oxides. To protect the iron from rusting, it is covered with a thin layer of other metals (zinc, nickel, chromium, etc.) or with oil paints and varnishes, or the formation of iron on the surface is achieved. thin film of nitrous oxide - Fe 3 O 4 (bluing of steel).

Zh. belongs to the elements with variable valence, and therefore its compounds are able to take part in redox reactions. Compounds of bi-, tri- and hexavalent iron are known.

The most stable are compounds of bi- and trivalent iron. Oxygen compounds Zh. - oxide (FeO) and oxide (Fe 2 O 3) - have basic properties and form salts with to-tami. Hydrates of these oxides Fe(OH) 2 , Fe(OH) 3 are insoluble in water. Salts of ferrous, i.e. divalent, liquid (FeCl 2, FeSO 4, etc.), called Fe (II) salts or ferrosalts, are colorless in the anhydrous state, and in the presence of crystallization water or in the dissolved state they have a bluish green color;, they dissociate with the formation of Fe 2+ ions. The crystalline hydrate of double ammonium sulphate and divalent J. (NH 4) 2 SO 4 -FeSO 4 -6H 2 O is called Mohr's salt. A sensitive reaction to salts of Fe (II) is the formation of a precipitate of turnbull blue - Fe 3 2 with p-rum K 3 Fe (CN) 6 .

Salts of oxide, i.e. trivalent iron or Fe (III), called Fe (III) salts or ferrisols, are colored yellow-brown or red-brown, for example, ferric chloride, which is commercially available in the form of a yellow hygroscopic FeCl crystalline hydrate 3 -6H 2 O. Double sulfate salts of Fe (III), called iron alum, for example, iron-ammonium alum (NH 4) 2 SO 4 Fe 2 (SO 4) 3 24H 2 O. In the solution of Fe salts (III) dissociate with the formation of Fe 3+ ions. Sensitive reactions to Fe (III) salts are: 1) the formation of a precipitate of Prussian blue Fe 4 3 with a solution of K 4 Fe (CN) 6 and 2) the formation of red rhodan iron Fe (CNS) 3 with the addition of thiocyanate salts (NH 4 CNS or KCNs).

Compounds of hexavalent iron are salts of iron to-you (ferrates K2FeO4, BaFeO4). Corresponding to these salts iron to - that (H2FeO4) and its anhydride are unstable and in a free state are not received. Ferrates are strong oxidizing agents, they are unstable and easily decompose with the release of oxygen.

There are a large number of complex compounds of liquid. For example, when potassium cyanide is added to salts of ferrous liquid, potassium cyanide first forms a precipitate of cyanide liquid. Fe (CN) 2, which then, with an excess of KCN, dissolves again to form K 4 Fe (CN) 6 [hexacyano- (II) potassium ferrate, potassium ferricyanide, or potassium ferricyanide]. Another example is K 3 Fe (CN) 6 [potassium hexacyano-(III) ferrate, potassium ferricyanide, or potassium ferrocyanide], etc. Ferrocyanide gives the Fe (CN) 4 - ion in solution, and ferricinide gives the Fe ( CN) 6 3- . Zh., contained in these anions, does not give qualitative reactions to iron ions Fe 3+ and Fe 2+. Zh. easily forms complex compounds with many organic acids, as well as with nitrogenous bases. The formation of colored complex compounds of iron with a, alpha1-dipyridyl or with o-phenanthroline underlies very sensitive methods for detecting and quantifying small amounts of iron. Substances such as heme (see Hemoglobin) of biogenic origin are also complex compounds of iron.

With carbon monoxide, iron gives volatile compounds - carbonyls. Carbonyl Zh. Fe (CO) 5 is called pentacarbonyl Zh. and is used to obtain the most pure, free from any impurities Zh. for the purposes of obtaining chemical. catalysts, as well as for some electrical purposes.

Iron in the human body

The body of an adult contains an average of 4-5 g of Fe, of which approx. 70% is in the composition of hemoglobin, (see), 5-10% - in the composition of myoglobin (see), 20-25% in the form of reserve Zh. and no more than 0.1% - in the blood plasma. A nek-swarm quantity Zh. is a part of various organic compounds intracellularly. OK. 1% Zh. is also part of a number of respiratory enzymes (see Respiratory pigments, Respiratory enzymes, Biological oxidation), which catalyze the processes of respiration in cells and tissues.

Zh., found in a blood plasma, is a transport form Zh., a cut is connected with protein transferrin representing beta-globulins and, possibly, alpha-globulins and albumins. Theoretically, 1.25 micrograms of fat can be associated with 1 mg of protein, i.e., in total, approx. 3 mg Zh. However, in fact, transferrin is saturated with Zh. only by 20-50% (an average of one third). Additional quantity Zh., a cut in certain conditions can contact transferrin, defines the unsaturated iron-binding ability (NZhSS) of blood; total amount Zh., a cut can be connected by transferrin, defines the general iron-binding ability (OZHSS) of blood. In the blood serum, the content of Zh. is determined according to Valkvist (V. Vahlquist) in the modification of Hagberg (V. Hagberg) and E. A. Efimova. The method is based on the fact that iron-protein complexes in blood plasma in an acidic environment dissociate with the release of F. Proteins are precipitated, and in a protein-free filtrate, Fe (III) is converted to Fe (II), which forms a colored soluble complex with o-phenanthroline, the color intensity is horn is proportional to the amount of Zh. in the solution. For determination, 0.3 ml of non-hemolyzed blood serum is taken, the calculation is made according to the calibration curve.

The iron-binding ability of blood serum is determined by A. Schade in the modification of Rath (C. Rath) and Finch (C. Finch). The method is based on the fact that the interaction of beta-globulins and divalent iron produces an orange-red complex. Therefore, when ferrosalts (usually Mohr's salts) are added to the blood serum, the intensity of this color increases, edges sharply stabilize at the saturation point of the protein. By quantity Zh., necessary for saturation of protein, judge NZhSS. This value, summed up with the amount of fluid in the blood serum, reflects OZHSS.

Zh.'s maintenance in a blood plasma is subject to daily fluctuations; it decreases by the second half of the day. Zh.'s concentration in a blood plasma also depends on age: at newborns it is equal to 175 mcg%, at children at the age of 1 year - 73 mcg%; then the concentration of Zh. again increases to 110-115 μg% and does not change significantly until the age of 13. In adults, there are differences in the concentration of Zh. in the blood serum depending on gender: the content of Zh. in men is 120 mcg%, and in women - 80 mcg%. In whole blood, this difference is less pronounced. OZHSS of normal blood serum is 290-380 mcg%. With urine in a person, 60-100 mcg of F is excreted per day.

Deposition of iron in tissues

Zh., which is deposited in the tissues of the body, can be of exogenous and endogenous origin. Exogenous siderosis is observed in some professions as an occupational hazard, in particular among miners employed in the development of red iron ore, and among electric welders. In these cases, Fe (III) oxides (Fe 2 O 3) are deposited in the lungs, sometimes with the formation of siderotic nodules diagnosed by radiography. Histologically, nodules are an accumulation of dust containing iron in the lumen of the alveoli, in desquamated alveolar cells, in the interalveolar septa, and in the adventitia of the bronchi with development around the connective tissue. In electric welders, the amount of fluid deposited in the lungs is usually small; its particles are predominantly less than 1 micron; at miners massive deposits are observed., the amount to-rogo in both lungs can reach 45 g and make 39,6% of the weight of the ashes remaining after combustion of a lung. Pure siderosis of the lungs, for example, in electric welders, is not accompanied by pneumosclerosis and disability; miners, however, usually have sidero-silicosis with the development of pneumosclerosis (see).

Exogenous siderosis of the eyeball is observed when iron fragments, shavings, etc. are introduced into the eye; at the same time, metallic fluid passes into bicarbonate, then into hydrate of fluid oxide and is deposited in the processes of the ciliary body, the epithelium of the anterior chamber, the lens capsule, the episcleral tissue, the retina, and the optic nerve, where it can be detected using the appropriate microchem. reactions. Exogenous local siderosis can be observed around iron fragments that have fallen into tissues during household and combat trauma (fragments of grenades, shells, etc.).

The source of endogenous siderosis in the vast majority of cases is hemoglobin with its extra- and intravascular destruction. One of the end products of hemoglobin breakdown is the iron-containing pigment hemosiderin, which is deposited in organs and tissues. Hemosiderin was discovered in 1834 by I. Müller, but the term "hemosiderin" was proposed by A. Neumann only later, in 1888. Hemosiderin is formed by cleavage of heme. It is a polymer of ferritin (see) [Granik (S. Granick)]. Chemically, hemosiderin is an aggregate of Fe(III) hydroxide, more or less firmly bound to proteins, mucopolysaccharides, and cell lipids. The formation of hemosiderin occurs in cells of both mesenchymal and epithelial nature. These cells

V. V. Serov and V. S. Paukov proposed to call them sideroblasts. Hemosiderin granules are synthesized in siderosomes of sideroblasts. Microscopically, hemosiderin has the appearance of grains from yellowish to golden brown, located mostly inside the cells, but sometimes extracellularly. Hemosiderin granules contain up to 35% Zh.; hemosiderin never forms crystalline forms.

Due to the fact that the source of hemosiderin in most cases is hemoglobin, focal deposits of the latter can be observed anywhere in the human body where hemorrhage has occurred (see Hemosiderosis). In hemosiderosis, SH-ferritin (active sulfhydryl form), which has vasoparalytic properties, is detected in the places of hemosiderin deposition. Especially large deposits of hemosiderin, arising from ferritin due to a violation of cellular metabolism Zh., are observed with hemochromatosis (see); while in the liver the amount of deposited fat often exceeds 20-30 g. Deposits of fat in hemochromatosis, in addition to the liver, are observed in the pancreas, kidneys, myocardium, organs of the reticuloendothelial system, sometimes the mucous glands of the trachea, in the thyroid gland, muscles and epithelium of the tongue etc.

In addition to deposits of hemosiderin, sometimes there is impregnation (ferruginization) of the elastic framework of the lungs, elastic membranes of the vessels of the lung with brown induration, or cerebral vessels in the circumference of the hemorrhage (see Brown compaction of the lungs). There is also a ferruginization of individual muscle fibers in the uterus, nerve cells in the brain in certain mental illnesses (idiocy, early and senile dementia, Pick's atrophy, some hyperkinesis). These formations are impregnated with colloidal iron, and ferruginization can be detected only with the help of special reactions.

To detect ionized iron in tissues, the reaction of formation of turnbull blue according to Tiermann-Schmelzer to detect Fe (II) and the reaction of formation of Prussian blue [Perls method using Fe (III)] are most widely used.

The reaction for the formation of turnbull blue is carried out as follows: the prepared sections are placed for 1-24 hours in 10% ammonium sulfide solution to convert all of the fluid into bivalent sulfuric fluid. Then the sections thoroughly rinsed in distilled water are transferred for 10-20 minutes. in a freshly prepared mixture of equal parts of 20% solution of potassium ferricyanide and 1% solution of hydrochloric acid. Zh. is painted in a bright blue color; kernels can be finished with carmine. Use only glass needles to transfer sections.

According to the method of Perls, the sections are placed for several minutes in a freshly prepared mixture of 1 hour 2% aqueous solution of potassium ferricyanide and 1.5 hours 1% solution of hydrochloric acid; then the sections are rinsed with water and the kernels are stained with carmine. J. is painted blue. SH-ferritin is detected using cadmium sulfate (N. D. Klochkov).

Bibliography: Biochemical research methods in the clinic, ed. A. A. Pokrovsky, p. 440, M., 1969; In e r b about l the island and the p. A. and At t e sh e in A. B. Iron in an animal organism, Alma-Ata, 1967, bibliogr.; Glinka N. L. General chemistry, p. 682, L., 1973; Kassirsky I. A. and Alekseev G. A. Clinical hematology, p. 168, M., 1970, bibliogr.; Levin V.I. Production of radioactive isotopes, p. 149, M., 1972; Mashkovsky M. D. Medicines, part 2, p. 94, Moscow, 1977; Normal hematopoiesis and its regulation, ed. N. A. Fedorova, p. 244, M., 1976; Petrov V. N. and Shcherba M. M. Identification, prevalence and geography of iron deficiency, Klin, medical, t. 20, 1972, bibliogr.; P Ya-bov S. I. and Shostka G. D. Molecular genetic aspects of erythropoiesis, L., 1973, bibliogr.; Shch erb and M. M. Iron deficiency states, L., 197 5; Klinische Hamatologie, hrsg. v. H. Begemann, S. 295, Stuttgart, 1970; Pharmacological basis of therapeutics, ed. by L. S. Goodman a. A. Gilman, L., 1975.

G. E. Vladimirov; G. A. Alekseev (gem.), V. V. Bochkarev (rad.), A. M. Vikhert (stalemate. an.), V. V. Churyukanov (farm.).

Definition. Story. Geochemistry. properties of iron. Place of Birth. Physical and chemical properties. Connections. The use of iron.

Iron

Iron is an element of the eighth group (according to the old classification, a side subgroup of the eighth group) of the fourth period of the periodic system of chemical elements. I. Mendeleev with atomic number 26. Denoted 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 high humidity in air. In pure oxygen, iron burns, and in a finely dispersed state, it ignites spontaneously in air.
Actually, iron is usually called its alloys with a low content of impurities (up to 0.8%), which retain the softness and ductility of 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 (alloyed) steel with the addition of alloying metals (chromium, manganese, nickel, etc.). The combination of the specific properties of iron and its alloys make it "metal No. 1" in importance to humans.
In nature, iron is rarely found in its pure form, most often it occurs as part of iron-nickel meteorites. The prevalence of iron in the earth's crust is 4.65% (4th place after O, Si, Al). It is also believed that iron makes up most of the earth's core.

Story. Iron as an instrumental material has been known since ancient times. The oldest iron products found during archaeological excavations date back to the 4th millennium BC. e. and belong to the ancient Sumerian and ancient Egyptian civilizations. These are made of meteoric iron, that is, an alloy of iron and nickel (the content of the latter ranges from 5 to 30%), jewelry from Egyptian tombs (about 3800 BC) and a dagger from the Sumerian city of Ur (about 3100 BC). e.). Apparently, one of the names of iron in Greek and Latin comes from the celestial origin of meteoric iron: “sider” (which means “starry”).

Products made of iron obtained by smelting have been known since the time of the settlement of the Aryan tribes from Europe to Asia, the islands of the Mediterranean Sea, and beyond (the end of the 4th and 3rd millennium BC. The oldest known iron tools are steel blades found in the masonry of the pyramid of Cheops in Egypt (built around 2530 BC) As excavations in the Nubian desert have shown, even in those days the Egyptians, trying to separate the gold they mined from the heavy magnetite sand, calcined ore with bran and similar substances containing carbon. As a result, a layer of dough-like iron floated on the surface of the melted gold, which was processed separately. Tools were forged from this iron, including those found in the pyramid of Cheops. However, after the grandson of Cheops Menkaur (2471-2465 BC), Egypt began to turmoil: the nobility, led by the priests of the god Ra, overthrew the ruling dynasty, and a leapfrog of usurpers began, ending with the accession of the pharaoh of the next dynasty, Userkar, whom the priests declared the son and incarnation of the god Ra himself (since then this has become the official status of the pharaohs). During this turmoil, the cultural and technical knowledge of the Egyptians fell into decay, and, just as the art of building the pyramids degraded, the technology of iron production was lost, to the point that later, mastering the Sinai Peninsula in search of copper ore, the Egyptians did not pay any attention to iron ore deposits there, but received iron from neighboring Hittites and Mitannians.
The first mastered the method of smelting iron of the Hatti, this is indicated by the oldest (2nd millennium BC) mention of iron in the texts of the Hittites, who founded their empire on the territory of the Hatti (modern Anatolia in Turkey). So, in the text of the Hittite king Anitta (about 1800 BC) it says:
In ancient times, Khalibs were reputed to be masters of iron products. The legend of the Argonauts (their campaign to Colchis took place about 50 years before the Trojan War) tells that the king of Colchis, Eet, gave Jason an iron plow to plow the field of Ares, and his subjects, the halibers, are described:
They do not plow the land, do not plant fruit trees, do not graze herds in rich meadows; they extract ore and iron from the uncultivated land and barter food for them. The day does not begin for them without hard work, they spend in the darkness of the night and thick smoke, working all day ...
Aristotle described their method of obtaining steel: “the Khalibs washed the river sand of their country several times - thereby separating the black concentrate (a heavy fraction consisting mainly of magnetite and hematite), and melted it in furnaces; the metal thus obtained had a silvery color and was stainless."
Magnetite sands, which are often found along the entire coast of the Black Sea, were used as raw materials for steel smelting: these magnetite sands consist of a mixture of small grains of magnetite, titano-magnetite or ilmenite, and fragments of other rocks, so that the steel smelted by the Khalibs was alloyed, and had excellent properties. Such a peculiar way of obtaining iron suggests that the Khalibs only spread iron as a technological material, but their method could not be a method for the widespread industrial production of iron products. However, their production served as an impetus for the further development of iron metallurgy.
Clement of Alexandria in his encyclopedic work Stromata mentions that according to Greek legends, iron (apparently, smelting it from ore) was discovered on Mount Ida - this was the name of the mountain range near Troy (in the Iliad it is mentioned as Mount Ida, from which Zeus watched the battle of the Greeks with the Trojans). This happened 73 years after the Deucalion flood, and this flood, according to the Parian Chronicle, was in 1528 BC. e., that is, the method of smelting iron from ore was discovered around 1455 BC. e. However, from the description of Clement it is not clear whether he is talking about this mountain in Asia Minor (Ida Phrygian in Virgil), or about Mount Ida on the island of Crete, about which the Roman poet Virgil writes in the Aeneid as the ancestral home of the Trojans:
"The island of Jupiter, Crete, lies in the midst of a wide sea,
Our tribe is the cradle where Ida rises ... "
It is more likely that Clement of Alexandria speaks specifically of the Phrygian Ida near Troy, since ancient iron mines and centers of iron production were found there. The first written evidence of iron is found in clay tablets from the archives of the Egyptian pharaohs Amenhotep III and Akhenaten, and dates back to the same time (1450-1400 BC). It mentions the manufacture of iron in the south of Transcaucasia, which the Greeks called Colchis (and it is possible that the word "kolhidos" may be a modification of the word "halibos") - namely, that the king of the Mitanni country and the ruler of Armenia and South Transcaucasia sent the Egyptian pharaoh Amenhotep II " along with 318 concubines, daggers and rings of good iron.” The Hittites gave the same gifts to the pharaohs.
In the deepest antiquity, iron was valued more than gold, and according to Strabo's description, the African tribes gave 10 pounds of gold for 1 pound of iron, and according to the studies of the historian G. Areshyan, the cost of copper, silver, gold and iron among the ancient Hittites was in the ratio 1: 160 : 1280: 6400. In those days, iron was used as a jewelry metal, thrones and other regalia of royal power were made from it: for example, in the biblical book Deuteronomy 3.11, an “iron bed” of the Rephaim king Og is described.
In the tomb of Tutankhamen (circa 1350 BC) was found a dagger made of iron in a gold frame - possibly a gift from the Hittites for diplomatic purposes. But the Hittites did not strive for the widespread dissemination of iron and its technologies, which is also evident from the correspondence of the Egyptian pharaoh Tutankhamun and his father-in-law Hattusil, the king of the Hittites, that has come down to us. The pharaoh asks to send more iron, and the king of the Hittites evasively answers that the iron reserves have run out, and the blacksmiths are busy with agricultural work, so he cannot fulfill the request of the royal son-in-law, and sends only one dagger from “good iron” (that is, steel). As you can see, the Hittites tried to use their knowledge to achieve military advantages, and did not give others the opportunity to catch up with them. Apparently, therefore, iron products became widespread only after the Trojan War and the fall of the Hittites, when, thanks to the trading activity of the Greeks, iron technology became known to many, and new iron deposits and mines were discovered. So the Bronze Age was replaced by the Iron Age.
According to Homer's descriptions, although during the Trojan War (circa 1250 BC) weapons were mostly made of copper and bronze, iron was already well known and in great demand, although more as a precious metal. For example, in the 23rd canto of the Iliad, Homer relates that Achilles awarded the winner of a discus-throwing competition with an iron-scream discus. The Achaeans mined this iron from the Trojans and neighboring peoples (Iliad 7.473), including from the Khalibs.
Perhaps iron was one of the reasons that prompted the Achaean Greeks to move to Asia Minor, where they learned the secrets of its production. And excavations in Athens showed that already around 1100 BC. e. and later iron swords, spears, axes, and even iron nails were already widespread. The biblical book of Joshua 17:16 (cf. Judges 14:4) describes that the Philistines (biblical "PILISTIM", and these were proto-Greek tribes related to the later Hellenes, mainly Pelasgians) had many iron chariots, that is, in this iron has already become widely used in large quantities.
Homer calls iron difficult, because in ancient times the main method of obtaining it was the cheese-making process: alternating layers of> iron ore and charcoal were calcined in special furnaces (forges - from the ancient "Horn" - a horn, a pipe, originally it was just a pipe dug in ground, usually horizontally in the slope of a ravine). In the hearth, iron oxides are reduced to metal by hot coal, which takes away oxygen, oxidizing to carbon monoxide, and as a result of such calcination of ore with coal, doughy bloom (spongy) iron was obtained. Kritsu was cleaned of slag by forging, squeezing out impurities with strong hammer blows. The first hearths had a relatively low temperature - noticeably lower than the melting point of cast iron, so the iron turned out to be relatively low-carbon. In order to obtain strong steel, it was necessary to calcinate and forge the iron bar with coal many times, while the surface layer of the metal was additionally saturated with carbon and hardened. This was how “good iron” was obtained - and although it required a lot of work, the products obtained in this way were significantly stronger and harder than bronze ones.
Later, they learned how to make more efficient furnaces (in Russian - blast furnace, domnitsa) for the production of steel, and used furs to supply air to the furnace. Already the Romans were able to bring the temperature in the furnace to the melting of steel (about 1400 degrees, and pure iron melts at 1535 degrees). In this case, cast iron is formed with a melting point of 1100-1200 degrees, which is very brittle in the solid state (not even amenable to forging) and does not have the elasticity of steel. Initially, it was considered a harmful by-product, but then it was discovered that when re-melted in a furnace with increased air blowing through it, cast iron turns into good quality steel, as excess carbon burns out. Such a two-stage process for the production of steel from cast iron turned out to be simpler and more profitable than bloomery, and this principle has been used without much change for many centuries, remaining to this day the main method for the production of iron materials.

isotopes

Natural iron consists of four stable isotopes: 54Fe (isotopic abundance 5.845%), 56Fe (91.754%), 57Fe (2.119%) and 58Fe (0.282%). More than 20 unstable iron isotopes with mass numbers from 45 to 72 are also known, the most stable of which are 60Fe (half-life according to data updated in 2009 is 2.6 million years), 55Fe (2.737 years), 59Fe (44.495 days) and 52Fe (8.275 hours); the remaining isotopes have a half-life of less than 10 minutes.
The iron isotope 56Fe is among the most stable nuclei: all of the following elements can reduce the binding energy per nucleon by decay, and all the previous elements, in principle, could reduce the binding energy per nucleon due to fusion. It is believed that the series of synthesis of elements in the cores of normal stars ends with iron, and all subsequent elements can be formed only as a result of supernova explosions.

Geochemistry of iron

Iron is one of the most common elements in the solar system, especially on the terrestrial planets, in particular on Earth. A significant part of the iron of the terrestrial planets is located in the cores of the planets, where its content is estimated to be about 90%. The content of iron in the earth's crust is 5%, and in the mantle about 12%. Of the metals, iron is second only to aluminum in abundance in the crust. At the same time, about 86% of all iron is in the core, and 14% in the mantle. The content of iron increases significantly in the igneous rocks of the basic composition, where it is associated with pyroxene, amphibole, olivine and biotite. In industrial concentrations, iron accumulates during almost all exogenous and endogenous processes occurring in the earth's crust. Sea water contains iron in very small amounts of 0.002–0.02 mg/l. In river water, it is slightly higher - 2 mg / l.

Geochemical properties of iron

The most important geochemical feature of iron is that it has several oxidation states. Iron in a neutral form - metallic - composes the core of the earth, possibly present in the mantle and very rarely found in the earth's crust. Ferrous iron FeO is the main form of iron in the mantle and the earth's crust. Oxide iron Fe2O3 is characteristic of the uppermost, most oxidized, parts of the earth's crust, in particular, sedimentary rocks.
In terms of crystal chemical properties, the Fe2+ ion is close to the Mg2+ and Ca2+ ions, the other main elements that make up a significant part of all terrestrial rocks. Due to their crystal chemical similarity, iron replaces magnesium and, in part, calcium in many silicates. The content of iron in minerals of variable composition usually increases with decreasing temperature.
iron minerals. In the earth's crust, iron is widely distributed - it accounts for about 4.1% of the mass of the earth's crust (4th place among all elements, 2nd among metals). In the mantle and the earth's crust, iron is concentrated mainly in silicates, while its content is significant in basic and ultrabasic rocks, and low in acidic and intermediate rocks.
A large number of ores and minerals containing iron are known. Of the greatest practical importance are red iron ore (hematite, Fe2O3; contains up to 70% Fe), magnetic iron ore (magnetite, FeFe2O4, Fe3O4; contains 72.4% Fe), brown iron ore or limonite (goethite and hydrogoethite, respectively FeOOH and FeOOH nH2O ). Goethite and hydrogoethite are most often found in weathering crusts, forming the so-called "iron hats", whose thickness reaches several hundred meters. They can also be of sedimentary origin, falling out of colloidal solutions in lakes or coastal areas of the seas. In this case, oolitic, or legume, iron ores are formed. They often contain vivianite Fe3(PO4)2 8H2O, which forms black elongated crystals and radially radiant aggregates.
In nature, iron sulfides are also widespread - pyrite FeS2 (sulfur or iron pyrite) and pyrrhotite. They are not iron ore - pyrite is used to produce sulfuric acid, and pyrrhotite often contains nickel and cobalt.
In terms of iron ore reserves, Russia ranks first in the world.
The content of iron in sea water is 1·10−5—1·10−8%.
Other common iron minerals are:

• Siderite - FeCO3 - contains approximately 35% iron. It has a yellowish-white (with a gray or brown tint in case of contamination) color. The density is 3 g / cm³ and the hardness is 3.5-4.5 on the Mohs scale.
• Marcasite - FeS2 - contains 46.6% iron. It occurs as yellow, like brass, bipyramidal rhombic crystals with a density of 4.6-4.9 g / cm³ and a hardness of 5-6 on the Mohs scale.
• Lollingite - FeAs2 - contains 27.2% iron and occurs in the form of silver-white bipyramidal rhombic crystals. Density is 7-7.4 g / cm³, hardness is 5-5.5 on the Mohs scale.
• Mispicel - FeAsS - contains 34.3% iron. It occurs as white monoclinic prisms with a density of 5.6–6.2 g/cm³ and a hardness of 5.5–6 on the Mohs scale.
• Melanterite - FeSO4 7H2O - is less common in nature and is a green (or gray due to impurities) monoclinic crystals with a vitreous luster, fragile. The density is 1.8-1.9 g/cm³.
• Vivianite - Fe3 (PO4) 2 8H2O - occurs in the form of blue-gray or green-gray monoclinic crystals with a density of 2.95 g / cm³ and a hardness of 1.5-2 on the Mohs scale.

Main deposits

According to the US Geological Survey (2011 estimate), the world's proven reserves of iron ore are about 178 billion tons. The main iron deposits are in Brazil (1st place), Australia, USA, Canada, Sweden, Venezuela, Liberia, Ukraine, France, India. In Russia, iron is mined at the Kursk magnetic anomaly (KMA), the Kola Peninsula, in Karelia and Siberia, in Ukraine - Krivbass, Poltava region, Kerch Peninsula. Recently, bottom oceanic deposits have acquired a significant role, in which iron, together with manganese and other valuable metals, is found in nodules.

Receipt. In industry, iron is obtained from iron ore, mainly from hematite (Fe2O3) and magnetite (FeO·Fe2O3).

There are various ways to extract 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 sinter or pellets, and flux (eg limestone) are fed from above and are met by a stream of injected 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 recovers iron from the ore. To make this reaction go faster, heated carbon monoxide is passed through iron (III) oxide:

The flux is added to get rid of undesirable impurities (primarily from silicates; for example, quartz) in the mined ore. A typical flux contains limestone (calcium carbonate) and dolomite (magnesium carbonate). Other fluxes are used to eliminate other impurities.
The effect of the flux (in this case, calcium carbonate) is that when it is heated, it decomposes to its oxide:

Calcium oxide combines with silicon dioxide, forming a slag - calcium metasilicate:

Slag, unlike silicon dioxide, is melted in a furnace. Lighter than iron, slag floats on the surface - this property allows you to separate the slag from the metal. The slag can then be used in construction and agriculture. The molten iron obtained in a blast furnace contains quite a lot of carbon (cast iron). Except in such cases, when cast iron is used directly, it requires further processing.
Excess carbon and other impurities (sulphur, phosphorus) are removed from cast iron by oxidation in open-hearth furnaces or in converters. Electric furnaces are also used for smelting alloyed steels.
In addition to the blast furnace process, the process of direct production of iron is common. In this case, pre-crushed ore is mixed with special clay to form pellets. The pellets are roasted and treated in a shaft furnace with hot methane conversion products that contain hydrogen. Hydrogen easily reduces iron:
,
while there is no contamination of iron with impurities such as sulfur and phosphorus, which are common impurities in coal. Iron is obtained in solid form, and then melted down in electric furnaces.
Chemically pure iron is obtained by electrolysis of solutions of its salts.

Physical Properties

Iron is a typical metal, in the free state it is silvery-white in color with a grayish tint. Pure metal is ductile, various impurities (in particular, carbon) increase its hardness and brittleness. It has pronounced magnetic properties. The so-called "iron triad" is often distinguished - a group of three metals (iron Fe, cobalt Co, nickel Ni) that have similar physical properties, atomic radii and electronegativity values.
Iron is characterized by polymorphism, it has four crystalline modifications:

• up to 769 °C there is α-Fe (ferrite) with a body-centered cubic lattice and the properties of a ferromagnet (769 °C ≈ 1043 K is the Curie point for iron);
• in the temperature range 769–917 °C, β-Fe exists, which differs from α-Fe only in the parameters of the body-centered cubic lattice and the magnetic properties of the paramagnet;
• in the temperature range 917–1394 °C, there is γ-Fe (austenite) with a face-centered cubic lattice;
• above 1394 °C stable δ-Fe with a body-centered cubic lattice.

Metal science does not distinguish β-Fe as a separate phase, and considers it as a variety of α-Fe. When iron or steel is heated above the Curie point (769 °C ≈ 1043 K), the thermal motion of ions upsets the orientation of the spin magnetic moments of electrons, the ferromagnet becomes a paramagnet - a second-order phase transition occurs, but a first-order phase transition does not occur with a change in the basic physical parameters of the crystals.
For pure iron at normal pressure, from the point of view of metallurgy, there are the following stable modifications:

• from absolute zero to 910 °C, the α-modification with a body-centered cubic (bcc) crystal lattice is stable;
• from 910 to 1400 °C, the γ-modification with a face-centered cubic (fcc) crystal lattice is stable;
• from 1400 to 1539 °C, the δ-modification with a body-centered cubic (bcc) crystal lattice is stable.

The presence of carbon and alloying elements in steel significantly changes the phase transition temperatures (see the iron-carbon phase diagram). A solid solution of carbon in α- and δ-iron is called ferrite. Sometimes a distinction is made between high-temperature δ-ferrite and low-temperature α-ferrite (or simply ferrite), although their atomic structures are the same. A solid solution of carbon in γ-iron is called austenite.

• In the region of high pressures (over 13 GPa, 128.3 thousand atm.), a modification of ε-iron with a hexagonal close-packed (HCP) lattice appears.

The phenomenon of polymorphism is extremely important for steel metallurgy. It is thanks to the α-γ transitions of the crystal lattice that the heat treatment of steel occurs. Without this phenomenon, iron as the basis of steel would not have received such widespread use.
Iron is a moderately refractory metal. In a series of standard electrode potentials, iron stands before hydrogen and easily reacts with dilute acids. Thus, iron belongs to the metals of medium activity.
The melting point of iron is 1539 °C, the boiling point is 2862 °C.

Chemical properties

Characteristic oxidation states

For iron, the oxidation states of iron are characteristic - +2 and +3.
The +2 oxidation state corresponds to black oxide FeO and green hydroxide Fe(OH)2. They are basic. In salts, Fe(+2) is present as a cation. Fe(+2) is a weak reducing agent.
+3 oxidation states correspond to red-brown oxide Fe2O3 and brown hydroxide Fe(OH)3. They are amphoteric in nature, although their acidic and basic properties are weakly expressed. Thus, Fe3+ ions are completely hydrolyzed even in an acidic environment. Fe (OH) 3 dissolves (and even then not completely), only in concentrated alkalis. Fe2O3 reacts with alkalis only when fused, giving ferrites (formal salts of the acid HFeO2 that does not exist in free form):

Iron (+3) most often exhibits weak oxidizing properties.
The +2 and +3 oxidation states easily transition between themselves when the redox conditions change.
In addition, there is Fe3O4 oxide, the formal oxidation state of iron in which is +8/3. However, this oxide can also be considered as iron (II) ferrite Fe+2(Fe+3O2)2.
There is also an oxidation state of +6. The corresponding oxide and hydroxide do not exist in free form, but ferrate salts (for example, K2FeO4) have been obtained. Iron (+6) is in them in the form of an anion. Ferrates are strong oxidizing agents.

Iron(II) compounds

Iron oxide (II) FeO has basic properties, it corresponds to the base Fe (OH) 2. Salts of iron (II) have a light green color. When stored, especially in moist air, they turn brown due to oxidation to iron (III). The same process occurs during storage of aqueous solutions of iron(II) salts:

Of the iron(II) salts in aqueous solutions, Mohr's salt is stable - double ammonium and iron(II) sulfate (NH4)2Fe(SO4)2 6H2O.
Potassium hexacyanoferrate(III) K3 (red blood salt) can serve as a reagent for Fe2+ ions in solution. When Fe2+ and 3− ions interact, potassium-iron (II) hexacyanoferrate (III) precipitates (Prussian blue):

which rearranges intramolecularly to potassium-iron(III) hexacyanoferrate(II):

For the quantitative determination of iron (II) in solution, phenanthroline Phen is used, which forms a red FePhen3 complex with iron (II) (light absorption maximum - 520 nm) in a wide pH range (4-9).

Iron(III) compounds

Iron (III) oxide Fe2O3 is weakly amphoteric, it corresponds to an even weaker than Fe (OH) 2, Fe (OH) 3 base, which reacts with acids:

Fe3+ salts tend to form crystalline hydrates. In them, the Fe3+ ion is usually surrounded by six water molecules. These salts are pink or purple in color.
The Fe3+ ion is completely hydrolyzed even in an acidic environment. At pH>4, this ion almost completely precipitates as Fe(OH)3:

With partial hydrolysis of the Fe3+ ion, polynuclear oxo- and hydroxocations are formed, due to which the solutions become brown.
The main properties of iron(III) hydroxide Fe(OH)3 are very weakly expressed. It is able to react only with concentrated alkali solutions:

The resulting iron(III) hydroxocomplexes are stable only in strongly alkaline solutions. When solutions are diluted with water, they are destroyed, and Fe (OH) 3 precipitates.
When fused with alkalis and oxides of other metals, Fe2O3 forms a variety of ferrites:

Iron(III) compounds in solutions are reduced by metallic iron:

Iron(III) is able to form double sulfates with singly charged alum-type cations, for example, KFe(SO4)2 - iron-potassium alum, (NH4)Fe(SO4)2 - iron-ammonium alum, etc.
For the qualitative detection of iron(III) compounds in solution, the qualitative reaction of Fe3+ ions with inorganic thiocyanates SCN− is used. In this case, a mixture of bright red thiocyanate complexes of iron 2+, +, Fe(SCN)3, - is formed. The composition of the mixture (and hence the intensity of its color) depends on various factors, so this method is not applicable for the accurate qualitative determination of iron.
Another high-quality reagent for Fe3+ ions is potassium hexacyanoferrate(II) K4 (yellow blood salt). When Fe3+ and 4− ions interact, a bright blue precipitate of potassium-iron (III) hexacyanoferrate (II) precipitates:

Fe3+ ions are quantitatively determined by the formation of red (in a slightly acidic medium) or yellow (in a slightly alkaline medium) complexes with sulfosalicylic acid. This reaction requires a competent selection of buffers, since some anions (in particular, acetate) form mixed complexes with iron and sulfosalicylic acid with their own optical characteristics.

Iron(VI) compounds

Ferrates are salts of ferric acid H2FeO4 that does not exist in the free form. These are violet-colored compounds, reminiscent of permanganates in oxidizing properties, and sulfates in solubility. Ferrates are obtained by the action of gaseous chlorine or ozone on a suspension of Fe (OH) 3 in alkali:

Ferrates can also be obtained by electrolysis of a 30% alkali solution on an iron anode:

Ferrates are strong oxidizing agents. In an acidic environment, they decompose with the release of oxygen:

The oxidizing properties of ferrates are used to disinfect water.

Application

Iron is one of the most used metals, accounting for up to 95% of the world's metallurgical production.

• Iron is the main component of steels and cast irons, the most important structural materials.
• Iron can be included in alloys based on other metals, such as nickel.
• Magnetic iron oxide (magnetite) is an important material in the manufacture of long-term computer memory devices: hard drives, floppy disks, etc.
• Ultrafine magnetite powder is used in many black and white laser printers mixed with polymer granules as a toner. It uses both the black color of magnetite and its ability to adhere to a magnetized transfer roller.
• The unique ferromagnetic properties of a number of iron-based alloys contribute to their widespread use in electrical engineering for the magnetic circuits of transformers and electric motors.
• Iron(III) chloride (ferric chloride) is used in amateur radio practice for etching printed circuit boards.
• Ferrous sulfate (iron sulfate) mixed with copper sulphate is used to control harmful fungi in gardening and construction.
• Iron is used as an anode in iron-nickel batteries, iron-air batteries.
• Aqueous solutions of chlorides of divalent and ferric iron, as well as its sulfates, are used as coagulants in the purification of natural and waste water in the water treatment of industrial enterprises.