iron compounds. Iron: physical and chemical properties

Iron is a chemical element

1. The position of iron in the periodic table of chemical elements and the structure of its atom

Iron is a d-element of group VIII; serial number - 26; atomic mass Ar (Fe ) = 56; atom composition: 26-protons; 30 - neutrons; 26 - electrons.

Scheme of the structure of the atom:

Electronic formula: 1s 2 2s 2 2p 6 3s 2 3p 6 3d 6 4s 2

Medium activity metal, reducing agent:

Fe 0 -2 e - → Fe +2 , the reducing agent is oxidized

Fe 0 -3 e - → Fe +3 , the reducing agent is oxidized

Main oxidation states: +2, +3

2. Prevalence of iron

Iron is one of the most abundant elements in nature. . In the earth's crust, its mass fraction is 5.1%, according to this indicator, it second only to oxygen, silicon and aluminum. A lot of iron is also found in celestial bodies, which is established from the data of spectral analysis. In samples of lunar soil, which were delivered by the automatic station "Luna", iron was found in an unoxidized state.

Iron ores are quite widespread on Earth. The names of the mountains in the Urals speak for themselves: High, Magnetic, Iron. Agricultural chemists find iron compounds in soils.

Iron is found in most rocks. To obtain iron, iron ores with an iron content of 30-70% or more are used.

The main iron ores are :

magnetite(magnetic iron ore) - Fe 3 O 4 contains 72% iron, deposits are found in the Southern Urals, the Kursk magnetic anomaly:

hematite(iron sheen, bloodstone) - Fe2O3 contains up to 65% iron, such deposits are found in the Krivoy Rog region:

limonite(brown iron ore) - Fe 2 O 3 * nH 2 O contains up to 60% iron, deposits are found in the Crimea:

pyrite(sulfur pyrite, iron pyrite, cat's gold) - FeS 2 contains approximately 47% iron, deposits are found in the Urals.

3. The role of iron in human and plant life

Biochemists have discovered the important role of iron in the life of plants, animals and humans. Being part of an extremely complex organic compound called hemoglobin, iron determines the red color of this substance, which in turn determines the color of the blood of humans and animals. The body of an adult contains 3 g of pure iron, 75% of which is part of hemoglobin. The main role of hemoglobin is the transfer of oxygen from the lungs to the tissues, and in the opposite direction - CO 2.

Plants also need iron. It is part of the cytoplasm, participates in the process of photosynthesis. Plants grown on an iron-free substrate have white leaves. A small addition of iron to the substrate - and they turn green. Moreover, it is worth smearing a white sheet with a solution of salt containing iron, and soon the smeared place turns green.

So from the same reason - the presence of iron in juices and tissues - the leaves of plants turn green cheerfully and the cheeks of a person blush brightly.

4. Physical properties of iron.

Iron is a silvery-white metal with a melting point of 1539 o C. It is very ductile, therefore it is easily processed, forged, rolled, stamped. Iron has the ability to be magnetized and demagnetized, therefore it is used as the cores of electromagnets in various electrical machines and apparatuses. It can be given greater strength and hardness by methods of thermal and mechanical action, for example, by quenching and rolling.

There are chemically pure and technically pure iron. Technically pure iron, in fact, is a low-carbon steel, it contains 0.02 -0.04% carbon, and even less oxygen, sulfur, nitrogen and phosphorus. Chemically pure iron contains less than 0.01% impurities. chemically pure iron silvery-gray, shiny, in appearance very similar to platinum metal. Chemically pure iron is resistant to corrosion and well resists the action of acids. However, insignificant fractions of impurities deprive it of these precious properties.

5. Obtaining iron

Recovery from oxides with carbon or carbon monoxide (II), as well as hydrogen:

FeO + C = Fe + CO

Fe 2 O 3 + 3CO \u003d 2Fe + 3CO 2

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

Experience "Obtaining iron by aluminothermy"

6. Chemical properties of iron

As an element of a side subgroup, iron can exhibit several oxidation states. We will consider only compounds in which iron exhibits oxidation states +2 and +3. Thus, we can say that iron has two series of compounds in which it is divalent and trivalent.

1) In air, iron is easily oxidized in the presence of moisture (rusting):

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

2) A heated iron wire burns in oxygen, forming scale - iron oxide (II, III) - a black substance:

3Fe + 2O 2 = Fe 3 O 4

Coxygen in moist air forms Fe 2 O 3 * nH 2 O

Experience "Interaction of iron with oxygen"

3) At high temperatures (700–900°C), iron reacts with water vapor:

3Fe + 4H 2 O t˚C → Fe 3 O 4 + 4H 2

4) Iron reacts with non-metals when heated:

Fe + S t˚C → FeS

5) Iron readily dissolves in hydrochloric and dilute sulfuric acids under normal conditions:

Fe + 2HCl \u003d FeCl 2 + H 2

Fe + H 2 SO 4 (diff.) \u003d FeSO 4 + H 2

6) In concentrated acids - oxidizing agents, iron dissolves only when heated

2Fe + 6H 2 SO 4 (conc .) t˚C → Fe 2 (SO 4) 3 + 3SO 2 + 6H 2 O

Fe + 6HNO 3 (conc .) t˚C → Fe(NO 3) 3 + 3NO 2 + 3H 2 OIron(III)

7. The use of iron.

The main part of the iron produced in the world is used to produce iron and steel - iron alloys with carbon and other metals. Cast irons contain about 4% carbon. Steels contain less than 1.4% carbon.

Cast iron is needed for the production of various castings - the beds of heavy machines, etc.

Cast iron products

Steels are used for the manufacture of machines, various building materials, beams, sheets, rolled products, rails, tools and many other products. For the production of various grades of steel, the so-called alloying additives are used, which are various metals: M

Simulator №2 - Fe 3+ Genetic Series

Simulator No. 3 - Equations for the reactions of iron with simple and complex substances

Tasks for fixing

No. 1. Make up the equations for the reactions of obtaining iron from its oxides Fe 2 O 3 and Fe 3 O 4 using as a reducing agent:
a) hydrogen;
b) aluminum;
c) carbon monoxide (II).
For each reaction, make an electronic balance.

No. 2. Carry out the transformations according to the scheme:
Fe 2 O 3 -> Fe - + H2O, t -> X - + CO, t -> Y - + HCl -> Z
Name the products X, Y, Z?

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. To obtain strong steel, it was necessary to calcinate and forge the iron kritsa 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.

In the future, 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. 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

DEFINITION

Iron is the twenty-sixth element of the Periodic Table. Designation - Fe from the Latin "ferrum". Located in the fourth period, VIIIB group. Refers to metals. The nuclear charge is 26.

Iron is the most common metal on the globe after aluminum: it makes up 4% (mass) of the earth's crust. Iron occurs in the form of various compounds: oxides, sulfides, silicates. Iron is found in the free state only in meteorites.

The most important ores of iron include magnetic iron ore Fe 3 O 4 , red iron ore Fe 2 O 3 , brown iron ore 2Fe 2 O 3 ×3H 2 O and spar iron ore FeCO 3 .

Iron is a silvery (Fig. 1) ductile metal. It lends itself well to forging, rolling and other types of machining. The mechanical properties of iron strongly depend on its purity - on the content of even very small amounts of other elements in it.

Rice. 1. Iron. Appearance.

Atomic and molecular weight of iron

Relative molecular weight of a substance(M r) is a number showing how many times the mass of a given molecule is greater than 1/12 of the mass of a carbon atom, and relative atomic mass of an element(A r) - how many times the average mass of atoms of a chemical element is greater than 1/12 of the mass of a carbon atom.

Since in the free state iron exists in the form of monatomic Fe molecules, the values ​​of its atomic and molecular masses are the same. They are equal to 55.847.

Allotropy and allotropic modifications of iron

Iron forms two crystalline modifications: α-iron and γ-iron. The first of them has a cubic body-centered lattice, the second - a cubic face-centered one. α-Iron is thermodynamically stable in two temperature ranges: below 912 o C and from 1394 o C to the melting point. The melting point of iron is 1539 ± 5 o C. Between 912 o C and 1394 o C, γ-iron is stable.

The temperature ranges of stability of α- and γ-iron are due to the nature of the change in the Gibbs energy of both modifications with a change in temperature. At temperatures below 912 o C and above 1394 o C, the Gibbs energy of α-iron is less than the Gibbs energy of γ-iron, and in the range 912 - 1394 o C - more.

Isotopes of iron

It is known that iron can occur in nature in the form of four stable isotopes 54Fe, 56Fe, 57Fe, and 57Fe. Their mass numbers are 54, 56, 57 and 58, respectively. The nucleus of an atom of the iron isotope 54 Fe contains twenty-six protons and twenty-eight neutrons, and the remaining isotopes differ from it only in the number of neutrons.

There are artificial isotopes of iron with mass numbers from 45 to 72, as well as 6 isomeric states of nuclei. The most long-lived among the above isotopes is 60 Fe with a half-life of 2.6 million years.

iron ions

The electronic formula showing the distribution of iron electrons over the orbits is as follows:

1s 2 2s 2 2p 6 3s 2 3p 6 3d 6 4s 2 .

As a result of chemical interaction, iron gives up its valence electrons, i.e. is their donor, and turns into a positively charged ion:

Fe 0 -2e → Fe 2+;

Fe 0 -3e → Fe 3+.

Molecule and atom of iron

In the free state, iron exists in the form of monatomic Fe molecules. Here are some properties that characterize the atom and molecule of iron:

iron alloys

Until the 19th century, iron alloys were mainly known for their alloys with carbon, which received the names of steel and cast iron. However, in the future, new iron-based alloys containing chromium, nickel and other elements were created. At present, iron alloys are divided into carbon steels, cast irons, alloy steels and steels with special properties.

In technology, iron alloys are usually called ferrous metals, and their production is called ferrous metallurgy.

Examples of problem solving

EXAMPLE 1

Exercise	The elemental composition of the substance is as follows: the mass fraction of the iron element is 0.7241 (or 72.41%), the mass fraction of oxygen is 0.2759 (or 27.59%). Derive the chemical formula.
Solution	The mass fraction of the element X in the molecule of the HX composition is calculated by the following formula: ω (X) = n × Ar (X) / M (HX) × 100%. Let us denote the number of iron atoms in the molecule as "x", the number of oxygen atoms as "y". Let us find the corresponding relative atomic masses of the elements of iron and oxygen (the values ​​of the relative atomic masses taken from the Periodic Table of D.I. Mendeleev will be rounded up to integers). Ar(Fe) = 56; Ar(O) = 16. We divide the percentage of elements by the corresponding relative atomic masses. Thus, we will find the relationship between the number of atoms in the molecule of the compound: x:y= ω(Fe)/Ar(Fe) : ω(O)/Ar(O); x:y = 72.41/56: 27.59/16; x:y = 1.29: 1.84. Let's take the smallest number as one (i.e. divide all numbers by the smallest number 1.29): 1,29/1,29: 1,84/1,29; Therefore, the simplest formula for the combination of iron with oxygen is Fe 2 O 3.
Answer	Fe2O3

Iron is one of the most common chemical elements on earth. Since ancient times, people have learned to use it to facilitate their work. With the development of technology, its scope has expanded significantly. If several thousand years ago iron was used only for the manufacture of simple tools used for cultivating the land, now this chemical element is used in almost all areas of high-tech industries.

As Pliny the Elder wrote. “Iron miners provide man with the most excellent and most harmful tool. For with this tool we cut through the earth, we cultivate fertile gardens and, cutting wild vines with grapes, we force them to succumb every year. With this tool we build houses, break stones and use iron for all such needs. But with the same iron we carry out battles, battles and robberies, and we use it not only near, but we carry winged afar either from loopholes, or from powerful hands, or in the form of feathered arrows. The most vicious, in my opinion, is a trick of the human mind. For in order that death befall man sooner, they made it winged, and gave iron feathers. For this reason, let the guilt be attributed to man, and not to nature. Very often it is used for the manufacture of various alloys, the composition of which includes iron in different proportions. The best known of these alloys are steel and cast iron.

Electricity melts iron

The properties of steels are varied. There are steels designed for a long stay in sea water, steels that can withstand high temperatures and the aggressive action of hot gases, steels from which soft tie wires are made, and steels for making elastic and hard springs ...

Such a variety of properties results from the variety of steel compositions. So, from steel containing 1% carbon and 1.5% chromium, high-strength ball bearings are made; steel containing 18% chromium and 89% nickel is the well-known "stainless steel", and turning tools are made from steel containing 18% tungsten, 4% chromium and 1% vanadium.

This variety of steel compositions makes them very difficult to smelt. Indeed, in an open-hearth furnace and a converter, the atmosphere is oxidizing, and elements such as chromium are easily oxidized and turn into slag, i.e., are lost. This means that in order to obtain steel with a chromium content of 18%, much more chromium must be fed into the furnace than 180 kg per ton of steel. Chrome is an expensive metal. How to find a way out of this situation?

A way out was found at the beginning of the 20th century. For metal smelting, it was proposed to use the heat of an electric arc. Scrap metal was loaded into a circular furnace, cast iron was poured and carbon or graphite electrodes were lowered. Between them and the metal in the furnace ("bath") an electric arc with a temperature of about 4000°C. The metal melted easily and quickly. And in such a closed electric furnace, you can create any atmosphere - oxidizing, reducing or completely neutral. In other words, valuable items can be prevented from burning out. This is how the metallurgy of high-quality steels was created.

Later, another method of electric melting was proposed - induction. It is known from physics that if a metal conductor is placed in a coil through which a high-frequency current passes, then a current is induced in it and the conductor heats up. This heat is enough to melt the metal in a certain time. The induction furnace consists of a crucible with a spiral embedded in the lining. A high-frequency current is passed through the spiral, and the metal in the crucible is melted. In such a furnace, you can also create any atmosphere.

In electric arc furnaces, the melting process usually takes place in several stages. First, unnecessary impurities are burned out of the metal, oxidizing them (oxidation period). Then, slag containing oxides of these elements is removed (downloaded) from the furnace, and forroalloys are loaded - iron alloys with elements that need to be introduced into the metal. The furnace is closed and melting is continued without air access (recovery period). As a result, the steel is saturated with the required elements in a given amount. The finished metal is released into a ladle and poured.

Steels, especially high-quality ones, turned out to be very sensitive to the content of impurities. Even small amounts of oxygen, nitrogen, hydrogen, sulfur, phosphorus greatly impair their properties - strength, toughness, corrosion resistance. These impurities form non-metallic compounds with iron and other elements contained in the steel, which wedged between the grains of the metal, impair its uniformity and reduce quality. So, with an increased content of oxygen and nitrogen in steels, their strength decreases, hydrogen causes the appearance of flakes - microcracks in the metal, which lead to unexpected destruction of steel parts under load, phosphorus increases the brittleness of steel in the cold, sulfur causes red brittleness - the destruction of steel under load at high temperatures.

Metallurgists have been looking for ways to remove these impurities for a long time. After smelting in open-hearth furnaces, converters and electric furnaces, the metal is deoxidized - aluminum, ferrosilicon (an alloy of iron with silicon) or ferromanganese are added to it. These elements actively combine with oxygen, float into the slag and reduce the oxygen content in the steel. But oxygen still remains in the steel, and for high-quality steels, its remaining quantities are too large. It was necessary to find other, more effective ways.

In the 1950s, metallurgists began to evacuate steel on an industrial scale. A ladle with liquid metal is placed in a chamber from which air is pumped out. The metal begins to boil violently and gases are released from it. However, imagine a ladle with 300 tons of steel and estimate how long it will take until it boils completely, and how much the metal will cool during this time.

It will immediately become clear to you that this method is suitable only for small amounts of steel. Therefore, other, faster and more efficient vacuuming methods have been developed. Now they are used in all developed countries, and this has improved the quality of steel. But the requirements for it all grew and grew.

In the early 60s in Kyiv, at the All-Union Institute of Electric Welding. E. O. Paton, a method of electroslag remelting of steel was developed, which very soon began to be used in many countries. This method is very simple. In a water-cooled metal vessel - a mold - an ingot of metal is placed, which must be purified, and covered with slag of a special composition. Then the ingot is connected to a current source. An electric arc occurs at the end of the ingot, and the metal begins to melt. Liquid steel reacts with slag and is purified not only from oxides, but also from nitrides, phosphides and sulfides. A new ingot, purified from harmful impurities, solidifies in the mold. In 1963, for the development and implementation of the method of electroslag remelting, a group of workers of the All-Union Institute of Electric Welding, headed by B. I. Medovar and Yu. V. Latash, was awarded the Lenin Prize.

A slightly different path was taken by metallurgical scientists from the Central Research Institute of Ferrous Metallurgy. I. P. Bardina. In collaboration with metallurgical workers, they developed an even simpler method. Slags of a special composition for cleaning metal are melted and poured into a ladle, and then metal is released from the furnace into this liquid slag. The slag mixes with the metal and absorbs impurities. This method is fast, efficient and does not require large amounts of electricity. Its authors S. G. Voinov, A. I. Osipov, A. G. Shalimov and others were also awarded the Lenin Prize in 1966.

However, the reader probably already has a question: why all these difficulties? After all, we have already said that in a conventional electric oven you can create any atmosphere. This means that you can simply pump air out of the furnace and melt in a vacuum. But do not rush to the patent office! This method has long been used in small induction furnaces, and in the late 60s and early 70s it began to be used in fairly large electric arc and induction furnaces. Now, the methods of vacuum arc and vacuum induction remelting have become quite widespread in industrialized countries.

Here we have described only the main methods of cleaning steel from harmful impurities. There are dozens of their varieties. They help metallurgists remove the notorious fly in the ointment from a barrel of honey and get high-quality metal.

How to get iron without blast furnaces

It has already been said above that ferrous metallurgy from the point of view of a chemist is, to put it mildly, an illogical occupation. First, iron is saturated with carbon and other elements, and then a lot of labor and energy are spent to burn out these elements. Isn't it easier to immediately recover iron from ore. After all, this is exactly what the ancient metallurgists did, who received softened hot spongy iron in raw forges. In recent years, this point of view has already moved beyond the stage of rhetorical questions and is based on completely real and even implemented projects. Obtaining iron directly from the ore, bypassing the blast-furnace process, was engaged in the last century. Then this process was called direct reduction. However, until recently, it has not found wide distribution. Firstly, all proposed methods of direct reduction were inefficient, and secondly, the resulting product - sponge iron - was of poor quality and contaminated with impurities. And yet enthusiasts continued to work in this direction.

The situation has changed radically since the widespread use of natural gas in industry. It proved to be an ideal means of recovering iron ore. The main component of natural gas - methane CH 4 - is decomposed by oxidation in the presence of a catalyst in special apparatuses - reformers according to the reaction 2CH 4 + O 2 → 2CO + 2H 2.

It turns out a mixture of reducing gases - carbon monoxide and hydrogen. This mixture enters the reactor, which is fed with iron ore. Let's make a reservation right away - the forms and designs of reactors are very diverse. Sometimes the reactor is a rotating tubular cement type kiln, sometimes a shaft kiln, sometimes a closed retort. This explains the variety of names for direct reduction methods: Midrex, Purofer, Ohalata-i-Lamina, SL-RN, etc. The number of methods has already exceeded two dozen. But their essence is usually the same. Rich iron ore is reduced by a mixture of carbon monoxide and hydrogen.

But what to do with the received products? From sponge iron, not only a good ax - a good nail cannot be forged. No matter how rich the original ore is, pure iron will still not come out of it. According to the laws of chemical thermodynamics, it will not even be possible to restore all the iron contained in the ore; some of it will still remain in the product in the form of oxides. And here a tried friend comes to the rescue - an electric furnace. Sponge iron turns out to be an almost ideal raw material for electrometallurgy. It contains few harmful impurities and melts well.

So, again, a two-step process! But this is another way. The benefit of the direct reduction scheme - the electric furnace is its low cost. Direct reduction plants are much cheaper and use less energy than blast furnaces. Such a blast-furnace steelmaking technology was included in the project of the Oskol Electrometallurgical Plant.

In our country, near Stary Oskol, a large metallurgical plant is being built, which will work exactly according to this scheme. Its first phase has already been put into operation. Note that direct remelting is not the only way to use sponge iron in ferrous metallurgy. It can also be used as a substitute for scrap metal in open hearth furnaces, converters and electric arc furnaces.

The method of melting sponge iron in electric furnaces is also rapidly spreading abroad, especially in countries with large reserves of oil and natural gas, that is, in Latin America and the Middle East. However, already on the basis of these considerations (the availability of natural gas), there is still no reason to believe that the new method will ever completely replace the traditional two-stage method - a blast furnace - a steelmaking unit.

The future of iron

The Iron Age continues. Approximately 90% of all metals and alloys used by mankind are iron-based alloys. Iron is smelted in the world about 50 times more than aluminum, not to mention other metals. Plastics? But in our time, they most often play an independent role in various designs, and if, in accordance with tradition, they are trying to introduce them into the rank of “indispensable substitutes”, then more often they replace non-ferrous metals, not ferrous ones. Only a few percent of the plastics we consume are replacing steel.

Iron-based alloys are universal, technologically advanced, available and cheap in bulk. The raw material base of this metal also does not cause concern: already explored reserves of iron ore would be enough for at least two centuries to come. Iron has long to be the foundation of civilization.

Iron was known in prehistoric times, but it was widely used 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 meteorite 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 (genus case sideris) - a star, a celestial body. In the Hittite texts of the 14th century BC. e. Iron 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 Iron spread in Babylon, Egypt, Greece; The Bronze Age was replaced by the Iron Age. Homer (in the 23rd song of the Iliad) tells that Achilles awarded the winner of the discus throwing competition with an iron cry discus. In Europe and Ancient Rus' for many centuries, iron was obtained by the cheese-making process. Iron ore was reduced with charcoal in a furnace built in a pit; air was pumped into the hearth with furs, 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, that is, cast iron was obtained; this relatively fragile product was considered a waste product. Hence the name of cast iron "chushka", "pig iron" - English. pig iron. Later it was noticed that when not iron ore, but cast iron is loaded into the hearth, a low-carbon iron bloom is also obtained, and such a two-stage process turned out to be more profitable than a raw-blotted 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, the crucible process of obtaining steel began to be used in Europe, which was known in Syria in the early period of the Middle Ages, but later was forgotten. With this method, steel was obtained by melting a metal charge in small vessels (crucibles) from a highly refractory mass. In the last quarter of the 18th century, the puddling process of converting 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, the construction of railways, large bridges, and the steam fleet created an enormous demand for iron and its alloys. However, all existing methods of iron production 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 of iron in nature. In terms of content in the lithosphere (4.65% by weight), iron 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.). Iron takes an active part in magmatic, hydrothermal and supergene processes, which are associated with the formation of various types of its deposits. Iron is a metal of the earth's depths, it accumulates in the early stages of magma crystallization, in ultrabasic (9.85%) and basic (8.56%) rocks (it is only 2.7% in granites). 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 3-valent and vice versa. In the biosphere, in the presence of organic matter, Fe 3+ is reduced to Fe 2+ and easily migrates, and when it encounters atmospheric oxygen, Fe 2+ is oxidized, forming accumulations of trivalent iron hydroxides. Widespread compounds of 3-valent Iron are red, yellow, brown. This determines the color of many sedimentary rocks and their name - "red-colored formation" (red and brown loams and clays, yellow sands, etc.).

Physical properties of iron. The importance of iron 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 is the basis for obtaining a variety of iron alloys.

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

Polymorphic transformations of iron and steel during heating and cooling were discovered in 1868 by D.K. Chernov. Carbon forms interstitial solid solutions with iron, in which C atoms having a small atomic radius (0.77 Å) are located at the interstices of the metal crystal lattice, which consists of larger atoms (Fe atomic radius 1.26 Å). A solid solution of carbon in γ-Fe is called austenite, and in α-Fe it is called ferrite. A saturated solid solution of carbon in γ-Fe contains 2.0% C by mass at 1130 °C; α-Fe dissolves only 0.02-0.04% C at 723 °C, and less than 0.01% at room temperature. Therefore, when austenite is quenched, martensite is formed - a supersaturated solid solution of carbon in α-Fe, which is very hard and brittle. The combination of quenching with tempering (heating to relatively low temperatures to reduce internal stresses) makes it possible to give the steel the required combination of hardness and ductility.

The physical properties of Iron depend on its purity. In industrial iron materials Iron is usually 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 -2% P) - cold brittleness; carbon and nitrogen reduce plasticity, and hydrogen increases the brittleness of Iron (the 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 Iron, referring mainly to a metal with a total impurity content of less than 0.01% by mass:

Atomic radius 1.26Å

Ionic radii Fe 2+ 0.80Å, Fe 3+ 0.67Å

Density (20°C) 7.874 g/cm3

t bale about 3200°С

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

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

The heat capacity of Iron depends on its structure and changes in a complex way with temperature; average specific heat capacity (0-1000°C) 640.57 j/(kg K) .

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 4 10 -6

Shear modulus 84.0 10 3 MN/m 2

Short-term tensile strength 170-210 MN/m2

Relative elongation 45-55%

Brinell hardness 350-450 MN/m2

Yield strength 100 MN/m2

Impact strength 300 MN/m2

Chemical properties of iron. The configuration of the outer electron shell of the atom is 3d 6 4s 2 . Iron exhibits a variable valency (the most stable compounds are 2- and 3-valent Iron). With oxygen, Iron forms oxide (II) FeO, oxide (III) Fe 2 O 3 and oxide (II,III) Fe 3 O 4 (compound of FeO with Fe 2 O 3 having a spinel structure). In humid air at ordinary temperatures, iron becomes covered with loose rust (Fe 2 O 3 nH 2 O). 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 very thin oxide film, which protects the metal from corrosion at ordinary temperatures; this is the basis of the technical method of protecting Iron - 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. When in contact with air, Fe(OH) 2 first turns green, then turns black, and finally quickly turns into red-brown Fe(OH) 3 hydroxide. FeO oxide exhibits basic properties. Oxide Fe 2 O 3 is amphoteric and has a mildly acidic function; reacting with more basic oxides (for example, with MgO, it forms ferrites - compounds of the Fe 2 O 3 nMeO type, which have ferromagnetic properties and are widely used in radio electronics. Acidic properties are also pronounced 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.

Iron easily reacts with halogens and hydrogen halides, giving salts, such as chlorides FeCl 2 and FeCl 3 . When iron is heated with sulfur, FeS and FeS 2 sulfides are formed. Iron carbides - Fe 3 C (cementite) and Fe 2 C (e-carbide) - precipitate from solid solutions of carbon in iron upon cooling. Fe 3 C is also released from solutions of carbon in liquid Iron at high concentrations of C. Nitrogen, like carbon, gives interstitial solid solutions with Iron; nitrides Fe 4 N and Fe 2 N are isolated from them. With hydrogen, iron gives only slightly stable hydrides, the composition of which has not been precisely determined. When heated, iron reacts vigorously with silicon and phosphorus to form silicides (eg Fe 3 Si and phosphides (eg Fe 3 P).

Iron compounds with many elements (O, S and others), which form a crystalline 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 (II), 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.

The normal electrode potential of Iron in aqueous solutions of its salts for the reaction Fe = Fe 2+ + 2e is -0.44 V, and for the reaction Fe = Fe 3+ + 3e is -0.036 V. Thus, in the series of activities, iron is to the left of hydrogen. It readily dissolves in dilute acids with the release of H 2 and the formation of Fe 2+ ions. The interaction of iron with nitric acid is peculiar. Concentrated HNO 3 (density 1.45 g/cm 3) passivates Iron due to the formation of a protective oxide film on its surface; more dilute HNO 3 dissolves Iron with the formation of Fe 2+ or Fe 3+ ions, being reduced to NH 3 or N 2 and N 2 O. Solutions of salts of 2-valent Iron in air are unstable - Fe 2+ gradually oxidizes to Fe 3+. Aqueous solutions of iron salts are acidic due to hydrolysis. The addition of 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. Iron is characterized by the formation of complex compounds.

Getting Iron. 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. 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.

The use of iron. Iron is the most important metal of modern technology. In its pure form, due to its low strength, iron is practically not used, although steel or cast iron products are often called "iron" in everyday life. The bulk of iron is used in the form of alloys with very different compositions 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 iron-rich 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 and electroslag remelting, plasma and electron-beam melting, and others are used for the production of steels and iron alloys for particularly important purposes. Methods are being developed for smelting steel in continuously operating units that ensure high quality of the metal and automation of the process.

On the basis of iron, materials are created that can withstand 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.

Iron as an art material has been used since ancient times in Egypt, Mesopotamia, and India. Since the Middle Ages, numerous highly artistic iron products have been preserved in European countries (England, France, Italy, Russia and others) - forged fences, door hinges, wall brackets, weather vanes, chest fittings, lights. Forged through products from rods and products from 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, iron is used for the manufacture of lattices, fences, openwork interior partitions, candlesticks, and monuments.

Iron in the body. Iron is present in the organisms of all animals and in plants (about 0.02% on average); it is necessary mainly for oxygen exchange and oxidative processes. There are organisms (the so-called concentrators) capable of accumulating it in large quantities (for example, iron bacteria - up to 17-20% of Iron). Almost all of the iron in animal and plant organisms is associated with proteins. Iron deficiency causes growth retardation and plant chlorosis associated with reduced chlorophyll production. An excess of 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 that are inaccessible to plant roots are formed, and 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 iron compounds in soils, plant diseases can be observed in large areas.

Iron enters the body of animals and humans with food (liver, meat, eggs, legumes, bread, cereals, spinach, and beets are the richest in iron). Normally, a person receives 60-110 mg of Iron with the diet, which significantly exceeds his daily requirement. The absorption of iron ingested 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 the blood to various organs and tissues, where it is deposited in the form of an iron-protein complex - ferritin. The main depot of iron in the body is the liver and spleen. Due to ferritin, all the iron-containing compounds of the body are synthesized: the respiratory pigment hemoglobin is synthesized in the bone marrow, myoglobin is synthesized in the muscles, and cytochromes and other iron-containing enzymes are synthesized in various tissues. Iron 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 Iron varies with age and physical condition. For 1 kg of weight, children need - 0.6, adults - 0.1 and pregnant women - 0.3 mg of Iron per day. In animals, the need for Iron is approximately (per 1 kg of dry matter of the diet): for dairy cows - at least 50 mg, for young animals - 30-50 mg; for piglets - up to 200 mg, for pregnant pigs - 60 mg.