Application of barium. Barium

The content of the article

BARIUM– chemical element of the 2nd group of the periodic system, atomic number 56, relative atomic mass 137.33. Located in the sixth period between cesium and lanthanum. Natural barium consists of seven stable isotopes with mass numbers 130(0.101%), 132(0.097%), 134(2.42%), 135(6.59%), 136(7.81%), 137(11. 32%) and 138 (71.66%). Barium in most chemical compounds exhibits a maximum oxidation state of +2, but can also have a zero oxidation state. In nature, barium occurs only in the divalent state.

History of discovery.

In 1602, Casciarolo (Bolognese shoemaker and alchemist) picked up a stone in the surrounding mountains that was so heavy that Casciarolo suspected it was gold. Trying to isolate gold from a stone, the alchemist calcined it with coal. Although it was not possible to isolate gold, the experiment brought clearly encouraging results: the cooled calcination product glowed reddish in the dark. The news of such an unusual find created a real sensation in the alchemical community and the unusual mineral, which received a number of names - sunstone (Lapis solaris), Bolognese stone (Lapis Boloniensis), Bolognese phosphorus (Phosphorum Boloniensis) became a participant in various experiments. But time passed, and gold did not even think of standing out, so interest in the new mineral gradually disappeared, and for a long time it was considered a modified form of gypsum or lime. Only a century and a half later, in 1774, the famous Swedish chemists Karl Scheele and Johan Hahn carefully studied the “Bologna stone” and found that it contained some kind of “heavy earth”. Later, in 1779, Guiton de Morveau named this “land” barote (barote) from the Greek word “barue” - heavy, and later changed the name to baryte (baryte). Under this name, barium earth appeared in chemistry textbooks of the late 18th and early 19th centuries. For example, in the textbook by A.L. Lavoisier (1789), barite is included in the list of salt-forming earthy simple bodies, and another name for barite is given - “heavy earth” (terre pesante, Latin terra ponderosa). The still unknown metal contained in the mineral began to be called barium (Latin - Barium). In Russian literature of the 19th century. The names barite and barium were also used. The next known barium mineral was natural barium carbonate, discovered in 1782 by Withering and later named witherite in his honor. Barium metal was first prepared by Englishman Humphry Davy in 1808 by electrolysis of wet barium hydroxide with a mercury cathode and subsequent evaporation of mercury from barium amalgam. It should be noted that in the same 1808, somewhat earlier than Davy, barium amalgam was obtained by the Swedish chemist Jens Berzelius. Despite its name, barium turned out to be a relatively light metal with a density of 3.78 g/cm 3, so in 1816 the English chemist Clark proposed rejecting the name “barium” on the grounds that if barium earth (barium oxide) is indeed heavier than other earths (oxides), then the metal, on the contrary, is lighter than other metals. Clark wanted to name this element plutonium in honor of the ancient Roman god, ruler of the underground kingdom of Pluto, but this proposal did not meet with support from other scientists and the light metal continued to be called “heavy.”

Barium in nature.

The earth's crust contains 0.065% barium, it occurs in the form of sulfate, carbonate, silicates and aluminosilicates. The main barium minerals are the aforementioned barite (barium sulfate), also called heavy or Persian spar, and witherite (barium carbonate). The world's mineral resources of barite were estimated in 1999 at 2 billion tons, a significant part of them concentrated in China (about 1 billion tons) and Kazakhstan (0.5 billion tons). There are large reserves of barite in the USA, India, Turkey, Morocco and Mexico. Russian barite resources are estimated at 10 million tons, its production is carried out at three main deposits located in Khakassia, Kemerovo and Chelyabinsk regions. The total annual production of barite in the world is about 7 million tons, Russia produces 5 thousand tons and imports 25 thousand tons of barite per year.

Receipt.

The main raw materials for the production of barium and its compounds are barite and, less commonly, witherite. By reducing these minerals with coal, coke or natural gas, barium sulfide and barium oxide are obtained, respectively:

BaSO 4 + 4C = BaS + 4CO

BaSO 4 + 2CH 4 = BaS + 2C + 4H 2 O

BaCO 3 + C = BaO + 2CO

Barium metal is obtained by reducing it with aluminum oxide.

3BaO + 2Al = 3Ba + Al 2 O 3

This process was first carried out by the Russian physical chemist N.N. Beketov. This is how he described his experiments: “I took anhydrous barium oxide and, adding to it a certain amount of barium chloride, like flux, I put this mixture along with pieces of clay (aluminum) in a carbon crucible and heated it for several hours. After cooling the crucible, I found in it a metal alloy of a completely different type and physical properties than clay. This alloy has a coarse-crystalline structure, is very brittle, a fresh fracture has a faint yellowish sheen; analysis showed that at 100 hours it consists of 33.3 barium and 66.7 clay, or, otherwise, for one part of barium it contained two parts of clay...” Currently, the reduction process with aluminum is carried out in a vacuum at temperatures from 1100 to 1250 ° C, while the resulting barium evaporates and condenses on the cooler parts of the reactor.

In addition, barium can be obtained by electrolysis of a molten mixture of barium and calcium chlorides.

Simple substance.

Barium is a silvery-white malleable metal that shatters when struck sharply. Melting point 727° C, boiling point 1637° C, density 3.780 g/cm 3 . At normal pressure it exists in two allotropic modifications: a -Ba with a cubic body-centered lattice is stable up to 375° C; b -Ba is stable above 375° C. At elevated pressure, a hexagonal modification is formed. Metal barium has high chemical activity; it oxidizes intensively in air, forming a film containing BaO, BaO 2 and Ba 3 N 2, and ignites with slight heating or impact.

2Ba + O 2 = 2BaO; Ba + O 2 = BaO 2; 3Ba + N 2 = Ba 3 N 2,

Therefore, barium is stored under a layer of kerosene or paraffin. Barium reacts vigorously with water and acid solutions, forming barium hydroxide or the corresponding salts:

Ba + 2H 2 O = Ba(OH) 2 + H 2

Ba + 2HCl = BaCl 2 + H 2

With halogens, barium forms halides; with hydrogen and nitrogen, when heated, it forms hydride and nitride, respectively.

Ba + Cl 2 = BaCl 2; Ba + H 2 = BaH 2

Metallic barium dissolves in liquid ammonia to form a dark blue solution, from which ammonia Ba(NH 3) 6 can be isolated - crystals with a golden luster that easily decompose with the release of ammonia. In this compound, barium has zero oxidation state.

Application in industry and science.

The use of barium metal is very limited due to its high chemical reactivity; barium compounds are used much more widely. An alloy of barium with aluminum - an Alba alloy containing 56% Ba - is the basis of getters (absorbers of residual gases in vacuum technology). To obtain the getter itself, barium is evaporated from the alloy by heating it in a evacuated flask of the device, as a result of which a “barium mirror” is formed on the cold parts of the flask. In small quantities, barium is used in metallurgy to purify molten copper and lead from impurities of sulfur, oxygen and nitrogen. Barium is added to printing and antifriction alloys; an alloy of barium and nickel is used to make parts for radio tubes and spark plug electrodes in carburetor engines. In addition, there are non-standard uses of barium. One of them is the creation of artificial comets: barium vapor released from a spacecraft is easily ionized by solar rays and turns into a bright plasma cloud. The first artificial comet was created in 1959 during the flight of the Soviet automatic interplanetary station Luna-1. In the early 1970s, German and American physicists, conducting research on the Earth's electromagnetic field, released 15 kilograms of tiny barium powder over Colombia. The resulting plasma cloud stretched along the magnetic field lines, making it possible to clarify their position. In 1979, jets of barium particles were used to study the aurora.

Barium compounds.

Divalent barium compounds are of greatest practical interest.

Barium oxide(BaO): an intermediate product in the production of barium - a refractory (melting point about 2020 ° C) white powder, reacts with water, forming barium hydroxide, absorbs carbon dioxide from the air, turning into carbonate:

BaO + H 2 O = Ba(OH) 2; BaO + CO 2 = BaCO 3

When calcined in air at a temperature of 500–600° C, barium oxide reacts with oxygen, forming peroxide, which, upon further heating to 700° C, again transforms into an oxide, eliminating oxygen:

2BaO + O 2 = 2BaO 2 ; 2BaO2 = 2BaO + O2

This is how oxygen was obtained until the end of the 19th century, until a method for releasing oxygen by distilling liquid air was developed.

In the laboratory, barium oxide can be prepared by calcining barium nitrate:

2Ba(NO3)2 = 2BaO + 4NO2 + O2

Now barium oxide is used as a water-removing agent, to obtain barium peroxide and to make ceramic magnets from barium ferrate (for this, a mixture of barium and iron oxide powders is sintered under a press in a strong magnetic field), but the main use of barium oxide is the manufacture of thermionic cathodes. In 1903, the young German scientist Wehnelt tested the law of the emission of electrons by solids, discovered shortly before by the English physicist Richardson. The first of the experiments with platinum wire completely confirmed the law, but the control experiment failed: the flow of electrons sharply exceeded the expected one. Since the properties of the metal could not change, Wehnelt assumed that there was some kind of impurity on the surface of the platinum. After testing possible surface contaminants, he became convinced that the additional electrons were emitted by barium oxide, which was part of the lubricant of the vacuum pump used in the experiment. However, the scientific world did not immediately recognize this discovery, since its observation could not be reproduced. Only almost a quarter of a century later, the Englishman Kohler showed that in order to exhibit high thermionic emission, barium oxide must be heated at very low oxygen pressures. This phenomenon could only be explained in 1935. The German scientist Pohl suggested that electrons are emitted by a small impurity of barium in the oxide: at low pressures, part of the oxygen evaporates from the oxide, and the remaining barium is easily ionized to form free electrons, which leave the crystal when heated:

2BaO = 2Ba + O 2 ; Ba = Ba 2+ + 2е

The correctness of this hypothesis was finally established in the late 1950s by Soviet chemists A. Bundel and P. Kovtun, who measured the concentration of barium impurity in the oxide and compared it with the flux of thermionic electron emission. Now barium oxide is the active part of most thermionic cathodes. For example, a beam of electrons that forms an image on a TV screen or computer monitor is emitted by barium oxide.

Barium hydroxide, octahydrate(Ba(OH)2· 8H2O). White powder, highly soluble in hot water (more than 50% at 80° C), worse in cold water (3.7% at 20° C). The melting point of the octahydrate is 78° C; when heated to 130° C, it turns into anhydrous Ba(OH) 2. Barium hydroxide is produced by dissolving the oxide in hot water or by heating barium sulfide in a stream of superheated steam. Barium hydroxide easily reacts with carbon dioxide, so its aqueous solution, called “barite water,” is used in analytical chemistry as a reagent for CO 2. In addition, “barite water” serves as a reagent for sulfate and carbonate ions. Barium hydroxide is used to remove sulfate ions from plant and animal oils and industrial solutions, to obtain rubidium and cesium hydroxides, as a component of lubricants.

Barium carbonate(BaCO3). In nature, the mineral is witherite. White powder, insoluble in water, soluble in strong acids (except sulfuric acid). When heated to 1000° C, it decomposes, releasing CO 2:

BaCO 3 = BaO + CO 2

Barium carbonate is added to glass to increase its refractive index and is added to enamels and glazes.

Barium sulfate(BaSO4). In nature - barite (heavy or Persian spar) - the main mineral of barium - is a white powder (melting point about 1680 ° C), practically insoluble in water (2.2 mg / l at 18 ° C), slowly dissolves in concentrated sulfuric acid.

The production of paints has long been associated with barium sulfate. True, at first its use was of a criminal nature: crushed barite was mixed with lead white, which significantly reduced the cost of the final product and, at the same time, deteriorated the quality of the paint. However, such modified whites were sold at the same price as regular whites, generating significant profits for dye plant owners. Back in 1859, the Department of Manufactures and Domestic Trade received information about the fraudulent machinations of Yaroslavl factory owners who added heavy spar to lead white, which “deceives consumers about the true quality of the product, and a request was also received to prohibit the said manufacturers from using spar in the production of lead white.” " But these complaints came to nothing. Suffice it to say that in 1882 a spar plant was founded in Yaroslavl, which in 1885 produced 50 thousand pounds of crushed heavy spar. In the early 1890s, D.I. Mendeleev wrote: “...Barite is mixed into the mixture of white at many factories, since white brought from abroad contains this mixture to reduce the price.”

Barium sulfate is part of lithopone, a non-toxic white paint with high hiding power, widely in demand on the market. To make lithopone, aqueous solutions of barium sulfide and zinc sulfate are mixed, during which an exchange reaction occurs and a mixture of fine-crystalline barium sulfate and zinc sulfide - lithopone - precipitates, and pure water remains in the solution.

BaS + ZnSO 4 = BaSO 4 Ї + ZnSЇ

In the production of expensive grades of paper, barium sulfate plays the role of a filler and weighting agent, making the paper whiter and denser; it is also used as a filler for rubber and ceramics.

More than 95% of the barite mined in the world is used to prepare working solutions for drilling deep wells.

Barium sulfate strongly absorbs x-rays and gamma rays. This property is widely used in medicine for diagnosing gastrointestinal diseases. To do this, the patient is allowed to swallow a suspension of barium sulfate in water or its mixture with semolina porridge - “barium porridge” and is then exposed to x-rays. Those parts of the digestive tract through which the “barium porridge” passes appear as dark spots in the picture. This way the doctor can get an idea of ​​the shape of the stomach and intestines and determine the location of the disease. Barium sulfate is also used to make barite concrete, used in the construction of nuclear power plants and nuclear plants to protect against penetrating radiation.

Barium sulfide(BaS). Intermediate product in the production of barium and its compounds. The commercial product is a gray friable powder, poorly soluble in water. Barium sulfide is used to produce lithopone, in the leather industry to remove hair from hides, and to produce pure hydrogen sulfide. BaS is a component of many phosphors - substances that glow after absorbing light energy. This is what Casciarolo obtained by calcining barite with coal. By itself, barium sulfide does not glow: it requires the addition of activating substances - salts of bismuth, lead and other metals.

Barium titanate(BaTiO3). One of the most industrially important compounds of barium is a white, refractory (melting point 1616 ° C) crystalline substance, insoluble in water. Barium titanate is obtained by fusing titanium dioxide with barium carbonate at a temperature of about 1300° C:

BaCO 3 + TiO 2 = BaTiO 3 + CO 2

Barium titanate is one of the best ferroelectrics (), very valuable electrical materials. In 1944, Soviet physicist B.M. Vul discovered extraordinary ferroelectric abilities (very high dielectric constant) of barium titanate, which retained them in a wide temperature range - almost from absolute zero to +125 ° C. This circumstance, as well as great mechanical strength and The moisture resistance of barium titanate has contributed to its becoming one of the most important ferroelectrics, used, for example, in the manufacture of electrical capacitors. Barium titanate, like all ferroelectrics, also has piezoelectric properties: it changes its electrical characteristics under pressure. When exposed to an alternating electric field, oscillations occur in its crystals, and therefore they are used in piezoelements, radio circuits and automatic systems. Barium titanate was used in attempts to detect gravitational waves.

Other barium compounds.

Barium nitrate and chlorate (Ba(ClO 3) 2) are an integral part of fireworks; the addition of these compounds gives the flame a bright green color. Barium peroxide is a component of ignition mixtures for aluminothermy. Barium (Ba) tetracyanoplatinate(II) glows when exposed to X-rays and gamma rays. In 1895, the German physicist Wilhelm Roentgen, observing the glow of this substance, suggested the existence of a new radiation, later called X-rays. Now barium tetracyanoplatinate(II) is used to cover luminous instrument screens. Barium thiosulfate (BaS 2 O 3) gives colorless varnish a pearly tint, and by mixing it with glue, you can achieve a complete imitation of mother-of-pearl.

Toxicology of barium compounds.

All soluble barium salts are poisonous. Barium sulfate used in fluoroscopy is practically non-toxic. The lethal dose of barium chloride is 0.8–0.9 g, barium carbonate is 2–4 g. When poisonous barium compounds are ingested, a burning sensation in the mouth, pain in the stomach, salivation, nausea, vomiting, dizziness, muscle weakness, and shortness of breath occur. , slow heart rate and drop in blood pressure. The main treatment for barium poisoning is gastric lavage and the use of laxatives.

The main sources of barium entering the human body are food (especially seafood) and drinking water. According to the recommendation of the World Health Organization, the barium content in drinking water should not exceed 0.7 mg/l; in Russia, much more stringent standards apply - 0.1 mg/l.

Yuri Krutyakov

Barium(lat. Baryum), Ba, chemical element of group II of the periodic system of Mendeleev, atomic number 56, atomic mass 137.34; silvery-white metal. It consists of a mixture of 7 stable isotopes, among which 138 Ba (71.66%) predominates. The nuclear fission of uranium and plutonium produces the radioactive isotope 140 Va, which is used as a radioactive tracer. Barium was discovered by the Swedish chemist K. Scheele (1774) in the form of BaO oxide, called “heavy earth”, or barite (from the Greek barys - heavy). Metallic Barium (in the form of an amalgam) was obtained by the English chemist G. Davy (1808) by electrolysis of wet Ba(OH) 2 hydroxide with a mercury cathode. The content of Barium in the earth's crust is 0.05% by weight; it does not occur in nature in a free state. Of the Barium minerals, barite (heavy spar) BaSO 4 and the less common witherite BaCO 3 are of industrial importance.

Physical properties of Barium. The crystal lattice of Barium is cubic body-centered with a period a = 5.019 Å; density 3.76 g/cm 3, tnl 710°C, boiling point 1637-1640°C. Barium is a soft metal (harder than lead, but softer than zinc), its hardness on the mineralogical scale is 2.

Chemical properties of Barium. Barium belongs to the alkaline earth metals and is similar in chemical properties to calcium and strontium, surpassing them in activity. Barium reacts with most other elements, forming compounds in which it is usually 2-valent (there are 2 electrons in the outer electron shell of the Barium atom, its configuration is 6s 2). In air, Barium quickly oxidizes, forming a film of oxide (as well as peroxide and nitride Ba 3 N 2) on the surface. When heated, it ignites easily and burns with a yellow-green flame. Vigorously decomposes water, forming barium hydroxide: Ba + 2H 2 O = Ba(OH) 2 + H 2. Due to its chemical activity, Barium is stored under a layer of kerosene. BaO oxide - colorless crystals; in air it easily transforms into carbonate BaCO 3 and reacts vigorously with water, forming Ba(OH) 2. By heating BaO in air at 500 °C, BaO 2 peroxide is obtained, which decomposes at 700 °C into BaO and O 2. By heating the peroxide with oxygen under high pressure, higher peroxide BaO 4 is obtained - a yellow substance that decomposes at 50-60°C. Barium combines with halogens and sulfur, forming halides (for example, BaCl 2) and BaS sulfide, with hydrogen - BaH 2 hydride, which rapidly decomposes with water and acids. Of the commonly used Barium salts, barium chloride BaCl 2 and other halides, nitrate Ba(NO 3) 2, sulfide BaS, chlorate Ba(ClO 3) 2 are highly soluble, barium sulfate BaSO 4, barium carbonate BaCO 3 and chromate BaCrO 4 are sparingly soluble. .

Obtaining Barium. The main raw material for the production of Barium and its compounds is barite, which is reduced with coal in fiery furnaces: BaSO 4 + 4C = BaS + 4CO. The resulting soluble BaS is processed into other Barium salts. The main industrial method for producing metallic Barium is the thermal reduction of its oxide with aluminum powder: 4BaO + 2Al = 3Ba + BaO·Al 2 O 3 .

The mixture is heated at 1100-1200°C in vacuum (100 mn/m 2, 10 -3 mm Hg). Barium evaporates, depositing on the cold parts of the equipment. The process is carried out in periodic electric vacuum apparatuses, which make it possible to sequentially carry out the reduction, distillation, condensation and casting of the metal, obtaining a Barium ingot in one technological cycle. By double distillation in vacuum at 900°C, the metal is purified to an impurity content of less than 1·10 -4%.

Application of Barium. The practical use of barium metal is small. It is also limited by the fact that manipulation with pure Barium is difficult. Typically, Barium is either placed in a protective shell of another metal, or alloyed with some metal that gives Barium resistance. Sometimes metallic Barium is obtained directly in devices by placing tablets of a mixture of Barium and aluminum oxides into them and then carrying out thermal reduction in a vacuum. Barium, as well as its alloys with magnesium and aluminum, are used in high vacuum technology as an absorber of residual gases (getter). Barium is used in small quantities in the metallurgy of copper and lead for their deoxidation and purification from sulfur and gases. A small amount of Barium is added to some antifriction materials. Thus, the addition of Barium to lead significantly increases the hardness of the alloy used for printing fonts. Barium-nickel alloys are used in the manufacture of electrodes for engine spark plugs and in radio tubes.

Barium compounds are widely used. BaO 2 peroxide is used to produce hydrogen peroxide, for bleaching silk and plant fibers, as a disinfectant and as one of the components of ignition mixtures in aluminothermy. BaS sulfide is used to remove hair from skins. Perchlorate Ba(ClO 4) 2 is one of the best desiccants. Nitrate Ba(NO 3) 2 is used in pyrotechnics. Colored barium salts - BaCrO 4 chromate (yellow) and BaMnO 4 manganate (green) - are good pigments for making paints. Barium platinocyanate Ba is used to cover screens when working with X-ray and radioactive radiation (bright yellow-green fluorescence is excited in the crystals of this salt under the influence of radiation). Barium titanate BaTiO 3 is one of the most important ferroelectrics. Since Barium absorbs X-rays and gamma radiation well, it is included in protective materials in X-ray facilities and nuclear reactors. Barium compounds are inert carriers for the extraction of radium from uranium ores. Insoluble Barium sulfate is non-toxic and is used as a contrast material for X-ray examination of the gastrointestinal tract. Barium carbonate is used to kill rodents.

Barium in the body. Barium is present in all plant organs; its content in plant ash depends on the amount of Barium in the soil and ranges from 0.06-0.2 to 3% (in barite deposits). The accumulation coefficient of Barium (Barium in ash / Barium in soil) for herbaceous plants is 0.2-6, for woody plants 1-30. Barium concentration is greater in roots and branches, less in leaves; it increases as the shoots age. Barium (its soluble salts) is poisonous for animals, so herbs containing a lot of Barium (up to 2-30% in ash) cause poisoning in herbivores. Barium is deposited in bones and in small quantities in other animal organs. A dose of 0.2-0.5 g of barium chloride causes acute poisoning in humans, 0.8-0.9 g causes death.

DEFINITION

Barium located in the sixth period of group II of the main (A) subgroup of the Periodic table.

Belongs to the family s-elements. Metal. Designation - Ba. Serial number - 56. Relative atomic mass - 137.34 amu.

Electronic structure of the barium atom

The barium atom consists of a positively charged nucleus (+56), inside of which there are 56 protons and 81 neutrons, and 56 electrons move around in six orbits.

Fig.1. Schematic structure of the barium atom.

The distribution of electrons among orbitals is as follows:

56Ba) 2) 8) 18) 18) 8) 2 ;

1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 5s 2 5p 6 6s 2 .

The outer energy level of the barium atom contains 2 electrons, which are valence. The energy diagram of the ground state takes the following form:

The barium atom is characterized by the presence of an excited state. Electrons 6 s-sublevels steam out and one of them occupies vacant orbital 6 p-sublevel:

The presence of two unpaired electrons indicates that barium has an oxidation state of +2.

The valence electrons of a barium atom can be characterized by a set of four quantum numbers: n(main quantum), l(orbital), m l(magnetic) and s(spin):

Examples of problem solving

EXAMPLE 1

BARIUM, Ba (Latin Baryum, from the Greek barys - heavy * a. barium; n. Barium; f. barium; i. bario), - a chemical element of the main subgroup of group 11 of the Mendeleev periodic system of elements, atomic number 56, atomic mass 137.33. Natural barium consists of a mixture of seven stable isotopes; 138 Va (71.66%) predominates. Barium was discovered in 1774 by the Swedish chemist K. Scheele in the form of BaO. Metallic barium was first obtained by the English chemist H. Davy in 1808.

Obtaining barium

Barium metal is obtained by thermal reduction in a vacuum at 1100-1200°C of barium oxide powder. Barium is used in alloys - with lead (printing and antifriction alloys), aluminum and (gas absorbers in vacuum installations). Its artificial radioactive isotopes are widely used.

Applications of barium

Barium and its compounds are added to materials intended to protect against radioactive and x-ray radiation. Barium compounds are widely used: oxide, peroxide and hydroxide (to produce hydrogen peroxide), nitride (in pyrotechnics), sulfate (as a contrast agent in radiology, research), chromate and manganate (in the manufacture of paints), titanate (one of the most important ferroelectrics) , sulfide (in the leather industry), etc.

Barium is an element of the main subgroup of the second group, the sixth period of the periodic system of chemical elements of D.I. Mendeleev, with atomic number 56. It is designated by the symbol Ba (lat. Barium). The simple substance is a soft, malleable alkaline earth metal of a silvery-white color. Has high chemical activity.

Barium was discovered as the oxide BaO in 1774 by Karl Scheele. In 1808, the English chemist Humphry Davy obtained barium amalgam by electrolysis of wet barium hydroxide with a mercury cathode; After the mercury evaporated when heated, it released barium metal.

In 1774, the Swedish chemist Carl Wilhelm Scheele and his friend Johan Gottlieb Hahn investigated one of the heaviest minerals - heavy spar BaSO 4. They managed to isolate previously unknown “heavy earth,” which was later called barite (from the Greek βαρυς - heavy). And 34 years later, Humphry Davy, having subjected wet barite earth to electrolysis, obtained a new element from it - barium. It should be noted that in the same 1808, somewhat earlier than Davy, Jene Jacob Berzelius and his colleagues obtained amalgams of calcium, strontium and barium. This is how the element barium appeared.

Ancient alchemists calcined BaSO 4 with wood or charcoal and obtained phosphorescent “Bolognese gems”. But chemically these gems are not BaO, but barium sulfide BaS.

origin of name

It got its name from the Greek barys - “heavy”, since its oxide (BaO) was characterized as having an unusually high density for such substances.

The earth's crust contains 0.05% barium. This is quite a lot - significantly more than, say, lead, tin, copper or mercury. It is not found in the earth in its pure form: barium is active, it belongs to the subgroup of alkaline earth metals and, naturally, is bound quite tightly in minerals.

The main minerals of barium are the already mentioned heavy spar BaSO 4 (more often called barite) and witherite BaCO3, named after the Englishman William Withering (1741...1799), who discovered this mineral in 1782. A small concentration of barium salts is contained in many mineral waters and sea water. The low content in this case is a plus, not a minus, because all barium salts, except sulfate, are poisonous.

Based on mineral associations, barite ores are divided into monomineral and complex. Complex complexes are divided into barite-sulfide (contain sulfides of lead, zinc, sometimes copper and iron pyrite, less often Sn, Ni, Au, Ag), barite-calcite (contain up to 75% calcite), iron-barite (contain magnetite, hematite, and in the upper zones goethite and hydrogoethite) and barite-fluorite (in addition to barite and fluorite, they usually contain quartz and calcite, and zinc, lead, copper and mercury sulfides are sometimes present in the form of small impurities).

From a practical point of view, hydrothermal vein monomineral, barite-sulfide and barite-fluorite deposits are of greatest interest. Some metasomatic strata deposits and eluvial placers are also of industrial importance. Sedimentary deposits, which are typical chemical sediments of water basins, are rare and do not play a significant role.

As a rule, barite ores contain other useful components (fluorite, galena, sphalerite, copper, gold in industrial concentrations), so they are used in combination.

Natural barium consists of a mixture of seven stable isotopes: 130 Ba, 132 Ba, 134 Ba, 135 Ba, 136 Ba, 137 Ba, 138 Ba. The latter is the most common (71.66%). Radioactive isotopes of barium are also known, the most important of which is 140 Ba. It is formed by the decay of uranium, thorium and plutonium.

The metal can be obtained in different ways, in particular by electrolysis of a molten mixture of barium chloride and calcium chloride. It is possible to obtain barium by reducing it from its oxide using an aluminothermic method. To do this, witherite is fired with coal and barium oxide is obtained:

BaCO 3 + C → BaO + 2CO.

Then the mixture of BaO with aluminum powder is heated in vacuum to 1250°C. Reduced barium vapor condenses in the cold parts of the pipe in which the reaction takes place:

3BaO + 2Al → Al 2 O 3 + 3Ba.

It is interesting that the composition of ignition mixtures for aluminothermy often includes barium peroxide BaO 2.

It is difficult to obtain barium oxide by simply calcining witherite: witherite decomposes only at temperatures above 1800°C. It is easier to obtain BaO by calcining barium nitrate Ba(NO 3) 2:

2Ba (NO 3) 2 → 2BaO + 4NO 2 + O 2.

Both electrolysis and reduction with aluminum produce a soft (harder than lead, but softer than zinc) shiny white metal. It melts at 710°C, boils at 1638°C, and its density is 3.76 g/cm 3 . All this fully corresponds to the position of barium in the subgroup of alkaline earth metals.

There are seven known natural isotopes of barium. The most common of these is barium-138; its more than 70%.

Barium is very active. It self-ignites on impact and easily decomposes water to form soluble barium oxide hydrate:

Ba + 2H 2 O → Ba (OH) 2 + H 2.

An aqueous solution of barium oxide hydrate is called barite water. This “water” is used in analytical chemistry for the determination of CO 2 in gas mixtures. But this is already from the story about the use of barium compounds. Metallic barium finds almost no practical use. It is introduced in extremely small quantities into bearing and printing alloys. An alloy of barium and nickel is used in radio tubes, pure barium is used only in vacuum technology as a getter (gas absorber).

Metal barium is obtained from the oxide by reduction with aluminum in a vacuum at 1200-1250°C:

4BaO + 2Al = 3Ba + BaAl 2 O 4.

Barium is purified by vacuum distillation or zone smelting.

Preparation of barium titanium. It is relatively easy to obtain. Witherite BaCO 3 at 700...800°C reacts with titanium dioxide TiO 2, the result is exactly what is needed:

BaCO 3 + TiO 2 → BaTiO 3 + CO 2.

Basic prom. The method for obtaining barium metal from BaO is its reduction with A1 powder: 4BaO + 2A1 -> 3Ba + BaO*A1 2 O 3. The process is carried out in a reactor at 1100-1200 °C in an Ar atmosphere or in a vacuum (the latter method is preferable). The molar ratio of BaO:A1 is (1.5-2):1. The reactor is placed in a furnace so that the temperature of its “cold part” (the resulting barium vapors are condensed in it) is about 520 ° C. By distillation in vacuum, barium is purified to an impurity content of less than 10 ~ 4% by weight, and when using zone melting - up to 10 ~ 6%.

Small amounts of barium are also obtained by the reduction of BaBeO 2 [synthesized by the fusion of Ba(OH) 2 and Be(OH) 2 ] at 1300°C with titanium, as well as the decomposition at 120°C of Ba(N 3) 2 formed during exchange p- tions of barium salts with NaN 3.

Ba acetate (OOСSN 3), - colorless. crystals; m.p. 490°C (with decomposition); dense 2.47 g/cm3; sol. in water (58.8 g per 100 g at 0°C). Below 25 °C, trihydrate crystallizes from aqueous solutions, at 25-41 °C - monohydrate, above 41 °C - anhydrous salt. Receive interaction. Ba(OH)2, BaCO3 or BaS with CH3CO2H. Used as a mordant when dyeing wool and calico.

Manganate(VI) BaMnO 4 - green crystals; does not decompose up to 1000°C. Obtained by calcination of a mixture of Ba(NO 3) 2 with MnO 2. A pigment (Cassel, or manganese green) commonly used for fresco painting.

Chromate(VI) BaСrO 4 - yellow crystals; m.p. 1380°C; - 1366.8 kJ/mol; sol. in non-org. k-tah, not sol. in water. Receive interaction. aqueous solutions of Ba(OH) 2 or BaS with alkali metal chromates(VI). Pigment (barite yellow) for ceramics. MPC 0.01 mg/m 3 (in terms of Cr0 3). Pyrconate BaZrO 3 - colorless. crystals; m.p. ~269°C; - 1762 kJ/mol; sol. in water and aqueous solutions of alkalis and NH 4 HCO 3, decomposes by strong inorg. to-tami. Receive interaction. ZrO 2 with BaO, Ba(OH) 2 or BaCO 3 when heated. Ba zirconate mixed with BaTiO 3 is a piezoelectric.

Bromide BaBr 2 - white crystals; m.p. 847°C; dense 4.79 g/cm3; -757 kJ/mol; well sol. in water, methanol, worse - in ethanol. Dihydrate crystallizes from aqueous solutions, turning into monohydrate at 75°C, into anhydrous salt - above 100°C. In aqueous solutions, interaction. with CO 2 and O 2 of air, forming BaCO 3 and Br 2. Get BaBr 2 interaction. aqueous solutions of Ba(OH) 2 or BaCO 3 with hydrobromic acid.

Iodide BaI 2 - colorless. crystals; m.p. 740°C (with decomposition); dense 5.15 g/cm3; . -607 kJ/mol; well sol. in water and ethanol. From hot water solutions, the dihydrate crystallizes (dehydrates at 150°C), below 30°C - the hexahydrate. Get BaI 2 interaction. aqueous solutions of Ba(OH) 2 or BaCO 3 with hydroiodic acid.

Barium is a silvery-white malleable metal. If struck sharply, it breaks. There are two allotropic modifications of barium: α-Ba with a cubic body-centered lattice (parameter a = 0.501 nm) is stable up to 375 °C; β-Ba is stable above it.

Hardness on the mineralogical scale 1.25; Mohs scale 2.

Store barium metal in kerosene or under a layer of paraffin.

Barium is an alkaline earth metal. It oxidizes intensively in air, forming barium oxide BaO and barium nitride Ba 3 N 2 , and ignites with slight heating. Reacts vigorously with water, forming barium hydroxide Ba(OH) 2:

Ba + 2H 2 O = Ba(OH) 2 + H 2

Actively interacts with dilute acids. Many barium salts are insoluble or slightly soluble in water: barium sulfate BaSO 4, barium sulfite BaSO 3, barium carbonate BaCO 3, barium phosphate Ba 3 (PO 4) 2. Barium sulfide BaS, unlike calcium sulfide CaS, is highly soluble in water.

Nature Barium consists of seven stable isotopes since May. parts 130, 132, 134-137 and 138 (71.66%). The cross-section of thermal neutron capture is 1.17-10 28 m 2. External configuration electron shell 6s 2 ; oxidation state + 2, rarely + 1; ionization energy Ba°->Ba + ->Ba 2+ resp. 5.21140 and 10.0040 eV; Pauling electronegativity 0.9; atomic radius 0.221 nm, ionic radius Ba 2+ 0.149 nm (coordination number 6).

Reacts easily with halogens to form halides.

When heated with hydrogen, it forms barium hydride BaH 2 , which in turn forms the Li complex with lithium hydride LiH.

Reacts when heated with ammonia:

6Ba + 2NH 3 = 3BaH 2 + Ba 3 N 2

When heated, barium nitride Ba 3 N 2 reacts with CO, forming cyanide:

Ba 3 N 2 + 2CO = Ba(CN) 2 + 2BaO

With liquid ammonia it gives a dark blue solution, from which ammonia can be isolated, which has a golden sheen and easily decomposes with the elimination of NH 3. In the presence of a platinum catalyst, ammonia decomposes to form barium amide:

Ba(NH 2) 2 + 4NH 3 + H 2

Barium carbide BaC 2 can be obtained by heating BaO with coal in an arc furnace.

With phosphorus it forms phosphide Ba 3 P 2 .

Barium reduces the oxides, halides and sulfides of many metals to the corresponding metal.

An alloy of barium with A1 (Alba alloy, 56% Ba) is the basis of getters (gas absorbers). To obtain the getter itself, barium is evaporated from the alloy by high-frequency heating in an evacuated flask of the device; as a result, the so-called barium is formed on the cold parts of the flask. barium mirror (or diffuse coating during evaporation in a nitrogen environment). The active part of the vast majority of thermionic cathodes is BaO. Barium is also used as a deoxidizing agent for Cu and Pb, and as an additive to antifriction agents. alloys, ferrous and non-ferrous metals, as well as alloys from which printing fonts are made to increase their hardness. Alloys of barium with Ni are used for the manufacture of spark plug electrodes in internal engines. combustion and in radio tubes. 140 Va (T 1/2 12.8 days) is an isotopic indicator used in the study of barium compounds.

Barium metal, often alloyed with aluminum, is used as a getter in high-vacuum electronic devices.

Barium is added together with zirconium to liquid metal coolants (alloys of sodium, potassium, rubidium, lithium, cesium) to reduce the aggressiveness of the latter to pipelines and in metallurgy.

Barium fluoride is used in the form of single crystals in optics (lenses, prisms).

Barium peroxide is used for pyrotechnics and as an oxidizing agent. Barium nitrate and barium chlorate are used in pyrotechnics to color flames (green fire).

Barium chromate is used in the production of hydrogen and oxygen by thermochemical method (Oak Ridge cycle, USA).

Barium oxide, together with oxides of copper and rare earth metals, is used to synthesize superconducting ceramics operating at liquid nitrogen temperatures and above.

Barium oxide is used to melt a special type of glass - used to coat uranium rods. One of the widespread types of such glasses has the following composition - (phosphorus oxide - 61%, BaO - 32%, aluminum oxide - 1.5%, sodium oxide - 5.5%). Barium phosphate is also used in glass melting for the nuclear industry.

Barium fluoride is used in solid-state fluorine batteries as a component of the fluoride electrolyte.

Barium oxide is used in high-power copper oxide batteries as a component of the active mass (barium oxide-copper oxide).

Barium sulfate is used as a negative electrode active mass expander in the production of lead-acid batteries.

Barium carbonate BaCO 3 is added to the glass mass to increase the refractive index of the glass. Barium sulfate is used in the paper industry as a filler; The quality of paper is largely determined by its weight; barite BaSO 4 makes the paper heavier. This salt is necessarily included in all expensive types of paper. In addition, barium sulfate is widely used in the production of white paint lithopone - a product of the reaction of solutions of barium sulfide with zinc sulfate:

BaS + ZnSO 4 → BaSO 4 + ZnS.

Both salts, which are white, precipitate, leaving pure water in the solution.

When drilling deep oil and gas wells, a suspension of barium sulfate in water is used as a drilling fluid.

Another barium salt has important uses. This is barium titanate BaTiO 3 - one of the most important ferroelectrics (ferroelectrics are polarized on their own, without the influence of an external field. They stand out among dielectrics in the same way as ferromagnetic materials among conductors. The ability for such polarization is retained only at a certain temperature. Polarized ferroelectrics differ higher dielectric constant), which are considered very valuable electrical materials.

In 1944, this class was replenished with barium titanate, the ferroelectric properties of which were discovered by the Soviet physicist B.M. Vulom. The peculiarity of barium titanate is that it retains ferroelectric properties over a very wide temperature range - from close to absolute zero to +125°C.

Barium has also found application in medicine. Its sulfate salt is used in the diagnosis of gastric diseases. BaSO 4 is mixed with water and given to the patient to swallow. Barium sulfate is opaque to X-rays, and therefore those parts of the digestive tract through which the “barium porridge” passes remain dark on the screen. This way the doctor gets an idea of ​​the shape of the stomach and intestines and determines the place where an ulcer may occur.

The effect of barium on the human body

Routes of entry into the body.
The main route of entry of barium into the human body is food. Thus, some marine inhabitants are capable of accumulating barium from the surrounding water, and in concentrations 7-100 (and for some marine plants up to 1000) times higher than its content in sea water. Some plants (soybeans and tomatoes, for example) are also capable of accumulating barium from the soil 2-20 times. However, in areas where barium concentrations in water are high, drinking water may also contribute to total barium consumption. The intake of barium from the air is insignificant.

Health hazard.
Scientific epidemiological studies conducted under the auspices of WHO did not confirm the relationship between mortality from cardiovascular diseases and barium levels in drinking water. In short-term studies in volunteers, no harmful effects on the cardiovascular system were detected at barium concentrations up to 10 mg/l. True, in experiments on rats, when the latter consumed water even with a low barium content, an increase in systolic blood pressure was observed. This indicates a potential risk of increased blood pressure in people with long-term consumption of water containing barium (USEPA has such data).
USEPA data also suggests that even a single drink of water containing barium levels well above the maximum permissible levels can lead to muscle weakness and abdominal pain. It is necessary, however, to take into account that the standard for barium established by the USEPA quality standard (2.0 mg/l) significantly exceeds the value recommended by WHO (0.7 mg/l). Russian sanitary standards set an even more stringent MPC value for barium in water - 0.1 mg/l. Technologies for removing water: ion exchange, reverse osmosis, electrodialysis.