Where argon is used. Argon is the laziest gas

Argon is chemical element 18, denoted by the symbol Ar (from the Latin Argon). It is the third most common chemical element in the Earth's atmosphere, the first two being oxygen and nitrogen.

Argon was accidentally discovered by British scientist Henry Cavendish in 1795. However, no one paid attention to the discovery, because during the Cavendish experiments, a negligible amount of substance was released, the reasons for the appearance of which no one could understand, even the scientist himself. But in 1894, William Ramsay isolated 40 ml of a hitherto unknown gas and substantiated its existence. This chemical element turned out to be argon.

Argon use

Argon, as a chemical element, is in great demand, primarily as a substance that is not capable of chemical reactions. Having filled the installation or the entire workshop with argon, there is no need to be afraid that a heated metal part or workpiece will oxidize or be saturated with nitrogen, followed by the release of nitrides. For example, molybdenum and tungsten are prone to oxidation: many could observe the instant transformation of the filament of an incandescent lamp into a bluish powder when air enters it. Titanium, tantalum, niobium, beryllium, hafnium, zirconium, as well as uranium, thorium and plutonium are treated in argon. By blowing argon through the steel, gas inclusions are removed from it. A revolution in technology was made by the method of argon-arc welding: an argon flow supplied to the place where an electric arc is burning displaces air and prevents the metal from oxidizing - oxides reduce the strength of the seam, or even make welding of materials impossible. This method is used to weld alloy steels and non-ferrous metals, cut their thick sheets. This gas is also used in medicine - it is an argon cutter in surgery and caries treatment in dentistry, as well as disinfection of wounds. An argon laser is used to treat diabetes-related blindness. Such blindness appears due to the excessive development of blood vessels in the eye, and with an argon laser they can be painlessly thinned out.

Discovery history:

The first contribution to the discovery of argon was made by the English physicist and chemist Henry Cavendish. Studying in 1785 the oxidation of atmospheric nitrogen by oxygen under the action of an electric discharge, he found that a small volume of gas remains, which does not undergo oxidation. However, he did not find an explanation for this fact. In 1892, the English physicist J. Rayleigh discovered a slight (only 0.13%) excess of the density of nitrogen released from the air over the density of nitrogen obtained by chemical means. The English physicist W. Ramsay suggested that the reason for this could be an admixture of a still unknown heavier gas and proposed to isolate it. He and J. Rayleigh in 1894 succeeded in isolating this gas and using spectral analysis to prove that it is a new chemical element. Further research showed the complete chemical inertness of this substance. Due to its chemical inertness (and this was the first of the open inert gases), the new element got its name Argon (Greek argos - inactive, lazy).

Being in nature and receiving:

The atmospheric air contains 0.93% argon by volume (9.34 liters in 1m 3), its reserves in the atmosphere are estimated at 4 · 10 14 tons. Among other isotopes, argon-40 predominates, which is constantly formed during a nuclear reaction ("electronic capture ") from the natural isotope of potassium: 40 K + e \u003d 40 Ar + n e
In industry, argon is obtained as a by-product in the large-scale separation of air into oxygen and nitrogen. At a temperature of -185.9 ° C, argon condenses, at -189.4 ° C it crystallizes.

Physical properties:

Colorless, odorless gas. The boiling point of argon (at normal pressure) is -185.9 ° C, the melting point is -189.4 ° C. The density under normal conditions is 1.784 kg / m3. About 3.3 ml of argon dissolves in 100 ml of water at 20 ° C. argon dissolves much better in some organic solvents than in water. When an electric discharge is passed through a glass tube filled with argon, a blue-blue glow is observed.

Chemical properties:

Argon is chemically inert and does not form chemical compounds under normal conditions. However, with many substances, between the molecules of which hydrogen bonds act (water, phenol, hydroquinone, and others), it forms inclusion compounds (clathrates), where the argon atom, as a kind of "guest", is in the cavity formed in the crystal lattice by the molecules of the substance owner.
At extremely low temperatures, spectral methods have recorded the formation of some extremely unstable molecules containing argon.
The existence of so-called excimer molecules containing argon has been established. The transitions of these molecules from a metastable state to an unbound state generate laser radiation.

The most important connections:

Clathrate Ar * 6H 2 O - inclusion compound, decomposition temperature Аr 6Н2О at 101325 Pa 42.0 ° С.

Argon Hydrofluoride HArF - the first discovered, and so far the only chemical compound of argon with an electrically neutral molecule known in 2013. Obtained by UV irradiation of a mixture of argon and hydrogen fluoride at 8 K. It is unstable and decomposes already at 17 K into hydrogen fluoride and argon.

CU (Ar) O - the formation of such a compound at 3 K is assumed on the basis of spectral data. In this molecule, uranium must be bonded to three other atoms - carbon, argon and oxygen.

Application:

Argon is widely used to create an inert and protective atmosphere, primarily in the heat treatment of easily oxidized metals (argon melting, argon welding, and others). In an argon atmosphere, semiconductor crystals and many other ultrapure materials are obtained. Argon is often filled with light bulbs (to slow the evaporation of tungsten from the coil). This property is also used in argon welding, which allows you to connect aluminum and duralumin parts.

Argon (mixed with neon, mercury vapor) is used to fill gas discharge tubes (blue-blue glow), which is used in luminous advertising. Argon is also used in argon lasers.

In geochronology, the age of minerals is established by determining the ratio of 40 Ar / 40 K isotopes.

Mavlyanova N.Kh., Zhudin S.M.
Tyumen State University, group 501, 2013

Sources:
Argon / WebElements.narod.ru/ URL: http://webelements.narod.ru/elements/Ar.htm (date of access: 8.07.13).
Argon (element) // Wikipedia. URL: http://ru.wikipedia.org/wiki/Argon (date of access: 8.07.2013).

Argon- a monoatomic gas with a boiling point (at normal pressure) of 185.9 ° C (slightly lower than oxygen, but slightly higher than nitrogen). 3.3 ml of argon dissolves in 100 ml of water at 20 ° C; in some organic solvents, argon dissolves much better than in water.

So far, only 2 chemical compounds of argon are known - argon hydrofluoride and CU (Ar) O, which exist at very low temperatures. In addition, argon forms excimer molecules, that is, molecules in which the excited electronic states are stable and the ground state is unstable. There is reason to believe that the extremely unstable Hg-Ar compound formed in an electric discharge is a truly chemical (valence) compound. It is possible that other valence compounds of argon with fluorine and oxygen will be obtained, which should also be extremely unstable. For example, upon electrical excitation of a mixture of argon and chlorine, a gas-phase reaction with the formation of ArCl is possible. Also, with many substances, between the molecules of which hydrogen bonds act (water, phenol, hydroquinone and others), it forms inclusion compounds (clathrates), where the argon atom, as a kind of "guest", is in the cavity formed in the crystal lattice by the molecules of the substance owner.

The CU (Ar) O compound is obtained from the compound of uranium with carbon and oxygen CUO. The existence of compounds with Ar-Si and Ar-C bonds: FArSiF3 and FArCCH is likely.

Argon production

The Earth's atmosphere contains 66 1013 tons of argon. This source of argon is inexhaustible, especially since almost all argon sooner or later returns to the atmosphere, since it does not undergo any physical or chemical changes during use. The exception is very small amounts of argon isotopes, which are used to obtain new elements and isotopes in nuclear reactions.

Argon is obtained as a by-product when air is separated into oxygen and nitrogen. Typically, air separators of double rectification are used, consisting of a lower high pressure column (preliminary separation), an upper low pressure column and an intermediate condenser-evaporator. Ultimately, nitrogen is removed from the top and oxygen from the space above the condenser.

The composition of the argon fraction: 10 ... 12% argon, up to 0.5% nitrogen, the rest is oxygen. In an "argon" column connected to the main apparatus, argon is obtained with an admixture of 3 ... 10% oxygen and 3 ... 5% nitrogen.

Argon is produced on an industrial scale up to 99.99% purity. Argon is also extracted from the wastes of the ammonia production - from the nitrogen left after most of it has been bound with hydrogen.

Argon stored and transported in 40-liter cylinders, painted gray with a green stripe and green inscription. The pressure in them is 150 atm. The transportation of liquefied argon is more economical, for which Dewar vessels and special tanks are used. Artificial radioisotopes of argon were obtained by irradiating some stable and radioactive isotopes (37Cl, 36Ar, 40Ar, 40Ca) with protons and deuterons, as well as by irradiating the products formed in nuclear reactors during the decay of uranium with neutrons. Isotopes 37Ar and 41Ar are used as radioactive indicators: the first is in medicine and pharmacology, the second is in the study of gas flows, the efficiency of ventilation and in various scientific research. But, of course, these are not the most important uses of argon.

Argon use

The earth's atmosphere contains 66 1013 tons of argon. Argon is obtained as a by-product when air is separated into oxygen and nitrogen. The volatility of argon is greater than that of oxygen, but less than that of nitrogen. Therefore, the argon fraction is taken at a point located approximately one third of the height of the upper column, and taken to a special column. The composition of the argon fraction: 10-12% argon, up to 0.5% nitrogen, the rest is oxygen. In an "argon" column connected to the main apparatus, argon is obtained with an admixture of 3-10% oxygen and 3-5% nitrogen. This is followed by purification of "raw" argon from oxygen (by chemical means or adsorption) and from nitrogen (rectification).

As the most accessible and relatively inexpensive inert gas, argon has become a mass-produced product, especially in recent decades. The largest part of the argon produced goes to metallurgy, metalworking and some related industries.

In an argon environment, processes are carried out in which it is necessary to exclude the contact of molten metal with oxygen, nitrogen, carbon dioxide and air moisture. An argon medium is used in hot working of titanium, tantalum, niobium, beryllium, zirconium, hafnium, tungsten, uranium, thorium, and alkali metals. Plutonium is processed in an argon atmosphere, some compounds of chromium, titanium, vanadium and other elements (strong reducing agents) are obtained.

By blowing argon gas inclusions are removed from it through liquid steel. This improves the properties of the metal. Electric arc welding in argon is increasingly used. The argon jet can weld thin-walled products and metals that were previously considered difficult to weld.

The electric arc in an argon atmosphere revolutionized metal cutting technology. The process has accelerated much, it became possible to cut thick sheets of the most refractory metals. Argon blown along the arc column (mixed with hydrogen) protects the cut edges and the tungsten electrode from the formation of oxide, nitride and other films. At the same time, it compresses and concentrates the arc on a small surface, which makes the temperature in the cutting zone reach 4000-6000 ° C. In addition, this gas jet blows out the cut products. When welding in an argon stream, there is no need for fluxes and electrode coatings, and therefore, for cleaning the seam from slag and flux residues.

The desire to use the properties and capabilities of ultrapure materials is one of the trends in modern technology. For superpurity, inert protective media are needed, of course, also clean; argon is the cheapest and most readily available noble gas.

Argon characteristics

Argon welding

Argon is an inert gas that does not chemically interact with metal and does not dissolve in it. Inert gases are used for welding chemically active metals (titanium, aluminum, magnesium, etc.), as well as in all cases when it is necessary to obtain welds that are homogeneous in composition with the base and filler metal (high-alloy steels, etc.). Inert gases provide protection for the arc and the welded metal without having a metallurgical effect on it.

Pure gaseous argon is used in three grades: superior, first and second. Argon content, respectively, 99.99%; 99.98%; and 99.95%. Impurities - oxygen (<0,005), азот (< 0,004) , влага(<0,003). Аргон хранится и поставляется в баллонах вместимостью 40л, под давлением 150 ? 98,06 кПа. Цвет окраски баллону присвоен серый, надпись «Аргон чистый» зеленого цвета.

Argon arc welding - arc welding, in which argon is used as a shielding gas. Argon-arc welding with non-consumable tungsten and consumable electrodes is used. Welding can be manual or automatic. Argon arc welding with a tungsten electrode is intended for welding seams of butt, tee and fillet joints. Consumable electrode welding is used for welding non-ferrous metals (Al, Mg, Cu, Ti and their alloys) and alloy steels.

Argon is used in plasma welding as a plasma forming gas. In microplasma welding, most metals are welded in continuous or pulsed modes with an arc of straight polarity, burning between the tungsten electrode of the plasmatron and the product in a jet of a plasma-forming inert gas - (most often) argon.

Argon arc welding

An arc welding, in which apgon is used in the quality of the protective gas.

GOST 2601-84 Swap of metals. Terms and definitions of basic concepts (with amendments N 1, 2)

ISO 14555: 1998 Swap. ARC BREWING STUDS FROM METAL MATERIALS

Chemistry

Argon chemical element

In 1785 the English chemist and physicist G. Cavendish discovered some new gas in the air, which is unusually stable chemically. This gas accounted for about one hundred and twentieth of the volume of air. But what kind of gas it was, Cavendish could not find out.

This experience was recalled 107 years later, when John William Stratt (Lord Rayleigh) encountered the same impurity, observing that the nitrogen in the air was heavier than the nitrogen released from the compounds. Not finding a reliable explanation of the anomaly, Rayleigh, through the journal "Nature", turned to fellow natural scientists with a proposal to think together and work on unraveling its causes ...

Two years later, Rayleigh and W. Ramsay found that the nitrogen in the air really contains an admixture of an unknown gas, heavier than nitrogen and chemically extremely inert.

When they made a public announcement of their discovery, it made a stunning impression. It seemed incredible to many that several generations of scientists who had performed thousands of air analyzes would have overlooked its component, and even such a noticeable - almost a percentage!

By the way, it was on this day and hour, August 13, 1894, argon and got its name, which in translation from Greek means "inactive"... It was proposed by Dr. Medan, who presided over the meeting.

Meanwhile, there is nothing surprising in the fact that argon eluded scientists for so long. Indeed, in nature, he decidedly did not show himself! A parallel with nuclear energy suggests itself: speaking about the difficulties of its identification, A. Einstein noted that it is not easy to recognize a rich man if he does not spend his money ...

The skepticism of scientists was quickly dispelled by experimental verification and the establishment of the physical constants of argon. But it was not without moral costs: upset by the attacks of colleagues (mainly chemists), Rayleigh abandoned the study of argon and chemistry in general and focused his interests on physical problems. Great scientist. he also achieved outstanding results in physics, for which in 1904 he was awarded the Nobel Prize. Then in Stockholm he again met with Ramsay, who on the same day received the Nobel Prize for the discovery and study of noble gases, including argon.

The appearance of "inactive" gas

The chemical inertness of argon (like other gases in this group) and the monoatomic nature of its molecules are explained primarily by the maximum saturation of the electron shells. Nevertheless, the conversation about the chemistry of argon is not pointless today.

There is reason to believe that the extremely unstable Hg -Ar compound formed in an electric discharge is a truly chemical (valence) compound. It is possible that valence compounds of argon with fluorine and oxygen will be obtained, which, most likely, will be unstable, as unstable and even explosive oxides of xenon - a gas that is heavier and clearly more prone to chemical reactions than argon.

At the end of the last century, the Frenchman Vuillard, compressing argon under water at 0 ° C, obtained a crystalline hydrate of the composition Ar-6H 2 O, and in the 20-30s of the XX century B.A. Nikitin, R.A.Frankran and other researchers At high pressures and low temperatures, crystalline clathrate compounds of argon with H 2 S, SO 2, hydrogen halides, phenols and some other substances were obtained. In 1976, a report appeared on the synthesis of argon hydride, but this hydride is special.

In the metastable - electronically excited - state, argon, like other noble gases, is capable of forming short-lived compounds, the lifetime of which is measured in picoseconds. But as soon as the argon atom returns from this excited state to the ground state, these unusual compounds disintegrate. So far, all the successes of chemistry ...

Of the subgroup of heavy inert gases, argon is the lightest. It is 1.38 times heavier than air. It becomes a liquid at - 185.9 ° С, solidifies at - 189.4 ° С (under normal pressure). Unlike helium and neon, it adsorbs quite well on the surfaces of solids and dissolves in water (3.29 cm 3 in 100 g of water at 20 ° C). Argon dissolves even better in many organic liquids. But it is practically insoluble in metals and does not diffuse through them.

Like all inert gases, argon is diamagnetic. This means that its magnetic susceptibility is negative, it has more resistance to magnetic lines of force than emptiness. This property of argon (like many others) is explained by the "closedness" of the electron shells. Under the action of an electric current, argon glows brightly, the blue-blue glow of argon is widely used in lighting engineering.

Now about the effect of argon on a living organism

When a mixture of 69% Ar, 11% nitrogen and 20% oxygen is inhaled under a pressure of 4 atm, anesthesia phenomena occur, which are much more pronounced than when air is inhaled under the same pressure. The anesthesia disappears instantly after the argon supply is stopped. The reason is the non-polarity of argon molecules, while the increased pressure increases the solubility of argon in nerve tissues.

Biologists have found that argon is beneficial to plant growth. Even in an atmosphere of pure argon, the seeds of rice, corn, cucumbers and rye threw out sprouts. Onions, carrots and lettuce germinate well in an atmosphere of 98% argon and only 2% oxygen.

There is much more argon on Earth than all other elements of its group put together. Its average content in the earth's crust (clarke) is 14 times more than helium and 57 times more than neon. There is argon in water, up to 0.3 cm 3 in a liter of sea water and up to 0.55 cm 3 in a liter of fresh water. It is curious that more argon is found in the air of the swim bladder than in the atmospheric air. This is because argon is more soluble in water than nitrogen ...

The main "storage" of terrestrial argon is the atmosphere. It contains (by weight) 1.286%, and 99.6% of atmospheric argon is the heaviest isotope - argon-40. The fraction of this isotope is even greater in argon in the earth's crust. Meanwhile, for the overwhelming majority of light elements, the picture is the opposite - light isotopes predominate.

The reason for this anomaly was discovered in 1943. There is a powerful source of argon-40 in the earth's crust - the radioactive isotope of potassium 40 K. This isotope, at first glance, is not much in the interior - only 0.0119% of the total potassium content. However, the absolute amount of potassium-40 is large, since potassium is one of the most abundant elements on our planet. Each ton of igneous rocks contains 3.1 g of potassium-40.

The radioactive decay of atomic nuclei of potassium-40 goes simultaneously in two ways. Approximately 88% of potassium-40 is beta-decayed and converted to calcium-40. But in 12 cases out of 100 (on average) potassium-40 nuclei do not emit, but, on the contrary, capture one electron each from the K-orbit closest to the nucleus ("K-capture"). The captured electron combines with a proton - a new neutron is formed in the nucleus and a neutrino is emitted. The atomic number of the element decreases by one, while the mass of the nucleus remains practically unchanged. This is how potassium is converted to argon.

The half-life of 40 K is quite long - 1.3 billion years. Therefore, the process of 40 Ar formation in the Earth's interior will continue for a long, very long time. Therefore, although extremely slowly, the argon content in the earth's crust and atmosphere will grow steadily, where argon is “exhaled” by the lithosphere as a result of volcanic processes, weathering and recrystallization of rocks, as well as water sources.

True, during the existence of the Earth, the supply of radioactive potassium has been thoroughly depleted - it has become 10 times less (if the age of the Earth is considered equal to 4.5 billion years).

The isotope ratio 40 Ar: 40 K and 40 Ar: 36 Ar in rocks formed the basis of the argon method for determining the absolute age of minerals. Obviously, the larger this relationship, the older the breed. The argon method is considered to be the most reliable method for determining the age of igneous rocks and most potash minerals. For the development of this method, Professor E. K. Gerling was awarded the Lenin Prize in 1963.

So, all or almost all argon-40 originated on Earth from potassium-40. Therefore, the heavy isotope dominates in terrestrial argon. By the way, this factor explains one of the anomalies of the periodic system. Contrary to the original principle of its construction - the principle of atomic weights - argon is placed in the table ahead of potassium. If light isotopes predominated in argon, as in neighboring elements (as it seems to be the case in space), then the atomic weight of argon would be two or three units less ...

Now about light isotopes.

Where do 36 Ar and 38 Ar come from? It is possible that some part of these atoms of relic origin, that is, part of light argon, came into the earth's atmosphere from space during the formation of our planet and its atmosphere. But most of the light isotopes of argon were born on Earth as a result of nuclear processes.

Probably, not all such processes have been discovered yet. Most likely, some of them stopped long ago, since the short-lived atoms-"parents" have been exhausted, but there are still ongoing nuclear processes in which argon-36 and argon-38 are born. This is the beta decay of chlorine-36 shelling with alpha particles (in uranium minerals) sulfur-33 and chlorine-35: 36 17 Cl - β → 36 18 Ar + 0 -1 e + v, 33 16 S + 42 He → 36 18 Ar + 1 0 n, 35 17 Cl + 42 He → 38 18 Ar + 10n + 0 +1 e.

Argon is even more abundant in the matter of the Universe than on our planet. It is especially abundant in the matter of hot stars and planetary nebulae. It is estimated that there is more argon in space than chlorine, phosphorus, calcium, potassium - elements that are very common on Earth.

In cosmic argon isotopes 36 Ar and 38 Ar dominate, argon-40 in the Universe is very small. This is indicated by the mass spectral analysis of argon from meteorites. Calculations of the prevalence of potassium confirm the same. It turns out that in space potassium is about 50 thousand times less than argon, while on Earth their ratio is clearly in favor of potassium - 660: 1. And since there is little potassium, then where does argon-40 come from ?!

How argon is mined

The Earth's atmosphere contains 664,013 tons of argon. This source of argon is inexhaustible, especially since almost all argon sooner or later returns to the atmosphere, since it does not undergo any physical or chemical changes during use. The exception is very small amounts of argon isotopes, which are used to obtain new elements and isotopes in nuclear reactions.

The volatility of argon is greater than that of oxygen, but less than that of nitrogen. Therefore, the argon fraction is taken at a point located approximately one third of the height of the upper column, and taken to a special column. The composition of the argon fraction: 10-12% argon, up to 0.5% nitrogen, the rest is oxygen. In an "argon" column connected to the main apparatus, argon is obtained with an admixture of 3-10% oxygen and 3-5% nitrogen. This is followed by purification of "raw" argon from oxygen (by chemical means or adsorption) and from nitrogen (rectification). Argon is produced on an industrial scale up to 99.99% purity. Argon is also extracted from the wastes of the ammonia production - from the nitrogen left after most of it has been bound with hydrogen.

Argon is stored and transported in 40 liter cylinders, painted gray with a green stripe and green inscription. The pressure in them is 150 atm. Transportation of liquefied argon is more economical, for which Dewar vessels and special tanks are used.

Artificial radioisotopes of argon were obtained by irradiating some stable and radioactive isotopes (37 Cl, 36 Ar, \u200b\u200b40 Ar, 40 Ca) with protons and deuterons, as well as by irradiating with neutrons the products formed in nuclear reactors during the decay of uranium. Isotopes 37 Ar and 41 Ar are used as radioactive indicators: the first is in medicine and pharmacology, the second is in the study of gas flows, the efficiency of ventilation systems and in various scientific research. But, of course, these are not the most important uses of argon. As the most accessible and relatively cheap noble gas, argon has become a mass-produced product, especially in recent decades.

PREDICTION BY N. MOROZOV. In January 1881 in the Peter and Paul Fortress, and then in the Shlisselburg Fortress, a nugget Russian scientist, a man of encyclopedic mind Nikolai Morozov was imprisoned for his revolutionary activities. He spent a quarter of a century in prison. In the terrible conditions of the casemate, he thought over and wrote about 60 books and articles on various issues of natural science. Developing the ideas of Mendeleev, he built a table of "mineral elements", which, unlike Mendeleev's table, contained the last group; in it Morozov included the alleged chemically inactive elements with atomic masses of 4, 20, 36 (or 40), 82, etc. Later, in 1903, he wrote: “The analogy suggested that the missing elements must be ... gaseous ... Search for them, according to theory, should have been in the atmosphere. Atoms in these valences. gases should not be less durable than other elements. Great was my joy when the first news came to me about the discovery by Ramsay and Rayleigh of the first messenger from this missing series of elements - argon! "

AND THE GREATS HAVE ERRORS. Ramsay spoke about one of these mistakes in his autobiographical essay. After liquefying raw argon, he found a substance on the walls of the vessel, the evaporation of which formed a gas. The spectrum of the gas was unusual, and the scientist was quick to report the discovery of another component of air, which he called metargon. But upon subsequent verification, it turned out that this unusual spectrum was given by ... a mixture of argon with CO. Where the carbon monoxide got into the liquid air is hard to say. It is important that in this - not pleasant for a scientist - situation, Ramsay was at his best. Here are his own words on this matter: “It is regrettable, of course, if it happens to publish something inaccurate. Nevertheless, I dare to think that the accidental mistake is excuse. It is impossible to be infallible, and in case of mistakes there will always be a very large number of friends who will quickly correct the mistake. "

The story of the discovery of argon could serve as the basis for a good detective. Not all chemists believed in the announcement of the discovery of a new gas. Mendeleev himself doubted it. The discovery of argon, it seemed, could lead to the fact that the entire "building" of the periodic table would collapse. Argon had no analogues in the table, it had no place at all in the periodic system: where, tell me, can an element without chemical properties be placed?

Eighteenth element

Argon is one of the noble gases, and history is replete with truly dramatic moments. In 1785, the English chemist and physicist G. Cavendish discovered in the air some kind of new gas, unusually stable chemically. This gas accounted for about one hundred and twentieth of the volume of air. But what kind of gas, Cavendish was unable to find out.

This experience was recalled 107 years later, when John William Stratt (Lord Rayleigh) came across the same impurity, observing that the nitrogen in the air was heavier than the nitrogen released from the compounds. Not finding a reliable explanation for the anomaly, Rayleigh, through the journal Nature, turned to fellow naturalists with a proposal to think together and work on unraveling its causes ...

Two years later, Rayleigh and W. Ramsay found that in the nitrogen of the air there really is an admixture of an unknown gas, heavier than nitrogen. The gas behaved paradoxically: it did not react with chlorine, metals, acids, alkalis, i.e. was absolutely chemically inert. And one more surprise: Ramsay proved that the molecule of this gas consists of one atom - and until then monatomic gases were unknown.

When Rayleigh and Ramsay made a public announcement of their discovery, it was overwhelming. It seemed incredible to many that several generations of scientists who had performed thousands of air analyzes would have overlooked its component, and even such a noticeable - almost a percentage! By the way, it was on this day and hour, August 13, 1894, that argon received its name (from greek « argos"-" lazy "," indifferent ").

Not all chemists believed in the announcement of the discovery of a new gas; Mendeleev himself doubted it. The discovery of argon, it seemed, could lead to the fact that the entire "building" of the periodic table would collapse. The atomic mass of the gas (39.9) indicated its place between potassium (39.1) and calcium (40.1). But in this part of the table, all the cells have been occupied for a long time. Argon had no analogues in the table, it had no place at all in the periodic table.

Therefore, argon received official recognition only a quarter of a century later - after the discovery of helium. Now there was no room for two elements in the periodic table. After lengthy discussions, Mendeleev and Ramsay came to the conclusion that inert gases should be assigned a separate, so-called zero group between halogens and alkali metals.

The chemical inertness of argon (as well as other gases of the zero group) and the monoatomic nature of its molecules are explained primarily by the limiting saturation of the electron shells.

Of the subgroup of heavy inert gases, argon is the lightest. It is 1.38 times heavier than air. It becomes a liquid at -185.9 ° C, solidifies at -189.4 ° C (under normal pressure). The argon molecule is monoatomic.

Unlike helium and neon, it adsorbs quite well on the surfaces of solids and dissolves in water (3.29 cm 3 in 100 g of water at 20 ° C). Argon dissolves even better in many organic liquids. But it is practically insoluble in metals and does not diffuse through them.

Under the action of an electric current, argon glows brightly, and today the blue-blue glow of argon is widely used in lighting engineering.

On Earth and in the Universe

There is much more argon on Earth than all other elements of its group put together. Its average content in the earth's crust (clarke) is 0.04 g per ton, which is 14 times more than helium, and 57 times more than neon. There is argon in water, up to 0.3 cm 3 in a liter of sea water and up to 0.55 cm 3 in a liter of fresh water. It is curious that there is more argon in the air of the swim bladder of fish than in the atmospheric air. This is because argon is more soluble in water than nitrogen ...

How argon is mined

Earth atmosphere contains 66 1013 tons of argon. This source of gas is inexhaustible. Moreover, almost all argon sooner or later returns to the atmosphere, since during use it does not undergo any physical or chemical changes. The exception is very small amounts of argon isotopes, which are used to obtain new elements and isotopes in nuclear reactions.

Argon is obtained as by-product of the separation of air into oxygen and nitrogen... Typically, air separators of double rectification are used, consisting of a lower high pressure column (preliminary separation), an upper low pressure column and an intermediate condenser-evaporator. Ultimately, nitrogen is removed from the top and oxygen from the space above the condenser.

The volatility of argon is greater than that of oxygen, but less than that of nitrogen. Therefore, the argon fraction is taken at a point located approximately one third of the height of the upper column, and taken to a special column. The composition of the argon fraction: 10–12% argon, up to 0.5% nitrogen, the rest is oxygen. In an "argon" column connected to the main apparatus, argon is obtained with an admixture of 3-10% oxygen and 3-5% nitrogen. This is followed by the purification of "raw" argon from oxygen (chemically or by adsorption) and from nitrogen (rectification). Argon is obtained on an industrial scale up to 99.99% purity. Argon is also extracted from ammonia production waste - from the nitrogen left after most of it is bound with hydrogen.

The "lazy person" needed in the household

How the most accessible and relatively cheap inert gas argon became mass-produced product, especially in recent decades.

Initially, the main consumer of item # 18 was electrovacuum technology... And now the vast majority incandescent lamps (billions of pieces per year) are filled with a mixture of argon (86%) and nitrogen (14%). Switching from pure nitrogen to this mixture increased the light output of the lamps. Since argon successfully combines significant density with low thermal conductivity, the metal of the filament evaporates more slowly in such lamps, and the transfer of heat from the filament to the bulb is less in them. Argon is also used in modern fluorescent lamps for easier ignition, better current transfer and protection of cathodes from destruction.

However, in recent decades, most of the argon produced does not go to light bulbs, but to metallurgy, metalworking and some related industries. In an argon environment, processes are carried out in which it is necessary to exclude contact of the molten metal with oxygen, nitrogen, carbon dioxide and air moisture. An argon medium is used in hot working of titanium, tantalum, niobium, beryllium, zirconium, hafnium, tungsten, uranium, thorium, and alkali metals. Plutonium is processed in an argon atmosphere, some compounds of chromium, titanium, vanadium and other elements (strong reducing agents) are obtained.

There are already metallurgical workshops with a volume of several thousand cubic meters with an atmosphere consisting of high-purity argon. In these workshops, they work in insulating suits, and breathe with air supplied through hoses (exhaled air is also removed through the hoses); spare breathing apparatus are attached to the workers' backs.

Argon performs protective functions and growing single crystals (semiconductors, ferroelectrics), as well as in the production of carbide tools. By blowing argon through liquid steel, gas inclusions are removed from it. This improves the properties of the metal.

Increasingly used arc electric welding in argon. The argon jet can weld thin-walled products and metals that were previously considered difficult to weld.

It is no exaggeration to say that an electric arc in an argon atmosphere revolutionized the technique of cutting metals. The process has accelerated much, it became possible to cut thick sheets of the most refractory metals. Argon blown along the arc column (mixed with hydrogen) protects the cut edges and the tungsten electrode from the formation of oxide, nitride and other films. At the same time, it compresses and concentrates the arc on a small surface, which makes the temperature in the cutting zone reach 4000-6000 ° C. In addition, this gas jet blows out the cut products. When welding in an argon stream, there is no need for fluxes and electrode coatings, and therefore, for cleaning the seam from slag and flux residues.