Argon 

  

 

Argon

 

Argon - the main element of the subgroup of the eighth group, the third period of the periodic table of chemical elements of Mendeleyev, with atomic number 18. Denoted by Ar (Latin Argon). The third most common element in the Earth's atmosphere (after nitrogen and oxygen) - 0,93% by volume. Simple stuff argon - an inert monatomic gas without color, taste and smell.
    History of the discovery of argon could serve as a basis for a good detective. Announcement of the discovery of new gas believed not all chemists. Even the Mendeleev doubted it. Discovery of argon, it seemed, could lead to that all the "building" of the periodic system will collapse. Argon had no analogues in the table, he never found a place in the periodic system: where, say, you can put an element, devoid of chemical properties?
    Eighteen elements
    Argon is one of the noble gases, but history is replete with truly dramatic moments. In 1785, English chemist and physicist G. Cavendish discovered in the air, some new gas, extremely stable chemically. The share of natural gas accounted for about one 120th of the volume of air. But what kind of gas, Cavendish did not know.
This experience remembered 107 years later, when John William Strutt (Lord Rayleigh) ran into the same mixture, noting that the nitrogen in the air is heavier than nitrogen, selected from the compounds. Unable to find plausible explanations for the anomalies in Raleigh journal Nature asked fellow naturalists with a proposal to think and work on the clue of its causes ...
Two years later, Rayleigh and William Ramsay found that the nitrogen in the air really is an admixture of an unknown gas, heavier than nitrogen. Gas behaved paradoxically: he does not react with chlorine, metals, acids, alkalis, ie, was completely chemically inert. And another surprise: Ramsay showed that the molecule of this gas consists of a single atom - but until then monatomic gases were unknown.
    When the Rayleigh and Ramsay made a public presentation on his discovery, it made a stunning impression. To many it seemed incredible that several generations of scientists, fulfilled thousands of tests of air, missed its components, but still a prominent - almost percentage! Incidentally, in this day and hour, August 13, 1894, argon and got its name (from the Greek. "Argos" - "lazy", "indifferent").
    Announcement of the discovery of new gas believed not all chemists, questioned him and he Mendeleev. Discovery of argon, it seemed, could lead to the fact that all the "building" of the periodic system will collapse. Atomic mass of gas (39,9) pointed out to him a place between potassium (39,1) and calcium (40,1). But in this part of the table all the cells had long occupied. Argon had no analogues in the table, he never found a place in the periodic system.
Therefore, the official recognition of argon received only a quarter of a century later - after the discovery of helium. Now the two elements had no place in the periodic system. After lengthy discussions, Mendeleev and Ramsay came to the conclusion that the inert gases should be removed form a separate, so-called zero-group between halogens and alkali metals.
Chemical inertness of argon (and other gases, the zero group), and its monatomic molecules are primarily due to the limiting saturation of the electron shells.
Of the subgroup of heavy inert gases argon, the easiest. It is heavier than air in 1,38 times. The liquid becomes in -185,9 ° C, solidifies at -189,4 ° C (under normal pressure). Molecule monatomic argon.
    In contrast to the helium and neon, it is fairly well absorbed on the surfaces of solids and soluble in water (3.29 cm 3 in 100 g of water at 20 ° C). Even better is dissolved argon, in many organic liquids. But it is practically insoluble in metals and does not diffuse through them.
    An electric current argon glow brightly, and now the blue glow of argon is widely used in lighting technology.
    Biologists have found that argon favors the growth of plants. Even in an atmosphere of pure argon seeds of rice, corn, cucumbers, and rye shoots thrown. Onions, carrots and lettuce sprout well in an atmosphere consisting of 98% argon, and only 2% of oxygen.
    The Earth and the Universe
    On Earth, argon is much more than all the other elements of his team combined. Its average content in the crust (Clark) - 0,04 g per tonne, which is 14 times greater than the helium, and in 57 - than neon. There are argon and in water, up to 0,3 cm 3 per liter of sea and up to 0.55 cm3 in the liter of fresh water. Curiously, in the air bladder of fish argon is higher than in the air. This is because the water soluble argon is better than nitrogen ...
    The main "repository" world argon - atmosphere. He was in it (by weight) of 1,286%, with 99,6% of the atmospheric argon - the heaviest isotope - argon-40. More proportion of this isotope in argon crust. Meanwhile, the vast majority of the light elements the pattern is reversed - is dominated by light isotopes.
In the matter of the universe argon before more abundant than on our planet. Especially a lot of his stuff in hot stars and planetary nebulae. It is estimated that the argon in space longer than chlorine, phosphorus, calcium and potassium - elements are very common on Earth.
    How to extract argon
    The Earth's atmosphere contains 66 • 1013 tons of argon. This source of gas is inexhaustible. Especially since almost all the argon sooner or later returned to the atmosphere, because when you use it does not undergo any physical or chemical changes. The exceptions are very small quantities of isotopes of argon spent on getting in nuclear reactions of new elements and isotopes.
    Get argon as a byproduct of the separation of air into oxygen and nitrogen. Usually used air separation double distillation apparatus consisting of the bottom of the column of high pressure (pre-division), the upper column of low pressure and intermediate condenser-evaporator. In the end, nitrogen is given above, and oxygen - from the space above the capacitor.
    Volatility argon more than oxygen, but less than nitrogen. Therefore, argon fraction are selected at a point approximately one third the height of the upper column, and assign a special column. The composition of argon fraction: 10-12% argon, up to 0.5% nitrogen, the rest - oxygen. The "argon" column, attached to the main unit, receive argon with an admixture of 3-10% oxygen and 3-5% nitrogen. Then follows purification "crude" argon from oxygen (chemically or by adsorption) and nitrogen (rectification). In an industrial scale is now given Ar to 99,99% nd purity. Argon is extracted from the waste and ammonia production - from nitrogen remaining after most of it tied up with hydrogen.
    Needed in the economy "bummer"
    As the most accessible and relatively cheap inert argon gas was the product of mass production, especially in recent decades.
    Initially, the main consumer of the item number 18 was Electrovacuum technique. And now the vast majority of incandescent lamps (billions of pieces per year) is filled with a mixture of argon (86%) and nitrogen (14%). The transition from pure nitrogen to the mixture increased the light output of lamps. Since argon combines high density with low thermal conductivity, the metal filament in the filament evaporates slowly, the transfer of heat from the filament to the bulb in the lower. Argon is used in modern fluorescent lamps in order to facilitate the ignition, the best current transfer and protection of cathodes from destruction.
    However, in recent decades, received the largest share of argon is not in the bulb, and in metallurgy, metal, and some related to their industry. In argon are processes in which you want to exclude contact of the molten metal with oxygen, nitrogen, carbon dioxide and atmospheric moisture. Argon environment is used during hot processing of titanium, tantalum, niobium, beryllium, zirconium, hafnium, tungsten, uranium, thorium, and alkali metals. In an atmosphere of argon is treated with plutonium, are some compounds of chromium, titanium, vanadium and other elements (strong reducing agents).
    Already there are metallurgical plant of a few thousand cubic meters of the atmosphere, consisting of high purity argon. In these shops operate in insulating suits and breathe through hoses filed with air (exhaled air is also given through the tubes), spare breathing apparatus attached to the backs of workers.
Protective functions are performed by argon and in growing single crystals (semiconductors, ferroelectrics), as well as the production of carbide tools. Blowing argon through the liquid steel from it removed gas inclusions. This improves the properties of the metal.
    It is increasingly applied electric welding arc in argon. In argon-jet can be welded thin-walled products and metals that were previously considered trudnosvarivaemymi.
It is no exaggeration to say that the electric arc in argon atmosphere has made a revolution in the technique of cutting metals. The process is much accelerated, it became possible to cut thick sheets of the most refractory metals. Scavenged along the arc column argon (in a mixture with hydrogen) protects the edge of the cut and the tungsten electrode from the formation of oxide, nitride and other films. At the same time it compresses and concentrates the arc to the small surface, thereby raising the temperature in the cutting area up to 4000-6000 ° C. Moreover, this gas jet blows the products of cutting. When welding in the argon jet, there is no need for flux and electrode coatings, and hence, in cleaning the seam of the slag and flux residues.
    The desire to use the properties and capabilities of ultra-pure materials - one of the trends of modern technology. For sverhchistoty need inert protective environment, of course, too clean; argon - the cheapest and most accessible of the noble gases. Therefore, its production and consumption grow, grow   and grow.

Indicators of argon gas GOST 10157-79

Volume fraction, %The highest classFirst quality
Argon, not less then 99,993 99,987
Oxygen max 0,0007 0,002

Nitrogen max

0,005 0,01

Water vapor, max

0,0009 minus 61 0,001 minus 58

The amount of carbon-containing compounds in terms of CO2

0,0005 0,001

 

 

Indicators of high-purity argon gas TU 2114-002-49632579-2006

Volume fraction, %Норма
Argon, not less then 99,998
Oxygen max 0,0002
Nitrogen max 0,0006
Water vapor, max 0,0009
Carbon dioxide, not more 0,00002
Methane not more 0,0001

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