Argon

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Argon, 18Ar
Vial containing a violet glowing gas
Argon
Pronunciation/ˈɑːrɡɒn/ (AR-gon)
Appearancecolorless gas exhibiting a lilac/violet glow when placed in an electric field
Standard atomic weight Ar°(Ar)
Argon in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Ne

Ar

Kr
chlorineargonpotassium
kJ/mol
Heat of vaporization6.53 kJ/mol
Molar heat capacity20.85[4] J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K)   47 53 61 71 87
Atomic properties
Lord Rayleigh and William Ramsay (1894)
Isotopes of argon
Main isotopes[8] Decay
abun­dance half-life (t1/2) mode pro­duct
36Ar 0.334%
stable
37Ar trace 35 d ε 37Cl
38Ar 0.0630% stable
39Ar trace 268 y
β
39K
40Ar 99.6% stable
41Ar trace 109.34 min β
41K
42Ar synth 32.9 y β
42K
 Category: Argon
| references

Argon is a

Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abundant as water vapor (which averages about 4000 ppmv, but varies greatly), 23 times as abundant as carbon dioxide (400 ppmv), and more than 500 times as abundant as neon (18 ppmv). Argon is the most abundant noble gas in Earth's crust
, comprising 0.00015% of the crust.

Nearly all argon in Earth's atmosphere is

argon-36 is by far the most common argon isotope, as it is the most easily produced by stellar nucleosynthesis in supernovas
.

The name "argon" is derived from the Greek word ἀργόν, neuter singular form of ἀργός meaning 'lazy' or 'inactive', as a reference to the fact that the element undergoes almost no chemical reactions. The complete octet (eight electrons) in the outer atomic shell makes argon stable and resistant to bonding with other elements. Its triple point temperature of 83.8058 K is a defining fixed point in the International Temperature Scale of 1990.

Argon is extracted industrially by the

fluorescent lighting, and other gas-discharge tubes. It makes a distinctive blue-green gas laser
. It is also used in fluorescent glow starters.

Characteristics

A small piece of rapidly melting solid argon

Argon has approximately the same solubility in water as oxygen and is 2.5 times more soluble in water than nitrogen. Argon is colorless, odorless, nonflammable and nontoxic as a solid, liquid or gas.[10] Argon is chemically inert under most conditions and forms no confirmed stable compounds at room temperature.

Although argon is a

excited-state complexes, such as ArF, have been demonstrated. Theoretical calculation predicts several more argon compounds that should be stable[14]
but have not yet been synthesized.

History

A: test-tube, B: dilute alkali, C: U-shaped glass tube, D: platinum electrode

Argon (Greek ἀργόν, neuter singular form of ἀργός meaning "lazy" or "inactive") is named in reference to its chemical inactivity. This chemical property of this first noble gas to be discovered impressed the namers.[15][16] An unreactive gas was suspected to be a component of air by Henry Cavendish in 1785.[17]

Argon was first isolated from air in 1894 by

Ruhmkorff coil
of medium size. The alkali absorbed the oxides of nitrogen produced by the arc and also carbon dioxide. They operated the arc until no more reduction of volume of the gas could be seen for at least an hour or two and the spectral lines of nitrogen disappeared when the gas was examined. The remaining oxygen was reacted with alkaline pyrogallate to leave behind an apparently non-reactive gas which they called argon.

Captioned "Argon", caricature of Lord Rayleigh in Vanity Fair, 1899

Before isolating the gas, they had determined that nitrogen produced from chemical compounds was 0.5% lighter than nitrogen from the atmosphere. The difference was slight, but it was important enough to attract their attention for many months. They concluded that there was another gas in the air mixed in with the nitrogen.[21] Argon was also encountered in 1882 through independent research of H. F. Newall and W. N. Hartley.[22] Each observed new lines in the emission spectrum of air that did not match known elements.

Until 1957, the symbol for argon was "A", but now it is "Ar".[23]

Occurrence

Argon constitutes 0.934% by volume and 1.288% by mass of

Earth's atmosphere.[24] Air is the primary industrial source of purified argon products. Argon is isolated from air by fractionation, most commonly by cryogenic fractional distillation, a process that also produces purified nitrogen, oxygen, neon, krypton and xenon.[25] Earth's crust and seawater contain 1.2 ppm and 0.45 ppm of argon, respectively.[26]

Isotopes

The main isotopes of argon found on Earth are 40
Ar
(99.6%), 36
Ar
(0.34%), and 38
Ar
(0.06%). Naturally occurring 40
K
, with a half-life of 1.25×109 years, decays to stable 40
Ar
(11.2%) by electron capture or positron emission, and also to stable 40
Ca
(88.8%) by beta decay. These properties and ratios are used to determine the age of rocks by K–Ar dating.[26][27]

In Earth's atmosphere, 39
Ar
is made by

nuclear explosions. It has a half-life of 35 days.[27]

Between locations in the

probes
.

The atmospheres of Mars, Mercury and Titan (the largest moon of Saturn) contain argon, predominantly as 40
Ar
, and its content may be as high as 1.93% (Mars).[30]

The predominance of

radiogenic 40
Ar
is the reason the standard atomic weight of terrestrial argon is greater than that of the next element, potassium, a fact that was puzzling when argon was discovered. Mendeleev positioned the elements on his periodic table in order of atomic weight, but the inertness of argon suggested a placement before the reactive alkali metal. Henry Moseley later solved this problem by showing that the periodic table is actually arranged in order of atomic number (see History of the periodic table
).

Compounds

Space-filling model of argon fluorohydride

Argon's complete octet of

Argon-36, in the form of argon hydride (argonium) ions, has been detected in interstellar medium associated with the Crab Nebula supernova; this was the first noble-gas molecule detected in outer space.[35][36]

Solid argon hydride (Ar(H2)2) has the same crystal structure as the MgZn2 Laves phase. It forms at pressures between 4.3 and 220 GPa, though Raman measurements suggest that the H2 molecules in Ar(H2)2 dissociate above 175 GPa.[37]

Production

Argon is extracted industrially by the

cryogenic air separation unit; a process that separates liquid nitrogen, which boils at 77.3 K, from argon, which boils at 87.3 K, and liquid oxygen, which boils at 90.2 K. About 700,000 tonnes of argon are produced worldwide every year.[26][38]

Applications

Cylinders containing argon gas for use in extinguishing fire without damaging server equipment

Argon has several desirable properties:

  • Argon is a chemically inert gas.
  • Argon is the cheapest alternative when nitrogen is not sufficiently inert.
  • Argon has low
    thermal conductivity
    .
  • Argon has electronic properties (ionization and/or the emission spectrum) desirable for some applications.

Other

cryogenic air separation in the production of liquid oxygen and liquid nitrogen: the primary constituents of air are used on a large industrial scale. The other noble gases (except helium
) are produced this way as well, but argon is the most plentiful by far. The bulk of its applications arise simply because it is inert and relatively cheap.

Industrial processes

Argon is used in some high-temperature industrial processes where ordinarily non-reactive substances become reactive. For example, an argon atmosphere is used in graphite electric furnaces to prevent the graphite from burning.

For some of these processes, the presence of nitrogen or oxygen gases might cause defects within the material. Argon is used in some types of arc welding such as gas metal arc welding and gas tungsten arc welding, as well as in the processing of titanium and other reactive elements. An argon atmosphere is also used for growing crystals of silicon and germanium.

Argon is used in the poultry industry to asphyxiate birds, either for mass culling following disease outbreaks, or as a means of slaughter more humane than electric stunning. Argon is denser than air and displaces oxygen close to the ground during inert gas asphyxiation.[39][40] Its non-reactive nature makes it suitable in a food product, and since it replaces oxygen within the dead bird, argon also enhances shelf life.[41]

Argon is sometimes used for extinguishing fires where valuable equipment may be damaged by water or foam.[42]

Scientific research

Liquid argon is used as the target for neutrino experiments and direct

ICARUS and MicroBooNE, both of which use high-purity liquid argon in a time projection chamber
for fine grained three-dimensional imaging of neutrino interactions.

At Linköping University, Sweden, the inert gas is being utilized in a vacuum chamber in which plasma is introduced to ionize metallic films.[45] This process results in a film usable for manufacturing computer processors. The new process would eliminate the need for chemical baths and use of expensive, dangerous and rare materials.

Preservative

A sample of caesium is packed under argon to avoid reactions with air

Argon is used to displace oxygen- and moisture-containing air in packaging material to extend the shelf-lives of the contents (argon has the

European food additive code E938). Aerial oxidation, hydrolysis, and other chemical reactions that degrade the products are retarded or prevented entirely. High-purity chemicals and pharmaceuticals are sometimes packed and sealed in argon.[46]

In winemaking, argon is used in a variety of activities to provide a barrier against oxygen at the liquid surface, which can spoil wine by fueling both microbial metabolism (as with acetic acid bacteria) and standard redox chemistry.

Argon is sometimes used as the propellant in aerosol cans.

Argon is also used as a preservative for such products as varnish, polyurethane, and paint, by displacing air to prepare a container for storage.[47]

Since 2002, the American

Constitution within argon-filled cases to inhibit their degradation. Argon is preferable to the helium that had been used in the preceding five decades, because helium gas escapes through the intermolecular pores in most containers and must be regularly replaced.[48]

Laboratory equipment

Gloveboxes are often filled with argon, which recirculates over scrubbers to maintain an oxygen-, nitrogen-, and moisture-free atmosphere

Argon may be used as the inert gas within Schlenk lines and gloveboxes. Argon is preferred to less expensive nitrogen in cases where nitrogen may react with the reagents or apparatus.

Argon may be used as the carrier gas in

scanning electron microscopy. Argon gas is also commonly used for sputter deposition of thin films as in microelectronics and for wafer cleaning in microfabrication
.

Medical use

gas embolism and has resulted in the death of at least one patient.[49]

Blue

argon lasers are used in surgery to weld arteries, destroy tumors, and correct eye defects.[26]

Argon has also been used experimentally to replace nitrogen in the breathing or decompression mix known as

Argox, to speed the elimination of dissolved nitrogen from the blood.[50]

Lighting

Argon gas-discharge lamp forming the symbol for argon "Ar"

argon-ion lasers
.

Miscellaneous uses

Argon is used for thermal insulation in energy-efficient windows.[51] Argon is also used in technical scuba diving to inflate a dry suit because it is inert and has low thermal conductivity.[52]

Argon is used as a propellant in the development of the Variable Specific Impulse Magnetoplasma Rocket (VASIMR). Compressed argon gas is allowed to expand, to cool the seeker heads of some versions of the AIM-9 Sidewinder missile and other missiles that use cooled thermal seeker heads. The gas is stored at high pressure.[53]

Argon-39, with a half-life of 269 years, has been used for a number of applications, primarily

argon-argon dating are used to date sedimentary, metamorphic, and igneous rocks.[26]

Argon has been used by athletes as a doping agent to simulate hypoxic conditions. In 2014, the World Anti-Doping Agency (WADA) added argon and xenon to the list of prohibited substances and methods, although at this time there is no reliable test for abuse.[54]

Safety

Although argon is non-toxic, it is 38% more dense than air and therefore considered a dangerous asphyxiant in closed areas. It is difficult to detect because it is colorless, odorless, and tasteless. A 1994 incident, in which a man was asphyxiated after entering an argon-filled section of oil pipe under construction in Alaska, highlights the dangers of argon tank leakage in confined spaces and emphasizes the need for proper use, storage and handling.[55]

See also

References

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  9. ^ In older versions of the periodic table, the noble gases were identified as Group VIIIA or as Group 0. See Group (periodic table).
  10. ^ "Material Safety Data Sheet Gaseous Argon". UIGI.com. Universal Industrial Gases, Inc. Retrieved 14 October 2013.
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  13. ^ Belosludov, V. R.; Subbotin, O. S.; Krupskii, D. S.; Prokuda, O. V.; et al. (2006). "Microscopic model of clathrate compounds". .
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  20. ^ Ramsay, W. (1904). "Nobel Lecture".
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  21. ^ "About Argon, the Inert; The New Element Supposedly Found in the Atmosphere". The New York Times. 3 March 1895. Retrieved 1 February 2009.
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  23. ^ Holden, N. E. (12 March 2004). "History of the Origin of the Chemical Elements and Their Discoverers". National Nuclear Data Center.
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  52. ^ Nuckols M. L.; Giblo J.; Wood-Putnam J. L. (15–18 September 2008). "Thermal Characteristics of Diving Garments When Using Argon as a Suit Inflation Gas". Proceedings of the Oceans 08 MTS/IEEE Quebec, Canada Meeting. Archived from the original on 21 July 2009. Retrieved 2 March 2009.{{cite journal}}: CS1 maint: unfit URL (link)
  53. ^ "Description of Aim-9 Operation". planken.org. Archived from the original on 22 December 2008. Retrieved 1 February 2009.
  54. ^ "WADA amends Section S.2.1 of 2014 Prohibited List". 31 August 2014. Archived from the original on 27 April 2021. Retrieved 1 September 2014.
  55. ^ Alaska FACE Investigation 94AK012 (23 June 1994). "Welder's Helper Asphyxiated in Argon-Inerted Pipe – Alaska (FACE AK-94-012)". State of Alaska Department of Public Health. Retrieved 29 January 2011.{{cite web}}: CS1 maint: numeric names: authors list (link)

Further reading

External links

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