Everything about Argon totally explained
» This article pertains to the chemical element. For other uses, see argon (disambiguation).
Argon is a
chemical element designated by the symbol
Ar. Argon has
atomic number 18 and is the third element in group 18 of the
periodic table (
noble gases). Argon is present in the
Earth's atmosphere at 0.93%, making it the most abundant noble gas on Earth. Its full outer 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.
Characteristics
Argon has approximately the same
solubility in water as oxygen gas and is 2.5 times more soluble in water than
nitrogen gas. Argon is colorless, odorless, tasteless and nontoxic in both its liquid and
gaseous forms. Argon is inert under most conditions and forms no confirmed stable compounds at room temperature.
Although argon is a
noble gas, it has been found to have the capability of forming some compounds. For example, the creation of
argon hydrofluoride (HArF), a metastable compound of argon with
fluorine and
hydrogen, was reported by researchers at the
University of Helsinki in 2000. Although the neutral ground-state chemical compounds of argon are presently limited to HArF, argon can form
clathrates with
water when atoms of it are trapped in a lattice of the water molecules. Also argon-containing
ions and
excited state complexes, such as ArH+ and ArF, respectively, are known to exist. Theoretical calculations have shown several argon compounds that should be stable but for which no synthesis routes are currently known.
History
Argon (
Greek meaning "inactive," in reference to its chemical inactivity) was suspected to be present in air by
Henry Cavendish in 1785 but wasn't discovered until 1894 by
Lord Rayleigh and Sir
William Ramsay in Scotland in an experiment in which they removed all of the
oxygen and
nitrogen from a sample of air. They had determined that nitrogen produced from chemical compounds was one-half percent lighter than nitrogen from the atmosphere. The difference seemed insignificant, 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. Argon was also encountered in 1882 through independent research of H.F. Newall and W.N. Hartley. Each observed new lines in the color spectrum of air but were unable to identify the element responsible for the lines. Argon became the first member of the noble gases to be discovered. The symbol for argon is now
Ar, but up until 1957 it was
A.
Occurrence
Argon constitutes 0.934% by volume and 1.29% by mass of the
Earth's atmosphere, and air is the primary raw material used by industry to produce 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.
The
Martian atmosphere in contrast contains 1.6% of argon-40 and 5
ppm of argon-36. The
Mariner spaceprobe fly-by of the
planet Mercury in 1973 found that Mercury has a very thin atmosphere with 70% argon, believed to result from releases of the gas as a decay product from radioactive materials on the planet. In 2005, the
Huygens probe also discovered the presence of argon-40 on
Titan, the largest moon of
Saturn.
Isotopes
The main
isotopes of argon found on Earth are
40Ar (99.6%),
36Ar (0.34%), and
38Ar (0.06%). Naturally occurring
40K with a
half-life of 1.25 years, decays to stable
40Ar (11.2%) by
electron capture and
positron emission, and also to stable
40Ca (88.8%) via
beta decay. These properties and ratios are used to determine the age of
rocks.
In the Earth's
atmosphere,
39Ar is made by
cosmic ray activity, primarily with
40Ar. In the subsurface environment, it's also produced through
neutron capture by
39K or
alpha emission by
calcium.
37Ar is created from the decay of
40Ca as a result of subsurface
nuclear explosions. It has a half-life of 35 days. It is stable up to 40
kelvins (−233 °
C).
The discovery of argon difluoride (ArF
2) was announced in 2003, but this is unconfirmed and most probably incorrect.
See also:-Ar
Production
Industrial
Argon is produced industrially by the partial
distillation of
liquid air, a process that separates
liquid nitrogen, which boils at 77.3K, from argon, which boils at 87.3 K and oxygen, which boils only at 90.2 K. About 700 000 tons of argon are produced worldwide every year.
In radioactive decays
Argon-40, the most abundant
isotope of argon, is produced by the decay of
potassium-40 with a half-life of 1.26e+9 years by
electron capture or
positron emission.
Potassium-argon dating
Applications
There are several different reasons why argon is used in particular applications:
- An inert gas is needed. In particular, argon is the cheapest alternative when diatomic nitrogen isn't sufficiently inert.
- Low thermal conductivity is required.
- The electronic properties (ionization and/or the emission spectrum) are necessary.
Other
noble gases would probably work as well in most of these applications, but argon is by far the cheapest. Argon is inexpensive since it's a byproduct of the production of
liquid oxygen and
liquid nitrogen, both of which 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 since it has the highest concentration in the atmosphere.
The bulk of argon applications arise simply because it's inert and relatively cheap. Argon is used:
As a fill gas in incandescent lighting, because argon won't react with the filament of light bulbs even at high temperatures.
As an inert gas shield in many forms of welding, including metal inert gas welding and tungsten inert gas welding. For metal inert gas welding Argon is often mixed with CO2.
For extinguishing fires where damage to equipment is to be avoided (see photo).
As the gas of choice for the plasma used in ICP spectroscopy.
As a non-reactive blanket in the processing of titanium and other reactive elements.
As a protective atmosphere for growing silicon and germanium crystals, and in partial pressure heat treat furnaces.
By museum conservators to protect old materials or documents, which are prone to gradual oxidation in the presence of air.
To keep open bottles of wine from oxidizing, and in a number of dispensing units and keeper cap systems.
In winemaking to top off barrels, displacing oxygen and thus preventing the wine from turning to vinegar during the aging process.
In the pharmaceutical industry to top off bottles of intravenous drug preparations (for example intravenous paracetamol), again displacing oxygen and therefore prolonging the drug's shelf-life.
Used to cool the seeker head of the US Air Force version of the AIM-9 Sidewinder missile. The gas is stored at high pressure, and the expansion of the gas cools the seeker.
As an atmosphere in graphite electric furnaces, to keep graphite from oxidizing.
The next most common reason for using argon is its low thermal conductivity.
It is used for thermal insulation in energy efficient windows. Argon is also used in technical scuba diving to inflate a dry suit, because it's inert and has low thermal conductivity. It is also used to replace nitrogen in the breathing or decompression mix, to reduce the onset of nitrogen narcosis, or to speed the elimination of dissolved nitrogen from the blood. See Argox (scuba).
Argon is also used for the specific way it ionizes and emits light. It is used in plasma globes and calorimetry in experimental particle physics. Blue argon lasers are used in surgery to weld arteries, destroy tumors, and to correct eye defects. In microelectronics, argon ions are used for sputtering.
Finally, there are a number of miscellaneous uses. Argon-39, with a half life of 269 years, has been used for a number of applications, primarily ice core and ground water dating. Also, potassium-argon dating is used in dating igneous rocks.
Cryosurgery procedures such as cryoablation use liquified argon to destroy cancer cells. In surgery it's used in a procedure called "argon enhanced coagulation" which is a form of argon plasma beam electrosurgery. The procedure carries a risk of producing gas embolism in the patient and has resulted in the death of one person via this type of accident.
Potential hazards
Although Argon is non-toxic, it doesn't satisfy the body's need for oxygen and is a simple asphyxiant, and, in confined spaces, is known to result in death due to asphyxiation. A recent multiple fatality in Florida (USA) highlights the dangers of Argon tank leakage in confined spaces, and, emphasizes the need for it's proper use, storage and handling.
Further Information
Get more info on 'Argon'.
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