Argon gas is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third most abundant gas in Earth’s atmosphere, at 0.934% (9340 ppmv). It is more than twice as abundant as water vapor (about 4000 ppmv on average, but varies greatly), 23 times more carbon dioxide (400 ppmv), and 500 times more than neon (18 ppmv). Argon is the most abundant noble gas in the Earth’s crust, comprising 0.00015% of the crust.
See more articles: What is Argon gas?. Properties and applications of argon gas
Nearly all of the argon gas in the Earth’s atmosphere is radioactive argon40, which is derived from the breakdown of kali40 in the Earth’s crust. In the universe, argon40 is by far the most common isotope of argon, as it is the most easily produced by stellar nucleosynthesis in supernovae.
The name “argon” is derived from the Greek word for ἀργόν , the only neuter form of meaning “lazy” or “inactive”, as a reference to the fact of having to undergo weakness. The element has almost no chemical reaction. The complete octet (eight electrons) in the outer atomic shell makes argon gas stable and resistant to bonding with other elements. Its triple point temperature of 83.8058K is a definite fixed point in the 1990 international temperature scale.
Argon gas is extracted industrially by fractional distillation of liquid air. Argon is mostly used as an inert shielding gas in welding and other high temperature industrial processes where normally inactive substances become reactive. For example, an argon atmosphere is used in graphite electric furnaces to prevent graphite from burning.
Argon is also used in incandescent, fluorescent and other gas discharge tubes. Argon produces a gas laser of a distinctive blue color. Argon is also used in fluorescent starters.
Features of Argon gas
Argon has a water solubility comparable to that of oxygen and is 2.5 times more soluble in water than nitrogen. Argon is colorless, odorless, non-flammable and non-toxic as a solid, liquid or gas. Argon is chemically inert under most conditions and does not form any confirmed stable compounds at room temperature.
Although argon gas is a noble gas, it can form a number of compounds under various extreme conditions. Argon fluorohydride (HArF), a compound of argon gas with fluorine and hydrogen stable below 17 K (−256.1°C; −429.1°F), has been demonstrated.
Although the ground-state neutral chemical compounds of argon gas are currently limited to HArF, argon gas can form clathrates with water when its atoms are trapped in a lattice of molecules. water death. Ions, such as ArH+, and excited-state complexes, such as ArF, have been demonstrated. Theoretical calculations predict some argon gas compounds to be more stable but have not yet been synthesized.
History of Argon
Argon (Greek ἀργόν, neuter singular form of ἀργός meaning “lazy” or “inactive”) is named for its chemical inactivity. The chemistry of this first noble gas to be discovered impressed those who gave it its name. An unreactive gas was suspected by Henry Cavendish as a component of air in 1785.
Argon was first isolated from the air by Lord Rayleigh and Sir William Ramsay at University College London in 1894 by removing oxygen, carbon dioxide, water and nitrogen from a clean air sample. They first did this by replicating an experiment by Henry Cavendish.
They mixed atmospheric air with supplemental oxygen in a test tube (A) upside down over a large amount of dilute lye (B), which in Cavendish’s early experiments was potassium hydroxide, and passed an electric current. through conductors insulated with a U-shaped glass tube (CC) sealed around the platinum wire electrodes, leaving the ends of the conductors (DD) in contact with the gas and insulated with the alkaline solution.
The arc is powered by a battery of five Grove cells and a medium sized Ruhmkorff coil. The alkali absorbs the oxides of nitrogen produced by the arc and also the carbon dioxide. They operated the arc until no more volume reduction was observed for at least an hour or two and the nitrogen spectral lines disappeared when the gas was examined. The remaining oxygen is reacted with alkaline pyrogallate leaving a seemingly unreactive gas they call argon.
Before isolating the gas, they determined that nitrogen made from chemical compounds was 0.5 percent lighter than nitrogen from the atmosphere. The difference is small, but it is significant enough to hold their attention for months. They concluded that there was another gas in the air mixed with nitrogen. Argon was also encountered in 1882 through independent research by HF Newall and WN Hartley. New lines have been observed in the emission spectrum of air that do not match known elements.
Until 1957, the symbol for argon was “A”, but now it is “Ar”.
The prevalence of argon gas
Argon makes up 0.934% of the volume and 1.288% of the mass of the Earth’s atmosphere. Air is the main industrial source of pure argon products. Argon is isolated from air by fractional distillation, most commonly cryogenic fractional distillation, a process that also produces pure nitrogen, oxygen, neon, krypton, and xenon. Earth’s crust and seawater contain 1.2 ppm and 0.45 ppm argon, respectively.
Isotope of Argon
The major isotopes of argon found on Earth are 40Ar (99.6%),36Ar (0.34%) and 38Ar (0.06%). Naturally occurring 40K , with half-life 1.25 × 109 years, decays to stable 40Ar (11.2%) by electron capture or positron emission, and also stable 40Ca (88.8%) ) by beta decay . These properties and ratios are used to determine the age of the rock by K – Ar chronology.
In Earth’s atmosphere, 39Ar is produced by cosmic ray activity, primarily by neutron capture of 40Ar followed by emission of two neutrons. In the subsurface environment, it is also produced through neutron capture by 39K , followed by proton emission. 37Ar is produced by neutron capture by 40Ca followed by kếtemissionsalpha particles result of subsurface nuclear explosions . It has a half-life of 35 days.
Between locations in the Solar System , the isotope composition of argon varies widely. Where the primary source of argon is the decomposition of K in rocks, Ar will be the predominant isotope, as on Earth. Argon is directly produced by the stellar nuclear fusion process which is dominated by the nuclidean of the alpha Ar process . Correspondingly, solar argon contains 84.6% Ar (according to solar wind measurements), and the ratio of the three isotopes Ar: Ar: Ar in the atmospheres of the outer planets is 8400: 1600:1. This is in contrast to the low abundance of primordial Ar in Earth’s atmosphere, only 31.5 ppmv (= 9340 ppmv × 0.337%), which is comparable to neon (18.18 ppmv) on Earth, and with interplanetary gas, as measured by probes .
The atmospheres of Mars, Mercury and Titan (Saturn’s largest moon) contain argon, mainly Ar40, and its content can be as high as 1.93% (Mars).
The predominance of the radioactive Ar is the reason why the standard atomic weight of terrestrial argon is greater than the next atomic weight , potassium , a fact that was puzzling when argon was discovered. Mendeleev positioned the elements in his periodic table in order of atomic weight, but argon’s inertness suggested a position before reactive alkali metals . Henry Moseley later solved this problem by showing that the periodic table is indeed arranged in numerical order atomic.
A complete electron of Argon indicates full s and p subshells. This full valence shell makes argon very stable and extremely resistant to bonding with other elements. Prior to 1962, argon and other noble gases were considered chemically inert and could not form compounds; however, compounds of heavier noble gases have been synthesized. The first argon compound with tungsten pentacarbonyl, W(CO)5Ar, was isolated in 1975. However, it was not widely recognized at the time.
In August 2000, another argon compound, argon fluorohydride (HArF), was formed by researchers at the University of Helsinki, by shining ultraviolet light on frozen argon containing small amounts of hydrogen fluoride with cesium. iodide . This discovery led to the realization that argon could form weakly bound compounds, although it was not the first.
It is stable up to 17 kelvins (−256°C). The metastable ArCF2 + 2 dications, which are valence-isoelectrons with carbonyl fluoride and phosgene , were observed in 2010. Argon-36 , in the form of argon hydride ( argonium ) ions, was detected in the medium. stars associated with the Crab Nebula supernova ; This is the first noble gas molecule discovered in space.
Solid hydrogen argon (Ar(H2)2 ) has the same crystal structure as the MgZn2 Laves phase. It forms at pressures between 4.3 and 220 GPa, although Raman measurements show that the H2 molecules in Ar(H2)2 dissociate above 175 GPa.
Argon gas production
Argon produced in industry
Argon is extracted industrially by fractional distillation of liquid air in a 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 tons of argon are produced worldwide each year.
During radioactive decay
Ar40, the most abundant isotope of argon, is produced by the decay of 40K with a half-life of 1.25 × 10 9 years by electron capture or positron emission. Therefore, it is used in kali-argon dating to determine the age of rocks.
Argon has several desirable properties:
- Argon is a chemically inert gas.
- Argon is the cheapest alternative when nitrogen is not sufficiently inert.
- Argon has a low thermal conductivity.
- Argon has electronic properties (ionization and/or emission spectra) desirable for a number of applications.
Other noble gases would be equally suitable for most of these applications, but argon is by far the cheapest. Argon is inexpensive, as it occurs naturally in air and is easily obtained as a by-product of cryogenic separation in the production of liquid oxygen and liquid nitrogen: the major components of air used used on a large industrial scale. Other noble gases (except helium) are also produced in this way, but argon is by far the most abundant. The majority of argon applications arise simply because it is inert and relatively inexpensive.
Argon is used in a number of high-temperature industrial processes where normally unreacted substances become reactive. For example, argon gas is used in graphite furnaces to prevent graphite from burning.
For some of these processes, the presence of nitrogen or oxygen gas can cause defects within the material. Argon is used in several 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. The argon atmosphere is also used to grow silicon and germanium crystals.
Argon is used in the poultry industry to suffocate poultry, or for mass destruction after disease outbreaks, or as a means of slaughter more humane than electrical stun. Argon is denser than air and transfers oxygen near the ground during inert gas asphyxiation. Its non-reactive nature makes it suitable in a food product, and since it replaces the oxygen inside dead birds, argon also helps increase shelf life.
Liquid argon is used as a target for neutrino experiments and direct searches for dark matter. The interaction between the hypothesized WIMP and a light-producing argon gas nucleus was detected by the photomultiplier tube. A two-phase argon detector was used to detect ionized electrons generated during WIMP nuclear scattering.
Like most other liquefied noble gases, argon gas has a high luminous efficiency (about 51 photons/keV), is transparent to its own light irradiation, and is relatively easy to purify. Compared with xenon, argon gas is cheaper and has a separate illumination time profile, allowing the electron shock to be separated from the nuclear recoil. On the other hand, its intrinsic beta-ray background is greater than 39 degrees
Ar infection. Most of the argon gas in the Earth’s atmosphere is produced by capturing the long-lived electrons 40K (40K + e – →40Ar + ν) found naturally in Earth’s potassium. Ar39 Atmospheric Ar activity is maintained by cosmogenesis through the Ar40(n,2n) Ar39 knockout reaction and similar reactions.
The half-life of 39Ar is only 269 years. Therefore, the underground Ar, shielded by rocks and water, has at least 39Ar. Dark-problem detectors currently working with liquid argon include Darkside, Warp, ArDM, microCLEAN and DEAP. Neutrino experiments include ICARUS and MicroBooNE, both of which use high-purity liquid argon in a time-projected chamber to generate fine-grained three-dimensional images of neutrino interactions.
At Linköping University, Sweden, inert gases are being used in a vacuum chamber in which plasma is introduced to ionize metal films. This process produces a film that can be used to manufacture computer microprocessors. The new process will eliminate the need for chemicals and use expensive, dangerous and rare materials.
Argon is used to move oxygenated air and moisture within the packaging material to extend the shelf life of products (argon has the European food additive code E938). Oxidation in the air, hydrolysis and other chemical reactions that degrade the product will be slowed down or completely prevented. High purity chemicals and pharmaceuticals are sometimes packaged and sealed in argon.
In winemaking, argon is used in a variety of operations to provide a barrier against oxygen at the liquid surface, which can damage wine by providing energy for both metabolism. of microorganisms (as with acetic acid bacteria) and standard redox processes.
Argon is sometimes used as a propellant in aerosols.
Argon is also used as a preservative for products such as varnishes, polyurethanes and paints, by shifting air to prepare a container for preservation.
Since 2002, the United States National Archives has stored important national documents such as the Declaration of Independence and the Constitution in boxes filled with argon to prevent their degradation. Argon is preferred over the helium that had been used for the previous five decades, because helium escapes through the intermolecular pores in most containers and must be replaced frequently.
The glove box is usually filled with argon, which circulates in the filter to maintain an atmosphere free of oxygen, nitrogen and moisture.
Argon can be used as an inert gas in Schlenk chains and glove boxes. Argon is preferred over cheaper nitrogen in cases where nitrogen can react with reagents or equipment.
Argon can be used as a carrier gas in gas chromatography and ionization mass spectrometry; it is the gas of choice for plasma used in ICP spectroscopy. Argon is preferred for sputter coating of specimens for scanning electron microscopy. Argon gas is also commonly used for sputtering deposition of thin films such as in microelectronics and wafer cleaning in microfabrication.
Cryosurgery procedures such as cryotherapy use liquid argon gas to destroy tissue such as cancer cells. It is used in a procedure known as “argon gas-enhanced coagulation“, a form of argon gas plasma beam electrosurgery. This procedure carries the risk of creating air embolism and resulting in the death of at least one patient.
Green argon gas lasers are used in surgery to seal arteries, destroy tumors, and correct eye defects.
Argon has also been used experimentally to replace nitrogen in a breathing or decompression mixture known as Argox, to speed the removal of dissolved nitrogen from the blood.
Argon gas discharge lamps form the symbol for argon “Ar“
Incandescent lamps are filled with argon gas, to preserve high-temperature filaments from oxidizing. It is used for the specific way in which it ionizes and emits light, such as in plasma spheres and calorimetry in experimental particle physics. Discharge lamps filled with pure argon gas provide a violet light, with argon gas and a small amount of mercury, a blue light. Argon is also used for blue and green argon ion lasers.
Argon is used for insulation in energy-efficient windows. Argon is also used in technical scuba diving to inflate a dry suit because it is inert and has low thermal conductivity.
Argon was used as a propellant in the development of the Variable Specific Shock Magnetoplasma Rocket (VASIMR). Compressed argon gas is allowed to expand, to cool the probes of some versions of the AIM-9 Sidewinder and other rockets that use a cooled heat detector. The gas is stored at high pressure.
Argon-39, with a half-life of 269 years, has been used for a number of applications, mainly dating ice cores and groundwater. In addition, kali-argon dating and related argon-argon dating are used to date sedimentary, metamorphic, and igneous rocks.
Argon has been used by athletes as a doping agent to simulate hypoxia. In 2014, the World Anti-Doping Agency (WADA) added argon and xenon gases to the list of prohibited substances and methods, although at this time there are no reliable tests for abuse.
Safety when using argon gas
Although argon gas is not toxic, it is 38% denser than air and is therefore considered a dangerous asphyxiant in enclosed areas. It is difficult to detect because it is colorless, odorless, and tasteless.
A 1994 incident in which a man suffocated after entering an argon-filled oil pipeline under construction in Alaska, highlighted the dangers of argon cylinder leaks in confined space. preparation and emphasizes the need for proper use, storage and handling.