Argon gas (Ar)

May 30, 2020 | Air Gases, Element gases, Industrial Gases | 0 comments

Ms.Rozita Dehbasteh

Ms.Rozita Dehbasteh

Bachelor of applied Chemistry
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Argon gas (Ar)
Argon is a colorless, odorless, non-reactive, inert gas. In high concentrations, it has an asphyxiating effect. As argon is an atmospheric gas (0.93% vol.), it is generally sourced by separating air. A crude Argon stream containing up to 5% oxygen is removed from the main air separation column and purified to produce the commercial purity grade required.

On Earth, the vast majority of Argon is the isotope Argon-40, which arises from the radioactive decay of potassium-40. But in space, Argon is made in stars, when a two hydrogen nuclei, or alpha-particles, fuse with silicon-32. The result is the isotope Argon-36. (Isotopes of an element have varying numbers of neutrons in the nucleus.) 

Though inert, Argon is far from rare; it makes up 0.94 percent of Earth’s atmosphere. That translates to 65 trillion metric tons — and the number increases over time as potassium-40 decays. [1] , [2]


The name argon comes from the Greek word “argos” meaning “lazy” or “inactive”. Argon was the first noble gas to be discovered. The first hint of its existence came from English scientist Sir Henry Cavendish as far back as 1785. Cavendish used an electric spark in air to react the oxygen and nitrogen to form nitrogen oxides. He then added additional oxygen until all the nitrogen had reacted. Nitrogen oxides are acidic. Cavendish used aqueous sodium hydroxide to remove them from the apparatus. He removed the remaining oxygen using potassium polysulfides. A small bubble of gas remained [mostly Argon].

After all tries for discovering, Rayleigh and Ramsay carried out further experiments, keeping in touch with one another about their progress. In August 1894 Ramsay took air and removed its components – oxygen, carbon dioxide and nitrogen. After removing all the known gases from air, he found gas remaining that occupied one-eightieth of the original volume. Its spectrum matched no known gas. Rayleigh and Ramsay wrote a joint paper in 1895 notifying the world of their discovery. The new gas wouldn’t react with anything, so they named it Argon. In his Nobel Prize winning address, Rayleigh said: “Argon must not be deemed rare. A large hall may easily contain a greater weight of it than a man can carry.” [3]

Argon atomic spectrum [4]


Three isotopes of argon exist naturally. They are argon-36, argon-38, and argon-40. Isotopes are two or more forms of an element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.

Six radioactive isotopes of argon are known also. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive.

No radioactive isotopes of argon have any practical application. One non-radioactive isotope is used, however, to find the age of very old rocks. [5] , [6]

Physical properties

Argon appears as a colorless odorless noncombustible gas. Heavier than air and can asphyxiate by displacement of air. Exposure of the container to prolonged heat or fire can cause it to rupture violently and rocket . If liquefied, contact of the very cold liquid with water may cause violent boiling. If the water is hot, there is the possibility that a liquid “superheat” explosion may occur. Contacts with water in a closed container may cause dangerous pressure to build.[7]

Chemical properties
It is an inert gas, meaning that it typically doesn’t react with other elements to form compounds. When argon is excited by a high voltage electric field it glows in a violet color.
Argon has been found to form one neutral compound with fluorine and hydrogen called argon fluorohydride (HArF). However, this compound is only stable at very cold temperatures (-256 degrees C).[8] , [9]

Table: Argon properties

Atomic number(Z)18
Atomic mass(amu)39.95
Periodic tableSeries-noble gases;group8-period3
Electron configuration[Ne]3s2 3p6
Atomic radius(Å)0.88
Atomic volume(cm3/mol)28.5
Number of (electrons/protons)/neutrons18-22
Covalent radius(Å)0.98
Crystal structureCubic face centered
Heat of fusion(kJ/mol)1.188
Melting point(0C)-189.35
Boiling point(0C)-185.35
Thermal conductivity(W/mK) at 273K0.0165
Density(kg/m3) at 273K1.784
Heat capacity(J/mol.K)20.8
Water solubility(mg/lit) at 200C and 1 bar62
Isotopes at atmospheric pressure40Ar(99.5%)-36Ar(0.35%)-38Ar(0.06%)

Color of Argon cylinder

The color of the gas cylinder indicates the hazard but not the filled gas. Inert gas cylinders are bright green.[10]

Use  of Argon in welding Systems

Argon is used as a shielding in the welding  systems. During the welding, process metals are exposed to temperatures of upwards of 7000 Degrees. At these temperatures, most metals become liquid, which allows the formation of the weld. Argon is used to protect the molten pool of metal against elements in the Atmosphere including Oxygen, Nitrogen, and Hydrogen. These elements cause reactions with the liquid weld pool, such as porosity and increased weld spatter. Argon also plays an important role in maintaining Arc stability, which leads to increased weld penetration, better filler wire transfer, and better weld appearance.

Kind of Argon Gas

Its  recommended using 99.996% pure Argon (Argon 4.6). This is one of the most commonly used welding gasses in the world. Every major gas supply company will carry this. It is the same as welding  gas used in a traditional TIG welding Setup. Pure Argon refers to the gas being just Argon, and not mixed with another gas.

Other shielding gasses such as CO2 and Argon-CO2 mixes, do not work as well as pure Argon. Ultra high purity or medical grade Argon is not required.

Need of Argon Regulator

When you get your Argon Cylinder it will not come with an Argon Regulator. We strongly recommend purchasing the regulator. This will ensure that you will have the proper type of regulator and make things much easier for you.[11]


Argon has safety concerns to be aware of, but for the most part is a very safe gas. It is non-toxic and non-flammable, therefore it is not poisonous, and it will not burn. Argon does come in a compressed tank, and proper safety protocol should be followed when working with compressed tanks. Argon is 38% denser than air so when working within confined areas ensure that you have proper air ventilation. [12]

Effects of exposure:

 Inhalation: Dizziness. Dullness. Headache. Suffocation.

 Skin on contact with liquid: frostbite.

 Eyes on contact with liquid: frostbite.

 Inhalation in excessive concentrations can result in dizziness, nausea, vomiting, loss of consciousness, and death. Death may result from errors in judgment, confusion, or loss of consciousness which prevent self-rescue. At low oxygen concentrations, unconsciousness and death may occur in seconds without warning.[13] , [14]


Neon lights that shine blue actually contain Argon. The classic neon lamp is made up of a glass tube containing a mixture of neon(99.5%) and Argon gas. there are two electrodes, one positive, and the other negative. Voltage rises and an ARC is struck between. Argon gas is used in other fluorescents as well because of a lower striking temperature. After the Argon strikes an ARC the neon gas is warmed and current is able to flow through the neon gas, ionizing more atoms as the current rises.[15] , [16]

Argon is generally used for TIG welding of unalloyed steels, low-alloyed steels and stainless steels. For mechanised welding the shielding is typically argon, with an admixture of helium or hydrogen in order to increase heat input. Hydrogen also helps to reduce oxide formation, and produces a smoother weld.

When making quality welds with TIG, it is also very common to use a root gas in order to protect the root side of the weld against oxidation. This is particularly important in the case of stainless steels or when welding easily-oxidised materials. The root gas is often a mixture of nitrogen/hydrogen, or pure Argon.[17]

Here are some other recent researches about Ar usage;

Argon attenuates the emergence of secondary injury after traumatic brain injury within a 2-hour incubation period compared to desflurane: An in vitro study:

Within a 2-hour incubation time neither Ar nor desflurane could affect PI-detectable cell death in an in Vitro TBI model in comparison to the standard atmosphere, although cell death was less with Ar than with desflurane. This shows that within this short time period processes concerning the development of secondary injury have already taken place and may be manipulated by Argon. [18]


Argon is a mixture of stable isotopes and the argon method is applied to geochronology to date the age of ancient materials, because argon has been found in rocks and fossils. Geochronology is the science of determining the age of rocks, fossils, and sediments, within a certain degree of uncertainty inherent to the applied method. A variety of dating methods are used by the geologists leading to the elaboration of different schemes, classifications and terminologies. The approach using several methods simultaneously is preferred for achieving better results.[19]

Effect of Argon‐plasma treatment on proliferation of human‐skin–derived fibroblast on chitosan membrane:

Chitosan is not only a nontoxic, biocompatible, and biodegradable polymer, but also has a chemical structure similar to glycosaminoglycans (GAGs), which promote scarless wound healing of skin. In this study, chitosan membranes were treated with Argon plasma to improve their surface hydrophilicity. The results showed that the water contact angles of these surface‐treated membranes were significantly reduced from 60.76 to 11.57°.
The total surface energy was increased from 41.06 to 67.31 mJ/m2, with 60–86.95% improvement in the gamma‐negative component and a 20% difference in the nonpolar component. Argon‐plasma–treated chitosan membranes exhibited excellent attachment, migration, and proliferation of the human‐skin–derived fibroblasts (hSFs) compared to the untreated ones. It was found that the duration of argon‐plasma treatment influenced the cell proliferation, and the optical densities in MTT assay were enhanced. Argon‐plasma treatment improved the surface hydrophilicity of chitosan membranes and promoted the attachment and proliferation of hSFs.[20]

Argon reduces the pulmonary vascular tone in rats and humans by GABA-receptor activation:

argon decreased the pulmonary vascular tone of the rat, if PVR was enhanced, but it did not affect the airway tone. In view of the pulmonary vasorelaxant potential of argon, activation of GABAA/B-receptors plays a pivotal role. Finally, our results support the application of argon for neuroprotection in patients with critical pulmonary haemodynamics based on PH, RV failure or LHD. The relevance of our findings is strengthened by the fact that argon also relaxed human PAs.[21]

Argon Plasmas

High purity argon gas (≥ 99.999%) is commonly used in the low and high pressure plasma technology. Its applications ranging from pure research to specific fields such as medicine (dermatology, ophthalmology, for example), semiconductor industry, analytical chemistry, nanotechnology, among others.

Compared to the traditional Inductively Coupled Plasma (ICP) mass spectrometers, the microtorch has a simple construction, runs at low argon flow and can be integrated in a portable system suitable for in-situ simultaneous determination of the consisting elements. In laboratory the analytical performance of a medium power (275 W) argon CCP torch with a Mo tubular electrode and single or double ring electrodes used in the multielemental analysis by atomic emission spectrometry (CCP-AES) of pneumatically nebulized liquid samples was investigated.[22]


The production of Argon is an important economic factor in the industrial gas industry. Generally argon is a by-product of cryogenic air separation. However, a number of additional processing steps are necessary to produce a required purity of argon. One of the critical purity requirements is the concentration of contained nitrogen. Many applications of argon demand that it be essentially free of nitrogen.

 In the past, the production of high purity argon involved a number of processing steps to produce a crude argon stream which was then upgraded in a refinery. Argon processing starts with the low pressure column of a cryogenic air separation plant. A low grade argon stream is withdrawn from an intermediate point in the low pressure column. The low grade argon stream is then fed into an argon column where it is separated into an overhead crude argon stream containing about 97.5 percent argon and a bottom stream which is returned to the low pressure column. The crude argon stream from the top of the argon column is then warmed to about ambient temperature, at which time hydrogen is added and the mixture is compressed and sent to a Deoxocatalytic furnace where the oxygen is removed. Then the combusted argon is cooled, dried and further cooled to essentially liquefaction temperature. The cold argon stream is sent to the refinery column where the excess hydrogen and remaining nitrogen are removed. Normal production provides an argon product stream containing less than 5ppm nitrogen or oxygen.

 Nowadays, the air feed is compressed prior to the removal of the primary impurities of H2O and CO2 via adsorption. The air is then cooled by heat exchange with exiting product and waste streams and then sent to a set of mass and energy integrated distillation columns where the air is separated into oxygen, nitrogen, and argon. Liquid products are sent to storage and the gaseous products are re-warmed by the feed streams and compressed to the required final product pressure(s).[23]

Medical Argon

For medical instruments/ devices using contactless methods of APC (argon plasma coagulation) and APP (cold plasma method):
In cryotherapy for the destruction of diseased cells, in particular the prostate and the kidney. The decompression of 300 to 240 bar of Argon makes it possible to produce the temperature necessary for the cooling of cryosurgery needles. The gas is used as an accessory to the cryotherapy device and does not come into contact with the patient.[24]
In eye surgeries, Medical Argon is used as a resonator gas in laser devices to create a laser beam. Medical Argon as resonator gas could also be used for other laser applications in medicine. Another medically used for argon gas knife, gas knife, and other surgical instruments.[25]

Argon as pipeline

The principle application of Argon-CO2 pipeline with benefits includes:

Being a versatile gas, Argon Carbon Dioxide blends are used for all kinds of structural steel, farm implements and machinery.

Argon is the common shielding gas and used as the base for the more specialized gas mixes, which includes a mixing a good proportion of CO2. Industries could use the solution for short ARC welding of pipes.( C-50:( 50% argon-50% CO2). Other application includes the production environment for carbon and low allow steels. The gas pipeline fitting solutions can be resused. Minimum leakage or leakage proof application.[26]

Environmental effect

No known ecological damage caused by argon. No adverse environmental consequences are expected. Argon gas occurs naturally in the environment. The gas will dissipate rapidly in well ventilated areas.

The effects of argon on plants or animals is not currently known. It is not expected to harm aquatic life. Argon does not contain any ozone depleting chemicals and is not listed as a marine pollutant.[27]









[9]: Argon properties, production and recent applications. January 2013. B.N. Sismanoglu. Rodrigo Pessoa. R. Caetano. Y. D. 

[10]: INDUSTRIAL GAS CYLINDERS COLOR CODING TD 08/15/E. MIDDLE EAST GASES ASSOCIATION (MEGA)   European Business Center, Office BC – 25   Dubai Investments Park, PO Box: 166 Dubai-UAE 

[11] , [12]:


[14]: Material Safety Data Sheet for Argon. Reference: Voltaix, Inc. MSDS Document Number -Ar000 (revision dated 02 Aug 96).



[17]: Welding Processes Handbook (Second edition)

Woodhead Publishing Series in Welding and Other Joining Technologies .2012, Pages 63-69.Klas weman

[18]:Linda Gruber. Matthias Krings. Rosmarie Blaumeiser-Debarry. Benedikt Kremer. April 2017. DOI: 10.4103/2045-9912.208512

[19]: Argon properties, production and recent applications. January 2013. B.N. Sismanoglu. Rodrigo Pessoa. R. Caetano. Y. D. 

[20]: Xiao Zhu .Kerm Sin Chian  .Mary Bee Eng Chan‐Park .Seng Teik Lee.23 March 2005. Journal of Biomedical Material research

[21]: Said SuleimanSergej KlassenIra KatzGalina BalakirskiJulia KrabbeSaskia von StillfriedSvetlana KintslerTill BraunschweigAaron BabendreyerJan SpillnerSebastian KalverkampThomas SchröderManfred MoellerMark CoburnStefan UhligChristian Martin & Annette D. Rieg. Article number: 1902 (2019) 

[22]: Argon properties, production and recent applications. January 2013. B.N. Sismanoglu. Rodrigo Pessoa. R. Caetano. Y. D. 

[23]: Argon properties, production and recent applications. January 2013. B.N. Sismanoglu. Rodrigo Pessoa. R. Caetano. Y. D. 





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