Argon gas - chemical properties and scope of application

Inert gases practically do not react with other substances, so they cannot be used, for example, for heating a home or producing chemical compounds. Despite their “asocial nature,” such elements have become very widespread in industry due to the presence of very interesting physical properties. Argon gas is one of these elements.

The main qualities of argon, as well as the areas of its application, will be discussed in detail in this article.

History of discovery

The background to the discovery of Ar began in 1785. An outstanding scientist and naturalist from Great Britain, Henry Cavendish, studied the composition of air. He subjected nitrogen to oxidation and weighed the resulting oxides. At the end of the experiment, gas remained in the vessel. Cavendish determined its volume to be 0.8% of the initial volume of air.

The scientist was unable to determine the composition of this gas. A century later, Sirs John Rayleigh and William Ramsay returned to the problem. During their experiments, they discovered that nitrogen released from the air has a higher density than nitrogen obtained during the decomposition reaction of ammonium nitrite.

in 1884 they managed to isolate a certain gas from the air that was denser than nitrogen. This substance had a monatomic molecular structure and was extremely inert - i.e. did not react with other substances.

At a meeting of the Royal Society, the new gas was given the name “argon”, which translated from ancient Greek meant “calm, lazy”

Argon crystal lattice:

Argon in nature

Due to its almost complete inertness, Ar is present in the natural environment exclusively in unbound form. Its percentage in different parts of the Earth is approximately:

• earth's crust - 0.00012%;
• sea ​​water - 0.00045%;
• atmosphere - 0.926%.

The proportion of Ar in the air is higher than the total proportion of all other inert gases. The main source for its production is our atmosphere.

Content of gases in the atmosphere

Argon is also contained in the Earth's crust in the form of the radioactive isotope Argon-40 and appears during the decay reaction of Potassium isotopes.

Modern science, along with other inert gaseous elements, classifies Ar into group VIII of the periodic table.

Argon: facts and facts

A. Motylyaev “Chemistry and Life” No. 7, 2015

How did argon confound D.I. Mendeleev and other eminent chemists?

Argon was first discovered by Henry Cavendish in 1795: he passed an electric discharge through the air for several weeks, while oxygen reacted with nitrogen (they were then called “dephlogiston air” and “phlogiston air,” respectively) and produced nitrous acid, which was absorbed by potash. The volume of gas in the vessel decreased, but the gas did not disappear completely: something remained that did not react. No one paid much attention to Cavendish's discovery. But in 1882, Lord Rayleigh began a series of tedious experiments to measure the density of gases. And all the time it turned out that the ratio of the weight of hydrogen and the gas under study was slightly less than an integer. Physicists, who did not yet suspect the existence of isotopes, really wanted it to be integer. Wanting to find the source of the error, Rayleigh decided to obtain pure, non-atmospheric, nitrogen. To do this, he passed a mixture of ammonia and oxygen over hot copper: the ammonia decomposed, producing nitrogen and water. This nitrogen turned out to be half a percent lighter than atmospheric nitrogen. And in 1894, William Ramsay discovered that nitrogen was absorbed by hot magnesium. It was he who decided to isolate the heavy impurity discovered by Rayleigh in nitrogen. Soon Ramsay had 40 ml of gas in his hands, which was not absorbed by magnesium. Measurements showed that its molecular weight was 40. Since all gases known at that time were diatomic, the resulting atomic weight was 20, which looked strange - heavier than fluorine, lighter than sodium. A monatomic gas would be too heavy and would not fit into the Periodic Table in any way - such an element should be placed between two metals - potassium and calcium. Therefore, a hypothesis arose that Ramsay discovered triatomic nitrogen, fortunately 40 is approximately three times greater than 14. Here is how Mendeleev writes about this in the “Addition to the 5th chapter” of the sixth edition of “Fundamentals of Chemistry”: “The hypothesis A = 40 is not at all gives place to argon in the periodic table... It seems to me simpler to assume that argon contains N3, especially since argon is contained in nitrogen..." Rayleigh, upset by the rejection of his new gas, no longer studied chemistry and received the Nobel Prize in physics in 1904 for study of gas densities and the discovery of argon in connection with this. And Ramsay received a prize in chemistry in the same year for the discovery and study of elements of group zero.

Why is argon with a weight of 39.9 listed in the table before potassium, which has a weight of 39.1?

Argon has three stable isotopes with weights 36, 38 and 40. There are more light isotopes in the Universe, and there is very little argon-40. At the same time, there is a lot of argon in planetary nebulae and in the matter of stars; it prevails over such common elements on Earth as potassium, calcium, fluorine and chlorine. But on our planet there is not much argon itself, and its light isotopes are negligible - apparently, they have flown to the periphery of the solar system. We did not inherit Argon-40 from a protoplanetary cloud; it is formed here and now - as a result of the radioactive transformation of potassium-40. Typically, in this isotope, which provides the bulk of the natural background radiation, the neutron becomes a proton with the emission of a positron, and the next element is obtained - calcium-40. But in every fifth case, the so-called K-capture occurs: an electron from the lower orbital falls into the nucleus, one of the protons becomes a neutron with the emission of neutrinos, and the atom goes to the previous cell of the Periodic Table. It is precisely because of the lack of light isotopes of argon on Earth that its weight, measured by chemists, turned out to be greater than that of potassium, which comes next, represented by all isotopes.

Is there radioactive argon on Earth?

There is almost no radioactive argon in nature, since the longest-living one, argon-39, has a half-life of 269 years.
However, highly active argon-41 with a half-life of 1.85 hours is continuously formed in a nuclear reactor, and if there is a malfunction in the ventilation system, it can also get beyond it. Once the thermonuclear reactor is launched, the problem will become more complicated. According to the calculations of Vladimir Khripunov from the Kurchatov Institute ( Fusion Engineering and Design
, 2015, DOI:10.1016/j.fusengdes.2015.02.058), with a massive neutron bombardment, we recall that it is precisely due to the braking of neutrons by the walls of the tokamak that it is planned to remove the heat released during thermonuclear fusion, argon-39 will begin to form in sufficient quantities to cause concern for the health of fusion plant workers.

How do you measure time with argon?

Potassium is one of the most abundant elements on Earth and other rocky planets, and potassium-40 has a half-life of 1.3 billion years.
The constantly formed argon-40 is enclosed in any rock, and its amount increases from the time it solidifies. Accordingly, by the ratio of argon-40 and potassium-40, you can find out when this rock (usually we are talking about basalt) was erupted from the bowels of the planet. Measurements are carried out by bombarding argon-40 with a stream of neutrons: short-lived argon-41 is obtained, its decay is easy to notice. Argon makes it possible to measure time on a scale from hundreds of millions to tens of thousands of years, that is, when the carbon method no longer works accurately. For the development of the method, Professor E. K. Gerling received the Lenin Prize in 1963. In particular, the first remains of Homo habilis, found in the Olduvei Gorge in Kenya, were dated by the argon method based on the age of the surrounding pebbles;
his age turned out to be 1.7 million years (see “Chemistry and Life”, 1967, No. 6).
Recent advances include new dating of the Deccan Traps ( Journal of Asian Earth Sciences
, 2014, 84, 9–23, DOI:10.1016/j.jseaes.2013.08.021), the largest lava flow, occupying a third of Hindustan on its western side. As it turned out, the age of the largest spills is statistically indistinguishable from the date of the catastrophe that killed the dinosaurs. The meteorite fall in the Yucatan region, which created the Chicxulub crater, according to the latest data, occurred 300 thousand years earlier than the mass extinction. In general, the Deccan hypothesis has long been competing with the Chicxulub hypothesis.

What reactions does argon undergo?

Having no free electrons and therefore being chemically inert, argon forms chemical compounds reluctantly and under very exotic conditions. However, it forms so-called clathrate compounds: an argon atom may be enclosed in a cavity formed by some kind of molecule, or in the crystal lattice of another substance. Like xenon, argon is also capable of forming compounds with proteins; As a result, at elevated pressure, the argon-oxygen mixture causes loss of consciousness - argon anesthesia.

Why is argon dangerous?

When working with installations filled with argon, precautions should be taken: argon is a heavy gas, it accumulates in all sorts of recesses, such as wells, displacing oxygen from there, that is, it can create an atmosphere unsuitable for breathing. If a worker, having lost consciousness, falls into such a depression, he will suffocate. Materials scientists working with argon say: “Argon will find a hole,” and equipment manufacturers take this fact into account. They tell the following story. At one enterprise they installed a new Swedish gasostat. This is a huge installation, as tall as a five-story building, that can subject parts to heat and high pressure to eliminate internal cavities in the metal that form during manufacturing. To avoid oxidation of the part, the gas stat is filled with an inert gas - argon. Since it is easier to dig down than to build up, they wanted to deepen the gasstat, but the manufacturers categorically forbade this precisely because the argon flowing from the installation should not accumulate anywhere. But argon has a good effect on plants: in an atmosphere of 98% argon and 2% oxygen, the seeds of onions, carrots and lettuce germinate quite successfully.

Why is a glass unit filled with argon?

To increase sound insulation and reduce thermal conductivity, argon has a higher modulus of elasticity and lower thermal conductivity than air. True, taking into account the rule “argon will find a hole,” it is not clear how long this gas will remain inside the double-glazed window.

How is argon produced?

When air is separated into oxygen and nitrogen in high-pressure columns. The volatility of argon is greater than that of oxygen and less than that of nitrogen, and it is taken from the upper third of the column. Argon is also separated from the waste product of ammonia production - that nitrogen that was not consumed in the reaction with hydrogen; it turns out to be enriched with argon itself.

How is argon used in technology?

Being the most common inert gas - after all, the third most important component of the Earth's atmosphere after nitrogen and oxygen - argon is in great demand, primarily as a substance incapable of chemical reactions. By filling the installation or the entire workshop with argon, you don’t have to worry that the heated metal part or workpiece will oxidize or become saturated with nitrogen, followed by the release of nitrides. Molybdenum and tungsten, for example, are prone to oxidation: many could observe the instant transformation of an incandescent lamp coil into a bluish powder when air enters it. Titanium, tantalum, niobium, beryllium, hafnium, zirconium, as well as uranium, thorium and plutonium are processed in argon. By blowing argon through the steel in the converter, gas inclusions are removed from it. A revolution in technology was made by the argon-arc welding method: a stream of argon supplied to the place where the electric arc burns displaces air and prevents the metal from oxidizing - oxides reduce the strength of the seam, or even make welding of materials impossible. This method is used to weld alloy steels and non-ferrous metals and cut their thick sheets. Another serious area is the spraying of all kinds of materials to obtain a powder free of oxides.

Rolling shop of pure refractory metals in a, 1968, No. 11)

What are argon clusters?

Beams of ionized clusters are a new method of surface treatment to atomic smoothness. Its essence is bombardment not with individual ions (this is called “ion etching”), but with much heavier particles consisting of tens or even thousands of atoms. Beams of argon clusters have become widespread due to the inertness of the gas and its relative cheapness. Clusters are formed by feeding gas under high pressure through a narrow nozzle. Passing through it, the gas flow expands sharply and cools; Argon atoms clump together into a solid, where they are held together by van der Waals forces. When a surface is bombarded with high-energy clusters, nanometer-sized craters are formed; This will be the smoothness of the entire surface. By repeating scanning with a beam of less energetic clusters, the smoothness is increased. This method is used to process semiconductors, thin films, the surface of computer disks, and much more. Cluster beams can also create nanopatterns on surfaces. They also allow, without heating the sample, to carry out a layer-by-layer study of its composition, gradually going deeper and deeper; This method is used to analyze the structure of organic substances.

How does argon work in nanotechnology?

Argon plasma or the addition of argon to the plasma of another gas is the most important method for obtaining all kinds of nanostructures: spherical nanoparticles, nanoblades, nanoneedles. The essence of the plasma method is that a substance divided into ions and electrons has the ability to activate chemical reactions and even makes possible those that are thermodynamically prohibited under normal conditions. Argon is an excellent activator: it does not interfere with the reaction, and the reaction products either condense into equiaxed particles or settle on the surface, giving non-equiaxed structures. It can also serve as a plasma diluter for another, reaction gas - in this way the process parameters are changed. Finally, high-temperature argon plasma is used to sputter a metal target and obtain nanopowders with particles of a given size from it. Other inert gases - neon, xenon - give their sizes. Argon is also used as a coolant: it blows powder out of the plasma zone, which again makes it possible to regulate the particle size, since it depends on the time the material is in the plasma zone.

Who needs argon foam?

Using argon, it is possible to make porous templates from gelatin for their subsequent population with cells when growing artificial organs. The advantage of argon here is obvious - its chemical inertness.

What is an argon laser?

Invented in 1964, this laser uses a tube filled with argon as the light generator.
The electrodes create a plasma with a high density of argon ions in it, and a coil wound around the tube forms a magnetic field, further increasing the plasma density. This laser is cheaper than solid-state analogues, produces powerful - 20-30 watts - radiation in the blue-green part of the spectrum, and its color can be switched between 14 spectral lines. Such lasers are used to pump other lasers, for light shows, and also to stimulate fluorescence in the chemical analysis of complex organic substances. With its help, for example, traces of RNA are found in the amount of picograms, that is, as much as there is in one cell ( Electrophoresis
, 2015, DOI:10.1002/elps.201500117). An argon laser is also used in the treatment of blindness caused by diabetes - it appears due to the excessive development of blood vessels in the eye, and they can be painlessly thinned out with a laser.

How is argon sterilized?

Cold argon plasma is used to kill bacteria.
Such a plasma contains hot electrons, and the temperature of the ions is equal to room temperature, that is, it cannot burn, but retains the ability to activate reactions. These reactions depend both on the method of producing plasma (on the temperature of its electrons) and on the addition of other gases. For example, irradiation of mammalian cells in saline with pure or moist argon produced primarily a hydroxyl radical, which inhibited cell development. But plasma from argon with the addition of 1% oxygen or 1% air most likely gave atomic oxygen. Reacting with chloride ion, it generated Cl2– or ClO– radicals, which had a destructive effect on cells, and no antioxidant enzymes like superoxide dismutase could cope with them. The lifetime of such radicals turned out to be about half an hour ( Biointerphases
, 2015, 10, 2: 029518; DOI:10.1116/1.4919710).
The result is clear: argon plasma can be used for “cold” disinfection. Thus, E. coli can be limed on a sample in 10 minutes ( Applied Biochemistry & Biotechnology
, 2013, 171, 7; DOI:10.1007/s12010-013-0430-9), and with the addition of 0.5% oxygen - in 30 seconds (
International Journal of Radiation Biology
, 2009, 85, 4; DOI:10.1080/09553000902781105).
In general, cold plasma from various gases cleans the surface of meat, poultry, vegetables, and fruits from microbes such as E. coli, listeria, salmonella, and Staphylococcus aureus in a matter of seconds. And no antimicrobial “chemistry” that frightens the consumer. However, this technology is new, the equipment is not standardized, each generator produces its own plasma, and it is difficult to compare the results of experiments. It is also unknown how such processing will affect the quality of food when mass processed ( Annual Review of Food Science & Technology
. 2012, 3, 125-42; DOI:10.1146/annurev-food-022811-101132).

A plasma brush in action and the bacteria destroyed by it ( pictured below

).
From the article by Bo Yang et al. Oral Bacterial Deactivation Using a Low-Temperature Atmospheric Argon Plasma Brush, Journal of Dentistry
, 2011, 39, 1.

How is argon used in medicine?

Different ways.
For example, plasma can be useful for the same disinfection of wounds, although in the case of trophic ulcers the results were ambiguous: it seemed that the number of bacteria did not decrease as quickly as when using the medicine, but the ulcers healed at the same speed. This may be because plasma can treat smaller ulcers and heal faster ( Journal of Wound Care
, 201, 24, 5; DOI:10.12968/jowc.2015.24.5.196). Plasma treatment does not cause the same side effects as drugs, so the authors recommend continuing research with different sources of plasma, especially since resistance to it cannot develop by definition, which cannot be said about drugs.

With the help of a specially invented plasma brush, it is possible to destroy bacteria that cause caries. But there are nuances here. Thus, the main pests of teeth are Streptococcus mutans

and
Lactobacillus acidophilus
, which form bacterial mats on the enamel and produce a lot of acid.
Streptococcus cells are small and are destroyed in just 13 seconds. But lactobacilli are large, forming thick layers, and it takes minutes to get rid of them ( Journal of Dentistry
, 2011, 39, 1; DOI:10.1016/j.jdent.2010.10.002).
It is unlikely that such a brush will appear in everyday life, but it will be useful for a dentist to disinfect a freshly treated hollow. In addition, plasma changes the surface of the tooth substance, which increases the strength of its connection with the filling by 60%. The main thing here is not to overdo it: treatment within 30 seconds gives the effect, but a few minutes, on the contrary, worsens adhesion ( European Journal of Oral Science
. 2010, 118, 5; DOI:10.1111/j.1600-0722.2010.00761).
Argon plasma can quickly stop blood from internal bleeding. Argon inhalation protects neurons damaged by ischemic stroke or trauma ( PLoS One
, 2014, 9, 12:e115984, DOI:10.1371/journal.pone.0115984).

How does argon cryosurgery work?

Cryosurgery is the destruction of diseased tissue by rapid freezing. It is used for a variety of indications, from reducing warts and smoothing scars to removing tumors. If warts are frozen from the outside with cotton wool soaked in liquid nitrogen, then scars and tumors are frozen from the inside by inserting a hollow needle into them - a cryoprobe, through which a cold substance is pumped. They also use cryoapplicators - they are applied to the object to be frozen. Installation with liquid nitrogen is much simpler and cheaper, but it uses thick probes with a diameter of 6 mm. Argon, on the other hand, is much more complicated and requires highly qualified personnel, in particular special knowledge of working with high pressure, but allows very precise freezing of tissue: the diameter of the needle can be as small as a millimeter, such a needle easily passes through the skin. Freezing is carried out with argon gas. The gas is stored under a pressure of 400 atmospheres, and, passing through a narrow nozzle and then expanding sharply, it cools to –140°C due to the Joule-Thomson effect. If thermal sensors inserted near the place of freezing indicate that the temperature has dropped too much and healthy tissue may be damaged, helium is supplied to the probe, which warms the frozen tissue. This way, controlled freezing-thawing cycles can be carried out, which increases the efficiency of the procedure, and the frozen cryoprobe is easier to remove.

A nitinol stent easily expands the lumen of a vessel

How do surgeons use an argon cutter?

Using an argon plasma cutter, you can perform operations of amazing virtuosity - cutting stents inserted into the intestines, or thin ducts of the digestive system, for example those that deliver bile and pancreatic secretions.
For various reasons (tumor, stones, etc.), the duct may become blocked. For treatment, a tube is inserted there - a stent, for example, made of NiTi intermetallic compound - nitinol. Initially, its diameter is small, but once in place and heated, the product, due to the shape memory effect of nitinol, increases in size and expands the lumen of the vessel. However, it may happen that the size of the stent is chosen incorrectly or becomes unsuitable over time due to changes in the body. In addition, the stent can become overgrown or move out of place and block the channel so much that you cannot get to it with the endoscope with which the stent was placed. Then a plasma cutter with a power of several tens of watts is introduced and the stent is trimmed. In many cases, this operation is quite successful, does not cause any damage to blood vessels or bleeding (and if it does, the same plasma can stop the bleeding), but for the patient’s well-being it is much better than removing the old stent and installing a new one ( Endoscopy
, 2005, 37, 5,434–438). This is important because the patient may be old.

How is argon produced?

Due to the industrially significant content of argon in the air, it is obtained as an additional product of the cryogenic distillation of O2 and N2.

The technology is based on the fact that the boiling (or liquefaction) point of Ar lies between the temperatures of N2 and O2.

Before the process begins, the air is thoroughly cleaned of dust in multi-stage filters, dried from water vapor, and then compressed by powerful compressors until it turns into a liquid state. The liquid is distilled in a distillation column to separate it into its individual substances.

Installation for argon production

Nitrogen is the first to evaporate at -195 °C; its vapors are collected on the appropriate rectifier plate and discharged into a separate tank. The next highest (and at a boiling point of -185 °C) is the argon fraction, containing 12% Ar, less than half a percent nitrogen and oxygen. It is fed into the next distillation column, in which the percentage of Ar is brought to 85, the remainder being oxygen with traces of nitrogen. This substance is called raw argon, the starting material for producing purified gas.

Several methods are used in industry to purify raw argon from impurities.

Hydrogen added to the raw material is oxidized by a catalyst and heated to 500 °C, thus removing oxygen from the mixture. The water vapor formed on the catalyst is removed using a moisture separator. The gas is then dried. Argon with the nitrogen remaining in it is rectified again.

Alternative methods for obtaining Ar are also used. During the synthesis of ammonia from nitrogen and hydrogen in chemical reactors, Ar is obtained as a by-product. The technological component of this synthesis - purge gas - contains up to 20% Ar. The calmest element is extracted from this gas. The production cost, which consists mainly of the costs of cooling and heating the components, is divided between ammonia and argon, and is significantly lower.

The quality of the gas obtained by any method is determined by the technology for purifying it from small amounts of residual N2, O2, water vapor and H2.

A device that receives argon ion beams

Where is argon used?

Argon has become widespread in industry. The inert properties of this gas are especially in demand in various production processes where it is necessary to displace one of the most active elements - oxygen. The use of argon is very cheap compared to other inert volatile substances, so the gas is indispensable when a protective environment is required when welding metals, as well as displacing moisture and oxygen in containers where food products are stored.

Filling the bulbs of incandescent lamps with inert gas can significantly increase the operating life of the lighting device. In addition to increased service life, such elements have greater brightness. Inert gas is also used in the production of fluorescent lamps. The use of argon makes it easier to start an electric arc discharge, as well as significantly increase the service life of the electrodes.

When making double-glazed windows, the cavities between the glasses are filled with inert gas, which can significantly improve the thermal insulation properties. Considering the fact that argon is absolutely transparent, its use is not limited in any way even in the manufacture of multilayer structures.

The inert gas argon is also used in plasma cutting systems for metals. The advantage of using this gas is that it does not require too high a voltage to initiate an arc, so such installations can be of very simple design. Plasma generation using argon produces minimal harmful gases during cutting, making this method ideal for hand-held devices.

Due to the ability to form plasma at a relatively low voltage, this noble gas is used in medicine for argon coagulation. This method is successfully used to remove tumors, as well as to stop bleeding.

Argon is also used in the chemical industry. Due to the lack of interaction with other elements, this gas is used to obtain ultrapure substances, as well as for their analysis. In the metallurgical industry, noble gas allows the processing of metals such as titanium, tantalum, niobium, beryllium, zirconium, etc. In addition, the gas is used to mix molten substances and reduce the oxidation of chromium in the production of chrome steel.

General characteristics of Ar

Ar belongs to the group of inert gases. The charge of its nucleus is 18; the element is located under the same number in the periodic table.

Of all the members of group VIIIA, it is the most commonly found in nature. The volume fraction of Ar in the atmosphere is 0.93%, the mass fraction is 1.28%. The element is a colorless, tasteless and odorless gas. Chemically inactive - argon does not react and practically does not combine with any elements or substances, with the exception of CU(Ar)O and argon hydrofluoride.

Very poorly soluble in water, slightly greater solubility is observed when interacting with organic solvents.

Interesting Facts

There are a lot of interesting facts related to argon. It’s worth starting with the fact that argon has been banned for use by the international anti-doping company since 2014. The lack of oxygen from inhalation likely activates the body's own erythropoietin (EPO). It is also worth noting that argon at a pressure of about 24 bar can have an analgesic effect. An interesting point is that argon reserves in the atmosphere are replenished on Earth due to solar rays, and in the earth's crust due to underground nuclear explosions.

Types of argon

When talking about types or varieties of Ar, we must understand that these are the same chemical substance. Types differ in the degree of purification from impurities.

• Top grade. Ar content is not less than 99.99%. This grade of especially high purity is used for critical welding work, such as welding materials that are chemically active in a heated state: some non-ferrous alloys, primarily titanium, stainless steel, etc. It is also used for welding highly loaded structural steel products.
• First grade. Ar content not less than 99.98%, used for welding aluminum-based alloys with other metals and alloys, for less active non-ferrous metals.
• Second grade. Ar content not less than 99.95%. Used for welding parts made of heat-resistant steel alloys, aluminum and structural steels. The use of pure Ar in these cases is undesirable, since it leads to increased porosity of the weld material and does not protect the weld pool from high humidity and other contaminants. To avoid the occurrence of such a defect, carbon dioxide and oxygen are added to the mixture of protective gases, which bind the hydrogen and other impurities released during welding. The slags formed during these reactions float to the surface of the weld pool and, after solidification, are removed along with the scale.

Methods for producing argon

A significant amount of gas is contained in the air. Therefore, it is isolated from the air mass using low-temperature distillation units. This process occurs in several stages:

1. The air is cleaned of dust particles and compressed to produce liquid.
2. In liquid form, air is rectified from nitrogen, oxygen, and argon.
3. Having separated the nitrogen, the mixture of oxygen and argon is purified using electrolytic hydrogen.

In a rectification plant, inert gas boils at −185.3˚C, oxygen three degrees higher, nitrogen thirteen degrees lower.

Argon is also produced in manufacturing processes as a by-product. It is extracted by producing ammonia. In this case, Ar is mixed with nitrogen and is of no value; it costs much less than cryogenic argon.

Physical and chemical properties

The properties of argon are typical of a member of group VIII.

At ordinary temperatures, Ar is in a gaseous state. The molecule includes a single atom, the chemical formula is very simple: Ar. The boiling point is very low: -185.8 °C at atmospheric pressure.

Solubility in water is low - only 3.29 ml per 100 ml of liquid

The density of argon under normal conditions is 1.78 kg/m3. The molar heat capacity of the gas is 20.7 J/Kmol.

Characteristics of argon and other inert gases

The gas is almost completely inert. To date, scientists have managed to obtain only two of its compounds - CU(Ar)O and argon hydrofluoride. The compounds exist only at ultra-low temperatures. It is assumed that Ar may be part of excimer-type molecules that are unstable in the normal state. Such molecules can only exist in an excited state, for example, during a high-intensity electrical discharge. Such compounds are possible with mercury, oxygen and fluorine.

Electronegativity on the Pauling scale is 4.3.

Both the oxidation state and the electrode potential have a zero value, which is typical for an inert gas.

The ionic radius is 154, the covalence radius is 106 PM. Ionization threshold - 1519 kJ/mol

Atomic and molecular mass

Such important parameters as atomic and molecular masses show how much the mass of a molecule of a substance and the mass of its atom, respectively, exceed a value equal to one twelfth of the mass of a hydrogen atom.

Due to the fact that the Ar molecule consists of a single atom, the molecular and atomic mass of argon are identical and amount to 39.984.

Argon structure and properties

Isotopes

Under natural conditions, Ar occurs as three stable isotopes

• 36Ar – the percentage of this isotope is 0.337% in the nucleus of 18 protons and 18 neutrons;
• 38Ar - its share is only 0.063%, there are 18 protons and 20 neutrons in the nucleus;
• 40Ar is the most common, its share is 99.6%, the nucleus also has 18 protons, but already 22 neutrons.

It was possible to artificially obtain isotopes with a mass index from 32 to 55, the most stable of which was 39Ar, whose half-life is 268 years.

The large percentage of 40Ar among the isotopes found in nature is caused by its constant formation during the decay reaction of the potassium-40 isotope. Per 1000 kg of potassium during such reactions no more than 3100 40Ar atoms are formed per year. But, since these reactions take place continuously over hundreds of millions of years, the isotope has accumulated in nature in significant volumes.

The dominance of the heavy isotope in nature determines the fact that the atomic weight of Ar exceeds the atomic weight of potassium, which is located next to it in the table. When the Periodic Table was created, there was no such contradiction, since argon was discovered and its properties were studied much later, in the first decade of the 20th century. Ar was initially placed in the first group of the table; the eighth group was allocated later.

Ions

Like other noble gases (such as He and Ne), Ar is susceptible to ionization. When atoms are excited and given high energies, molecular Ar2+ ions appear.

Molecule and atom

For inert gases, these concepts are identical, since these elements do not want to enter into a chemical bond even with their own kind. The molecule includes one atom, the chemical formula of the gas does not differ from the designation of the element: Ar.

Molar mass

The molar mass of argon is 39.95 g/mol.

There are several methods for calculating it:

• Using the relative atomic mass M and the proportionality coefficient k, expressing the relationship between the relative mass and the molar mass. This coefficient is a universal constant and is equal for all elements. Molar mass M is expressed as the product of the proportionality coefficient and the relative mass.
• Using molar volume. You will need to find the volume occupied by a certain mass of gas under normal conditions, then calculate the mass of 22.4 liters of the substance under the same conditions.
• Using the Mendeleev-Clapeyron equation simulating an ideal gas.

pV = mRT / M,

Having carried out the transformations, we obtain the expression for the molar mass:

M=mRT/pV

Where

• p – pressure in pascals,
• V – volume in cubic meters
• m – mass in grams,
• T - temperature in Kelvin,
• R is a constant whose value is 8.314 J/(mol×K).

Technical requirements

In terms of physical and chemical parameters, gaseous and liquid argon must comply with the standards in accordance with GOST 10157:

The guaranteed shelf life of argon gas is 18 months. from the date of manufacture.

Application area

Argon is most widely used for welding. It is used to create a protective atmosphere around the weld pool, displacing O2 and N2 contained in the atmosphere from the working area. This is especially important for welding non-ferrous metals, many of which, for example, Ti, are characterized by high chemical activity when heated. Inert gas is also indispensable for permanent connections of stainless and high-alloy alloys.

It is also widely used in the installation of highly loaded building structures, such as frames of high-rise buildings, bridge trusses and many others. Here its use ensures high quality, uniformity and durability of critical connections. In the construction industry, argon welding dominates among other methods.

Argon welding

Argon arc welding

Argon welding is no less widely used in mechanical engineering, primarily in the chemical and food industries. The seams are durable and reliable, even when exposed to aggressive environments.

The oil and gas industries also use argon welding in the installation of pipelines, gas pumping stations and oil refineries.

The method is also used in the nuclear industry, transport engineering and the aerospace industry.

In households, argon welding is not so widespread. This is explained:

• high cost of equipment and consumables;
• the need for sufficient qualification of the welder;
• lower loads experienced by home structures;
• lower requirements for the strength and durability of welded joints.

If a household has an occasional need for such welding work, then it is cheaper, faster and more reliable to invite a specialist welder.

Double-glazed window with argon

The principle of operation of a double-glazed window with argon

A characteristic property of Ar is its higher density compared to air. Therefore, the maximum efficiency of argon welding is achieved in the lower welding position. In this case, the inert substance spreads over the surface of the part and forms a protective cloud of considerable extent, allowing welding to be carried out both with high currents and at high speed. When welding in an inclined and upper position, it is necessary to take into account the “falling through” of argon through the air. To compensate for this phenomenon, either increase the gas supply or carry out work in a sealed room filled with inert gas. In both cases, the cost of work increases.

Since the ionization potential of Ar is low, its use ensures ideal geometric characteristics of the weld, especially the profile. An excited electric arc in an argon atmosphere is also characterized by high stability of its parameters. On the other hand, a low ionization potential also causes a lower arc ignition and maintenance voltage. This reduces its heat generation and complicates the penetration of thick sheets of metal.

The higher arc temperature in an argon atmosphere significantly increases weld penetration. This allows welding to be carried out in one pass, provided that the parameters of the gap between the workpieces are strictly observed.

When using the TIG welding method, the argon atmosphere protects not only the welding zone, but also the end of the infusible electrode from corrosive influences.

In a number of specific cases, helium is added to the protective gas mixture.

In addition to being used for welding, argon is used:

• As a plasma-forming substance in installations for plasma cutting of metal.
• To create an inert environment in food packaging. It displaces air oxygen and water vapor from bags and containers, which adversely affect the shelf life of products. Products in a protective atmosphere are stored several times longer than in conventional packaging. This method is also used for packaging medical products and drugs, allowing them to be kept in proper sterility and chemical purity.
• As an active agent in fire extinguishing installations. Argon displaces oxygen (or other gas) from the combustion site, stopping it.
• To create a protective environment in technological installations when processing semiconductor devices, creating microcircuits and other electronic components or materials of high purity levels.
• Filler for electric lamps.
• In advertising fluorescent tubes.

Safety requirements

Argon is non-toxic and non-explosive, but it is dangerous to life: if it is inhaled, a person instantly loses consciousness from suffocation, and death can occur within a few minutes. To ensure the safety of workers, equipment and facilities must be sealed, and production premises must be provided with ventilation. Argon gas is heavier than air and can accumulate in poorly ventilated areas near the floor and in pits, as well as in the internal volumes of equipment intended for the production, storage and transportation of gaseous and liquid argon. At the same time, the oxygen content in the air decreases, which leads to oxygen deficiency, and with a significant decrease in oxygen content - to suffocation, loss of consciousness and death of a person. In places where argon gas may accumulate, it is necessary to control the oxygen content in the air (the volume fraction of oxygen in the air must be at least 19%). Liquid argon is a low-boiling liquid that can cause frostbite to the skin and damage to the mucous membrane of the eyes. When sampling and analyzing liquid argon, it is necessary to wear safety glasses.

Dependence of argon pressure in a cylinder on temperature

As it heats up, the pressure of the gaseous substance in a closed volume increases. The table shows approximate pressure values ​​in the cylinder depending on the ambient temperature.

It should be borne in mind that the balloon pressure does not change instantly, but as it warms up or cools down.

First aid

If workers exhibit symptoms of prolonged exposure to small concentrations of nitrogen, it is necessary to take the victim out into the open air, provide rest and plenty of warm, sweet drinks. If there are signs of exposure to argon in high concentrations (loss of consciousness, wheezing), perform the following actions:

1. The victim is taken out into the fresh air.
2. Remove tight clothing, unbutton collar and trouser belt.
3. Perform artificial respiration.
4. Calling an ambulance.

If it is impossible to quickly remove a person poisoned by argon into the air, you should ventilate the room as much as possible - open and secure all windows and entrances. It is important to prevent further filling of the room with argon - tighten the taps on the cylinders and call the gas service.

When performing artificial respiration, it is desirable to provide additional access of oxygen to the victim’s respiratory system, for which medical oxygen pillows are used, and in their absence, oxygen can be pumped through a gas outlet hose from industrial cylinders for welding. It should be remembered that before pumping oxygen from a cylinder, you need to make sure that there are no oily rags or flammable substances within a radius of 15 meters from the victim.

If a person has been exposed to welding argon for more than 2 hours, he needs to receive artificial ventilation in the hospital to prevent complications. The person providing assistance must record the start time of first aid and inform it to the emergency doctors.

It is important to note that when evacuating victims from a closed room filled with argon, rescuers need to use hose gas masks or an isolated oxygen supply system.