In 1785, an English philosopher and scientist Henry Cavendish found a non-reactive gas during the fractional distillation of air. Unfortunately, there were no spectroscopic techniques available at that time, so there was no other way to study that gas further. A century later in 1894, a British Physicist Lord Rayleigh and a Scottish Chemist William Ramsay, was trying to figure out why the density of nitrogen extracted from the fractional distillation of liquid air was different from that extracted by decomposing ammonia. When Ramsay separated all of the nitrogen in the form of solid magnesium nitride, he was left with a gas that would not react with any other compound, even under extreme conditions. With the help of spectroscopy, they found a new group of blue, red, and green lines in the spectrum of the gas. They isolated this first noble gas and named it as Argon.
At left above is the spectral tube, excited by a 5000-volt transformer. At right is the spectrum seen through a 600 lines/mm diffraction grating
Argon is a noble gas element present in the eighteenth group of the periodic table with atomic no. 18. It is the third most abundant gas in the earth’s atmosphere, at nearly 9340 parts per million by volume. On the cosmic scale, Argon holds the 12th position in ranking for abundance. Like many other chemical elements, the name argon is also derived from a Greek word(ἀργός), which means “lazy” or “inactive”, as a reference to its non-reactive nature. Due to its adequate amounts in the earth’s atmosphere, argon has a wide range of applications in various industries.
Occurrence
The natural source of Argon in the earth’s atmosphere is Potassium _{ }^{ 40 }{ K }. Potassium’s radioactive decay, with a half-life of 1.25×{ 10 }^{ 9 } years, produces stable _{ }^{ 40 }{ Ar } by the process of electron capture or positron emission.
The industrial approach for argon production is the cryogenic fractional distillation of air, which is also used for the production of purified nitrogen, oxygen, neon, krypton, and xenon.
An Industrial Cryogenic Gas Plant
Around 50trillion tonne of argon is hovering around in our atmosphere. With the production of about “700,000 tonnes” of argon per year, the world has an unconfined supply of argon.
Isotopes
Out of 26 known isotopes, with the mass number ranging from _{ }^{ 29 }{ Ar } to _{ }^{ 54 }{ Ar }, only three are known to be stable. _{ }^{ 40 }{ Ar }, _{ }^{ 36}{ Ar }, and _{ }^{ 38 }{ Ar } are the three stable isotopes of argon that can be found in the earth’s atmosphere, their abundance in the atmosphere is 99.6%, 0.34%, and 0.06% respectively. Potassium _{ }^{ 40 }{ K } is the main source of _{ }^{ 40 }{ Ar } in the earth’s atmosphere, whereas the primary sources of _{ }^{ 36 }{ Ar } and _{ }^{ 38 }{ Ar } are stellar nucleosynthesis and primordial star-formation.
The presence of Argon in other terrestrial planets such as, Mercury, Mars, and even Titan (Saturn’s moon), contains a significant amount of argon in their atmosphere. All these planets show a predominance in _{ }^{ 40 }{ Ar } over _{ }^{ 36 }{ Ar } and _{ }^{ 38 }{ Ar }.
Properties of Argon
Physical Properties
Argon is a colourless, odourless, tasteless, non-flammable, and non-toxic inert element. These properties of argon remain the same in all of its phases. However, it emits purple light in a discharge tube. Its solubility in water is similar to that of oxygen but, it is 2.5 times more soluble in water than nitrogen. The density of argon is 1.784 gm per cubic litre, which is quite similar to the density of air (1.20 gram per litre cube). The boiling point of argon is -185.7 °C and the melting point is -189°C. It generally exists in a gaseous phase at room temperature. The thermal conductivity of argon at room temperature is 17.72 mW/mK (milliWatts per meter per degree) whereas for air it is 26mW/mK.
Chemical Properties
Argon is a noble gas with the electronic configuration [Ne] 3{ s }^{ 2 }3{ p }^{ 6 }. Due to its fully-filled valance shell, argon is inert under most conditions and do not form any stable compounds at room temperature. Although argon is a noble gas, and scientists were unable to combine it with any other element for more than a century, in the year 2000, Markku Räsänen, a chemist at the University of Helsinki in Finland, along with his research scholars, managed to form a compound named argon fluorohydride (HArF).
They made it by condensing a mixture of argon and hydrogen fluoride onto caesium iodide at -265°C and exposing it to UV light. On warming just above -246°C, it reverted right back to argon and hydrogen fluoride. Argon is also known to form clathrates with water when atoms of argon are trapped inside a lattice of the water molecule.
Uses of Argon
For a chemically lazy gas, argon has proved to be eminently employable. Argon has many practical properties such as inert nature, abundance, low thermal conductivity, and ionization that makes it very advantageous for various applications. The most important of these properties is its inexpensive availability, which makes it stand out from the other noble gases in a profitable point of view. Let’s discuss some of its uses in various fields.
1. Industrial Applications
Due to its abundance, inexpensive, and truly inert nature, argon has a wide range of applications in various industrial sectors. It is used whenever a complete non-reactive atmosphere is required.
a. Welding
Argon is used as a shielding gas to prevent the hot welding to react with oxygen present in the air. Pure argon, or argon mixed with other gases, is commonly used in TIG (Tungsten inert gas) welding which is used to weld feed electrodes together, whereas in MIG(Metal inert Gas) welding, a mixture of carbon and argon is used to weld ordinary steel components.
Plasma-arc cutting and plasma-arc welding employ plasma gas (argon and hydrogen) to provide a very high temperature when used with a special torch.
b. Metal Manufacturing
Most argon goes into making steel, where it is blown through the molten iron along with oxygen. Argon helps in reducing chromium loss, whereas oxygen reduces the carbon content by forming CO2. Argon also helps in preventing the formation of nitrides while making superior quality steel.
It is also used in aluminium manufacture to provide degasification and to remove dissolved hydrogen from molten aluminium. To avoid oxidation and reaction with nitrogen, argon is used as an inert atmosphere in the manufacturing of titanium.
c. Electronics Industry
To reduce the sublimation rate of the tungsten filament in the incandescent and fluorescent bulbs, argon is used as a filler gas. It provides higher temperature stability to the filament.
Mixed with methane, argon is used as a filler gas and as a high purity inert shield gas in the manufacture of silicon and germanium crystals used in the semiconductor industry.
2. Research and Medicine
Argon based scintillation devices are used to detect interactions between argon and Weakly Interacting Massive Particles(WIMPs), which are the prime proposed candidates in the current research for Dark Matter. Argon is also used as the carrier gas in gas chromatography and electrospray ionization mass spectrometry.
Simulation For Wimp Detection
Argon is used to perform precise cryosurgery, which is the use of extreme cold, to selectively destroy small areas of diseased or abnormal tissue, in particular on the skin. Very cold argon is created at the site by the controlled expansion of argon gas, and directed to the treatment point using a cryoneedle. This provides better control of the process than earlier techniques employing liquid nitrogen. A similar technique, cryoablation, is used to treat heart arrhythmia by destroying cells that interfere with the normal distribution of electrical impulses.
Health care industries also use argon-dye lasers to treat several skin conditions and eye defects. It has also been used to eliminate nitrogen from blood vessels in hospitals, along with oxygen.
3. Preservatives
Argon is a safe gas that has been used to preserve almost everything from wine to the U.S. Declaration Of Independence. It is also a better preservative for food items, as it can flush out any residue oxygen that can oxidize the food. Argon is also used as a preservative for chemicals such as, varnish, polyurethane, and paint, by displacing air to prepare a container for storage.
The Declaration Of Independence preservation case filling up with Argon
4. Miscellaneous application
One of the most exotic uses of argon is in the tires of luxury cars. Not only it protects the tire rubber from oxygen, but also helps to reduce the tier noise when the car is moving at a high speed.
Racing Car Tyers Being Filled Up With Argon
As argon has a low thermal conductivity than air, it is used as a filler gas inside the glass panes of the window. It is also used in scuba diving suits because it provides thermal shielding when the temperature can fall drastically under the deep sea.
A radiometric dating method used by archaeologists and geochronologists is based on potassium-argon dating.
Health Aspects
Argon is essentially inert and therefore has no toxic properties, but it can act as an asphyxiant by displacing the oxygen in a closed and contained environment below a required point to support life. Being an odourless, colourless, tasteless, and non-irritating gas, it does not have any warning indicators, and humans do not possess any senses that can detect an argon leak in the air. Inhalation of argon in excessive amounts can cause dizziness, nausea, vomiting, loss of consciousness, and death. Death may result from errors in judgment, confusion, or loss of consciousness that prevents self-rescue.
