Argon

Description

Argon belongs to the family of inert, rare gases of the atmosphere. It is plentiful compared to the other rare atmospheric gases; I million ft3 (28 300 m3) of dry air contains 9340 ft3 (264 m3 ) of argon. Argon is colorless, odorless, tasteless, and nontoxic. It is extremely inert and forms no known chemical compounds. It is slightly soluble in water.

Chemical properties

colourless odourless gas

Chemical properties

With the symbol A, argon is a nonflammable gas; one of the elements in the inert gas category. It is colorless.

Physical properties

Argon is a colorless, odorless, tasteless, chemically inert noble gas that makes up about0.93% of the Earth’s atmosphere. It is the third most abundant gas in the atmosphere, meaningit is more common than carbon dioxide, helium, methane, and hydrogen.
Its melting point is –189.35°C, its boiling point is –185.85°C, and its density is0.0017837g/cm³.

Isotopes

There are a total of 24 isotopes of argon, three of which are stable. They areAr-36, which constitutes just 0.3365% of the natural amount of argon; Ar-38, which contributesjust 0.0632% to the amount of argon on Earth; and Ar-40, which, by far, constitutesthe most argon on Earth, 99.6003% of its natural abundance.

Origin of Name

The name “argon” is derived from the Greek word argos, meaning “inactive.”

Occurrence

Argon is the 56th most abundant element on Earth. It is the most abundant of all the noblegases found in the atmosphere. In fact, the only source of argon is the atmosphere, where it isfound at just under 1% of air by volume.
There are several methods of producing argon. The most common is by fractional distillationof liquid air. Argon is collected as a by-product of this large-scale commercial process.During fractional distillation, argon boils off at its own unique temperature. It is then collectedand purified by passing it through charcoal to filter out helium and other gases, producingsignificant amounts of argon.

History

The presence of Argon in air was suspected by Cavendish in 1785, discovered by Lord Rayleigh and Sir William Ramsay in 1894. The gas is prepared by fractionation of liquid air, the atmosphere containing 0.94% argon. The atmosphere of Mars contains 1.6% of ⁴⁰Ar and 5 p.p.m. of ³⁶Ar. Argon is two and one half times as soluble in water as nitrogen, having about the same solubility as oxygen. It is recognized by the characteristic lines in the red end of the spectrum. It is used in electric light bulbs and in fluorescent tubes at a pressure of about 400 Pa, and in filling photo tubes, glow tubes, etc. Argon is also used as an inert gas shield for arc welding and cutting, as a blanket for the production of titanium and other reactive elements, and as a protective atmosphere for growing silicon and germanium crystals. Argon is colorless and odorless, both as a gas and liquid. It is available in high-purity form. Commercial argon is available at a cost of about 3￠ per cubic foot. Argon is considered to be a very inert gas and is not known to form true chemical compounds, as do krypton, xenon, and radon. However, it does form a hydrate having a dissociation pressure of 105 atm at 0°C. Ion molecules such as (ArKr)+, (ArXe)+, (NeAr)+ have been observed spectroscopically. Argon also forms a clathrate with β-hydroquinone. This clathrate is stable and can be stored for a considerable time, but a true chemical bond does not exist. Van der Waals’ forces act to hold the argon. In August 2000, researchers at the University of Helsinki, Finland reported they made a new argon compound HArF 4-4 The Elements by shining UV light on frozen argon that contained a small amount of HF. Naturally occurring argon is a mixture of three isotopes. Seventeen other radioactive isotopes are now known to exist. Commercial argon is priced at about $70/300 cu. ft. or 8.5 cu. meters.

Characteristics

Although argon is considered chemically inert, at low temperatures it is possible to combineargon with other atoms to form very fragile compounds, which exist only at those verylow temperatures. For instance, it can combine with fluorine and hydrogen to form argonfluorohydride (HArF). It is only slightly soluble in water.

The Uses of Argon

Gas as shield in gas metal-arc welding, in metal processing; carrier in gas-liquid and gas-solid chromatography; gas filler for incandescent light bulbs. Gas in fluorescent tubes analogous to neon lights, but produces a blue-purplish light; in rectifier tubes; in thermometers above mercury; in lasers; wherever an inert atmosphere is desired and the much cheaper nitrogen cannot be used; in ionization chambers and particle counters; in mixtures with He and Ne in Geiger counters; in argon-oxygen-decarburizing process for stainless steel; in manufacture of semiconducting devices; in gas mixtures as the working fluid in plasma arc devices. Liquid as cryogen to produce low temperetures. The isotope 40Ar is always found in minerals contg potassium, since it is a product of 40K decay; measuring the amount of 40Ar and 40K can be used for determining the geologic age of minerals and meteors.

The Uses of Argon

Argon is used when an inert atmosphere is required. Individually, or as mixture with otherinert gases, it is used to fill electric light bulbs, fluorescent tubes, lasers, and so forth. Byreplacing oxygen in incandescent light bulbs, it prevents oxygen from corroding the bulb’sfilament. It is also used as a nonoxidizing gas for welding and to decarbonize steel and as aninert atmosphere in which to grow semiconductor crystals.

The Uses of Argon

Argon is extensively used in filling incandescent and fluorescent lamps, and electronic tubes; as an inert gas shield for arc welding and cutting; as a blanket in the production of titanium, zirconium, and other reactive metals; to flush molten metals to eliminate porosity in castings; and to provide a protective shield for growing silicon and germanium crystals.

Definition

A nonmetallic element of atomic number 18, in the noble gas group of the Periodic System. Aw 39.948. Present in atmosphere to 0.94% by volume.

Definition

An inert colorless odorless monatomic element of the rare-gas group. It forms 0.93% by volume of air. Argon is used to provide an inert atmosphere in electric and fluorescent lights, in welding, and in extracting titanium and silicon. The element forms no known compounds.
Symbol: Ar; m.p. –189.37°C; b.p. –185.86°C; d. 1.784 kg m^-3 (0°C); p.n. 18; r.a.m. 39.95.

Definition

argon: Symbol Ar. A monatomicnoble gas present in air (0.93%); a.n.18; r.a.m. 39.948; d. 0.00178 g cm^–3;m.p. –189°C; b.p. –185°C. Argon isseparated from liquid air by fractionaldistillation. It is slightly solublein water, colourless, and has nosmell. Its uses include inert atmospheresin welding and special-metalmanufacture (Ti and Zr), and (whenmixed with 20% nitrogen) in gas-filledelectric-light bulbs. The element isinert and has no true compounds.Lord Rayleigh and Sir WilliamRamsey identified argon in 1894.

General Description

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 Argon 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.

Reactivity Profile

These substances undergo no chemical reactions under any known circumstances. They are nonflammable, noncombustible and nontoxic. They can asphyxiate.

Hazard

Argon is nontoxic, but as an asphyxiant gas, it can smother by replacing oxygen in thelungs.

Health Hazard

Vapors may cause dizziness or asphyxiation without warning. Vapors from liquefied gas are initially heavier than air and spread along ground.

Fire Hazard

Non-flammable gases. Containers may explode when heated. Ruptured cylinders may rocket.

Industrial uses

A chemical element (symbol Ar), argon is thethird member of the gaseous elements calledthe noble, inert, or rare gases, although argonis not actually rare. The earth’s atmosphere isthe only commercial argon source; however,traces of the gas are found in minerals andmeteorites.Argon is colorless, odorless, and tasteless.The element is a gas under ordinary conditions,but it can be liquefied, solidified readily, and isa major industrial gas.Argon does not form any chemical compoundsin the ordinary sense of the word,although it does form some weakly bondedclathrate compounds with water, hydroquinone,and phenol. There is one atom in each moleculeof gaseous argon.
The oldest large-scale use for argon is infilling electric lightbulbs. Welding and cuttingmetal consumes the largest amount of argon.Metallurgical processing constitutes an importantapplication.Argon and Ar–Kr mixtures are used, alongwith a little mercury vapor, to fill fluorescentlamps. The inert gases make the lamps easierto start, help to regulate the voltage, and supplementthe radiation produced by the excitedmercury vapor.Argon mixed with a little neon is used tofill luminous electric-discharge tubes employedin advertising signs (similar to neon signs)when a blue or green color is desired instead ofthe red color of neon.Argon is used to fill the space between thepanes of higher-quality double-pane windows,reducing heat transfer by gaseous conductionby about 30% compared to air filling.Argon is also used in gas-filled thyratrons.Geiger–Müller radiation counters, ionizationchambers that measure cosmic radiation, andelectron tubes of various kinds. Argon atmospheresare used in dry boxes during manipulationof very reactive chemicals in the laboratoryand in sealed-package shipments of suchmaterials. In high-energy physics research, atank of liquid argon can form a calorimeter todetect certain subatomic particles.

Materials Uses

Gaseous argon is noncorrosive and inert, and consequently may be contained in systems constructed of any common metals and designed to safely withstand the pressures involved. At the temperature of liquid argon, ordinary carbon steels and most alloy steels lose their ductility and are considered unsafe for liquid argon service. Satisfactory materials for use with liquid argon include austenitic stainless steel (for example, types 304 and 316), copper, Monel, brass, aluminum, and other nickel-chromium alloys.

Safety Profile

A simple asphyxlant gas. As an inert gas, it has no specific inherent dangerous properties. Gases of this type have no specific toxicity effect, but they act by excluding O2 from the lungs. The effect of simple asphyxiant gases is proportional to the extent to whch they dirmnish the amount (partial pressure) of O2 in the air that is breathed. The oxygen may be diminished to 75% of its normal percentage in air before appreciable symptoms develop, and t h s in turn requires the presence of a simple asphyxiant in a concentration of 33% in the mixture of air and gas. When the simple asphyxiant reaches a concentration of 50%, marked symptoms can be produced. A concentration of 75% is fatal in a matter of minutes. The first symptoms produced by simple asphyxiant gases such as argon are rapid respirations and air hunger. Mental alertness is diminished and muscular coordination is impaired. Later, judgment becomes faulty and all sensations are depressed. Emotional instability often results and fatigue occurs rapidly. As the asphyxia progresses, there may be nausea and vomiting, prostration, and loss of consciousness, and finally, convulsions, deep coma, and death.

Potential Exposure

Argon is used in metal fabrication and steel making; as an inert gas shield in arc welding; as an inert atmosphere in electric lamps; as a blanketing agent in metals refining (especially titanium and zirconium).

Physiological effects

Argon is nontoxic and largely inert. It can act as a simple asphyxiant by diluting the concentration of oxygen in air below levels necessary to support life. Inhalation of it 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 prevents self-rescue. At low-oxygen concentrations, unconsciousness and death may occur in seconds without warning.
Gaseous argon must be handled with all the precautions necessary for safety as with any nonflammable, nontoxic compressed gas. All precautions necessary for the safe handling of any gas liquefied at very low temperatures must be observed with liquid argon. Extensive tissue damage or burns can result from exposure to liquid argon or cold argon vapors.

First aid

: If contact with liquid argon occurs, seek medicalattention immediately; do NOT rub the affected areas orflush them with water. In order to prevent further tissuedamage, do NOT attempt to remove frozen clothing fromfrostbitten areas. If frostbite has NOT occurred, immediatelyand thoroughly wash contaminated skin with warm water.Seek medical attention immediately. If this chemical hasbeen inhaled, remove from exposure, begin rescue breathing(using universal precautions, including resuscitation mask)if breathing has stopped and CPR if heart action has stopped.Transfer promptly to a medical facility.

storage

Gaseous argon is commonly stored in high pressure cylinders, tubes, or tube trailers. Liquid argon is commonly stored at the consumer site in cryogenic liquid containers and specially designed vacuum-insulated cryogenic storage tanks.
All of the precautions necessary for the handling of any nonflammable gas or cryogenic liquid must be taken.
Liquid and gaseous systems should be designed and installed only under the direction of personnel thoroughly familiar with liquid and gaseous argon equipment and in compliance with state, provincial, and local requirements.

Shipping

UN1006 Argon, compressed, Hazard Class: 2.2; Labels: 2.2-Nonflammable compressed gas. Cylinders must be transported in a secure upright position, in a wellventilated truck. Protect cylinder and labels from physical damage. The owner of the compressed gas cylinder is the only entity allowed by federal law (49CFR) to transport and refill them. It is a violation of transportation regulations to refill compressed gas cylinders without the express written permission of the owner.

Purification Methods

Argon is rendered oxygen-free by passage over reduced copper at 450o, or by bubbling through alkaline pyrogallol and H2SO4, then dried with CaSO4, Mg(ClO4)2, or Linde 5A molecular sieves. Other purification steps include passage through Ascarite (CARE: asbestos impregnated with sodium hydroxide), through finely divided uranium at about 800o and through a -78o cold trap. Alternatively the gas is passed over CuO pellets at 300o to remove hydrogen and hydrocarbons, over Ca chips at 600o to remove oxygen and, finally, over titanium chips at 700o to remove nitrogen. It has also been purified by freeze-pump-thaw cycles and by passage over sputtered sodium [Arnold & Smith J Chem Soc, Faraday Trans 2 77 861 1981]. Arsenic acid (arsenic pentoxide hydrate, arsenic V oxide hydrate, orthoarsenic acid) [12044-50-7] M 229.8 + xH2O, pK 1 2.26, pK 2 6.76, pK 3 11.29 (H3AsO4). The acid crystallises from concentrated solutions of boiling conc HNO3 as rhombic crystals. Dry it in a vacuum to give the hemihydrate (hygroscopic). Heating above 300o yields As2O5. [Thaler Z Anorg Allgem Chem 246 19 1941, Schenk in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I p 601 1963.]

Waste Disposal

Vent to atmosphere. Return refillable compressed gas cylinders to supplier.