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/cm
3.
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.
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.
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.
History
Argon was discovered by a Scottish chemist, Sir William Ramsay and an English chemist, Lord Rayleigh in 1894. However, an English scientist, Henry Cavendish identified the presence of argon 200 years before its discovery when he found a small amount of gas left behind while separating nitrogen and oxygen from air. Although he anticipated the presence of another element in the air, he was unable to confirm that. Ramsay repeated Cavendish's experiment in 1894 and analyzed the left over unknown gas using spectroscopy. Meanwhile, Rayleigh was also performing the same experiment, almost at the same time. Both the scientists together revealed the unidentified gas and named it Argon.
Uses
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.
Uses
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.
Uses
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.
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.
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
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.
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.
Synthesis
There is more than one way to prepare argon gas. The most common is through the fractional distillation of liquid air. Argon gas is a byproduct of this large-scale commercialization process. During fractional distillation, argon boils at a fixed temperature. It is then collected and purified through charcoal to filter out helium and other gases to produce large quantities of argon.
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.
