Argon (Ar) is a monatomic, colorless, odorless, tasteless and nontoxic gas, present in the atmosphere at a concentration of just under 1% (0.934%) by volume. Argon is a member of a special group of gases known as the “rare,” “noble,” or “inert” gases. Other gases in this group are helium, neon, krypton, xenon and radon. They are monatomic gases with a totally filled outermost shell of electrons. The terms "noble" and "inert" have been used to indicate that their ability to chemically interact with other materials is extremely weak. All members of this group emit light when electrically excited. Argon produces a pale blue-violet light.
Argon's normal boiling point is a very cold –302.6°F (–185.9°C). The gas is approximately 1.4 times as heavy as air and is slightly soluble in water. Argon's freezing point is only a few degrees lower than its normal boiling point, –308.8°F (–199.3°C).
Argon is valued for its total inertness, in particular at high temperatures. Argon is used in critical industrial processes such as the manufacturing of high quality stainless steels and production of impurity-free silicon crystals for semi-conductor manufacture. Argon is also used as an inert filler gas for light bulbs and as a dry, heavier-than-air-or-nitrogen filler for the space between glass panels in high-efficiency multi-pane windows.
Argon is the most abundant of the truly inert or "rare" gases. It is produced, most commonly, in conjunction with the manufacture of high purity oxygen using cryogenic distillation of air. Since the boiling point of argon is very close to that of oxygen (a difference of only 5.3°F or 2.9°C) separating pure argon from oxygen (while also achieving high recovery of both products) requires many stages of distillation.
For many decades, the most common argon recovery and purification process used several steps: 1) taking a "side-draw" stream from the primary air separation distillation system at a point in the low-pressure column where the concentration of argon is highest, 2) processing the feed in a crude argon column which returns the nitrogen to the low pressure column and produces a crude argon product, 3) warming the crude argon and reacting the (typically about 2%) oxygen impurity in the stream with a controlled amount of hydrogen to form water, 4) removing the water vapor by condensation and adsorption, 5) re-cooling the gas to cryogenic temperature, and 6) removing the remaining non-argon components (small amounts of nitrogen and unconsumed hydrogen) through further distillation in a pure argon distillation column.
With the development of packed column technology, which allows cryogenic distillations to be performed with low-pressure-drop, most new plants now utilize an all-cryogenic distillation process for argon recovery and purification.
Argon may be referred to as "PLAR" (pure liquid argon) or "CLAR" (crude liquid argon), or by its chemical designation, "Ar". Crude argon is usually thought of as an intermediate product in a facility that makes pure argon, but it may be a final product for some lower capacity air separation plants which ship it to larger facilities for final purification. Some crude argon is also sold as a final product for uses that do not need high purity oxygen (e.g. some steelmaking and welding applications).
Commercial quantities of argon may also be produced in conjunction with the manufacture of ammonia. Air is the ultimate source of the argon, but in the traditional ammonia production process the route to argon recovery is quite different. Natural gas is "reformed" with steam to produce a "synthesis gas" containing hydrogen, carbon monoxide and carbon dioxide. "Secondary reforming" with air and steam converts the CO to CO2 and additional hydrogen, and adds the nitrogen necessary to make ammonia (NH3). The mix of nitrogen and hydrogen (along with a small amount of argon) is then compressed to high pressure and reacted with the aid of a catalyst. Argon, being non-reactive, accumulates in the ammonia synthesis loop, and it must be removed in a purge stream to maintain production capacity and process efficiency. UIG offers equipment to process the purge gas stream. Ammonia is removed and recovered while the hydrogen is removed and recycled to the synthesis gas feed to the ammonia process to improve overall process efficiency. Methane, which is formed in the ammonia process, is recycled to fuel for the fired heater providing heat to drive the synthesis gas generation process. Argon is recovered and purified for sale as a commercial product.
Some newer ammonia plants do not use air as a direct feed to the ammonia production process, but process it through an air separation unit, with the argon removed upstream of the ammonia synthesis loop. The high purity oxygen and nitrogen feed streams produced by the air separation unit are individually fed to the hydrogen production and ammonia production portions of the ammonia plant. This newer ammonia production approach avoids argon build up in the ammonia synthesis loop, and allows direct recovery of argon as a valuable co-product.
English Units |
Normal Boiling Point (1 atm) | Gas Phase Properties @ 32°F & @1 atm | Liquid Phase Properties @ B P& @ 1 atm | Triple Point | Critical Point | |||||||||
| Temp. | Latent Heat of Vaporization | Specific Gravity | Specific Heat (Cp) | Density | Specific Gravity | Specific Heat (Cp) | Temp. | Pressure | Temp. | Pressure | Density | |||
| Substance | Chemical Symbol | Mol. Weight | ° F | BTU/lb | Air = 1 | BTU/lb °F | lb/cu. ft | Water = 1 | BTU/lb °F | °F | psia | °F | psia | lb/cu ft |
| Argon | Ar | 39.95 | -185.9 | 162.3 | 1.39 | 0.523 | 1.7837 | 1.40 | 1.078 | -189.3 | 68.9 | -122.3 | 4905 | 535.6 |
Metric Units |
Boiling Point @ 101.325 kPa | Gas Phase Properties @ 0° C & @ 101.325 kPa | Liquid Phase Properties @ B.P., & @ 101.325 kPa | Triple Point | Critical Point | |||||||||
| Temp. | Latent Heat of Vaporization | Specific Gravity | Specific Heat (Cp) | Density | Specific Gravity | Specific Heat (Cp) | Temp. | Pressure | Temp. | Pressure | Density | |||
| Substance | Chemical Symbol | Mol. Weight | °C | kJ/kg | Air = 1 | kJ/kg ° C | kg/m3 | Water = 1 | kJ/kg ° C | °C | kPa abs | ° C | kPa abs | kg/m3 |
| Argon | Ar | 39.95 | -185.9 | 162.3 | 1.39 | 0.523 | 1.7837 | 1.40 | 1.078 | -189.3 | 68.9 | -122.3 | 4905 | 535.6 |
Argon is the most abundant, and least expensive, truly inert gas. It is used where a completely non-reactive gas is needed.
Pure argon, and argon mixed with various other gases, is used as a shield gas in TIG welding ("tungsten inert gas" or gas tungsten arc welding) which uses a non-consumable tungsten electrode, and in MIG ("metal inert gas", also called gas metal arc welding, or wire feed welding) which employs a consumable wire feed electrode. The function of the shielding gas is to protect the electrode and the weld pool against the oxidizing effect of air. Pure argon is often used with aluminum. A mixture of argon and carbon dioxide is often used for MIG welding of ordinary structural steel.
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.
When steel is made in a converter, oxygen and argon are blown into the molten metal. The addition of argon reduces chromium losses and the desired carbon content is achieved at a lower temperature.
Argon is used as a blowing gas during manufacture of higher quality steels to avoid the formation of nitrides.
Argon is also used as a shield gas in casting and stirring of ladles.
Argon is used in aluminum manufacture to aid degasification and to remove dissolved hydrogen and particulates from molten aluminum.
Argon is used as an inert gas in the manufacture of titanium to avoid oxidation and reaction with nitrogen (titanium is the only metal that will burn in a 100% nitrogen atmosphere).
Argon is used in the manufacture of zirconium.
Argon is used as a filler gas in fluorescent and incandescent light bulbs. This excludes oxygen and other reactive gases and reduces the evaporation rate (sublimation rate) of the tungsten filament, thereby permitting higher filament temperature. Most common of the mixtures is 93% argon and 7% nitrogen at a pressure of 70 kPa (10.15 psig).
It is used as a filler gas between the glass panels of high-efficiency thermo pane windows, as it is not only dry and colorless, but a relatively heavy gas that minimizes heat transmission between panels by slower convective movement of the filler gas between the glass panels in the window.
Argon is used with methane as a filler gas, and as a high purity inert shield gas in the manufacture of silicone and germanium crystals used in the semiconductor industry.
Argon is used in winemaking to displace oxygen in barrels and thus prevent the formation of vinegar. Similarly, it is used in restaurant, bar and home wine dispensing units to allow storage of opened bottles without degradation of the contents.
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 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 which interfere with the normal distribution of electrical impulses.
Argon is used to provide a protective atmosphere for old documents to prevent their degradation in storage and while on display.