Inert gas

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An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. The noble gases often do not react with many substances [1] and were historically referred to as the inert gases. Inert gases are used generally to avoid unwanted chemical reactions degrading a sample. These undesirable chemical reactions are often oxidation and hydrolysis reactions with the oxygen and moisture in air. The term inert gas is context-dependent because several of the noble gases can be made to react under certain conditions.

Contents

Purified argon gas is the most commonly used inert gas due to its high natural abundance (78.3% N2, 1% Ar in air [2] ) and low relative cost.

Unlike noble gases, an inert gas is not necessarily elemental and is often a compound gas. Like the noble gases, the tendency for non-reactivity is due to the valence, the outermost electron shell, being complete in all the inert gases. [3] This is a tendency, not a rule, as all noble gases and other "inert" gases can react to form compounds under some conditions.

Need and necessity

The inert gases are obtained by fractional distillation of air, with the exception of helium which is separated from a few natural gas sources rich in this element, [4] through cryogenic distillation or membrane separation. [5] For specialized applications, purified inert gas shall be produced by specialized generators on-site. They are often used by chemical tankers and product carriers (smaller vessels). Benchtop specialized generators are also available for laboratories.

Applications on inert gas

Because of the non-reactive properties of inert gases, they are often useful to prevent undesirable chemical reactions from taking place. Food is packed in an inert gas to remove oxygen gas. This prevents bacteria from growing. [6] It also prevents chemical oxidation by oxygen in normal air. An example is the rancidification (caused by oxidation) of edible oils. In food packaging, inert gases are used as a passive preservative, in contrast to active preservatives like sodium benzoate (an antimicrobial) or BHT (an antioxidant).

Historical documents may also be stored under inert gas to avoid degradation. For example, the original documents of the U.S. Constitution are stored under humidified argon. Helium was previously used, but it was less suitable because it diffuses out of the case more quickly than argon. [7]

Inert gases are often used in the chemical industry. In a chemical manufacturing plant, reactions can be conducted under inert gas to minimize fire hazards or unwanted reactions. In such plants and in oil refineries, transfer lines and vessels can be purged with inert gas as a fire and explosion prevention measure. At the bench scale, chemists perform experiments on air-sensitive compounds using air-free techniques developed to handle them under inert gas. Helium, neon, argon, krypton, xenon, and radon are inert gases.

Inert gas systems on ships

Inert gas is produced on board crude oil carriers (above 8,000 tonnes from Jan 1, 2016) by burning kerosene in a dedicated inert gas generator. The inert gas system is used to prevent the atmosphere in cargo tanks or bunkers from coming into the explosive range. [8] Inert gases keep the oxygen content of the tank atmosphere below 5% (on crude carriers, less for product carriers and gas tankers), thus making any air/hydrocarbon gas mixture in the tank too rich (too high a fuel to oxygen ratio) to ignite. Inert gases are most important during discharging and during the ballast voyage when more hydrocarbon vapor is likely to be present in the tank atmosphere. Inert gas can also be used to purge the tank of the volatile atmosphere in preparation for gas freeing - replacing the atmosphere with breathable air - or vice versa.

The flue gas system uses the boiler exhaust as its source, so it is important that the fuel/air ratio in the boiler burners is properly regulated to ensure that high-quality inert gases are produced. Too much air would result in an oxygen content exceeding 5%, and too much fuel oil would result in the carryover of dangerous hydrocarbon gas. The flue gas is cleaned and cooled by the scrubber tower. Various safety devices prevent overpressure, the return of hydrocarbon gas to the engine room, or having a supply of IG with too high oxygen content.

Gas tankers and product carriers cannot rely on flue gas systems (because they require IG with O2 content of 1% or less) and so use inert gas generators instead. The inert gas generator consists of a combustion chamber and scrubber unit supplied by fans and a refrigeration unit which cools the gas. A drier in series with the system removes moisture from the gas before it is supplied to the deck. Cargo tanks on gas carriers are not inerted, but the whole space around them is.

Inert gas systems on aircraft

Inert gas is produced on board commercial and military aircraft in order to passivate fuel tanks. On hot days, fuel vapour in fuel tanks may otherwise form a flammable or explosive mixture which if oxidized, could have catastrophic consequences. Conventionally, Air Separation Modules (ASMs) have been used to generate inert gas. ASMs contain selectively permeable membranes. They are fed compressed air that is extracted from a compressor stage of a gas turbine engine. The pressure drives the separation of oxygen from the air due to the increased permeability of oxygen through the ASMs in comparison to nitrogen. For fuel tank passivation, it is not necessary to remove all oxygen, but rather enough to stay below the lean flammability limit and the lean explosion limit. An oxygen concentration of 10% to 12% is common over the course of a flight.

Welding

In gas tungsten arc welding (GTAW), inert gases are used to shield the tungsten from contamination. It also shields the fluid metal (created from the arc) from the reactive gases in air which can cause porosity in the solidified weld puddle. Inert gases are also used in gas metal arc welding (GMAW) for welding non-ferrous metals. [9] Some gases which are not usually considered inert but which behave like inert gases in all the circumstances likely to be encountered in some use can often be used as a substitute for an inert gas. This is useful when an appropriate pseudo-inert gas can be found which is inexpensive and common. For example, carbon dioxide is sometimes used in gas mixtures for GMAW because it is not reactive to the weld pool created by arc welding. But it is reactive to the arc. The more carbon dioxide that is added to the inert gas, such as argon, will increase your penetration. The amount of carbon dioxide is often determined by what kind of transfer you will be using in GMAW. The most common is spray arc transfer, and the most commonly used gas mixture for spray arc transfer is 90% argon and 10% carbon dioxide.

Diving

In underwater diving an inert gas is a component of the breathing mixture which is not metabolically active and serves to dilute the gas mixture. The inert gas may have effects on the diver, but these are thought to be mostly physical effects, such as tissue damage caused by bubbles in decompression sickness. The most common inert gas used in breathing gas for commercial diving is helium.

See also

Related Research Articles

<span class="mw-page-title-main">Argon</span> Chemical element, symbol Ar and atomic number 18

Argon is a chemical element; it has symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third most abundant gas in Earth's atmosphere, at 0.934%. It is more than twice as abundant as water vapor, 23 times as abundant as carbon dioxide, and more than 500 times as abundant as neon. Argon is the most abundant noble gas in Earth's crust, comprising 0.00015% of the crust.

<span class="mw-page-title-main">Noble gas</span> Group of low-reactive, gaseous chemical elements

The noble gases are the naturally occurring members of group 18 of the periodic table: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). Under standard conditions, these elements are odorless, colorless, monatomic gases with very low chemical reactivity and cryogenic boiling points.

<span class="mw-page-title-main">Period (periodic table)</span> Method of visualizing the relationship between elements

A period on the periodic table is a row of chemical elements. All elements in a row have the same number of electron shells. Each next element in a period has one more proton and is less metallic than its predecessor. Arranged this way, elements in the same group (column) have similar chemical and physical properties, reflecting the periodic law. For example, the halogens lie in the second-to-last group and share similar properties, such as high reactivity and the tendency to gain one electron to arrive at a noble-gas electronic configuration. As of 2022, a total of 118 elements have been discovered and confirmed.

A propellant is a mass that is expelled or expanded in such a way as to create a thrust or another motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicles, the engine that expels the propellant is called a reaction engine. Although technically a propellant is the reaction mass used to create thrust, the term "propellant" is often used to describe a substance which contains both the reaction mass and the fuel that holds the energy used to accelerate the reaction mass. For example, the term "propellant" is often used in chemical rocket design to describe a combined fuel/propellant, although the propellants should not be confused with the fuel that is used by an engine to produce the energy that expels the propellant. Even though the byproducts of substances used as fuel are also often used as a reaction mass to create the thrust, such as with a chemical rocket engine, propellant and fuel are two distinct concepts.

<span class="mw-page-title-main">Arc welding</span> Process used to fuse metal by using heat from an electrical arc

Arc welding is a welding process that is used to join metal to metal by using electricity to create enough heat to melt metal, and the melted metals, when cool, result in a binding of the metals. It is a type of welding that uses a welding power supply to create an electric arc between a metal stick ("electrode") and the base material to melt the metals at the point of contact. Arc welding power supplies can deliver either direct (DC) or alternating (AC) current to the work, while consumable or non-consumable electrodes are used.

<span class="mw-page-title-main">Breathing gas</span> Gas used for human respiration

A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed habitats. Oxygen is the essential component for any breathing gas. Breathing gases for hyperbaric use have been developed to improve on the performance of ordinary air by reducing the risk of decompression sickness, reducing the duration of decompression, reducing nitrogen narcosis or allowing safer deep diving.

An inerting system decreases the probability of combustion of flammable materials stored in a confined space. The most common such system is a fuel tank containing a combustible liquid, such as gasoline, diesel fuel, aviation fuel, jet fuel, or rocket propellant. After being fully filled, and during use, there is a space above the fuel, called the ullage, that contains evaporated fuel mixed with air, which contains the oxygen necessary for combustion. Under the right conditions this mixture can ignite. An inerting system replaces the air with a gas that cannot support combustion, such as nitrogen.

<span class="mw-page-title-main">Gas tungsten arc welding</span> Welding process

Gas tungsten arc welding is an arc welding process that uses a non-consumable tungsten electrode to produce the weld. The weld area and electrode are protected from oxidation or other atmospheric contamination by an inert shielding gas. A filler metal is normally used, though some welds, known as 'autogenous welds', or 'fusion welds' do not require it. A constant-current welding power supply produces electrical energy, which is conducted across the arc through a column of highly ionized gas and metal vapors known as a plasma.

<span class="mw-page-title-main">Plasma arc welding</span> Welding process

Plasma arc welding (PAW) is an arc welding process similar to gas tungsten arc welding (GTAW). The electric arc is formed between an electrode and the workpiece. The key difference from GTAW is that in PAW, the electrode is positioned within the body of the torch, so the plasma arc is separated from the shielding gas envelope. The plasma is then forced through a fine-bore copper nozzle which constricts the arc and the plasma exits the orifice at high velocities and a temperature approaching 28,000 °C (50,000 °F) or higher.

Shielding gases are inert or semi-inert gases that are commonly used in several welding processes, most notably gas metal arc welding and gas tungsten arc welding. Their purpose is to protect the weld area from oxygen, and water vapour. Depending on the materials being welded, these atmospheric gases can reduce the quality of the weld or make the welding more difficult. Other arc welding processes use alternative methods of protecting the weld from the atmosphere as well – shielded metal arc welding, for example, uses an electrode covered in a flux that produces carbon dioxide when consumed, a semi-inert gas that is an acceptable shielding gas for welding steel.

<span class="mw-page-title-main">Industrial gas</span> Gaseous materials produced for use in industry

Industrial gases are the gaseous materials that are manufactured for use in industry. The principal gases provided are nitrogen, oxygen, carbon dioxide, argon, hydrogen, helium and acetylene, although many other gases and mixtures are also available in gas cylinders. The industry producing these gases is also known as industrial gas, which is seen as also encompassing the supply of equipment and technology to produce and use the gases. Their production is a part of the wider chemical Industry.

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Inert gas generator (IGG) refers to machinery on board marine product tankers. Inert gas generators consist distinctively of a gas producer and a scrubbing system.

In chemistry, the term chemically inert is used to describe a substance that is not chemically reactive. From a thermodynamic perspective, a substance is inert, or nonlabile, if it is thermodynamically unstable yet decomposes at a slow, or negligible rate.

<span class="mw-page-title-main">Nitrogen generator</span>

Nitrogen generators and stations are stationary or mobile air-to-nitrogen production complexes.

<span class="mw-page-title-main">Cryogenic gas plant</span> Industrial facility that creates cryogenic liquid at relatively high purity

A cryogenic gas plant is an industrial facility that creates molecular oxygen, molecular nitrogen, argon, krypton, helium, and xenon at relatively high purity. As air is made up of nitrogen, the most common gas in the atmosphere, at 78%, with oxygen at 19%, and argon at 1%, with trace gasses making up the rest, cryogenic gas plants separate air inside a distillation column at cryogenic temperatures to produce high purity gasses such as argon, nitrogen, oxygen, and many more with 1 ppm or less impurities. The process is based on the general theory of the Hampson-Linde cycle of air separation, which was invented by Carl von Linde in 1895.

<span class="mw-page-title-main">Gas metal arc welding</span> Industrial welding process

Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal inert gas (MIG) and metal active gas (MAG) is a welding process in which an electric arc forms between a consumable MIG wire electrode and the workpiece metal(s), which heats the workpiece metal(s), causing them to fuse. Along with the wire electrode, a shielding gas feeds through the welding gun, which shields the process from atmospheric contamination.

Gas blending is the process of mixing gases for a specific purpose where the composition of the resulting mixture is specified and controlled. A wide range of applications include scientific and industrial processes, food production and storage and breathing gases.

In fire and explosion prevention engineering, purging refers to the introduction of an inert purge gas into a closed system to prevent the formation of an ignitable atmosphere. Purging relies on the principle that a combustible gas is able to undergo combustion (explode) only if mixed with air in the right proportions. The flammability limits of the gas define those proportions, i.e. the ignitable range.

In fire and explosion prevention engineering, inerting refers to the introduction of an inert (non-combustible) gas into a closed system to make a flammable atmosphere oxygen deficient and non-ignitable.

References

  1. ↑ IUPAC , Compendium of Chemical Terminology , 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) " inert gas ". doi : 10.1351/goldbook.I03027
  2. ↑ "Argon - Element information, properties and uses | Periodic Table". www.rsc.org. Retrieved 2024-04-07.
  3. ↑ Singh, Jasvinder. The Sterling Dictionary of Physics. New Delhi, India: Sterling, 2007. 122.
  4. ↑ "Qatargas - Operations". www.qatargas.com. Archived from the original on 2020-04-28. Retrieved 2018-08-31.
  5. ↑ "SEPURAN® Noble for helium recovery - SEPURAN® - Efficient gas separation". www.sepuran.com. Archived from the original on 2020-08-06. Retrieved 2018-08-31.
  6. ↑ Maier, Clive & Teresa Calafut. Polypropylene: The Definitive User's Guide and Databook. Norwich, New York: Plastics Design Library, 1998. 105.
  7. ↑ "Charters of Freedom Re-encasement Project". National Archives. Retrieved 2012-02-11.
  8. ↑ International Maritime Organization. Tanker yes Familiarization London: Ashford Overload Services, 2000. 185.
  9. ↑ Davis, J.R., ed. Corrosion: Understanding the Basics. Materials Park, Ohio: ASM International, 2000. 188.
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