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Cryogenic Gases


Liquid nitrogen is nitrogen that is cold enough to exist in liquid form. It is used for many cooling and cryogenic applications. Here are some liquid nitrogen facts and information about handling liquid nitrogen safely.

Liquid Nitrogen Facts:

•Liquid nitrogen is the liquefied form of the element nitrogen that is commercially produced by fractional distillation of liquid air.
•Sometimes liquid nitrogen is denoted as LN2, LN, or LIN.
•Liquid nitrogen has the UN number 1977.
•At normal pressure, liquid nitrogen boils at 77 K (−195.8°C or −320.4°F).
•The liquid to gas expansion ratio of nitrogen is 1:694, which means liquid nitrogen boils to fill a volume with nitrogen gas very quickly.
•Nitrogen is non-toxic, odorless, and colorless. It is relatively inert. It is not flammable.
•Nitrogen gas is slightly lighter than air once it reaches room temperature. It is slightly soluble in water.

Liquid Nitrogen Safety:

•Liquid nitrogen is cold enough to cause severe frostbite upon contact with living tissue. Wear proper safety gear when handling liquid nitrogen to prevent contact or inhalation of extremely cold vapor. Make sure exposed skin surfaces are covered and preferably insulated.
•Because it boils so rapidly, the phase transition from liquid to gas can generate a lot of pressure very quickly. Do not enclose liquid nitrogen in a sealed container, as this may result in bursting or an explosion.
•Adding a lot of nitrogen to the air reduces the relative amount of oxygen. This can result in an asphyxiation risk. Cold nitrogen gas is heavier than air, so the risk is greatest near the ground. Use liquid nitrogen in a well-ventilated area.
•Liquid nitrogen containers may accumulate oxygen which is condensed from the air. As the nitrogen evaporates, there is a risk of violent oxidation of organic matter.

Liquid Nitrogen Uses:
•Freezing and transport of food products.
•Cryopreservation of biological samples.
•Coolant for superconductors, vacuum pumps, and other materials and equipment.
•Cryotherapy to remove skin abnormalities.
•Shielding materials from oxygen exposure.
•Cooling materials for easier machining or fracturing.


Physical properties

Liquid oxygen has a pale blue color and is strongly paramagnetic and can be suspended between the poles of a powerful horseshoe magnet.[1] Liquid oxygen has a density of 1.141 g/cm3 (1.141 kg/L) and is cryogenic with a freezing point of 50.5 K (−368.77 °F; −222.65 °C) and a boiling point of 90.19 K (−297.33 °F, −182.96 °C) at 101.325 kPa (760 mmHg). Liquid oxygen has an expansion ratio of 1:861 at 20 °C (68 °F);[2][3] and because of this, it is used in some commercial and military aircraft as a source of breathing oxygen.

Because of its cryogenic nature, liquid oxygen can cause the materials it touches to become extremely brittle. Liquid oxygen is also a very powerful oxidizing agent: organic materials will burn rapidly and energetically in liquid oxygen. Further, if soaked in liquid oxygen, some materials such as coal briquettes, carbon black, etc., can detonate unpredictably from sources of ignition such as flames, sparks or impact from light blows. Petrochemicals often exhibit this behavior, including asphalt.

In commerce, liquid oxygen is classified as an industrial gas and is widely used for industrial and medical purposes. Liquid oxygen is obtained from the oxygen found naturally in air by fractional distillation in a cryogenic air separation plant.

Liquid oxygen is a common liquid oxidizer propellant for spacecraft rocket applications, usually in combination with liquid hydrogen or kerosene. Liquid oxygen is useful in this role because it creates a high specific impulse. It was used in the very first rocket applications like the V2 missile (under the name A-Stoff and Sauerstoff) and Redstone, R-7 Semyorka, Atlas boosters, and the ascent stages of the Apollo Saturn rockets. Liquid oxygen was also used in some early ICBMs, although more modern ICBMs do not use liquid oxygen because its cryogenic properties and need for regular replenishment to replace boiloff make it harder to maintain and launch quickly. Many modern rockets use liquid oxygen, including the main engines on the Space Shuttle.

Liquid oxygen also had extensive use in making oxyliquit explosives, but is rarely used now due to a high rate of accidents


(Ar), chemical element, inert gas of Group 0 (noble gases) of the periodic table, terrestrially the most abundant and industrially the most frequently used of the noble gases. Colourless, odourless, and tasteless, argon gas was isolated (1894) from air by the British scientists Lord Rayleigh and Sir William Ramsay. Henry Cavendish, while investigating atmospheric nitrogen ("phlogisticated air"), had concluded in 1785 that not more than 1/120 part of air might be some inert constituent. His work was forgotten until Lord Rayleigh, more than a century later, found that nitrogen prepared by removing oxygen from air is always about 0.5 percent more dense than nitrogen derived from chemical sources such as ammonia. The heavier gas remaining after both oxygen and nitrogen had been removed from air was the first of the noble gases to be discovered on Earth and was named argon because of its chemical inertness. (Helium had been spectroscopically detected in the Sun in 1868.)
Argon constitutes 1.3 percent of the atmosphere by weight and 0.94 percent by volume and is found occluded in rocks. A major portion of terrestrial argon has been produced, since the Earth's formation, in potassium-containing minerals by decay of the rare, naturally radioactive isotope potassium-40. The gas slowly leaks into the atmosphere from the rocks in which it is still being formed. The production of argon-40 from potassium-40 decay is utilized as a means of determining the Earth's age (potassium-argon dating). On Earth, naturally occurring argon is a mixture of three stable isotopes: argon-36 (0.34 percent), argon-38 (0.06 percent), and argon-40 (99.60 percent).

Argon is isolated on a large scale by the fractional distillation of liquid air. It is used in gas-filled electric light bulbs, radio tubes, and Geiger counters. It also is widely utilized as an inert atmosphere for arc-welding metals, such as aluminum and stainless steel; for the production and fabrication of metals, such as titanium, zirconium, and uranium; and for growing crystals of semi-conductors, such as silicon and germanium.

Argon gas condenses to a colourless liquid at -185.8° C (-302.4° F) and to a crystalline solid at -189.4° C (-308.9° F). The gas cannot be liquefied by pressure above a temperature of -122.3° C (-188.1° F), and at this point a pressure of at least 48 atmospheres is required to make it liquefy. At 12° C (53.6° F), 3.94 volumes of argon gas dissolve in 100 volumes of water. An electric discharge through argon at low pressure appears pale red and at high pressure, steely blue.

The outermost (valence) shell of argon has eight electrons, making it exceedingly stable and, thus, chemically inert. Argon atoms do not combine with one another; nor have they been observed to combine chemically with atoms of any other element. Argon atoms have been trapped mechanically in cagelike cavities among molecules of other substances, as in crystals of ice or the organic compound hydroquinone.

Atomic number 18
Atomic weight 39.948
Melting point -189.2° C (-308.6° F)
Boiling point -185.7° C (-302.3° F)
Density (1 atm, 0 C) 1.784 g/litre


Uses: Helium - He - Helium is a colorless, odorless and tasteless gas. It is present in dry air in a concentration of 5.24 ppm by volume. Used extensively in the welding industry as an inert shielding gas in arc welding. Used as a leak detector and as a carrier in gas chromatography.

(He), chemical element, inert gas of Group 0 (noble gases) of the periodic table. The second lightest element (only hydrogen being lighter), helium is a colorless, odorless, and tasteless gas that becomes liquid at -268.9° C (-452° F). Only under increased pressure (approximately 25 atmospheres) does helium solidify. Below 2.17 kelvins, the isotope helium-4 has unique properties: it becomes a superfluid (its viscosity nearly vanishes) and its thermal conductivity becomes more than 1,000 times greater than that of copper. In this state it is called helium II to distinguish it from normal liquid helium I. Chemically inert, helium does not form compounds, and its molecules consist of single atoms.

Helium was discovered in the gaseous atmosphere surrounding the Sun by the French astronomer Pierre Janssen, who detected a bright yellow line in the spectrum of the solar chromosphere during an eclipse in 1868; this line was initially assumed to represent the element sodium. That same year, the English astronomer Joseph Norman Lockyer observed a yellow line in the solar spectrum that did not correspond to the known D1 and D2 lines of sodium, and so he named it the D3 line. Lockyer concluded that the D3 line was caused by an element in the Sun that was unknown on Earth; he and the chemist Edward Frankland used the Greek word for sun, helios, in naming the element. The British chemist Sir William Ramsay discovered the existence of helium on Earth in 1895. Ramsay obtained a sample of the uranium-bearing mineral cleveite, and upon investigating the gas produced by heating the sample, he found that a unique bright-yellow line in its spectrum matched that of the D3 line observed in the spectrum of the Sun; the new element of helium was thus conclusively identified. In 1903 Ramsay and Frederick Soddy further determined that helium is a product of the spontaneous disintegration of radioactive substances.

Helium constitutes about 23 percent of the mass of the universe and is thus second in abundance to hydrogen in the cosmos. Helium is concentrated in stars, where it is synthesized from hydrogen by nuclear fusion. Although helium occurs in the Earth's atmosphere only to the extent of 1 part in 200,000 (0.0005 percent), and small amounts occur in radioactive minerals, meteoric iron, and mineral springs, great volumes of helium are found as a component (up to 7.6 percent) in natural gases in the United States (especially in Texas, New Mexico, Kansas, Oklahoma, Arizona, and Utah). Smaller supplies have been discovered in Canada and South Africa and in the Sahara Desert.

The helium that is present on Earth is not a primordial component of the Earth but has been generated by radioactive decay. Alpha particles, ejected from the nuclei of heavier radioactive substances, are nuclei of the isotope helium-4. Unlike argon gas, helium does not accumulate in large quantities in the atmosphere because Earth's gravity is not sufficient to prevent its gradual escape into space. The trace of the isotope helium-3 on Earth is attributable to the negative beta decay of the rare hydrogen-3 isotope (tritium). Thus, the helium that is found in large quantities on Earth consists of a mixture of two stable isotopes: helium-4 (99.99987 percent) and helium-3 (0.00013 percent).

Helium gas (98.2 percent pure) is isolated from natural gas by liquefying the other components at low temperatures and under high pressures. Adsorption of other gases on cooled, activated charcoal yields 99.995 percent pure helium. Helium is used as an inert-gas atmosphere for welding metals such as aluminum; in rocket propulsion (to pressurize fuel tanks, especially those for liquid hydrogen, because only helium is still a gas at liquid-hydrogen temperature); in meteorology (as a lifting gas for instrument-carrying balloons); in cryogenics (as a coolant because liquid helium is the coldest substance); and in high-pressure breathing operations (mixed with oxygen, as in scuba diving and caisson work, especially because of its low solubility in the blood-stream). Meteorites and rocks have been analyzed for helium content as a means of dating.

Atomic number 2
Atomic weight 4.0026
Melting point - none
Boiling point -268.9° C (-452° F)
Density (1 atm, 0 C) 0.1785 g/litre


Uses: Hydrogen is widely used for the hydrogenation of vegetable and animal oils and fats. Hydrogen also finds uses in the metallurgy field because of its ability to reduce metal oxides and prevent oxidation of metals in heat treating certain metals and alloys. Hydrogen is extensively used in the synthesis of ammonia and in petroleum refining operations. Liquefied hydrogen has been used primarily as a rocket fuel for combustion with oxygen or fluorine, and as a propellant for nuclear-powered rockets and space vehicles.

(H), a colourless, odourless, tasteless, flammable gaseous substance that is the simplest member of the family of chemical elements. The hydrogen atom has a nucleus consisting of a proton bearing one unit of positive electrical charge; an electron, bearing one unit of negative electrical charge, is associated with this nucleus. Although on Earth hydrogen ranks ninth among the elements in abundance, making up 0.9 per-cent of the mass of the planet, it is by far the most abundant element in the universe, accounting

for about 75 percent of the mass of all matter. Collected by gravitational forces in stars, hydrogen is converted into helium by nuclear fusion, a process that supplies the energy of the stars, including the Sun. Hydrogen is present in all animal and vegetable substances in the form of compounds in which it is combined with carbon and other elements. In the form of hydrocarbons, it is a constituent of petroleum and coal. It also constitutes nearly 11 percent of the mass of seawater. The hydrogen content of the Earth's atmosphere remains low because of the continual escape of the gas into space.

Liquid hydrogen is used in the laboratory to produce extremely low temperatures and in bubble chambers for photographing the tracks of nuclear particles. Liquid hydrogen is of great importance in space-exploration programs as a rocket fuel with oxygen or fluorine as the oxidizer. The deuterium isotope of hydrogen is the key component of the thermonuclear bomb.

Hydrogen is the lightest chemical element, has the highest heat conductivity, and has the highest coefficient of diffusion of all the gases. Chemically, hydrogen resembles the elements of groups I and VII of the periodic classification. Under proper conditions, it combines directly with most of the lighter elements and with many of the heavier elements. In compounds with metals, the hydrogen atom acquires a second electron, forming the negatively charged hydride ion, H-; with nonmetals, it shares its electron to form covalently bonded molecules such as methane, ammonia, water, and hydrogen chloride. In certain cases, the covalent bond is easily broken, forming the hydrogen ion, H+, and a negative ion from the remainder of the original molecule. The properties of most acids, particularly in aqueous solutions, arise from the presence of the hydrogen ion. For additional information about the major hydrogen compounds, see alcohol; ammonia; hydride; hydrocarbon.

Hydrogen reacts violently with fluorine, even at extremely low temperatures; with many other elements, hydrogen reacts upon heating or in the presence of catalysts.
Naturally occurring hydrogen consists of three isotopes: hydrogen-1, or protium, 99.985 percent; hydrogen-2, or deuterium (q.v.), 0.015 percent; and hydrogen-3, or tritium (q.v.), a minute trace. Tritium can be produced artificially; it is radioactive, having a half-life of 12.26 years.

Atomic number 1
Atomic weight 1.00797
Melting point -259.2° C (-434.6° F)
Boiling point -252.8° C (-422.8° F)
Density 0.08988 g/1 (0 C, 1 atm)


Carbon dioxide bubbles in a soft drink.Carbon dioxide is used by the food industry, the oil industry, and the chemical industry.[16] It is used in many consumer products that require pressurized gas because it is inexpensive and nonflammable, and because it undergoes a phase transition from gas to liquid at room temperature at an attainable pressure of approximately 60 bar (870 psi, 59 atm), allowing far more carbon dioxide to fit in a given container than otherwise would. Life jackets often contain canisters of pressured carbon dioxide for quick inflation. Aluminum capsules of CO2 are also sold as supplies of compressed gas for airguns, paintball markers, inflating bicycle tires, and for making carbonated water. Rapid vaporization of liquid carbon dioxide is used for blasting in coal mines. High concentrations of carbon dioxide can also be used to kill pests.

A candy called Pop Rocks is pressurized with carbon dioxide gas at about 40 bar (580 psi). When placed in the mouth, it dissolves (just like other hard candy) and releases the gas bubbles with an audible pop.

Leavening agents produce carbon dioxide to cause dough to rise. Baker's yeast produces carbon dioxide by fermentation of sugars within the dough, while chemical leaveners such as baking powder and baking soda release carbon dioxide when heated or if exposed to acids.

BeveragesCarbon dioxide is used to produce carbonated soft drinks and soda water. Traditionally, the carbonation in beer and sparkling wine came about through natural fermentation, but many manufacturers carbonate these drinks artificially. In the case of bottled and kegged beer, artificial carbonation is now the most common method used. With the exception of British Real Ale, draught beer is usually transferred from kegs in a cold room or cellar to dispensing taps on the bar using pressurized carbon dioxide, often mixed with nitrogen.

Wine makingCarbon dioxide in the form of dry ice is often used in the wine making process to cool down bunches of grapes quickly after picking to help prevent spontaneous fermentation by wild yeasts. The main advantage of using dry ice over regular water ice is that it cools the grapes without adding any additional water that may decrease the sugar concentration in the grape must, and therefore also decrease the alcohol concentration in the finished wine.

Dry ice is also used during the cold soak phase of the wine making process to keep grapes cool. The carbon dioxide gas that results from the sublimation of the dry ice tends to settle to the bottom of tanks because it is heavier than air. The settled carbon dioxide gas creates a hypoxic environment which helps to prevent bacteria from growing on the grapes until it is time to start the fermentation with the desired strain of yeast.

Carbon dioxide is also used to create a hypoxic environment for carbonic maceration, the process used to produce Beaujolais wine.

Carbon dioxide is sometimes used to top up wine bottles or other storage vessels such as barrels to prevent oxidation, though it has the problem that it can dissolve into the wine, making a previously still wine slightly fizzy. For this reason, other gases such as nitrogen or argon are preferred for this process by professional wine makers.

Pneumatic systems
Carbon dioxide is one of the most commonly used compressed gases for pneumatic (pressurized gas) systems in portable pressure tools and combat robots.

Fire extinguisher
Carbon dioxide extinguishes flames, and some fire extinguishers, especially those designed for electrical fires, contain liquid carbon dioxide under pressure. Carbon dioxide extinguishers work well on small flammable liquid and electrical fires, but not on ordinary combustible fires, as it is so dry. Carbon dioxide has also been widely used as an extinguishing agent in
fixed fire protection systems for local application of specific hazards and total flooding of a protected space, (National Fire Protection Association Code 12). International Maritime Organization standards also recognize carbon dioxide systems for fire protection of ship holds and engine rooms. Carbon dioxide based fire protection systems have been linked to several deaths, because it does not support life in the concentrations used to extinguish fire (40% or so), however, it is not considered to be toxic to humans. A review of CO2 systems (Carbon Dioxide as a Fire Suppressant: Examining the Risks, US EPA) identified 51 incidents between 1975 and the date of the report, causing 72 deaths and 145 injuries.
[edit] WeldingCarbon dioxide also finds use as an atmosphere for welding, although in the welding arc, it reacts to oxidize most metals. Use in the automotive industry is common despite significant evidence that welds made in carbon dioxide are more brittle than those made in more inert atmospheres, and that such weld joints deteriorate over time because of the formation of carbonic acid. It is used as a welding gas primarily because it is much less expensive than more inert gases such as argon or helium.

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