Helium

Use

Helium is used:

with the pressurization of the cryogenic tanks;
in the liquid state in Cryogenics, in particular to cool the superconductive magnets used for example in IRM;
in combination with the Oxygen to form the Héliox, gas used for the Plunged underwater with great depth.
this same mixture is used in medicine to relieve the victims of breathing difficulties, helium penetrating more easily than nitrogen in the narrowed respiratory tracts;
in surgery, of the ionized helium beams resulting from a Synchrocyclotron is used to treat ocular tumors
in the radioactive Dating;
in the detection of the escapes fans of multiple applications of which also drains;
like gas of Lift for the inflation of the balloons of weather goldbeater's skin of monitoring and of the Airship S;
like carrier gas for the Gas chromatography;
like gas of protection for various industrial uses (such as the arc cutting and the growth of the sections of Silicon);
in partnership with neon in the lasers He-(which do not emit to 632.8 Nm).
with food products (food additive authorized under refers E 939) to allow a checking of the sealing of packing. List of the food additives

Therapeutic use

Helium is managed in mixtures containing a minimum of 20% of Oxygène, with patients with the catches with an obstruction of the higher or lower respiratory tracts. The low viscosity of helium makes it possible to decrease respiratory work.

Dangers connected to the inhalation

The inhalation of a low volume of helium temporarily modifies the voice which becomes acuter because the vocal cords vibrate more quickly in the presence of this gas, because of the relative weak density of helium compared to the air. This practice is inoffensive with small amounts, helium being an inert gas. On the other hand, a inhalation in greater quantity in only once, would produce light a Asphyxie, leading to short but dangerous loss of conscience. One counts also certain cases of cerebral Embolies or serious pulmonary problems at the people having inhaled helium under pressure (in a bottle). One also notes a deterioration of the vocal cords over one short duration after inhalation.

Notable characteristics

Obtaining helium

Currently, it is impossible to manufacture Hélium. The only means to get some are currently in the underground Gisement S of natural gas to the Texas, for example, or by " décomposition" air.

The price is really very high (approx. 100€/m3 at Liquid air) with the result that certain people rather use the Dihydrogène (formed molecule of two atoms of Hydrogène) which can be obtained after electrolysis water what makes its very low cost but which presents a principal disadvantage of that of being very flammable!

Gas phases and plasma

Helium is a colorless, odorless, and nontoxic gas. It is the least reactive of the elements of the groupe 18 (rare gases) of the periodic table and this virtually inert fact. Under standard conditions of temperature and pressure, helium practically behaves like an ideal gas. Virtually, helium is monoatomic under all the conditions. Its thermal conductivity is higher than all gases, hydrogen except, and its specific heat is exceptionally high. Helium is also the least water-soluble gas of all known gases and its speed of diffusion through the solids is three times higher than that of the air and approximately 65 % with that of hydrogen. The index of refraction of helium is closer to the unit than that of any other gas. The coefficient Joule-Thomson of this gas is negative with room temperature, which means warming when it can extend freely. It does not cool solely when it can extend freely when its temperature from inversion of Joule-Thomson (approximately 40 K is −233 °C; with a pressure of 1 atm). Once cooled in lower part of this temperature, helium can be liquefied by cooling due to its expansion.

Helium is chemically not reagent under all the normal conditions, because of its valence equalizes to 0. It is insulator electrical except when it is ionized. Like other rare gases, helium has metastable energy levels which enable him to remain ionized in an electric shock whose tension is lower than its potential of ionization. Helium can form unstable compounds with tungsten, iodine, fluorine, sulfur and phosphorus when it is prone to an electroluminescent discharge by a bombardment of electrons, or forms a plasma then. He , Hg He, W He and ions molecular He + , He ++ , HeH + , He D + were created in this manner. This technique also allowed the production of the neutral molecule He, which have a greater number of systems of bands, and HgHe, whose cohesion seems to rest only on forces of Polarization. Theoretically, other components as helium fluorohydrure (HHe F) are also possible.

Liquid and solid phases

Helium is solidified only under the effect of strong pressures. The practically invisible and colorless solid which results from it is strongly compressible; a compression in laboratory can reduce its volume of more than 30 %. With a cubic Modulus of elasticity about 50×10 6 Pa, it is 50 times more compressible than water. Contrary to the other elements, helium is not solidified and remains liquid until the absolute zero, under normal conditions of pressure. The solid Hélium requires a minimal pressure of approximately 26 atm. It is often rather difficult to distinguish the solid Hélium from liquid helium, their index of refraction being almost identical. The solid has a latent heat (fusion heat) high and a hexagonal crystalline structure, like that of water.

Liquid states of helium

In lower part of its point of boiling of 4,216 K and above the Not lambda of 2,1768 K, the isotope ⁴He exists in a colorless normal liquid state, called hélium I. Following the example others liquid cryogenic, the hélium I enters in boiling when it is heated. It also contracts when the temperature is lowered until it reaches the point lambda, where it ceases boiling and dilates suddenly; (becoming hélium II). Its speed of dilation decrease in lower part of the point lambda until a temperature from approximately 1 K is reached; at this time, the hélium II cease completely to dilate and starts again to contract.

The Index of refraction of the hélium I of 1,026 is similar to that of other gases, which makes its surface so difficult to perceive that a fine layer of Styromousse is often used to highlight it. Helium I, colorless liquid, are slightly viscous and its density corresponds to 1/8e of that of water, that is to say 1/4 only of the value envisaged by traditional physics. The quantum Mécanique is necessary to explain this property, and so the various types of liquid helium are called fluid quantum, which means that they show their atomic properties on a macroscopic scale. This is probably due to the point of boiling so close to the Absolute zero which prevents the random molecular movement (due to heat) from masking the atomic properties.

History

helium|helium

The existence of the helium (of the Greek ἥλιος, photogravure : Sun) was highlighted for the first time by Jules Jansen, a astronomer French, in the solar crown at the time of the eclipse of the August 18th 1868 and simultaneously by the British astronomer to sir Joseph Norman Lockyer, by an unknown yellow line in the spectrum. The name “helium” was proposed, little time after, by this last and the chemist to sir Edward Frankland, in reference to the Greek symbol of the Sun, Hélios. Its presence on the Earth was detected in 1895 by Lord Rayleigh and to sir William Ramsay, chemist. Since then, of great helium reserves were found in the natural gas fields of the the United States, by making the largest suppliers of this gas in the world. In 1960, they decided to constitute a reserve which reached in 1995 the volume of a billion cubic meters. That is to say approximately: 180000 tons of gas.

The Helium Privatization Act of 1996 authorized to start this reserve as from 2005.

Nevertheless, at the end of 2006, the scientific world and industrialist seems in a state of effective helium shortage what in fact a strategic raw material.

References

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