Helium is a chemical element with symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table. It’s boiling and melting points are the lowest among all the elements. Helium is the second least reactive noble gas, after neon, and thus the second least reactive of all elements. It is inert and monatomic in all standard conditions. Since, helium has relatively low molar (atomic) mass, its thermal conductivity, specific heat, and sound speed in the gas phase are all greater than any other gas except hydrogen.
For similar reasons, and also due to the small size of helium atoms, helium’s diffusion rate through solids is three times that of air and around 65% that of hydrogen. Helium is the least water-soluble monatomic gas, and it’s refraction index’ is closer to unity than that of any other gas. The speed of sound in helium is nearly three times the speed of sound in air.
Helium is the second most abundant as well as the lightest element in the observable universe, being present at about 24% of the total elemental mass, which is more than 12 times the mass of all the heavier elements, combined. On Earth it is relatively rare — 5.2 ppm by volume in the atmosphere. Helium is a finite resource, and once released into the atmosphere, it readily escapes into space.
This gas has a negative Joule-Thomson coefficient at normal ambient temperatures, meaning it heats up when allowed to freely expand.Once it reaches below Joule-Thomson inversion temperature ( of about 32 to 50k at 1 atmosphere), it freely expands and cools. Once pre-cooled below this temperature, helium can be liquefied through expansion cooling.
Helium is named for the Greek god of the Sun, Helios. The formal discovery of the element was made in 1895 by two Swedish chemists, Per Teodor Cleve and Nils Abraham Langlet, who found helium emanating from the uranium ore cleveite.
Inhaling helium can be dangerous if done to excess, since helium is a simple asphyxiant and so displaces oxygen needed for normal respiration. Breathing pure helium continuously causes death by asphyxiation within minutes. Inhaling helium directly from pressurized cylinders is extremely dangerous, as the high flow rate can result in barotrauma, fatally rupturing lung tissue.
7 m3 cylinder at 150 kg/cm2
Liquid helium is used in cryogenics (its largest single use, absorbing about a quarter of production), particularly in the cooling of superconducting magnets, with the main commercial application being in MRI scanners.
Helium’s other industrial uses—as a pressurizing and purge gas, as a protective atmosphere for arc welding and in processes such as growing crystals to make silicon wafers—account for half of the gas produced.
A well-known but minor usage of it is, as a lifting gas in balloons and airships.
Like any other gas, whose density differs from that of air, inhaling a small volume of helium temporarily changes the timbre and quality of the human voice.
In scientific research, the behavior of the two fluid phases of helium-4 (helium I and helium II) is important to researchers studying quantum mechanics (in particular the property of super fluidity) and to those looking at the phenomena, such as superconductivity, produced in matter near absolute zero.
Helium and Oxygen mixture is used in “technical scuba diving (SCUBA-Self Contained Underwater Breathing Apparatus)”