Helium
Helium (from Greek: ἥλιος, romanized: helios, lit. 'sun') is a chemical element; it has symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table.[a] Its boiling point is the lowest among all the elements, and it does not have a melting point at standard pressures. It is the second-lightest and second most abundant element in the observable universe, after hydrogen. It is present at about 24% of the total elemental mass, which is more than 12 times the mass of all the heavier elements combined. Its abundance is similar to this in both the Sun and Jupiter, because of the very high nuclear binding energy (per nucleon) of helium-4, with respect to the next three elements after helium. This helium-4 binding energy also accounts for why it is a product of both nuclear fusion and radioactive decay. The most common isotope of helium in the universe is helium-4, the vast majority of which was formed during the Big Bang. Large amounts of new helium are created by nuclear fusion of hydrogen in stars.
This article is about the chemical element. For other uses, see Helium (disambiguation).Helium
colorless gas, exhibiting a gray, cloudy glow (or reddish-orange if an especially high voltage is used) when placed in an electric field
$_$_$DEEZ_NUTS#1__answer--2DEEZ_NUTS$_$_$
2
1s2
2
4.222 K (−268.928 °C, −452.070 °F)
0.1786 g/L
0.125 g/cm3
2.177 K, 5.043 kPa
5.1953 K, 0.22746 MPa
0.0138 kJ/mol
0.0829 kJ/mol
20.78 J/(mol·K)[3]
0
Pauling scale: no data
- 1st: 2372.3 kJ/mol
- 2nd: 5250.5 kJ/mol
28 pm
140 pm
hexagonal close-packed (hcp)
0.1513 W/(m⋅K)
−1.88×10−6 cm3/mol (298 K)[5]
972 m/s
7440-59-7
Norman Lockyer (1868)
Helium was first detected as an unknown, yellow spectral line signature in sunlight during a solar eclipse in 1868 by Georges Rayet,[14] Captain C. T. Haig,[15] Norman R. Pogson,[16] and Lieutenant John Herschel,[17] and was subsequently confirmed by French astronomer Jules Janssen.[18] Janssen is often jointly credited with detecting the element, along with Norman Lockyer. Janssen recorded the helium spectral line during the solar eclipse of 1868, while Lockyer observed it from Britain. However, only Lockyer proposed that the line was due to a new element, which he named after the Sun. The formal discovery of the element was made in 1895 by chemists Sir William Ramsay, Per Teodor Cleve, and Nils Abraham Langlet, who found helium emanating from the uranium ore cleveite, which is now not regarded as a separate mineral species, but as a variety of uraninite.[19][20] In 1903, large reserves of helium were found in natural gas fields in parts of the United States, by far the largest supplier of the gas today.
Liquid helium is used in cryogenics (its largest single use, consuming about a quarter of production), and in the cooling of superconducting magnets, with its main commercial application 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 small but well-known use is as a lifting gas in balloons and airships.[21] As with any 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 superfluidity) and to those looking at the phenomena, such as superconductivity, produced in matter near absolute zero.
On Earth, it is relatively rare—5.2 ppm by volume in the atmosphere. Most terrestrial helium present today is created by the natural radioactive decay of heavy radioactive elements (thorium and uranium, although there are other examples), as the alpha particles emitted by such decays consist of helium-4 nuclei. This radiogenic helium is trapped with natural gas in concentrations as great as 7% by volume, from which it is extracted commercially by a low-temperature separation process called fractional distillation. Terrestrial helium is a non-renewable resource because once released into the atmosphere, it promptly escapes into space. Its supply is thought to be rapidly diminishing.[22][23] However, some studies suggest that helium produced deep in the Earth by radioactive decay can collect in natural gas reserves in larger-than-expected quantities,[24] in some cases having been released by volcanic activity.[25]
History
Scientific discoveries
The first evidence of helium was observed on August 18, 1868, as a bright yellow line with a wavelength of 587.49 nanometers in the spectrum of the chromosphere of the Sun. The line was detected by French astronomer Jules Janssen during a total solar eclipse in Guntur, India.[26][27] This line was initially assumed to be sodium. On October 20 of the same year, English astronomer, Norman Lockyer, observed a yellow line in the solar spectrum, which, he named the D3 because it was near the known D1 and D2 Fraunhofer lines of sodium.[28][29] He concluded that it was caused by an element in the Sun unknown on Earth. Lockyer named the element with the Greek word for the Sun, ἥλιος (helios).[30][31] It is sometimes said that English chemist Edward Frankland was also involved in the naming, but this is unlikely as he doubted the existence of this new element. The ending "-ium" is unusual, as it normally applies only to metallic elements; probably Lockyer, being an astronomer, was unaware of the chemical conventions.[32]
Occurrence and production
Natural abundance
Although it is rare on Earth, helium is the second most abundant element in the known Universe, constituting 23% of its baryonic mass. Only hydrogen is more abundant.[27] The vast majority of helium was formed by Big Bang nucleosynthesis one to three minutes after the Big Bang. As such, measurements of its abundance contribute to cosmological models. In stars, it is formed by the nuclear fusion of hydrogen in proton–proton chain reactions and the CNO cycle, part of stellar nucleosynthesis.[108]
In the Earth's atmosphere, the concentration of helium by volume is only 5.2 parts per million.[127][128] The concentration is low and fairly constant despite the continuous production of new helium because most helium in the Earth's atmosphere escapes into space by several processes.[129][130][131] In the Earth's heterosphere, a part of the upper atmosphere, helium and other lighter gases are the most abundant elements.
Most helium on Earth is a result of radioactive decay. Helium is found in large amounts in minerals of uranium and thorium, including uraninite and its varieties cleveite and pitchblende,[19][132] carnotite and monazite (a group name; "monazite" usually refers to monazite-(Ce)),[133][134] because they emit alpha particles (helium nuclei, He2+) to which electrons immediately combine as soon as the particle is stopped by the rock. In this way an estimated 3000 metric tons of helium are generated per year throughout the lithosphere.[135][136][137] In the Earth's crust, the concentration of helium is 8 parts per billion. In seawater, the concentration is only 4 parts per trillion. There are also small amounts in mineral springs, volcanic gas, and meteoric iron. Because helium is trapped in the subsurface under conditions that also trap natural gas, the greatest natural concentrations of helium on the planet are found in natural gas, from which most commercial helium is extracted. The concentration varies in a broad range from a few ppm to more than 7% in a small gas field in San Juan County, New Mexico.[138][139]
As of 2021 The world's helium reserves were estimated at 31 billion cubic meters, with a third of that being in Qatar.[140] In 2015 and 2016 additional probable reserves were announced to be under the Rocky Mountains in North America[141] and in the East African Rift.[142]
Modern extraction and distribution
For large-scale use, helium is extracted by fractional distillation from natural gas, which can contain as much as 7% helium.[143] Since helium has a lower boiling point than any other element, low temperatures and high pressure are used to liquefy nearly all the other gases (mostly nitrogen and methane). The resulting crude helium gas is purified by successive exposures to lowering temperatures, in which almost all of the remaining nitrogen and other gases are precipitated out of the gaseous mixture. Activated charcoal is used as a final purification step, usually resulting in 99.995% pure Grade-A helium.[29] The principal impurity in Grade-A helium is neon. In a final production step, most of the helium that is produced is liquefied via a cryogenic process. This is necessary for applications requiring liquid helium and also allows helium suppliers to reduce the cost of long-distance transportation, as the largest liquid helium containers have more than five times the capacity of the largest gaseous helium tube trailers.[80][144]
In 2008, approximately 169 million standard cubic meters (SCM) of helium were extracted from natural gas or withdrawn from helium reserves, with approximately 78% from the United States, 10% from Algeria, and most of the remainder from Russia, Poland, and Qatar.[145] By 2013, increases in helium production in Qatar (under the company Qatargas managed by Air Liquide) had increased Qatar's fraction of world helium production to 25%, making it the second largest exporter after the United States.[146]
An estimated 54 billion cubic feet (1.5×109 m3) deposit of helium was found in Tanzania in 2016.[147] A large-scale helium plant was opened in Ningxia, China in 2020.[148]
In the United States, most helium is extracted from the natural gas of the Hugoton and nearby gas fields in Kansas, Oklahoma, and the Panhandle Field in Texas.[80][149] Much of this gas was once sent by pipeline to the National Helium Reserve, but since 2005, this reserve has been depleted and sold off, and it is expected to be largely depleted by 2021[146] under the October 2013 Responsible Helium Administration and Stewardship Act (H.R. 527).[150] The helium fields of the western United States are emerging as an alternate source of helium supply, particularly those of the "Four Corners" region (the states of Arizona, Colorado, New Mexico and Utah).[151]
Diffusion of crude natural gas through special semipermeable membranes and other barriers is another method to recover and purify helium.[152] In 1996, the U.S. had proven helium reserves in such gas well complexes of about 147 billion standard cubic feet (4.2 billion SCM).[153] At rates of use at that time (72 million SCM per year in the U.S.; see pie chart below) this would have been enough helium for about 58 years of U.S. use, and less than this (perhaps 80% of the time) at world use rates, although factors in saving and processing impact effective reserve numbers.
Helium is generally extracted from natural gas because it is present in air at only a fraction of that of neon, yet the demand for it is far higher. It is estimated that if all neon production were retooled to save helium, 0.1% of the world's helium demands would be satisfied. Similarly, only 1% of the world's helium demands could be satisfied by re-tooling all air distillation plants.[154] Helium can be synthesized by bombardment of lithium or boron with high-velocity protons, or by bombardment of lithium with deuterons, but these processes are a completely uneconomical method of production.[155]
Helium is commercially available in either liquid or gaseous form. As a liquid, it can be supplied in small insulated containers called dewars which hold as much as 1,000 liters of helium, or in large ISO containers, which have nominal capacities as large as 42 m3 (around 11,000 U.S. gallons). In gaseous form, small quantities of helium are supplied in high-pressure cylinders holding as much as 8 m3 (approximately . 282 standard cubic feet), while large quantities of high-pressure gas are supplied in tube trailers, which have capacities of as much as 4,860 m3 (approx. 172,000 standard cubic feet).
As a contaminant
While chemically inert, helium contamination impairs the operation of microelectromechanical systems (MEMS) such that iPhones may fail.[179]
Inhalation and safety
Effects
Neutral helium at standard conditions is non-toxic, plays no biological role and is found in trace amounts in human blood.
The speed of sound in helium is nearly three times the speed of sound in air. Because the natural resonance frequency of a gas-filled cavity is proportional to the speed of sound in the gas, when helium is inhaled, a corresponding increase occurs in the resonant frequencies of the vocal tract, which is the amplifier of vocal sound.[27][180] This increase in the resonant frequency of the amplifier (the vocal tract) gives increased amplification to the high-frequency components of the sound wave produced by the direct vibration of the vocal folds, compared to the case when the voice box is filled with air. When a person speaks after inhaling helium gas, the muscles that control the voice box still move in the same way as when the voice box is filled with air; therefore the fundamental frequency (sometimes called pitch) produced by direct vibration of the vocal folds does not change.[181] However, the high-frequency-preferred amplification causes a change in timbre of the amplified sound, resulting in a reedy, duck-like vocal quality. The opposite effect, lowering resonant frequencies, can be obtained by inhaling a dense gas such as sulfur hexafluoride or xenon.
Hazards
Inhaling helium can be dangerous if done to excess, since helium is a simple asphyxiant and so displaces oxygen needed for normal respiration.[27][182] Fatalities have been recorded, including a youth who suffocated in Vancouver in 2003 and two adults who suffocated in South Florida in 2006.[183][184] In 1998, an Australian girl from Victoria fell unconscious and temporarily turned blue after inhaling the entire contents of a party balloon.[185][186][187]
Inhaling helium directly from pressurized cylinders or even balloon filling valves is extremely dangerous, as high flow rate and pressure can result in barotrauma, fatally rupturing lung tissue.[182][188]
Death caused by helium is rare. The first media-recorded case was that of a 15-year-old girl from Texas who died in 1998 from helium inhalation at a friend's party; the exact type of helium death is unidentified.[185][186][187]
In the United States, only two fatalities were reported between 2000 and 2004, including a man who died in North Carolina of barotrauma in 2002.[183][188] A youth asphyxiated in Vancouver during 2003, and a 27-year-old man in Australia had an embolism after breathing from a cylinder in 2000.[183] Since then, two adults asphyxiated in South Florida in 2006,[183][184][189] and there were cases in 2009 and 2010, one of whom was a Californian youth who was found with a bag over his head, attached to a helium tank,[190] and another teenager in Northern Ireland died of asphyxiation.[191] At Eagle Point, Oregon a teenage girl died in 2012 from barotrauma at a party.[192][193][194] A girl from Michigan died from hypoxia later in the year.[195]
On February 4, 2015, it was revealed that, during the recording of their main TV show on January 28, a 12-year-old member (name withheld) of Japanese all-girl singing group 3B Junior suffered from air embolism, losing consciousness and falling into a coma as a result of air bubbles blocking the flow of blood to the brain after inhaling huge quantities of helium as part of a game. The incident was not made public until a week later.[196][197] The staff of TV Asahi held an emergency press conference to communicate that the member had been taken to the hospital and is showing signs of rehabilitation such as moving eyes and limbs, but her consciousness has not yet been sufficiently recovered. Police have launched an investigation due to a neglect of safety measures.[198][199]
The safety issues for cryogenic helium are similar to those of liquid nitrogen; its extremely low temperatures can result in cold burns, and the liquid-to-gas expansion ratio can cause explosions if no pressure-relief devices are installed. Containers of helium gas at 5 to 10 K should be handled as if they contain liquid helium due to the rapid and significant thermal expansion that occurs when helium gas at less than 10 K is warmed to room temperature.[103]
At high pressures (more than about 20 atm or two MPa), a mixture of helium and oxygen (heliox) can lead to high-pressure nervous syndrome, a sort of reverse-anesthetic effect; adding a small amount of nitrogen to the mixture can alleviate the problem.[200][169]
General
More detail
Miscellaneous
Helium shortage