What is a meme phase diagram
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|R and S phrases||R: no R-phrases|
|As far as possible and customary, SI units are used. |
Unless otherwise noted, the data given apply to standard conditions.
helium (from Greek ἥλιοςhelios "Sun") is a colorless, odorless, tasteless, non-toxic chemical element. Helium belongs to the group of noble gases, its atomic number is 2, its element symbol is He. Helium remains gaseous down to very low temperatures; it only becomes liquid when it is close to absolute zero. It is the only substance that does not solidify at normal pressure, even at absolute zero (0 K or −273.15 ° C). Helium is the substance with the greatest known chemical inertness. Even under extreme conditions, no compounds of helium could be detected that do not disintegrate immediately after formation. As far as is known, helium occurs only in atomic form. Other forms are only conceivable under extreme conditions. The most common stable isotope is 4He; another stable isotope is the very rare one 3Hey
The behavior of the two liquid phases "Helium-I" and "Helium-II" (especially the phenomenon of superfluidity) of 4He is the subject of current research in the field of quantum mechanics. Furthermore, liquid helium is an indispensable tool for achieving the lowest temperatures necessary to investigate properties such as the superconductivity of matter at temperatures close to absolute zero.
After hydrogen, helium is the second most abundant element in the universe. Most of it was created in the first 3 minutes after the Big Bang. The rest is a product of the nuclear fusion of hydrogen in stars. On earth will 4He is formed in the form of alpha particles during the alpha decay of various radioactive elements such as uranium or radium. Helium is created when the alpha particle snatches two electrons from other atoms. The helium created in this way collects in natural gas deposits in concentrations of up to seven percent by volume. Therefore, helium can be obtained from natural gas by fractional distillation.
The first evidence of helium was discovered in 1868 by the French astronomer Pierre Janssen while studying the light spectrum of the sun's chromosphere, where he found the previously unknown yellow spectral line of helium.
Helium is used in cryogenic technology, in deep-sea breathing apparatus, as a coolant for superconducting magnets, for determining the age of rocks, as a filling gas for balloons and airships and as a protective gas for various industrial applications (for example, gas-shielded metal welding and the manufacture of silicon wafers ). After inhaling helium, the voice changes briefly due to the higher speed of sound compared to air ("Mickey Mouse voice“).
References to the element helium were first obtained from a bright yellow spectral line at a wavelength of 587.49 nanometers in the spectrum of the sun's chromosphere. The French astronomer Pierre Janssen made this observation during a total solar eclipse in India on August 18, 1868. When he made his discovery known, no one wanted to believe him at first, as a new element had never been found in space before the evidence on the Earth could be guided. On October 20 of the same year, the Englishman Norman Lockyer confirmed that the yellow line was indeed present in the solar spectrum and concluded that it was caused by a previously unknown element. Because this spectral line was close to the so-called Fraunhofer D line, he named the line D3 in order to be able to distinguish it from the nearby D1 and D2 lines of sodium. He and his English colleague Edward Frankland suggested naming the new element after the Greek word for sun. Since they assumed that the element was a metal, they added the usual ending for metals to the name -ium instead of the usual ending for noble gases -on.
On March 26, 1895, the British chemist William Ramsay won helium by adding mineral acids to the uranium mineral Cleverite and isolating the escaping gas. He was looking for argon but was able to observe the yellow D3 line after separating nitrogen and oxygen from the isolated gas. The same discovery was made almost simultaneously by the British physicist William Crookes and the Swedish chemists Per Teodor Cleve and Nicolas Langlet in Uppsala, Sweden. They collected sufficient quantities of the gas to be able to determine its atomic mass.
During an oil well in Dexter, Kansas, a natural gas well was found whose natural gas contained twelve percent by volume of an unknown gas. The American chemists Hamilton Cady and David McFarland of the University of Kansas discovered that it was helium. They published a report that helium can be obtained from natural gas. In the same year, Ernest Rutherford and Thomas Royds discovered that alpha particles are helium nuclei.
The first liquefaction of helium was carried out in 1908 by the Dutch physicist Heike Kamerlingh Onnes by cooling the gas to a temperature below 1 K. He also tried to solidify it at a temperature of 0.8 K, but failed because helium can only be solidified under pressure. Onnes also described for the first time the Onnes effect, which is now named after him. The first solidification was carried out in 1926 by Onnes' student Willem Hendrik Keesom, who cooled helium to a similar temperature and applied a pressure of 25 bar.
According to the big bang theory, most of the helium present in space today was created in the first three minutes after the big bang. The large occurrence in the universe supports the big bang theory. After hydrogen, helium is the second most common element. 23% of the mass of visible matter is made up of helium, although hydrogen atoms are eight times more abundant. In addition, helium is produced by nuclear fusion in stars. This so called Hydrogen burning supplies the energy that makes the stars on the main sequence, i.e. the majority of all stars, shine. This process provides the stars with energy for most of their lives. When most of the hydrogen in the core is used up at the end of a star's life, the core contracts and increases its temperature. As a result, helium can now be burned to carbon (helium flash, helium burning). The burning of hydrogen continues to take place in a shell around this core. Carbon can also be burned further to form other elements. This process usually continues down to the iron in the absence of a supernova explosion. A supernova explosion also synthesizes elements heavier than iron, which are then dispersed into space. In the course of time, the interstellar matter becomes enriched with helium and heavier elements, so that stars formed later also have a larger proportion of helium and heavier elements.
On star surfaces and in nebulae, helium is preferentially neutral or simply ionized. Contrary to what is common in physics and chemistry, astronomy does not use the notation with a superscript “+” (He+) is used because other elements can be so highly ionized that this notation becomes impractical, for example sixteen-fold ionized iron in the solar corona. Therefore, in astronomy, ionization levels are designated with Roman numerals, with neutral helium being referred to as He-I, simply ionized as He-II and fully ionized as He-III.
Helium is also present in various planetary atmospheres:
|Neptune||19 % ± 3,2 %|
|Uranus||15,2 % ± 3,3 %|
Meteorites and moon
Helium can also be generated in meteorites through interaction (spallation) with cosmic rays. Especially 3He can therefore be used to determine the so-called irradiation age, which usually corresponds to the period between the meteorite striking the mother body and its arrival on earth. Next to it arises 4He in meteorites from the decay of heavy radioactive elements. There are also other helium components in meteorites, which originate from the time the solar system was formed, but were also partly captured from the solar wind. The same applies to lunar rocks, which come from the surface of the moon. Since this was often exposed to the solar wind or cosmic radiation for a very long time, such moon rocks are particularly rich in helium, especially the isotope 3Hey If it is possible to develop nuclear fusion reactors for deuterium-tritium fusion, the extraction of helium-3 from the moon could become economically interesting. China's current energy demand required 3 tons of helium-3 annually
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