helium

He. An element with atomic number 2. It is one of the rare gas elements in Group 18 of the periodic table with an electron configuration of 1s ^2. Its atomic weight is 4.002602(2). Naturally occurring isotopes are ^3He (0.000137(3)%) and ^4He (99.999863(3)%). In addition, radioactive nuclides with mass numbers between 5 and 10 have been reported. In 1868, PJC Janssen observed helium as an emission line (587.49 nm) in the solar spectrum during a solar eclipse, and JN Lockyer and E. Frankland named it helium after the Greek word for sun, Ηλιο (hèlios).
In 1895, W. Ramsay separated and refined it from the uranium mineral clevite. On Earth, it is found in small amounts in natural gas and in uranium minerals as a product of alpha decay, making up 0.000524(5)% of the Earth's atmosphere by volume. It is rarer than gold and silver, but exists in the universe in large quantities (26% by mass), second only to hydrogen (74% by mass). Industrially, it is obtained by repeatedly liquefying and distilling natural gas produced in Texas, Kansas, Oklahoma, etc. Reserves are related to natural gas reserves, but due to variations in helium concentration, about 1/4 of the total confirmed reserves are in Qatar, 1/5 each in Algeria and the United States, followed by Russia. Colorless, odorless gas. Boiling point 4.230 K. Critical constants: 5.1953 K, 0.22746 MPa, 69.641 g cm ^-3 . Liquid ^4He exhibits superfluidity below 2.173 K (lambda point) (see alternative terminology: liquid helium). At 0.0025 K, ^3He also enters a superfluid state. It is the only example of a liquid that does not solidify even at around 0 K under normal pressure, but it will solidify if 26 atm is applied at 0.95 K. The solid phase also exhibits special properties, such as its volume easily changing by about 30% when pressurized. First ionization energy: 24.588 eV. It is extremely inactive chemically and does not form compounds in the usual sense.
Pure helium is used as an inert atmosphere in arc welding and in the manufacture of high-purity materials for semiconductors, while a mixture of 80% He and 20% _O2 is used for deep-sea work or work under pressure. Helium is also important as an ultra-low temperature refrigerant, used in large quantities in medical superconducting MRIs and during the launch of the Space Shuttle. In recent years, helium has become an important industrial gas used not only in semiconductors, but also as an inert atmosphere in the manufacturing process of LCD TVs and optical fibers, and as a discharge gas for plasma TVs, and there has been a global shortage of helium gas. The United States has an underground storage facility in Texas that stockpiles large amounts of helium gas. Russia is also planning to build a storage facility in the oil fields of East Siberia. [CAS 7440-59-7]

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

He．原子番号2の元素．電子配置1s²の周期表18族希ガス元素の一つ．原子量4.002602(2)．天然に存在する同位体は ³He(0.000137(3)％)，⁴He(99.999863(3)％)．このほか，質量数5～10の放射性核種が報告されている．1868年にP.J.C. Janssenにより，日食の際の太陽スペクトル中に輝線(587.49 nm)として観測され，J.N. LockyerとE. Frankland(フランクランド)がギリシア語の太陽Ηλιο(hèlios)にちなんでヘリウムと命名した．
単体の分離精製は，1895年にW. Ramsay(ラムゼー)により，ウラン鉱物の一つ，クレーブ石(cleveite)から行われた．地球上では天然ガス中，あるいはα崩壊の産物としてウラン鉱物中に微量含まれ，体積で地球の大気の0.000524(5)％ を占める．金，銀よりも希少な元素であるが，全宇宙には水素(74質量％)についで大量(26質量％)に存在する．工業的には，テキサス，カンザス，オクラホマなどから産出する天然ガスの液化と分留の繰り返しで得られる．埋蔵量は天然ガス埋蔵量と関係があるが，ヘリウム濃度の高低があるため，確認埋蔵量は全量の約1/4がカタール，それぞれ1/5がアルジェリアとアメリカ，ついでロシア．無色，無臭の気体．沸点4.230 K．臨界定数5.1953 K，0.22746 MPa，69.641 g cm^－3．液体 ⁴He は2.173 K(λ点)以下で超流動性を示す([別用語参照]液体ヘリウム)．0.0025 K で ³He も超流動状態になる．常圧では0 K 付近でも固化しない唯一の例であるが，0.95 K で26 atm 加えれば固化する．固相も加圧により体積が容易に約30％ もかわるなど特殊な性質を示す．第一イオン化エネルギー24.588 eV.化学的にはきわめて不活性で，通常の意味の化合物はつくらない．
アーク溶接や半導体用高純度材料などの製造の際の不活性雰囲気として純ヘリウムが，深海作業あるいは加圧下の作業時にはHe 80％，O₂20％ の混合気体が用いられる．医療用超伝導MRIやスペースシャトル打ち上げの際にも大量に使用される超低温用の冷媒としても重要である．近年，半導体だけでなく，液晶テレビや光ファイバー製造工程の不活性雰囲気，プラズマテレビの放電ガスとしても使用される重要な産業用ガスで，世界的に供給が不足している．アメリカはテキサス州に地下貯蔵施設をもち，大量のヘリウムガスを備蓄している．ロシアも東シベリア油田地区に貯蔵施設建設を計画している．[CAS 7440-59-7]

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