アルゴン

性質

常温常圧でアルゴンは、無色無臭の気体です。他の物質と化学反応を起こしにくいため、不活性ガスと呼ばれます。三重点は83.8058Kです。

解説

アルゴン，Ar．原子番号18の元素．電子配置[Ne]3s23p6の周期表18族希ガス元素．原子量39.948(1)．40Ar99.6003(1)％，38Ar0.0632％，36Ar0.3365％ からなり単核種に近い．質量数30～53までの放射性核種が知られている．1894年，W. Ramsay(ラムゼー)とJ. Rayleighによって発見され，不活性なところから怠け者を意味するギリシア語αργοσをとって命名された．大気の9340体積 ppm を占める．火星の大気中にも1.6％Arが含まれる．液体空気の分留によって単体が得られる．精製は，分留の反復，アルカリ金属との加熱(窒素，酸素の除去)，活性炭による分別吸着，分別蒸発，ガスクロマトグラフィーによって精製される．無色，無臭の気体．融点83.8 K(－189.3 ℃)，沸点87.28 K(－185.87 ℃)．臨界点150.86 K(－122.3 ℃)．4.898 MPa(48.35 atm)．13.41 mol L－1(0.5356 g mL－1)．三重点87.78 K．液体の密度34.93 mol L－1(1.393 g mL－1)(沸点)．蒸発熱6.516 kJ mol－1(沸点)．第一イオン化エネルギー1520.4 kJ mol－1(15.760 eV)．化学的には不活性である．ヒドロキノンと[C6H4(OH)2]3･0.67Ar，水と6H2O･Arの包接化合物をつくる．アーク溶接，チタン，半導体用ケイ素，ゲルマニウム結晶製造の際の不活性雰囲気，白熱電球，蛍光灯充填ガスとして用いられる．液体は高エネルギー物理学用検出器の媒質に使われる．

用途

アーク溶接時の不活性ガスシールド

構造

アルゴンは第18族元素の貴ガスで、第3周期元素の1つであり、元素記号はAr、原子量は39.95です。最外殻には価電子がなく、オクテット則を満たすため、化学的に構造が安定しています。電子配置は、[Ne] 3s² 3p⁶です。

比重は−233°Cの固体状態で1.65、−186°Cの液体状態で1.39であり、空気に対する比重は1.38です。固体状態では、面心立方構造を取っています。

地球上に存在するほとんどのアルゴンは、質量数が40 (⁴⁰Ar) であり、地殻中にあるカリウム40 (⁴⁰K) の崩壊によって生成しました。⁴⁰Arの半減期は1.25×10⁹年です。その一方で、宇宙にはアルゴン36 (³⁶Ar) が最も多く、超新星爆発によって生じました。アルゴンの同位体の中で、安定同位体は³⁶Ar、³⁸Ar、⁴⁰Arの3種類です。

説明

Argon belongs to the family of inert, rare gases of the atmosphere. It is plentiful compared to the other rare atmospheric gases; I million ft3 (28 300 m3) of dry air contains 9340 ft3 (264 m3 ) of argon. Argon is colorless, odorless, tasteless, and nontoxic. It is extremely inert and forms no known chemical compounds. It is slightly soluble in water.

化学的特性

With the symbol A, argon is a nonflammable gas; one of the elements in the inert gas category. It is colorless.

物理的性質

Argon is a colorless, odorless, tasteless, chemically inert noble gas that makes up about0.93% of the Earth’s atmosphere. It is the third most abundant gas in the atmosphere, meaningit is more common than carbon dioxide, helium, methane, and hydrogen.
Its melting point is –189.35°C, its boiling point is –185.85°C, and its density is0.0017837g/cm³.

同位体

There are a total of 24 isotopes of argon, three of which are stable. They areAr-36, which constitutes just 0.3365% of the natural amount of argon; Ar-38, which contributesjust 0.0632% to the amount of argon on Earth; and Ar-40, which, by far, constitutesthe most argon on Earth, 99.6003% of its natural abundance.

名前の由来

The name “argon” is derived from the Greek word argos, meaning “inactive.”

天然物の起源

Argon is the 56th most abundant element on Earth. It is the most abundant of all the noblegases found in the atmosphere. In fact, the only source of argon is the atmosphere, where it isfound at just under 1% of air by volume.
There are several methods of producing argon. The most common is by fractional distillationof liquid air. Argon is collected as a by-product of this large-scale commercial process.During fractional distillation, argon boils off at its own unique temperature. It is then collectedand purified by passing it through charcoal to filter out helium and other gases, producingsignificant amounts of argon.

特性

Although argon is considered chemically inert, at low temperatures it is possible to combineargon with other atoms to form very fragile compounds, which exist only at those verylow temperatures. For instance, it can combine with fluorine and hydrogen to form argonfluorohydride (HArF). It is only slightly soluble in water.

使用

Gas as shield in gas metal-arc welding, in metal processing; carrier in gas-liquid and gas-solid chromatography; gas filler for incandescent light bulbs. Gas in fluorescent tubes analogous to neon lights, but produces a blue-purplish light; in rectifier tubes; in thermometers above mercury; in lasers; wherever an inert atmosphere is desired and the much cheaper nitrogen cannot be used; in ionization chambers and particle counters; in mixtures with He and Ne in Geiger counters; in argon-oxygen-decarburizing process for stainless steel; in manufacture of semiconducting devices; in gas mixtures as the working fluid in plasma arc devices. Liquid as cryogen to produce low temperetures. The isotope 40Ar is always found in minerals contg potassium, since it is a product of 40K decay; measuring the amount of 40Ar and 40K can be used for determining the geologic age of minerals and meteors.

定義

An inert colorless odorless monatomic element of the rare-gas group. It forms 0.93% by volume of air. Argon is used to provide an inert atmosphere in electric and fluorescent lights, in welding, and in extracting titanium and silicon. The element forms no known compounds.
Symbol: Ar; m.p. –189.37°C; b.p. –185.86°C; d. 1.784 kg m^-3 (0°C); p.n. 18; r.a.m. 39.95.

一般的な説明

A colorless odorless noncombustible gas. Heavier than air and can asphyxiate by displacement of air. Exposure of the container to prolonged heat or fire can cause Argon to rupture violently and rocket . If liquefied, contact of the very cold liquid with water may cause violent boiling. If the water is hot, there is the possibility that a liquid "superheat" explosion may occur. Contacts with water in a closed container may cause dangerous pressure to build.

反応プロフィール

These substances undergo no chemical reactions under any known circumstances. They are nonflammable, noncombustible and nontoxic. They can asphyxiate.

危険性

Argon is nontoxic, but as an asphyxiant gas, it can smother by replacing oxygen in thelungs.

健康ハザード

Vapors may cause dizziness or asphyxiation without warning. Vapors from liquefied gas are initially heavier than air and spread along ground.

火災危険

Non-flammable gases. Containers may explode when heated. Ruptured cylinders may rocket.

そ他情報

アルゴンの同位体

アルゴンには、25種類の同位体が知られています。地球の大気中には、圧倒的に⁴⁰Arが多いです。

宇宙線の作用によって、³⁹Arや⁴⁰Arが生成します。地球表面では、³⁹Kの中性子捕獲などによって³⁹Arが生じます。天然のアルゴンに含まれる³⁹Arの割合の測定値は、(8.0±0.6)×10⁻¹⁶g/gです。

さらに、大気圏での核実験によって、³⁷Arが生成します。³⁷Arの半減期は35日です。また、地球大気中の⁴²Arの割合は、およそ6×10⁻²¹です。

使用用途

アルゴンは、他の物質と反応しにくいため、不活性ガスとして製造現場で広く使用されています。代表的な用途として、溶接のシールドガスが挙げられます。

アルゴンに数%の酸素を加えたシールドガスを用いることで、局所的にアークを集中できるため、高品質なを行うことが可能です。また、半導体基板の材料であるシリコンウエハを製造する際の雰囲気ガスとしても、アルゴンがよく用いられています。

他の物質と反応しにくい不活性ガス雰囲気を用いて、純度99.99%の高品質なシリコンの製造も可能です。他にも、を製造する精錬炉の雰囲気ガスとしても広く使用されています。

精製

液体空気の分留により、アルゴンの単体を得られます。分留の反復以外にも、活性炭による分別吸着、アルカリ金属との加熱、ガスクロマトグラフィー、分別蒸発などで、アルゴンを精製できます。

材料の用途

Gaseous argon is noncorrosive and inert, and consequently may be contained in systems constructed of any common metals and designed to safely withstand the pressures involved. At the temperature of liquid argon, ordinary carbon steels and most alloy steels lose their ductility and are considered unsafe for liquid argon service. Satisfactory materials for use with liquid argon include austenitic stainless steel (for example, types 304 and 316), copper, Monel, brass, aluminum, and other nickel-chromium alloys.

安全性プロファイル

A simple asphyxlant gas. As an inert gas, it has no specific inherent dangerous properties. Gases of this type have no specific toxicity effect, but they act by excluding O2 from the lungs. The effect of simple asphyxiant gases is proportional to the extent to whch they dirmnish the amount (partial pressure) of O2 in the air that is breathed. The oxygen may be diminished to 75% of its normal percentage in air before appreciable symptoms develop, and t h s in turn requires the presence of a simple asphyxiant in a concentration of 33% in the mixture of air and gas. When the simple asphyxiant reaches a concentration of 50%, marked symptoms can be produced. A concentration of 75% is fatal in a matter of minutes. The first symptoms produced by simple asphyxiant gases such as argon are rapid respirations and air hunger. Mental alertness is diminished and muscular coordination is impaired. Later, judgment becomes faulty and all sensations are depressed. Emotional instability often results and fatigue occurs rapidly. As the asphyxia progresses, there may be nausea and vomiting, prostration, and loss of consciousness, and finally, convulsions, deep coma, and death.

職業ばく露

Argon is used in metal fabrication and steel making; as an inert gas shield in arc welding; as an inert atmosphere in electric lamps; as a blanketing agent in metals refining (especially titanium and zirconium).

貯蔵

Gaseous argon is commonly stored in high pressure cylinders, tubes, or tube trailers. Liquid argon is commonly stored at the consumer site in cryogenic liquid containers and specially designed vacuum-insulated cryogenic storage tanks.
All of the precautions necessary for the handling of any nonflammable gas or cryogenic liquid must be taken.
Liquid and gaseous systems should be designed and installed only under the direction of personnel thoroughly familiar with liquid and gaseous argon equipment and in compliance with state, provincial, and local requirements.

輸送方法

UN1006 Argon, compressed, Hazard Class: 2.2; Labels: 2.2-Nonflammable compressed gas. Cylinders must be transported in a secure upright position, in a wellventilated truck. Protect cylinder and labels from physical damage. The owner of the compressed gas cylinder is the only entity allowed by federal law (49CFR) to transport and refill them. It is a violation of transportation regulations to refill compressed gas cylinders without the express written permission of the owner.

純化方法

Argon is rendered oxygen-free by passage over reduced copper at 450o, or by bubbling through alkaline pyrogallol and H2SO4, then dried with CaSO4, Mg(ClO4)2, or Linde 5A molecular sieves. Other purification steps include passage through Ascarite (CARE: asbestos impregnated with sodium hydroxide), through finely divided uranium at about 800o and through a -78o cold trap. Alternatively the gas is passed over CuO pellets at 300o to remove hydrogen and hydrocarbons, over Ca chips at 600o to remove oxygen and, finally, over titanium chips at 700o to remove nitrogen. It has also been purified by freeze-pump-thaw cycles and by passage over sputtered sodium [Arnold & Smith J Chem Soc, Faraday Trans 2 77 861 1981]. Arsenic acid (arsenic pentoxide hydrate, arsenic V oxide hydrate, orthoarsenic acid) [12044-50-7] M 229.8 + xH2O, pK 1 2.26, pK 2 6.76, pK 3 11.29 (H3AsO4). The acid crystallises from concentrated solutions of boiling conc HNO3 as rhombic crystals. Dry it in a vacuum to give the hemihydrate (hygroscopic). Heating above 300o yields As2O5. [Thaler Z Anorg Allgem Chem 246 19 1941, Schenk in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I p 601 1963.]

廃棄物の処理

Vent to atmosphere. Return refillable compressed gas cylinders to supplier.