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性質
六フッ化硫黄は、無色、無臭、無毒の気体です。常温常圧では化学的な安定度が高く、不燃性です。融点は-50.8°Cで、昇華点は-63.8°Cです。水に溶けにくいですが、エチルアルコールにはやや溶けます。
六フッ化硫黄を吸い込んで声を出すと、音域が低くなります。空気より重い気体では、音が低くなるためです。
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反応
六フッ化硫黄の反応はあまり知られておらず、溶融した金属ナトリウムとも反応しません。硫黄中心がフッ素で囲まれており、分子全体の極性がほぼないためです。
金属リチウムとは反応し、フッ化リチウムと硫化リチウムが生成します。この反応で生じた熱エネルギーは、魚雷の推進力に利用されています。反応生成物の体積は六フッ化硫黄とリチウムよりも小さく、従来の魚雷のように機外へ生成物を排出する必要もありません。そのため、魚雷の性能の向上に寄与しています。ジシラン (英: disilane) とは激しく反応して、爆発します。
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解説
六フッ化硫黄 (英: sulfur hexafluoride) とは、硫黄の六フッ化物のことです。
不燃性、耐熱性、非腐食性に優れ、高い絶縁性能を持っています。化学的にも非常に安定性が高く、大気中での寿命は約3,200年です。
温室効果ガスの1つで、地球温暖化係数はの2万倍以上であり、排出抑制対象ガスの一つに指定されています。使用量はあまり多くありませんが、新しい用途開発の進展に伴って、近年需要量が増加しており、大気へ放出される六フッ化硫黄のほとんどは、人為的な理由だと考えられています。
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用途
六フッ化硫黄の高い誘電効率および電気火花発生時に電子を補足する性能があるため電子機器装置に利用
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構造
六フッ化硫黄は硫黄原子1つとフッ素原子6つから構成され、化学式はSF6で示されます。分子量は146.06です。硫黄原子を中心として、フッ素原子は正八面体構造を取っています。
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合成
六フッ化硫黄はそれぞれの元素の単体であるS8とF2から合成可能です。副生成物として他のフッ化硫黄類も生じます。S2F10は加熱によって不均化し、SF4は水酸化ナトリウム水溶液で洗浄すると分解できるため除去可能です。
原料にSF4を用いて、六フッ化硫黄と構造がよく似たSF5Clを合成できます。SF5Clの酸化力は強く、加水分解によって硫酸になります。
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効能
診断補助薬 (超音波造影剤)
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説明
Sulfur hexafluoride is a colorless, odorless,
nontoxic, nonflammable gas that has a high dielectric strength and serves widely as an insulating gas in electrical equipment. At atmospheric pressures it sublimes directly from the
solid to the gas phase and does not have a stable
liquid phase unless under a pressure of more
than 32 psia (221 kPa, abs). It is shipped as a
liquefied compressed gas at its vapor pressure
of 298 psig at 70°F (2050 kPa at 21.1°C).
One of the most chemically inert gases
known, it is completely stable in the presence of
most materials to temperatures of about 400°F
(204°C) and has shown no breakdown or reaction in quartz at 900°F (482°C). Sulfur hexafluoride is slightly soluble in water and oil. No
change in pH occurs when distilled water is
saturated with sulfur hexafluoride.
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化学的特性
Chemical properties of sulfur hexafluoride are very stable. And compared to selenium hexafluoride, the hydrolysis rate of sulfur hexafluoride is extremely low, this is due to the small radius sulfur atom, which resulting in six fluorine atoms form a larger steric hindrance around. However, the fluorine atom radius is not big, so the repulsive force between the six fluorine atoms is not too large, S-F bond is not easy to dissociate. Enthalpy of formation of sulfur hexafluoride is-1220 kJ/mol, but enthalpy of formation of sulfur hexafluoride is-74 kJ/mol. Thus, the radius of fluorine atom and sulfur atom radius cause the very stable of sulfur hexafluoride molecule together---the molecules themselves are difficult to disconnect bond and break down and the attack group is difficult to approach to the central atom, in the thermodynamics and kinetics, they are both stable. Studies have said sulfur hexafluoride can be stably present in the atmosphere for thousands of years.
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物理的性質
Colorless, odorless gas; density 6.41 g/L; about five times heavier than air; liquefies at -50.7°C (triple point); density of liquid 1.88 g/mL at -50.7°C; sublimes at -63.8°C; critical temperature 45.54°C; critical pressure 37.13 atm; critical volume 199 cm3/mol; slightly soluble in water; soluble in ethanol.
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使用
Sulfur hexafluoride is used extensively as a gaseous dielectric in various kinds of electrical power equipment, such as switchgear, transformers, condensers, and circuit breakers. It has also been used as a dielectric at microwave frequencies and as an insulating medium for the power supplies of high-voltage machines.
Sulfur hexafluoride is also gaining use in nonelectrical applications, including blanketing of molten magnesium, leak detection, and plasma etching in the semiconductor industry. Sulfur hexafluoride also has some limited medical applications.
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製造方法
Sulfur hexachloride may be prepared by reacting fluorine with sulfur or sulfur dioxide.
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反応プロフィール
This substance undergoes chemical reactions only under relatively severe circumstances. They are resistant to ignition, although they may become flammable at very high temperatures. They may be resistant to oxidation reduction, except in the most severe conditions. These materials may be nontoxic. They can asphyxiate. Contact of very cold liquefied gas with water may result in vigorous or violent boiling of the product and extremely rapid vaporization due to the large temperature differences involved. If the water is hot, there is the possibility that a liquid "superheat" explosion may occur. Pressures may build to dangerous levels if liquid gas contacts water in a closed container [Handling Chemicals Safely 1980].
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危険性
Asphyxiant.
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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. Contact with gas or liquefied gas may cause burns, severe injury and/or frostbite. Fire may produce irritating, corrosive and/or toxic gases.
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火災危険
Some may burn but none ignite readily. Containers may explode when heated. Ruptured cylinders may rocket.
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使用用途
六フッ化硫黄は高い絶縁性能を有する気体で、大気中で非常に安定性が高く、人体に対しても安全性が高いです。そのため、電子機器のとして幅広く使用されています。具体例として、ガス遮断器、ガス変圧器、ガス絶縁開閉装置のような電力機器などが挙げられます。
また、マグネシウム合金溶解炉の酸化を防止可能です。それに加えて、液晶パネルや半導体製品のドライエッチング工程にも利用可能です。特殊な使用例として、リチウムと組み合わせた魚雷用エンジンの燃料もあります。
さらに眼科領域では、網膜を眼球壁へ押し付けるために使用可能です。具体的には、網膜剥離治療のための硝子体手術後に、六フッ化硫黄を眼内に充満させます。その後、1週間程度うつむき姿勢を取り、網膜を眼球壁に押し付けて、網膜が眼球壁に吸着する力を高めます。
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材料の用途
Sulfur hexafluoride is noncorrosive to all metals. It may be partially decomposed if subjected
to an electrical discharge. Some of the breakdown products are corrosive; this corrosion is
enhanced by the presence of moisture or at high
temperature. Sulfur hexafluoride decomposes
very slightly in the presence of certain metals at
temperatures in excess of 400°F (204°C); this
effect is most pronounced with silicon and carbon steels. Such breakdown, presumably catalyzed by the metals, is only several tenths of 1
percent over 1 year. Decomposition at elevated
temperatures does not occur with aluminum,
copper, brass, and silver.
Most common gasket materials, including
Teflon, neoprene, and natural rubber are suitable for sulfur hexafluoride service.
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安全性プロファイル
This material is chemically inert in the pure state and is considered to be physiologcally inert as well. However, as it is ordinarily obtainable, it can contain variable quantities of the lowsulfur fluorides. Some of these are toxic, very reactive chemically, and corrosive in nature. These materials can hydrolyze on contact with water to yield hydrogen fluoride, which is highly toxic and very corrosive. In high concentrations and when pure it may act as a simple asphyxiant. Incompatible with disilane. Vigorous reaction with disilane. May explode. When heated to decomposition emits highly toxic fumes of Fand SOx.
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職業ばく露
May contain highly toxic sulfur pentafluoride as an impurity. SF6 is used in various electric power applications as a gaseous dielectric or insulator. The most extensive use is in high-voltage transformers. SF6 is also used in waveguides, linear particle accelerators; Van de Graaff generators; chemically pumped continuous-wave lasers; transmission lines; and power distribution substations. Nonelectrical applications include use as a protective atmosphere for casting of magnesium alloys and use as a leak detector or in tracing moving air masses. Several sources note that vitreous substitution of SF6 in owl monkeys results in a greater ocular vascular permeability than that caused by saline. This implies that SF6 could have an important use in retinal surgery.
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特徴
フッ素と硫黄から構成される無機化合物には、異性体を含めて6種類知られています。常温常圧で十フッ化二硫黄のみが液体で、それ以外は気体です。
二フッ化二硫黄は一フッ化硫黄とも呼ばれます。二フッ化二硫黄には2種類の異性体が存在し、S=SF2とF−S−S−Fです。二フッ化硫黄の化学式はSF2ですが、生成が困難であり、気相中で観測されているのみです。
四フッ化硫黄は無色気体の化合物で、化学式はSF4と表されます。十フッ化二硫黄は化学式がS2F10の、揮発性の無色の液体です。十フッ化二硫黄は五フッ化硫黄とも呼ばれます。
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貯蔵
All ofthe precautions necessary for the handling
of any nonflammable gas must be taken.
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輸送方法
UN1080 Sulfur hexafluoride, 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.
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不和合性
May contain impurities that cause it to hydrolyze on contact with water, forming corrosive and toxic hydrogen fluoride. Vigorous reaction with disilane.
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廃棄物の処理
Return refillable compressed gas cylinders to supplier. Seal unused cylinders and return to suppliers.
