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Thread: Possible uses of a heavier-than-air gas: sulfur hexafluoride

  1. #1

    Possible uses of a heavier-than-air gas: sulfur hexafluoride

    Many people have seen or may even have played with helium and giggled at the high-pitched voice that this lighter-than-air gas produces. The prediction is that a heavier-than-air gas would produce a lower-pitch voice. Such a gas is sulphur hexafluoride and the following video not only illustrates this phenomenon but raises questions concerning the possibilities of such a gas

    The video shows a person taking in a lungful of this gas and then talking with it. It then shows a model boat floating on this gas and the sinking of the boat when beakers of the gas was poured into the boat.

    According to , sulfur hexafluoride is a gas under standard temperature and pressure conditions. It has an octahedral geometry of six fluorine atoms attached to a central sulfur atom. Under standard atmospheric conditions, it weighs approximately 6.3 grams/liter, about 5.11 times heavier than air. Readily prepared by exposing sulfur (S8) to fluorine (F2) and then heated to remove SF4, SF6 is odorless, colorless, non-toxic, non-flammable, and relatively non-soluble in water. It is remarkably non-reactive even to sodium and has a much higher dielectric strength than air at temperatures up to 400 degrees F. It is therefore often used as a gaseous insulator for electrical equipment. Its only drawback is the electrical arcing can produce S2F10 which is highly toxic and was used as a toxic gas during World War II. In very high RF fields, the molecule dissociated to form reactive fluoride ions that are very useful for etching tungsten and tungsten silicide films. Because of its non-reactivity and non-solubility in water, it is used by oceanographers to trace ocean currents and engineers to assess ventilator efficiency of heavier-than-air gases. Although it is a potent greenhouse gas (i.e. absorbs sunlight 22,000 more than CO2), it has a 365 lower atmospheric mixing ratio than CO2 and therefore contributes much less to global warming.

    The gas has several medical applications.
    • Because SF6 bubbles do not dissolve readily in water, they are are long-lasting and are used in eye operations to create a tamponade to hold detached retinas in place.
    • Microbubbles of SF6 are excellent for enhancing ultrasonic images of blood vessels in tissues (Source)... in fact, I became interested in this gas because I was looking for something non-toxic that we can use to enhance ultrasound images of the spinal cord in animals and in human surgery.
    • It may also useful as a heavier-than-air gas storage medium for drugs, organic molecules (such as RNA, DNA, proteins), and even tissue samples that tend to oxidize in air.
    • Finally, it can be readily detected in very low concentrations (1 ppm) and therefore may be useful for measuring blood flow as well.


  2. #2
    Interesting stuff. Based just on the elements, I would have guessed it was very toxic. I suppose that the reason for it being benign is that the molecule is so tightly bound.
    - Richard

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