Sulfur Hexafluoride

What Is Sulfur Hexafluoride?

Sulfur Hexafluoride is a contrast gaseous agent. It contains six atoms of fluorine bound to a single sulfur atom, hence the name Sulfur Hexafluoride. It is an inorganic fluorinated inert gas with potential imaging-based diagnostic activity. The gas on inhalation is spread all over the lungs. Upon subsequent imaging by ultrasound technology, lung vasculature can be imaged. Thus, pulmonary perfusion assessment becomes easy. In water and some other liquids, it is soluble. 

General Properties of Sulfur Hexafluoride

It is a colourless, odourless, tasteless, non-combustible gas. It is liquefied under its vapour pressure when sent to another location. Contact with the gas may lead to frostbite. While exposed to fire or heat for an extended period, there’s a possibility of rupturing the container with great sound. The estimated lifetime of SF6 is in the range of 800-3200 years.

  • Atomic Structure

(Image to be added soon)

This picture depicts the structure of sulfur hexafluoride. 

  • Density

The density of a gas is 6.5g/L, and that of liquid is 1.67

  • Stability

Sulfur Hexafluoride is stable under specified storage conditions, and its shelf-life is 2 years. After reconstitution, the physical and chemical stability of the compound is approximately 6 hours. For microbiological experiments, it is recommended to be used immediately.

  • Decomposition

The major products obtained on decomposition are Sulfuryl and Thionyl fluorides.

If you apply heat to it for decomposition, it produces highly toxic Hydrogen Fluoride and Sulfur oxides.

  • Other Experimental Properties

It is one of the heaviest gases with its density almost 5 times that of air. It is inert and does not attack the glass. The gas is stable kinetically, however, very much unstable thermodynamically. It remains unchanged at 500.

Upon cooling, the gas directly condenses to solid.

  • Chemically and Thermally Inert

This is an unreactive compound and is not attacked by acids, bases or water at room temperature. Also, it does not get agitated by copper, carbon or magnesium at red hot condition. It reacts with hydrogen or sulfur vapour at 400 degrees Celsius.

It decomposed into lower fluorides of Sulfur in the presence of electrical discharge. 

  • Potent Greenhouse gas

This is the most potent greenhouse gas known so far with global warming capacity 23900 times more than that of Carbon-Di-Oxide over 100 years. The mixing ratio of SF6 is lower than that of Carbon-Di-Oxide. In 1990, it was about 4 parts per trillion (ppt ) whereas the mixing ratio of CO2 is 365 ppm.

  • Ozone Depletion Potential

There is no proof yet that SF6 contributes to ozone depletion, but it is found that its atmospheric lifetime is 800 to 3200 years which may cause an impact on the environment.   

Uses of Sulfur Hexafluoride

Echocardiography: You can find its use in adult patients with echocardiograms. It can improve the border line of the left ventricular endocardium.

Ultrasonography of the Liver: Sulfur hexafluoride with ultrasound is widely useful to characterise focal liver lesions of both the adult and pediatric patients.

Ectogenesis: This is a medicinal product used for the diagnostic purpose to enhance the echogenicity of blood or fluids.

You can also use it in ophthalmology, pneumonectomy, middle ear diseases, loss of hearing and middle ear infections.

Major Application Areas:

SF6 is excellent for high voltage applications as it is a dielectric gas. It is inert by nature and remains in the gaseous state even at considerably low temperature. Moreover, it is non-corrosive, non-toxic and non-combustible. You can achieve several advantages when combined with thermal, electrical or chemical properties.

It is especially apt for high voltage and medium-high voltage circuit breakers, high voltage cables, transducers, transformers, electron accelerators, X-ray machines, Ultra high-frequency transmission systems. It allows for designing switchgear that comes with high and moderate voltage. The switchgear will be silent, and of convenient size and weight with reliable maintenance. Its dielectric strength is outstanding, and the dielectric constant remains the same from a few Hz to several GHz. Furthermore, effective heat transfer is possible due to low viscosity and high molar heat capacity.

Sulfur Hexafluoride is used in diverse applications of both non-electric and electronic. It is used in magnesium casting as a protective gas mixture to stop the creation of unwanted by-products. SF6 gas mixture is also used in aluminium casting as refining agents of foundry applications.

Incredible electrical, chemical and thermal properties have made SF6 a leading compound in the construction of new equipment with better performance and higher capacity. The transformation process from ordinary dielectrics to sulfur hexafluoride, a heavy, non-toxic, non-inflammable, non-reactive gas leads to significant space and weight savings. It also improves the operational safety of the equipment.

In the semiconductor sector, you can utilise it as etching gases. It is also useful as a cleaning gas for cleaning the gas chamber after etching is done.

Apart from these, you can also apply SF6 in leak detection, loudspeakers, lasers, tracer gas studies.

FAQ (Frequently Asked Questions)

1. Is Sulfur Hexafluoride Bad To Inhale? Is It Dangerous For The Atmosphere?

Sulfur Hexafluoride is inert by nature, and it is non-toxic. It is widely used as a cardiac imaging agent, combined with ultrasound. But if you are forced to inhale it exclusively like Carbon dioxide or Nitrogen, it will create suffocation.

It has a high potential for global warming. Its proportion of the earth's atmosphere is rising quickly. It decomposes under electrical stress during the working cycle and produces harmful bi-products which is a severe health threat to the people exposed under the working environment.   

2. Why Is SF6 Used In GIS?

This is used in Gas Insulated Substation, GIS from 400 to 600kPa absolute. This pressure range is deliberately chosen because Sulfur Hexafluoride does not condense even at the lowest temperature that the instruments experience in general. And its insulating capability is double or triple of air, the pressure remaining the same for both. For interrupting arcs, SF6 is about a hundred times better than air. This decomposes in high temperature of an electric arc and again recombines back into SF6 without replenishment.