Sulfur hexafluoride

Sulfur hexafluoride (SF₆) is an inorganic compound of sulfur and fluorine. It is a colourless, odourless, non-flammable gas, about five times denser than air, and chemically very unreactive. It is the standard insulating gas in high-voltage electrical equipment, and is one of the most potent greenhouse gases known.

Beckons produce sulfur hexafluoride biologically, in gas glands. Adapted Beckons store it in their trunks, where it holds the body up, insulates it, stores energy for the winter and is vented to put out fires. Primitive Beckons release it into the air. Emissions from Primitive Beckons led to the sulfur hexafluoride case of 2020–2021, through which the parasites became public record. The gas makes up about 46% of the atmosphere of the Iris.

Properties

Physical

Each molecule is a sulfur atom bonded to six fluorine atoms, arranged as an octahedron. At ordinary pressure the solid sublimes at −64 °C without melting. The gas weighs about 6.2 grams per litre, and in still air it flows downhill and collects in hollows and enclosed low spaces. It conducts heat about half as well as air, and sound travels through it at about 136 metres per second, so that breathing it lowers the pitch of the voice. Its large molecules pass through rubber and polymer membranes far more slowly than those of air.

Chemical

The sulfur atom is enclosed by its six fluorines and has no site open to attack, and the gas does not react with water, acids, alkalis or oxygen under ordinary conditions. It is thermodynamically unstable in the presence of water: its breakdown to sulfate and fluoride releases about 4.6 MJ per kilogram, but the reaction does not take place without a catalyst. It is a strong oxidiser for reactive metals such as lithium, magnesium and aluminium, which burn in it.

Above about 500 °C, and in electric arcs, sulfur hexafluoride breaks down into thionyl fluoride, sulfuryl fluoride, sulfur dioxide and, in the presence of water, hydrogen fluoride. Traces of disulfur decafluoride, which is highly toxic, also form.

Production

Industrial

Sulfur hexafluoride was first prepared in 1901 by Henri Moissan and Paul Lebeau, by burning sulfur in fluorine. It is still made by that reaction, from sulfur recovered at oil refineries, and is purified to remove the other sulfur fluorides formed alongside it.

Biological

Beckons make sulfur hexafluoride from sulfate and fluoride in the soil. An activating enzyme joins sulfate to ATP, and a single enzyme complex replaces its oxygen atoms with fluorine one at a time while holding the sulfur bound to itself, so that the water-reactive intermediates never meet water. Only the finished gas is released. Each molecule costs about 30 molecules of ATP. The gas glands also run the reaction in reverse, breaking the gas down and recovering its energy. Production on Earth is limited by the fluoride the soil gives up.

Uses

In industry

The gas's resistance to electrical breakdown makes it the standard insulating and arc-quenching gas in high-voltage switchgear and circuit breakers, which account for most of its use. It has also been used in insulated glazing, in magnesium foundries, as a tracer gas in atmospheric and ventilation studies, and for inflating tyres, where its slow leakage keeps the pressure longer than air.

In Beckons

Adapted Beckons fill the sealed cells of their trunks with the gas at 1.5 to 3 bar. The pressure braces the flexible spine and holds the body upright; the gas leaks through the cell walls slowly enough to keep the pressure for years, and insulates the body. A 30-metre Adapted Beckon holds about half a tonne of it. Through Overwinter the Beckon breaks part of it down for energy and heat. When fire reaches its base it vents gas from the lower cells, and the dense gas flows down and smothers the flames.

Detection

Sulfur hexafluoride can be measured in air at concentrations of a few parts per quadrillion. Before 2020 the atmospheric background, almost all of it from leaking electrical equipment, was about 10 parts per trillion. Since 2020 monitoring networks in the European Federation have tracked emissions from Beckons, and the gas is used to map Beckon sites from the air.

Discovery of the Beckons

In 2020 the Federation's judicial authority sued H&A over anomalous concentrations of the gas in several Federation territories, which it attributed to H&A's manufacturing. H&A set up its Hyperbiology Division to contest the suit, and the division showed that the gas came from Primitive Beckons, from the location of the plumes, their daily cycle, the isotopes of their sulfur, the absence of industrial impurities and the gas glands of dissected Beckons. The case was heard in open session, and Hyperbiology's evidence became the first scientific record of the parasites.^[1]

Environmental effects

Sulfur hexafluoride's global warming potential is about 23,500 times that of carbon dioxide over a century, and it remains in the atmosphere for about 3,200 years. A Beckon that is burned or dies releases most of its gas, and since the mid-2020s Beckons have been the largest source of the gas on Earth. The Federation regulates sulfur hexafluoride emissions from the clearance of Beckons under its environmental law.

Hazards

The gas is not toxic but displaces air. It collects in cellars, trenches and hollows near Beckon ground, where it can suffocate people without warning, and towns next to infested ground in the Federation require oxygen alarms in basements. Smoke from a burning Beckon contains hydrogen fluoride and other breakdown products, and crews burning Beckons wear acid-gas respirators.

The Iris

The atmosphere of the Iris is about 46% sulfur hexafluoride, 37% oxygen and 12% nitrogen, with the remainder made up of carbon dioxide and other gases. Its sky is black-red. The sulfur hexafluoride gives the planet a strong greenhouse effect.

See also

• Gas gland
• Sulfur hexafluoride case
• Beckon anatomy
• The Iris

References

1. ^ Woods, Ashley (8 February 2021). "Biogenic sulfur hexafluoride from Primitive Beckons at four sites in the southern Federation". H&A Hyperbiology Division. arXiv:2102.03317. (PDF)