Tungsten hexafluoride is a colorless gas with the chemical formula WF₆, consisting of one tungsten atom surrounded by six fluorine atoms in an octahedral arrangement. First synthesized in 1931 by Otto Ruff and Eduard Ascher through direct fluorination of tungsten metal, this highly toxic and corrosive compound is the heaviest known gas at standard conditions – nearly 13 times denser than air. Despite its extreme reactivity with moisture, forming hydrofluoric acid and tungsten oxides on contact, WF₆ has become indispensable in semiconductor manufacturing for depositing tungsten metal films that form the microscopic interconnects in computer chips. This remarkable compound’s ability to decompose into pure tungsten at relatively low temperatures enables the creation of nanoscale features in modern electronics, though its density, toxicity, and corrosiveness make it one of the most challenging industrial gases to handle safely.

Find a review of the 50 most important industrial gases here.

20 Fun Facts About Tungsten Hexafluoride

Beyond the basics above, what else should we know about Tungsten Hexafluoride? Check out the 20 fun facts below!

1. WF₆ is the densest gas known at 12.4 g/L – so heavy that sound travels through it at just 80 m/s versus 340 m/s in air.
2. The molecule condenses at 17.1°C (63°F), meaning it can be liquid at room temperature on cool days.
3. A balloon filled with WF₆ falls like a rock, accelerating downward 10 times faster than an air-filled balloon rises.
4. The compound etches glass instantly by reacting with silicon dioxide, requiring storage in nickel or Monel containers.
5. Semiconductor fabs use 5,000 tons of WF₆ annually to fill 10-nanometer vias with tungsten in advanced processors.
6. Each W-F bond is 1.833 Angstroms long with bond energy of 456 kJ/mol, among the strongest single bonds known.
7. The gas hydrolyzes violently with moisture, creating HF acid clouds that etch workers’ glasses before they notice exposure.
8. WF₆ costs $2,000 per kilogram due to the difficulty of handling a gas that attacks almost all materials.
9. The molecule completes 10⁸ rotations per second, unusually slow due to tungsten’s massive 184 atomic mass.
10. Tungsten deposition occurs at just 300°C from WF₆, compared to 3,422°C needed to melt tungsten metal directly.
11. The compound glows green in electric discharge, used for specialized tungsten vapor lamps in microscopy.
12. Emergency responders can’t use water on WF₆ leaks – the reaction produces more toxic HF than the original gas.
13. Voice effects in WF₆ would be extreme, dropping pitch far below SF₆, but the gas would kill before anyone heard it.
14. The octahedral structure is so perfect that all F-W-F angles are exactly 90° and all W-F distances identical.
15. NASA considered WF₆ as a high-density rocket propellant but abandoned it due to extreme corrosion of engine parts.
16. The gas absorbs infrared at 712 cm⁻¹ so strongly that leak detectors can sense 0.1 ppm from 50 meters away.
17. Workers nickname WF₆ “heavy death” because victims’ lungs fill with tungsten oxide particles, causing suffocation.
18. The compound forms explosive mixtures with organic vapors, decomposing to release fluorine radicals at 400°C.
19. Double containment is mandatory for WF₆ systems after a 1987 leak created a 20-meter hydrofluoric acid cloud.
20. Tungsten hexafluoride ice at -9°C has a density of 4.56 g/cm³, making it denser than many rocks.

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