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what else can you float on SF6 other than foil boat and balloons? also how long will SF6 in a tank keep something afloat Answered

I am basically trying to figure out other things to float in a tank of SF6 ( or better, heavier gas?) Right now I have dandelion seeds, hair, insects in mind. Do you think these will float? 

also If i ended up using a foil boat, how long will SF6 keep this boat afloat? what if i seal up the fish tank really good, will the boat be afloat forever? Please let me know! thank you !



Jack A Lopez

7 years ago

Soap bubbles (that is soap bubbles filled with air) seem to work pretty well, as shown in this video:

The same video linked above also shows the aluminum foil boat trick, for anyone reading this who has not seen that one.

Regarding the question of keeping the floating indefinitely, I think the air, in the boat, and the SF6 beneath it, both of those gasses might be slowly diffusing into each other.  If they are, then eventually the boat, which is open at the top, will fill up with a gas just as dense as the gas beneath it, and then it will sink.

It would be different with a balloon, or a closed container, but then you still have to worry about gasses diffusing through the walls of the container. 

Can a hydrogen, or helium filled balloon stay floating in an air filled room forever?  This is almost the same problem.

haoishaoJack A Lopez

Answer 7 years ago

Jack A Lopez

diffusion is definitely something to consider, thank you very much

kelseymhJack A Lopez

Answer 7 years ago

Wow. That is an awesome video; thank you!

I would not have guessed that the foil boat would work -- I expected that the foil mass (higher than latex) would have been too much. Great to be proven wrong :-)

SF6 is a pretty large, heavy molecule, so I would expect that diffusion through a barrier (like a balloon or foil) would be extremely small. Helium is special -- the helium atom is the smallest of any stable material, and it can diffuse through inter-molecular spaces which no other material can.


Answer 7 years ago

Thank you so much kelseymh, this really gives me hope


7 years ago

1. You can float ANYTHING that displaces more Sf6 than the object masses.

2. In a sealed tank with little disturbance (put a lid on it) it should last forever - the gas has no where to go other than evaporate.

3. Look up Archimedes he discovered this principle.


Answer 7 years ago


Thank you so much for all the detailed information


7 years ago

How dense IS SF6 ? Its not exactly a common material to have on hand.



Answer 7 years ago

Can't imagine where a normal mortal would get enough to fill a tank.

Gas Properties
Molecular Weight

Molecular weight : 146.05 g/mol

Solid phase

Latent heat of fusion (1,013 bar, at triple point) : 39.75 kJ/kg

Liquid phase

Liquid density (at triple point) : 1880 kg/m3
Boiling point (Sublimation) : -63.9 °C
Latent heat of vaporization (1.013 bar at boiling point) : 162.2 kJ/kg
Vapour pressure (at 21 °C or 70 °F) : 21.5 bar

Critical point

Critical temperature : 45.5 °C
Critical pressure : 37.59 bar

Triple point

Triple point temperature : -49.4 °C
Triple point pressure : 2.26 bar

Gaseous phase

Gas density (1.013 bar and 15 °C (59 °F)) : 6.27 kg/m3
Compressibility Factor (Z) (1.013 bar and 15 °C (59 °F)) : 0.9884
Specific gravity (air = 1) (1.013 bar and 21 °C (70 °F)) : 5.114
Specific volume (1.013 bar and 21 °C (70 °F)) : 0.156 m3/kg
Heat capacity at constant pressure (Cp) (1.013 bar and 21 °C (70 °F)) : 0.097 kJ/(mol.K)
Viscosity (1.013 bar and 0 °C (32 °F)) : 0.000142 Poise
Thermal conductivity (1.013 bar and 0 °C (32 °F)) : 12.058 mW/(m.K)


Solubility in water (20 °C and 1 bar) : 0.007 vol/vol


Answer 7 years ago

Concorde Specialty Gases will sell you a standard tank full, plenty more than needed to fill an aquarium. So will AirGas, and you can probably get it from Air Liquide, Matheson, or any of the other gas supply houses.

It's colorless, odorless, fairly inert, and fairly non-toxic. Not a big deal for a do-it-yourself person, so long as they aren't stupid enough to open the tank in a closed shed.


7 years ago

Do you know how buoyancy works? Take the volume of your object, and its mass, and divide m/V. That is the density. If the density of your object is larger than the density of SF6, then your object will sink. Otherwise, your object will float.

The density of sulfur hexafluoride, 6.2 g/L, is only about six times that of air. It is not dense enough to behave like water. A small inflated balloon, such as a water balloon, should float in SF6, sort of the way a helium balloon floats in air.