Material not wetted by gallium

[Thomas Womack]

All the references say that gallium has about the melting point of
chocolate; and, indeed, I've picked up a small sample from ebay which
melts nicely.

They don't all point out that it sticks to pretty much everything; the
plastic vial with the sample in is mirror-coated on the interior, and
Web references state liquid gallium wets glass and porcelain (meaning
you can make mirrors with it).

Can you think of anything plausibly-available that gallium wouldn't
wet? I'm guessing teflon might work (to be obtained as smallest
available non-stick- coated bit of cookware not made of aluminium,
since liquid Ga dissolves aluminium nicely); is there a standard answer
to this?

Tom

[Uncle Al]

Post by Thomas Womack
All the references say that gallium has about the melting point of
chocolate; and, indeed, I've picked up a small sample from ebay which
melts nicely.
They don't all point out that it sticks to pretty much everything; the
plastic vial with the sample in is mirror-coated on the interior, and
Web references state liquid gallium wets glass and porcelain (meaning
you can make mirrors with it).
Can you think of anything plausibly-available that gallium wouldn't
wet? I'm guessing teflon might work (to be obtained as smallest
available non-stick- coated bit of cookware not made of aluminium,
since liquid Ga dissolves aluminium nicely); is there a standard answer
to this?

Try silanizing the glass with Rain-X.

[muha]

Yes, you have just discovered the Great Gallium Nuisance :) (another
nuisance is that gallium eats through some metals like aluminum quite
nicely).

When they manufacture the high-temperature thermometers with the liquid
Ga/In/Sn alloy, they have to coat the glass surface with gallium oxide
first. Ga2O3 is one of very few materials that does not get coated with
Ga.

[Aubrey McIntosh, Ph.D.]

Post by muha
Yes, you have just discovered the Great Gallium Nuisance :) (another
nuisance is that gallium eats through some metals like aluminum quite
nicely).
When they manufacture the high-temperature thermometers with the liquid
Ga/In/Sn alloy, they have to coat the glass surface with gallium oxide
first. Ga2O3 is one of very few materials that does not get coated with
Ga.

I had some Ga + In eutectic once. It would "eat" pieces of aluminum
cans and leave a black powder that had about the same ability to "dirty"
the bench that graphite powder would.

I had the idea that it dissolved the Al, much the same way that Hg would
dissolve Au or Ag. Then the Al would oxidize at the air / solution
interface. If that was true, the black powder would be very, very fine
aluminum oxide.

I didn't pursue this much, but I am curious if my idea was in the
ballpark. Does anyone else know more?

[Thomas Womack]

Post by Aubrey McIntosh, Ph.D.

Post by muha
Yes, you have just discovered the Great Gallium Nuisance :) (another
nuisance is that gallium eats through some metals like aluminum quite
nicely).
When they manufacture the high-temperature thermometers with the liquid
Ga/In/Sn alloy, they have to coat the glass surface with gallium oxide
first. Ga2O3 is one of very few materials that does not get coated with
Ga.

I had some Ga + In eutectic once. It would "eat" pieces of aluminum
cans and leave a black powder that had about the same ability to "dirty"
the bench that graphite powder would.
I had the idea that it dissolved the Al, much the same way that Hg would
dissolve Au or Ag. Then the Al would oxidize at the air / solution
interface. If that was true, the black powder would be very, very fine
aluminum oxide.

I'm not completely sure about oxidisation at the interface. Gallium
definitely dissolves aluminum in that way, but I believe the result
isn't very reactive with air (though the aluminium reacts
enthusiastically, leaving impure gallium) if you add water.

I'd not be amazed if the black powder were some element alloyed with
the cans; I don't know if Al cans are pure Al or not.

Tom

[Uncle Al]

Post by Aubrey McIntosh, Ph.D.

Post by muha
Yes, you have just discovered the Great Gallium Nuisance :) (another
nuisance is that gallium eats through some metals like aluminum quite
nicely).
When they manufacture the high-temperature thermometers with the liquid
Ga/In/Sn alloy, they have to coat the glass surface with gallium oxide
first. Ga2O3 is one of very few materials that does not get coated with
Ga.

I had some Ga + In eutectic once. It would "eat" pieces of aluminum
cans and leave a black powder that had about the same ability to "dirty"
the bench that graphite powder would.
I had the idea that it dissolved the Al, much the same way that Hg would
dissolve Au or Ag. Then the Al would oxidize at the air / solution
interface. If that was true, the black powder would be very, very fine
aluminum oxide.
I didn't pursue this much, but I am curious if my idea was in the
ballpark. Does anyone else know more?

Aluminum is alloyed with Fe, Mn, Si and other stuff for hardening.
The black crud was the micro-dispersed interstitial aluminides.

[r***@gmail.com]

Find the surface tension of liquid gallium. Any surface with
significantly lower solid surface tension will not be wet by gallium.
Polypropylene is wet, it has about ~30 dyn/cm. Lower still is an
alkylsilanated oriented film (~20 dyn/cm), like Rain-X as suggested
already. PTFE is about 18 dyn/cm. Polyvinylidene fluorides are about
19-20 dyn/cm. Best equilibrium surface known to my knowledge is an
oriented close-packed perfluoroalkylsilanated film, at about 8 dyn/cm.
Surface tension can be artificially lowered from its thermodynamic
prediction by introducing hysteresis in the form of surface roughness
on the nanoscale.

[Thomas Womack]

Post by r***@gmail.com
Find the surface tension of liquid gallium. Any surface with
significantly lower solid surface tension will not be wet by gallium.

The surface tension of liquid gallium is absolutely enormous;
V Kolevzon, G Gerbeth - Journal of Physics D, Applied Physics, 1996
and the CRC handbook suggest that it's something on the order of 700
dyn/cm, even more than mercury.

By that argument the liquid gallium should be sitting in a lovely
shiny sphere, scarcely touching the underlying material and definitely
not sticking to it, almost regardless of the material.

Tom

[r***@gmail.com]

Post by Thomas Womack
The surface tension of liquid gallium is absolutely enormous;
V Kolevzon, G Gerbeth - Journal of Physics D, Applied Physics, 1996
and the CRC handbook suggest that it's something on the order of 700
dyn/cm, even more than mercury.
By that argument the liquid gallium should be sitting in a lovely
shiny sphere, scarcely touching the underlying material and definitely
not sticking to it, almost regardless of the material.

The laws of physics should still hold here - pure mercury acts
appropriately for its surface tension. Virtually the only thing that
keeps it from having a 180 degree angle with a surface is its huge
density, so you have the classic balance between between surface
tension force and gravitational force. My first thought is that there
is some kind of surface contamination going on. In the paper you
cited, even this careful study came up with an "anomalously" low
surface tension for gallium, in the range of 700 instead of 900 dyn/cm,
which they attributed to a surface metal oxide or organic film.
Surface tension is an incredibly local event and can be completely
altered by the presence of a monolayer of a different material.

http://www.ubka.uni-karlsruhe.de/cgi-bin/psview?document=2002/chemie/8&search=%2f2002%2fchemie%2f8&format=1&page=40

This website actually talks about the difficulty of getting _pure_
gallium to WET a surface! They have to go so far as to glow discharge
a molybdenum (high energy) surface just to get pure gallium to wet it.
So I think I've convinced myself anyway that it's surface contamination
that causes the anomalous wetting. Gallium is so high energy that it
collects everything around it and forms a film on its surface that
causes it to wet. So again, going to an oriented -CH3 terminated film
or -(CF2)nCF3 film should work! (lower surface tension than the
probable organic contaminants)

[Blake Brigance]

Post by r***@gmail.com

Post by Thomas Womack
The surface tension of liquid gallium is absolutely enormous;
V Kolevzon, G Gerbeth - Journal of Physics D, Applied Physics, 1996
and the CRC handbook suggest that it's something on the order of 700
dyn/cm, even more than mercury.
By that argument the liquid gallium should be sitting in a lovely
shiny sphere, scarcely touching the underlying material and definitely
not sticking to it, almost regardless of the material.

The laws of physics should still hold here - pure mercury acts
appropriately for its surface tension. Virtually the only thing that
keeps it from having a 180 degree angle with a surface is its huge
density, so you have the classic balance between between surface
tension force and gravitational force. My first thought is that there
is some kind of surface contamination going on. In the paper you
cited, even this careful study came up with an "anomalously" low
surface tension for gallium, in the range of 700 instead of 900 dyn/cm,
which they attributed to a surface metal oxide or organic film.
Surface tension is an incredibly local event and can be completely
altered by the presence of a monolayer of a different material.
http://www.ubka.uni-karlsruhe.de/cgi-bin/psview?document=2002/chemie/8&search=%2f2002%2fchemie%2f8&format=1&page=40
This website actually talks about the difficulty of getting _pure_
gallium to WET a surface! They have to go so far as to glow discharge
a molybdenum (high energy) surface just to get pure gallium to wet it.
So I think I've convinced myself anyway that it's surface contamination
that causes the anomalous wetting. Gallium is so high energy that it
collects everything around it and forms a film on its surface that
causes it to wet. So again, going to an oriented -CH3 terminated film
or -(CF2)nCF3 film should work! (lower surface tension than the
probable organic contaminants)

what

[Blake Brigance]

Post by r***@gmail.com

Post by Thomas Womack
The surface tension of liquid gallium is absolutely enormous;
V Kolevzon, G Gerbeth - Journal of Physics D, Applied Physics, 1996
and the CRC handbook suggest that it's something on the order of 700
dyn/cm, even more than mercury.
By that argument the liquid gallium should be sitting in a lovely
shiny sphere, scarcely touching the underlying material and definitely
not sticking to it, almost regardless of the material.

The laws of physics should still hold here - pure mercury acts
appropriately for its surface tension. Virtually the only thing that
keeps it from having a 180 degree angle with a surface is its huge
density, so you have the classic balance between between surface
tension force and gravitational force. My first thought is that there
is some kind of surface contamination going on. In the paper you
cited, even this careful study came up with an "anomalously" low
surface tension for gallium, in the range of 700 instead of 900 dyn/cm,
which they attributed to a surface metal oxide or organic film.
Surface tension is an incredibly local event and can be completely
altered by the presence of a monolayer of a different material.
http://www.ubka.uni-karlsruhe.de/cgi-bin/psview?document=2002/chemie/8&search=%2f2002%2fchemie%2f8&format=1&page=40
This website actually talks about the difficulty of getting _pure_
gallium to WET a surface! They have to go so far as to glow discharge
a molybdenum (high energy) surface just to get pure gallium to wet it.
So I think I've convinced myself anyway that it's surface contamination
that causes the anomalous wetting. Gallium is so high energy that it
collects everything around it and forms a film on its surface that
causes it to wet. So again, going to an oriented -CH3 terminated film
or -(CF2)nCF3 film should work! (lower surface tension than the
probable organic contaminants)

what

say I put Teflon spray on a paper plate would liquid gallium stick to it

[Dean]

Post by Blake Brigance

Post by r***@gmail.com

Post by Thomas Womack
The surface tension of liquid gallium is absolutely enormous;
V Kolevzon, G Gerbeth - Journal of Physics D, Applied Physics, 1996
and the CRC handbook suggest that it's something on the order of 700
dyn/cm, even more than mercury.
By that argument the liquid gallium should be sitting in a lovely
shiny sphere, scarcely touching the underlying material and definitely
not sticking to it, almost regardless of the material.

The laws of physics should still hold here - pure mercury acts
appropriately for its surface tension. Virtually the only thing that
keeps it from having a 180 degree angle with a surface is its huge
density, so you have the classic balance between between surface
tension force and gravitational force. My first thought is that there
is some kind of surface contamination going on. In the paper you
cited, even this careful study came up with an "anomalously" low
surface tension for gallium, in the range of 700 instead of 900 dyn/cm,
which they attributed to a surface metal oxide or organic film.
Surface tension is an incredibly local event and can be completely
altered by the presence of a monolayer of a different material.
http://www.ubka.uni-karlsruhe.de/cgi-bin/psview?document=2002/chemie/8&search=%2f2002%2fchemie%2f8&format=1&page=40
This website actually talks about the difficulty of getting _pure_
gallium to WET a surface! They have to go so far as to glow discharge
a molybdenum (high energy) surface just to get pure gallium to wet it.
So I think I've convinced myself anyway that it's surface contamination
that causes the anomalous wetting. Gallium is so high energy that it
collects everything around it and forms a film on its surface that
causes it to wet. So again, going to an oriented -CH3 terminated film
or -(CF2)nCF3 film should work! (lower surface tension than the
probable organic contaminants)

what

say I put Teflon spray on a paper plate would liquid gallium stick to it

After 15 years, I doubt it matters now ;)

[Ethan Humphrey]

What about Galinstan? Would a teflon coated steel muffin tin work to make it with a small propane torch?

[Peter Fairbrother]

Post by Ethan Humphrey
What about Galinstan? Would a teflon coated steel muffin tin work to make it with a small propane torch?

I wouldn't use teflon with a torch; when teflon gets hot (above ~260 C)
it gives off really nasty gasses. As tin melts at 232 C you will almost
certainly exceed the maximum temperature tolerance of teflon when making
galinstan, especially with a torch.

Also, tin fumes will make you ill. Probably indium fumes too. I'd want
better temperature control than a gas torch can provide, but ymmv.
Probably won't kill you though, unlike overheated teflon which might.


Never made galinstan, but I use an electric solder pot for making and
melting similar gallium-containing solders, it's very heavily anodised
aluminium. Probably shouldn't do that, as gallium and aluminium don't
mix (or rather they do mix, far too well).

Been in use for a couple of years now, but I don't recommend it. Been
meaning to get an inert liner for it since I got it, just never got
around to it.


You could use a silica or alumina crucible. Not very expensive,
especially considering indium and gallium are expensive anyway. I'd
avoid graphite.

Glass or pottery is probably ok for short-term use only.

But please, not teflon.


Peter Fairbrother