Titi - 26-2-2024 at 14:31
Hi everyone,
I am quite fascinated by this element, gallium, especially in respect to mercury. Both are liquid metal (at least above 30C, which is reasonnable),
and so I guess that many properties of mercury also appear in gallium.
Gallium is more reactive than mercury. However, how much more? Does it oxidise readily in air? Reduces water to hydrogen? I wonder for example if it
is possible to remove oxygen from air by bubling it through gallium (maybe ligthly heated). This would be a nice way to make a nitrogen generator.
Conversely, I saw a video reducing gallium in aqueous solution by electrochemestry, so reusing it should be possible. And probably simpler that the
"red hot copper" method I read about.
Mercury is also used in chloralkali cells. I wonder if it is also possible to use gallium instead? Does gallium amalgamates with alkali metals, and is
it possible to use it as a liquid cathode? An interesting point is that gallium has a very high boiling point, so almost no vapours. Would it be then
possible to distillate the amalgam, for potassium for example, which has a low boiling point?
For a more practical point, there is also that gallium expends when freezing. I don't know if it is really bordersome, like breaking glassware easily
(even using round bottom flasks).
clearly_not_atara - 26-2-2024 at 18:35
The key role of mercury in the chloralkali process is to dissolve sodium. But the interaction of sodium with gallium produces the solid intermetallic
Ga4Na and sodium does not dissolve appreciably in liquid gallium below 300 C. This essentially kills any attempt to use gallium in the Castner-Kellner
process. On the other hand, sodium dissolves in liquid mercury up to about 5% at ambient temperature before forming intermetallics. The solubility of
potassium in gallium is similarly low.
However, magnesium does dissolve in gallium to an appreciable extent below the boiling point of water. Unfortunately, this is rather useless for a
chloralkali cell, because magnesium hydroxide is insoluble and will precipitate, and anyway it is not much of an alkali. I was not able to find data
on the alloy chemistry of gallium and calcium.
Gallium does not readily react with air or neutral water, since it has an SEP above -0.82 V (= reduction of H2O to OH- + H2) for formation of the Ga3+
ion, but it can dissolve in alkali due to the formation of Ga(OH)4-.
Gallium does not readily react with oxygen, but will react at high temperatures. But this is probably inconvenient.
Gallium salts are Lewis acid catalysts in the Friedel-Crafts reaction and similar reactions. They are rarely used because the metal is expensive.
knowledgevschaos - 26-2-2024 at 21:24
Working with potassium vapor seems almost suicidal, although maybe it could be done commercially. Gallium forms alloys with many metals, a lot which
are inferior to the pure metals. Gallium's alloy with aluminium is very reactive because the gallium prevents the protective oxide layer from forming.
This causes it to oxidize in air and react with water to produce hydrogen. Maybe it could be used in this way to produce hydrogen, and regenerated
with the electrochemistry you mentioned to be reused.
What is the red hot copper method?
Titi - 27-2-2024 at 09:22
This red copper method I saw it from this thread
http://www.sciencemadness.org/talk/viewthread.php?tid=726
But your idea with aluminium is interesting. Looking at the phase diagram
https://bioage.typepad.com/.shared/image.html?/photos/uncate...
It seems it would need to be less than 5% aluminium to stay liquid at reasonnable temperatures (let say less than 200C). There is an eutectic at 0.8%,
which is really too few aluminium. At 5%, it means that for say 100 ml of gallium, you can dissolve 12 g of Al, which would react with around 10g of
oxygen, so around 35L of air, making 28L of nitrogen. So not too bad! I guess that water vapour would react too, making the gas quite dry too.
I don't know if gallium itself would react? If not, it could be even better for reuse. Does the aluminium oxide disolve in gallium or precipitate?
Because then we could just add aluminium power, the gallium would just be a catalyst for the aluminium oxygen reaction (funnily, the aluminium used to
be expensive, so I guess that oxidizing copper was a much cheaper method than using aluminium).
About distilling potassium, I thought this impossible, and then I saw this video
https://www.youtube.com/watch?v=Y7YdT-vavHQ
Just looking at the video, I don't know how this guy is still alive. There is like 100g of boiling potassium less than 50 cm of his face, casually
heated by a blowtorch...
About the chloralkali process, I found this
https://datapdf.com/the-activity-of-sodium-and-potassium-dis...
So it seems that indeed this is very bad. In fact even much worse for potassium than sodium. But anyway, with at most 10^(-5) for the sodium
concentration, this is not usable.
I wonder if there are other liquid metals which could be useful as liquid cathode?
EF2000 - 27-2-2024 at 11:39
I guess that as a gallium fan, you'll find that thread about galinstan/Al interesting: https://www.sciencemadness.org/whisper/viewthread.php?tid=70...
knowledgevschaos - 27-2-2024 at 18:49
That's a great thread!
They only used a 5% alloy of galinstan in aluminium, so I'd guess by using a much larger percentage of galinstan would give you a liquid alloy at a
lower temperature.
I'd expect aluminium oxide will not dissolve in gallium.
To remove oxygen you might not need a liquid alloy at all.