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I melted about 2 kg of gallium and put it in a plastic container, in order to make crystals. After letting them grow and extracting them, I let the gallium freeze at the room temperature, which is below the melting point.

However, for some reason there is a small quantity of gallium (10-20 g) that is not freezing after days. I extracted the liquid then froze it in a refrigerator. But if I put it outside again, it melts, so this is not supercooled gallium, a well documented phenomenon.

It behaves like normal gallium with slightly lower melting point, something like a Galinstan eutectic. However this is 99.99% pure gallium (that was fully solid) and I am pretty sure that I never contaminated it...

Any idea what is happening?

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    $\begingroup$ One wonders how reliable that 99.99% purity claim is... Without specialised equipment, it's generally difficult to distinguish purities of any substance above ~95-98%. If the average consumer can't tell, the supplier has the perverse incentive to cut the cost. $\endgroup$
    – Nicolau Saker Neto
    Jul 20, 2019 at 0:28
  • $\begingroup$ A pdf at this link would seem to indicate that typical impurities are a mishmash of elements. documents.indium.com/qdynamo/download.php?docid=1107 $\endgroup$
    – MaxW
    Jul 20, 2019 at 2:39
  • $\begingroup$ It would really be neat to throw this inn an XRF and look for the differences. $\endgroup$
    – MaxW
    Jul 20, 2019 at 4:10

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It's possible that the gallium is not as pure as advertised. If it has (say) some indium as an impurity, the indium-gallium alloy would have a lower melting point, potentially below room temperature.

I thought that partial freezing might have crystallized out more pure gallium, and left less pure gallium as the melt, but I'm not sure that's how indium-gallium alloys work. I made a few grams of the alloy, and I never saw any such behavior in it -- then again, I never experimented much along those lines.

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  • $\begingroup$ Every reason to believe that liquid gallium has more impurities than the average over the bulk 2 kg mass. Even if the bulk is 99.99% pure, 20 g would only be 1% of the 2 kg mass. Assuming the 20 g mass has 50% of the total impurities would mean that the 20g has 1% impurities. $\endgroup$
    – MaxW
    Jul 20, 2019 at 2:29

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