Gallium


Through the magic of ebay, I bought some gallium. It's strange stuff. Apparently whether it's listed as liquid or solid on periodic tables depends on where the table is printed; the melting point is 30°C, so it's solid at room temperature if the room's in Canada in March. But it'll melt in your hand, though it's a slow process.

Gallium is a crystalline solid; I suppose many metals are, but the crystals are really obvious when gallium solidifies. I thought I'd take a video of gallium crystallizing, but it has a tendency to supercool, so after sitting at room temperature for hours it was still liquid. I dropped a crystal of gallium in, though, and I got this beautiful slow crystal formation:
video
This video is shown at twelve frames per second, each frame is 60 seconds of real time. (It starts when it does because that's when I realized nothing was going to happen immediately; it ends when it does because that's when my camera overheated (!).)

Those vague angular patterns on the surface are actually crystals forming underneath. When I tipped the dish so the liquid flowed away I saw this:


Unfortunately, gallium is directly below aluminum on the periodic table, so, like aluminum, it reacts very rapidly with air, forming a sticky surface scum. When gallium is liquid, though, this scum can't stay in place to protect the surface; instead it sticks to everything around it. Rolling gallium through your fingers feels very peculiar — it's decidedly denser than water, though not tangibly more viscous, and it doesn't feel cool (its vapor pressure at room temperature is tiny). But because of the oxidation, it leaves a gray scum all over your hands. Pieces of gallium left in air also quickly start looking dull and dirty.

2 comments:

iBad said...

Hi! I love this post! One thing... is there anyway to get rid of the surface oxidized layer? I read that by heating mercury-oxide you can make it dissociate from oxygen.... so what if you heat the gallium... would the grundge disappear?

Anne M. Archibald said...

You can get rid of the grunge very easily, as it sticks to everything. Unfortunately like its cousin aluminum, gallium is so reactive new grunge forms immediately. I tried putting it under a carbon dioxide atmosphere but it didn't seem to help; either I didn't manage to adequately flush the system or gallium (like magnesium) is reactive enough to pull the oxygen out of carbon dioxide. A helium flush should work, though.

There was an error in this gadget