How to Coalesce Potassium

Uploaded by NurdRage on 30.12.2011

Molten potassium is extremely dangerous.
Full fire safety protocols must be in place including protective clothing, goggles and face shields.
Burning potassium cannot be extinguished by conventional means
and water only serves to increase its danger.
This experiment should only be performed by an experienced chemist in a fume hood.
Greetings fellow nerds.
A question that comes up when making potassium
is how to coalesce separate spheres of potassium.
This can be a major issue if you have a low density solvent
and end up getting a lots of pebbles of potassium.
Melting together on air is really dangerous as it can catch fire,
and melting it together under mineral oil is notoriously difficult
since the surface tension of the potassium is too high.
But in this video I’ll show you a couple of tricks to coalescing potassium.
I have here a glass vial of many deformed pieces of potassium in fresh mineral oil.
This particular sample is a week old so it’s still safe to handle.
Place in the center of a stir plate.
Now open it up and add a few drops of the tertiary alcohol you used to make them.
Put the lid back on but don’t screw it tightly,
we need the hydrogen gas to escape.
Turn on the heating enough until the potassium melts and turn on the stirring to maximum.
Potassium is paramagnetic and conductive
so the rotating magnetic field of the stir plate
and the resulting eddy currents causes the potassium to rotate as well.
The alcohol helps to clean and reduce the surface tension of the potassium,
while the self-stirring brings them together and causes them to coalesce.
You may have to add a few more drops of alcohol as the run progresses
if you see oxides building up on the surface.
Eventually with time, the potassium will coalesce into large spheres.
If it stirs too fast the potassium might deform and fly apart again into small spheres.
Slow down the stirring in that case but remember that it still needs to stir fast enough
to break the surface tension between the spheres and merge together.
Once you have the size you like stop the stirring and let it cool.
Here I'm placing the sealed vial in cold water to help this along.
As the potassium cools it forms these beautiful striations across the surface
as it simultaneously crystallizes and contracts as it solidifies.
And that’s how you coalesce small potassium bits into larger spheres.
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