Sodium is quite reactive and it spontaneously reacts with both moisture
and oxygen in the air. Because of this the surface of the sodium can become
quite dirty.
This here is about a hundred grams of my very very dirty sodium metal.
Depending what you want the final form of sodium to be the technique to clean
it will vary a little bit. If you want small pieces of sodium
you're going to have to wash it several times with mineral oil, but if you want one piece,
in theory you probably only need to do one washing. I went ahead and did both
techniques to show you how they vary.
First, enough mineral oil is added to a dish that would be able to submerge all
of the sodium. With stirring the mineral oil was then heated up to about a
130 degrees Celsius which is much higher than the melting point of
sodium which is around 98 degrees Celsius.
Once the oil is hot enough the stir bar was removed and a small piece of sodium was
dipped inside.
Immediately you can see bits of oxidized sodium products falling to the bottom of
the crystallizing dish.
The sodium is dropped to the bottom and eventually it liquefies.
However even when the sodium is agitated and it's in its liquid form,
it's still covered with a bunch of the brown crap.
Here I simply put a large piece in standing up and wait for it to melt
because I thought it might be a little interesting.
Then just like the other one I break it up into pieces using a pair of pliers.
Then after got tired of playing with the sodium I added in the rest. To keep the
splashing of the hot oil to a minimum
I picked out a few of the large pieces and put them in individually.
After all the sodium was added it had what resembled to me some sort of
underwater aquatic environment.
Anyway this environment was quickly destroyed by stirring all the sodium
with a glass rod.
You'll notice that the more that the sodium is stirred the dirtier the
mineral oil gets but the sodium does not seem to clump together.
Instead the sodium seems to form small little nice clean beads.
If the small beads of sodium is what is desired that it's going to be necessary
to do several washing with the mineral oil.
After the oil was allowed to cool as much of the dirty oil as possible was
transferred to a beaker. The transfer was a little sloppier than ideal and a
little bit of sodium is lost.
Once the dirty mineral oil was removed the sodium is transferred to the beaker.
A little bit of clean mineral oil is added on top and stirred with the sodium.
This washing was then combined with the other dirty mineral oil.
The washing cycle is then repeated where fresh mineral oil is poured in and it's
heated up to about 130 to 140 C.
The sodium is then mixed thoroughly and you can see that the mineral oil again
turns a brown color.
As the sodium is mixed the mineral oil gets darker and darker and the sodium
get shinier and shinier and you can actually see some of the sodium starts to coalesce.
Although some of the sodium coalesces a lot of it still remains as the small beads.
The length of the washing is somewhat arbitrary and you'll have to just decide when it's done.
When it's done, just like the other one the mineral oil is allowed to cool down, the sodium
solidifies and the dirty upper layer is decanted.
Then, some new fresh mineral oil is added on top and it's mixed around a little.
Before proceeding on the largest pieces of sodium were picked out using a pair
of pliers and placed into some clean mineral oil.
You notice that there's a lot of brown garbage still at the bottom so again the
sodium is transferred into a new beaker.
At the bottom you can see the brown crap that remains and mixed in with a little
bit of sodium and this is going to be a loss.
Just like before again the sodium was mixed around with some fresh mineral oil
and heated up. The sodium is stirred for several minutes and you can see that it
all eventually became nice shiny beads.
However I did not want the small beaded form of sodium however nice it may be, so
I decided to proceed on and actually coalesce all of the sodium into one large chunk.
I'm doing this after several washes of the sodium but if your goal is to
coalesce the sodium into one large piece,
you do not have to work through all these washing steps.
The trick to coalescing all the sodium is to simply add a small amount of
isopropyl alcohol.
The boiling point of isopropyl alcohol is about 82 which is much less than the
melting point of sodium,
so no matter what you do the isopropyl alcohol is going to boil off.
You can see that pretty quickly after adding it a lot of the sodium actually
becomes dark and discolored.
More isopropyl alcohol is occasionally added and the sodium is stirred.
As stirring is continued you should notice that some of the sodium start to
become shiny again.
Eventually after a few minutes of stirring the majority of the sodium is shiny.
And soon enough larger sodium spheres start to appear.
Upon standing, some of the
spheres will spontaneously join with another and eventually ideally you'll be
left with one large solid piece of sodium.
After cooling the sodium was removed
from the beaker by stabbing a glass stir rod into it.
We are left with a large shiny piece of sodium metal.
The sodium is cleaned using a paper towel but you can see in this shot that
compared to the last it had quickly tarnished.
Using a knife the sodium was simply cut up into four large pieces.
This is all of the dirty mineral oil and garbage that remains after all the washing.
I decided to combine the spheres of sodium that I isolated earlier with the four
large chunks that I made in the last step.
This step also acts as one final washing step to further purify the sodium.
These steps are exactly the same as the ones we just did,
so first all of the sodium is added to some hot mineral oil.
Then some isopropyl alcohol is added and the sodium is mixed.
Just like before all of the sodium coalesces.
Then after cooling were left with one solid piece of shiny sodium.
This time the sodium was removed from the beaker by simply stabbing it with a knife.
Again the sodium tarnish is extremely quickly in air so it's no longer
nice and shiny like it was just a second ago. And then just like before I cut the
large piece of sodium into four equal sized pieces.
The four pieces are then placed into mineral oil. The glass jar that it's
stored in, is capable of an airtight seal. The jars then topped off with mineral
oil and it's clamped shot. You notice bubbles coming off of the sodium and
this is because sodium is reacting with some of the moisture in the mineral oil.
This is fine but the pressure that's produced by these bubbles is going to
need to be vented off every so often for the first few weeks of storage.
If you don't want this to happen you can simply pre dry mineral oil using sodium
before adding your fresh sodium into it.