Storing sodium

I have seen very very old alkalis in various storage mediums thanks to a new contact of mine.

When I got my sodium, it had been in a lab occasionally used for 11 years maximum. It was under parafin oil (not wax), a liquid less viscous than mineral oil. I transfered it to a jar of mineral oil a while ago, the oxidation layer does not seem much thicker if at all, but only time can tell.

I also attempted to get some lithium, but the bottle was ancient and over time the parafin oil had evaporated(cap was leaky) leaving the top 4 cm of the lithium sticks exposed. An entire 100g bottle of lithium rods was mostly lithium hydroxide with perhaps 5g of lithium metal left.
(sorry ChrisTG, I tried)

I have seen sodium stored under benzene, big brick sized lumps of sodium with an oxide layer which looks really thick. Oxygen must dissolve in benzene apreciably.

I attempted obtaining potassium as well, however the can available was really, really old, most of the K must have reacted making KOH which was eating away at the can. It looked like it had tumors. Due to potential superoxide formation I left this can alone.

I would say that tightly sealed containers of alkalis under mineral oil are the best, any oxygen in the container will react with the sodium making the oxide layer, with a tightly sealed container hopefully no more oxygen can get into react. Just keep the container closed and minimize how much you play with the contents.

I would only go with vaccuum ampoules if you want to keep it shiny. Interestingly enough, my lab job has taught me how to make vaccuum ampoules by use of 2 sizes of glass tube, oxy hydrogen torch and a vaccuum pump. Learning to work with glass takes a lot of patience (and burns)

[Edited on 15-5-2006 by rogue chemist]

Just keep it under kerosene or mineral oil in a tightly sealed bottle, just as everyone else has recommended. I've seen pounds of it stored in the stock room that's over 40 years old, and it's still in good condition. So don't worry about it oxidizing to dust. A couple months ago, I opened a 22 year old 100g can of it (rusted completely) to find a white brick After inspection with a large, flat-bladed spatula, I realized that the oxide was only 1/4" thick, underneath that was the whitish/gold sodium. Despite how soft it was, it was still a pain to cut. Once you warm some up in your gloved hand, it's kind of like cold butter.

1)get 2 small diameter glass tubes, these will be the neck of the ampoule, choose size accordingly. Also get a larger diameter glass tube for the main ampoule body
2) Using a graphite rod for manipulation and a very hot torch(I use oxy-hydrogen) and wearing special goggles, glass gets white hot, play the hot ends of the small diameter glass tubes into flared ends. Symetry good here.
3) Insert flared small glas tube into larger diameter glass tube. Heat large glass tube on edge and using the graphite rod while rotating the tube assembly push the heated outer glass onto the inner flare.
4) While rotating the tube with the flame on the joint gently pull the tubes in oposite directions. Play the glass with graphite rod if you gotta fill little holes. 3 hands would be nice here, I usually rotate with my left hand, steady other side and pull with right pinky while holding the graphite with the first 3 fingers of my right hand.
5) Repeat for other small flared tube and oposite side of large tube.
6) once satisfied that you have no holes(vaccuum pump makes funny sounds later if they arent sealed) heat the centre of the tube while rotating. Draw out glass when soft. Use graphite to get nice ends on ampoule bottoms.
7) Ampoules get filled, attached to the vaccuum line, evacuated for 30 min, and under vaccuum the neck of the ampoule is heated while rotating(otherwise vaccuum sucks glass in and can pop the tube there) and carefully drawn out/sealed.

Wear gloves when beginning! Worst part is flaring the small tubes, heat goes through tube and out other end, right where your gloved hand is. With non-dry tubes steam comes out which gets painful.

And a paint diagram:

Update: I checked on the metal today. There was still no air present in the bottle and the sodium was still relatively shiny.

This storage method is definitely working but it has some drawbacks. To get small amounts of Na out, you must cast it as small globules before putting it in the bottle. This is long, tedious, and exposes a huge surface for oxidation. You can only really get the pieces in and out if you use a wide-mouthed bottle and large tweezers.

To close the bottle, you need to top off the oil, screw the lid on, and hope there’s no air bubble in the bottle. This always causes some oil to spill, making this process messy and a general pain. Don't even think about putting labels on these bottles because they will get oily fast.

I have a new idea, but I'm not sure if it's worth the extra effort.

First, start with a suitably sized syringe. Add some mineral oil and remove the air bubbles. Then, simply suck up your sodium into the syringe. When you’re done, plug the end.

This way, oxygen has only two ways to get to the sodium. The first is between the rubber septum and the plastic wall of the syringe. This is supposed to be a tight fit, so I doubt much diffusion will happen here. Just to be safe, you could fill the air space between the septum and the plastic wall (a ring of air, several mL) with vaseline. This would harden on cooling, impeding air molecules. (Wax wouldn’t work because it contracts too much on cooling. Plain mineral oil might also do the job.)

The second way in is through the exit point of the syringe. This is only a couple of mm² and can easily be plugged.

This would have its own ritual to extract the sodium, of course. First the whole mess would need to be melted with a steam bath or maybe a blow dryer. The tip would be plugged to keep air out and the piston would be allowed to move freely to accommodate the volume changes that occur from melting. Next, the desired amount of liquid metal could be squeezed out, the tip replugged, and the whole thing be allowed to cool down. This way oxidation is kept to an absolute minimum without an inert atmosphere.

The main problem here is the rubber in the septum. I don’t know what these are usually made of. Some rubbers (e.g. neoprene) contain chlorine, others sulfur, but I have no idea what kind they use in syringes. Does anyone know?

Storing alkali metals is a royal pain in the ass. With Cesium and Rubidium, at least you have but one option and that's sealing the metals inside a glass ampoule. (My Rb and Cs are still bright and shiney to this day. ). But for Li, Na, and K you just need to accept "some" loss due to oxidation.

Lithium, in particular, is the most difficult because of the fact that it not only reacts with oxygen, but with nitrogen as well at room temperature. Therefore, it will react with 90+ percent of the composition of the atmosphere. In addition, it is so incredibly not dense that it will float in typical mineral oil.

What I've done to store my alkali metals is a multi-step process. The first thing I did was purchase some jars with a screw-top cap that could be vacuum sealed if one wanted to. (I just don't have the apparatus needed to seal the jars). The jars were thoroughly cleaned and some Teflon Tape was wrapped around the threads of the jars to ensure a tight fit was made. I then went and heated the mineral oil that I had until no more gas bubbles were forming and escaping. The oil was quickly placed into a bottle and the top put on it to prevent any gases from seeping back in.

At this point in time I took the alkali metals I had and scraped off some oxidation to leave one side bright and shiney and the rest quite oxidized. (As a way to show the oxidation of the metals). The sodium was just a bunch of chunks because I bought two ounces of it and they came in tiny little lumps. Some of it was cut, but most of it was just put right in. The jars were filled half-way with my still warm mineral oil. Then the metals were placed in there and the jars topped off with mineral oil. The tops were screwed on VERY tightly, then more Teflon Tape was wrapped around the outside sealing the area where the cap met the jar. I then wrapped some electrical tape on top of the Teflon Tape to provide yet another seal.

All of this was done about 5 or 6 months ago and the bright surfaces are as bright as they've ever been. On the potassium, however, something odd has begun to happen. I had excised some possible peroxide contamination on a freshly cut surface leaving a few areas that were pure metal; no oxidation. There areas where pure metal was showing have taken on a metallic, blood red color. The sheen is VERY metallic, but the color is a deep, dark red. This does not appear to be any type of peroxide/superoxide on the surface as those are generally yellow in color. I think what's happening is that any peroxide/superoxide on the crust of the potassium has begun to decay due to the lack of oxygen in the surrounding oil. This oxygen is then slowly reacting with the exposed metal surface forming an anondized layer of potassium oxide on the fresh metal surface. As K2O is far more stable than K2O2 or KO2, this layer will remain stable for a long, long time. Looking at all parts of this potassium chunk, I see little red dots in the pits of the oxide crust. I truly think this is being caused by slow decomposition of the peroxides/superoxides on the metal surface. It's actually really neat to see. I'm tempted to open up the jar and cut off some more fresh metal surface then re-seal again, but it's a lot of work to seal it up like I have it now.

Okay, below is as big a macro as I can get right now. The battery on my camera is just about to die so it has a good deal of trouble trying to zoom in. Hopefully there will be enough detail. My apologies for the poor quality of the photo. It's currently 6:30 at night and the sun is at a level which pretty much ruins any photography attempt while increasing the temperature in my abode by a great deal. (My Ga sample is liquid right now, so it's pretty warm in here).

I can see some brownish discoloration on areas of the potassium, and that appears to be some minor peroxide/superoxide formation. However it's not enough to cause me any concern. In reality, the amount is slowly going away which seems to confirm my initial belief that the unstable oxides are decomposing and a very thin oxide layer is forming on the bare metal spots.

Is mineral oil the best cover oil for sodium? I don't have any but see it on the shelves at the pharmacies. I have some odorless BBQ starter fluid which I believe is essentially kerosene. This seems like it would be easier to blot off the sodium when you want to use it. Or does it make any difference?

I don't have any sodium but plan to make it soon.

@ordenblitz: I know that I found a 3" diameter by 2" inch 118g piece of sodium in the stockroom (making Na methoxide) that was at least 25 years old and had never been opened. Upon opening it (in a metal can, with a screwdriver) I found that it was completely covered in its oxide and probably its carbonate as well. The thick white layer was about 1 cm or 3/8" thick. So, for unprotected sodium that is decades old it seems it does not oxidize to a severe extent.

I think there is a threshold where it will not progress any further into the metal. Upon cutting the rod in half, I could clearly see how thick the layer was since the rose-colored sodium is in stark contrast with the snow-white oxide. If you want to clean yours up, you can melt the sodium under mineral oil in a metal can or steel pipe and skim off the oxide and then 'cast' the sodium into cold oil. It will quickly solidify into shiny irregular lumps.

Since you have pounds of sodium, would you be inclined to sell any or trade any? I know you're a fan of stockpiling reagents, but c'mon Anyway, I'll u2u.

I also have some sodium (no, not pounds, just a few tens of grams ), and now I store it under colorless and clear paraffin oil. I wonder, can I store it under ligroin or petroleum ether? The fact, that it is stored under oil keeps me off from experimenting with it. It is a real mess to get out some of the Na-metal. It would be much more convenient to store it under a volatile liquid. When a piece is cut off, simply dab it with some cotton and then let the liquid evaporate. Nice and clean.

What is the reason that nobody does this?

I figured I would make a few little sodium ampoules today. I melted sodium under parafin oil/mineral oil and sucked it up in a pipet which I then sealed with a torch. Some turned out nicer than others. Melting was simply done over an alcohol burner, and the shinier samples I think are a result of the temp of the molten Na.

As long as the bag is sealed shut perfectly (and we discount diffusion through the plastic ) with say melting, the sodium will remove all of the CO2 and O2 out of the atmosphere of the bag. I store cut pieces of sodium under mineral oil, but that's only because they have a higher surface area and I want to keep them clean. The larger logs I keep in a large bag that I've melted shut, then put in another bag and melted shut again. The sodium creates a partial vacuum in the first bag because it reacts to form NaOH, Na2CO3, and Na2O. The oxidized portion is a very thin crust (maybe less than a fraction of a milimeter).

Here is a picture of that sodium metal from the can mentioned up above for reference. This was rather dirty sodium, but at least you all can see how soft it is. I am cutting it up on aluminum foil, like an idiot, but it was a spur of the moment thing. I could actually hear the hydroxide hissing and popping as it reacted with the aluminum. This was for reaction with anhydrous methanol to produce Na methoxide. The scrap trimmings went into a stockpot and were disposed of Apologies for the large photo.





[Edited on 2-1-2007 by Fleaker]

I`ve got mine stored in a food jar (airtight) under pharmacutical grade white parafin, it`s been there for over 5 years and beyond a little surface tarnish, it`s still perfectly fine and viable.

The Davster, I really like what you`ve done there! I stofe most of my elements in such ampuoles (also home made), I just havent gotten around to doing the Na yet, thnx for the Idea/Method

OK weird...remember Jdurg's red potassium? Well my homemade sodium ampoules turned blue.. Only the shiniest sample did not turn blue.

(pics tomorrow or day after, camera borrowed)

Quote:

Originally posted by The_Davster OK weird...remember Jdurg's red potassium? Well my homemade sodium ampoules turned blue.. Only the shiniest sample did not turn blue. (pics tomorrow or day after, camera borrowed)

A similar thing I noticed with cerium, stored under mineral oil. First, the sample was shiny, like this (I scratched away some of the blue layer):



Lateron it turns blue again:



So, this effect seems to be quite common and there are multiple metals, which are affected by it.

[Edited on 14-1-07 by woelen]

Here is the pic, some of the blue washed out though. It is important to note that blue 'stuff' formed on the areas of sodium where upon making the ampoules there was only a very thin layer of oxide on the sodium. Areas where there was absolutly no oxide layer were unaffected, and an amopule where an end was broken off allowing oxygen slowly in, did not show a blue color as it oxidized. The 3 leftmost are lighter blue than the second from the right, some colour washed out in the picture. Far right is the one open to the air, and has no blue whatsoever.

So far, what seems to happen is that the blue stuff forms on a thin oxide layer between sodium metal and glass when no more oxygen is allowed to get to it. Leading me to think it is some sort of suboxide. It could be some sort of reaction with glass as well, but Jdurg's sample is not in contact with glass. Could also be some sort of solid solution of sodium in sodium oxide that reflects light differently.

I have had the opportunity to work with the first 4 lanthanides by the kilo (they made the summer student(me) hacksaw the pieces into smaller pieces), so I saw all of them in their various oxidized states. When lumps of each are only exposed to the air for a few hours, usually a deep blue oxide layer forms on La, Ce, and to a lesser extent, Pr and Nd, Pr and Nd are still rather shiny after such time. After a few days on small pieces of the metal, they are simply a white powder. Never expierenced this with the ingots,these were too precious to leave out.

I kept the filings from such work, and in a sealed vial they were storing nicely, untill the humidity in my basement changed and I was left with vials of oxide. The showed the same colour changes from shiny to blue to black to white, as the degree of oxidation increased.

Cerium.

Dark piece cut this last summer, grenish piece(brownish in the pic) old stock from the 80s, it was stored under some funky liquid with a strong smell. I removed it and put it with this piece in mineral oil.

EDIT: I know I have said it before but rare earth ingots + bandsaw...YEEHAW

[Edited on 14-1-2007 by The_Davster]

Blueish lanthanum, it is very air reactive compared to the other lanthanides, even under mineral oil(actually I think its ~50/50 mineral oil/hexane) some whitish oxide can be seen falling off.

Most have suggested that sodium can be cleaned with xylene or toluene... But can it also be stored in these solvents.... Is it not stored under toluene because of the risk of fire? I stored a small amount of sodium under toluene for about two weeks and the metal is really shiny... Beautiful to see!

I have a small cylinder of welders argon which I use to flush containers with mineral oil in for storage of potassium and sodium. Before use I boiled and cooled the mineral oil and left some small pieces of sodium in it to dry it completely. The freshly cut or melted metal is put in and the container flushed with argon. I have potassium that looks pretty clean after months of storage. The lump of lanthanum is about 1cm by 2cm and has been stored under argon. It looks bluer than in the picture.

Quote: Originally posted by nezza

I have a small cylinder of welders argon which I use to flush containers with mineral oil in for storage of potassium and sodium.