Casting Sodium Metal

[wymanthescienceman]

Hi guys, I have a sort of problem for which I would like to find a remedy, and that is the casting of elemental sodium.

A while back I acquired a rather large quantity of sodium metal, about 6lb, and I've had a problem with storing it because it is formatted in two large 3" by 10-12" long ingots that are rather cumbersome to deal with. Currently they are in a large 5 gallon pail, and I would like to transfer them into a smaller container that is more air tight, as they have some oxidation that I would like to remove as well.

I thought about just cutting them up into smaller chunks, but the giant 3" diameter ingots are quite hard to cut through, even thought it IS sodium. I was hoping there might be a way to melt and recast the metal under mineral oil or even wax, but I am not sure on how I would go about doing this safely if it is possible.

I have searched this forum, Google, and SM, but came up short with answers. If anyone has any advice for me, such as a liquid to cast it under as well as casting molds, it would be greatly appreciated. If I find a way to do it I'll take pictures and post my procedure if anyone else is interested.

[Intrinsic]

I have seen videos from someone who held a 'sodium party', he too acquired several pounds of sodium. He used a very large straight knife, I'd guess it was 12+ inches, and did manage to cut it into several normal sized chunks for storage. He had to really use his body weight to get down through it, but it did cut.

The first couple of blocks the knife had some moisture (though he said he dried throughly); it only crackled a bit.

It was two or three years ago I came across it, but I will look around for it.

[hereno]

I have searched this forum, Google, and SM, but came up short with answers.

Did you look in in the prepublication section of SM? len1 demostrates it by melting sodium under paraffin, drawing it up and storing it in pipettes in easily managed amounts.

http://www.sciencemadness.org/talk/viewthread.php?tid=9797&page=1

[wymanthescienceman]

Ah, thank you for finding that for me. I could have sworn I had seen something like that being done before, but I couldn't for the life of me seem to locate it again. Everytime I searched I looked for casting or cast, and results showed up for cast iron among other things. This thread is rather helpful, I hope I can find a way to do it in some type of mold, to make them all regularly shaped as well.

Due to my sodium having a decent amount of (hydr)oxide formation, I am going to try it in really small amounts, to make sure the oxides dont happen to react with paraffin, though in that thread he doesn't seem to have a problem with it.

But I have one question left. In the thread he does not state if he is using paraffin oil or paraffin wax to melt the sodium under. I am assuming oil, and I don't think there would be much of a difference at the temperature I would be using, but I just wanted to hear what you all think.

[megalomania]

Likely the oil since that is what sodium is typically stored under. Just for reference in case anyone wants to know, the reason you do this under oil is to protect the sodium from air. Molten sodium is far more reactive, and so I am led to believe, could catch fire in the open air.

I remember reading an excerpt from a late 19th century or early 20th century chemistry book about casting sodium metal. I believe they pour, or forced, the metal through chamois bags to screen impurities, and then let it drip into cooled oil to solidify it into droplets. I have no idea what that book might be; perhaps it was one of the books from the "Making of America" website, which can be searched.

[FUTI]

Molten under paraffin oil I guess. I have done some reaction that way. You heat it around 200 degrees Celsius and it form small round droplets under vigorous stirring. I used magnetic stirrer with heating plate and it worked fine. You have to cut up that sodium to smaller pieces before that. Sodium is easy to cut, but do it under hexane for example. Crust of hydroxide and oxide on the surface of that bar/ingot of sodium is what make your job hard. Wherever sodium is - it will catch traces of water in it and around it. Byproduct is the white crust of (hydr)oxide on the surface that is ionic crystal thingy which crystal lattice is (wonder :-P) much harder then crystal lattice of sodium. My advice is...keep those ingots as is. Cut small pieces from ingot when it is needed to be used. Why? Crust forming is inevitable, but it will be promoted when you augment the surface of sodium by cutting it up. When the ingot is big after some time crust formed slow down that process so your sodium half-life will be higher.

[wymanthescienceman]

Thanks guys, you've been very helpful. I've tried melting the sodium on a small scale under oil, and it seems to work nicely, I just have to figure out a way to get more of the impurites out of it. The forcing through a chamois bag gives me an idea, but instead of chamois I thought about using a stainless steel screen because it doesn't seem to stick to stainless. The molten sodium has such a high surface tension it doesn't seem to want to stick to anything actually, it reminds me of mercury when it is molten.

I pretty much scrapped the idea of doing all of the sodium at the same time. I figured I would rather just purify a smaller lot of it (a few ounces) to use as needed, but keep the large ingots intact so they have a longer shelf life, as FUTI mentioned. So I'm basically going to cut the large ingots into a couple smaller pieces and store them in a 8L amber HDPE container ( It has a very good seal.) under kerosene, as it is the cheaper alternative to the oil since I can't seem to find a decent supply of mineral oil except in pint containers for about $4 each.

[javainmycoffee]

Are you keeping the big ingots submerged in oil too? I can't tell from your posts. It will increase it's shelf life dramatically if you do.

Also it won't spontaneously ignite. I had this happen to me (before I wised up a bit) because it can get fairly warm and humid where I live.