Be VERY careful with old potassium.

[jdurg]

Hello. Just a small warning from your friendly neighborhood element collector. Over the Thanksgiving weekend I decided to get rid of some old potassium that I had. I have one big chunk in a tightly sealed container filled with mineral oil, and I also had a smaller chunk in a not-so-tightly-sealed container. I decided to have some fun with my smaller chunk of potassium by throwing it in a snow pile in my backyard. (Some old leftover snow from about a week ago). I was outside cutting the chunk into two smaller pieces to avoid a big explosion, and as I was cutting the chunk I noticed that the piece had an "off-color" to it. As I was cutting, I realized that the off color was due to some peroxide/superoxide on the surface. As I was cutting the piece, it must have catalyzed the decomposition of said peroxide/superoxide. The small chunk immediately became VERY warm and began to ignite! I hurredly finished the cut and threw the chunk into the snow. The purple "KABOOM" was quite neat, but the fact that it ignited kind of frightend me. The peroxide/superoxide decomposed quite quickly and ignited the trace of mineral oil which was on the surface. Thankfully it was a small piece that was going to be "used" anyway, but it was pretty scary. If I didn't throw it as soon as it started to burn, I would have had a nasty accident. So if you have some old potassium, PLEASE be very careful with it. The bigger piece I have in oil will not be used like my spare piece was, but I'm fairly certain that if I tried to cut it the piece would ignite as well. (It's a sizeable chunk which has a very slight yellowish tinge to it due to the peroxides/superoxides on the surface. The oil itself, thankfully, is free of oxygen since the container is VERY tightly sealed. (I know this because the freshly cut side is still very metallic and shiny even though the piece was cut about two months ago. There's a slight purple tinge growing along the edge, but that is likely due to the peroxides/superoxides slowly decomposing into oxygen which the fresh surface is picking up and safely turning into a simple oxide). So no problems were encountered, but it was a bit frightening to feel and see the piece begin to burn just from cutting it.

[YT2095]

LOL, I have the same occurance here with my Sodium metal, also kept in mineral oil (about 100 grams and 5 years old) thats why you always cut it UNDER the oil

 

the Oxide and subsequent evolution of Hydrogen on contacy with water liberate Both gasses and plenty enough heat to ignite it (hydrogen and air can be bad enough).

 

it`s electro possitive enough to break down the oil molecules over time too, I actualy wondered if the dull white with a hint of yellow waxy outside coating was a soap? made from saponification of the oil? I`m still not sure what it is either.

 

sodium metal will strip the OH from Ethanol and replace it, I`m wondering what it does to oil molecules over time?

 

 

but YES, ALWAYS cut the peices off that you need under the oil, and then take that peice out, Never cut it open in fresh MOIST air!

[jdurg]

Actually, with old potassium cutting it under oil can be even more dangerous. This is because the peroxide/superoxide can generate enough heat to ignite the oil. The best bet with old potassium is to let it dry and cut it under an argon atmosphere. There's still a chance that it can ignite, but the 'incident' will be very subdued by the argon.

 

I have the SAME situation happening with some of my sodium! I bought far too much of it, so some of it had to be stored in a separate container. I bought some cheap mineral oil off of e-bay, and a short while later the oil had congealed into a yellow mass on the bottom of the jar and on the surface of the sodium. The sodium has turned a beautiful, shiny metallic color with no oxidation on the metal itself. If I take a piece out and rub the oil off of it, the metal immediately turns a blood-red color. The oil also has an amine-like fish-odor coming off of it. So I do think that the oxide on the sodium has saponified the oil. I'm just happy to see that it has happened with someone else as well. (The sodium in my other jar with higher grade oil has the standard gray oxide coating on it. That's the sodium I photographed for my element collection photo).

[YT2095]

cutting it under oil is standard practice, I fail to see how it can be "even more dangerous"?

 

as for the sodium, it`s only trace amounts on few sharp edged slices that it occurs on (prolly surface area). I used cheap as chips White Spirits as used in piant brushes for my oil, 5 years later it`s still good and no smellies

[jsatan]

I agree cutting under oil is the best thing, if there is enough heeat to ignite the oil then the metal is sure to burning already, lol.

 

I've gatta get me some of this stuff, never got round to it tho,

[jdurg]

Well, with old potassium the safest thing to do is just not cut it. I've read online that the proper method of disposal for peroxide/superoxide coated potassium is to dissolve it in 2-propanol (I believe that's isopropanol). My only question with that is won't the potassium immediately explode and ignite the alcohol?

 

With the under oil thing, the reason for not doing so with heavily oxidized potassium is that if it does ignite, ALL of the oil will ignite creating a bigger fire hazard than if you just have a surface coating on the potassium. (Either way, it's still dangerous. It's like the difference between only having the ignition charge of a nuclear bomb go off in your face, or having the entire nuclear bomb go off in your face. Either way, you're screwed. )

[YT2095]

it can`t ignite under the oil though, how would you get a flame under 5 inches of oil? rem also that oil has a Flash point and the whole lot would have to be a few 100c for that to happen!

 

you could be several kilometers away by the time that happened

[jdurg]

But under the oil, as the peroxide/superoxide decomposes it releases heat and oxygen. The oxygen will then react with the freshly cut metal surface releasing even more heat. You will have the oxygen intermittently mixed in with the oil and a good deal of heat being generated. Give me some time to find some references online and I'll post them here.

[YT2095]

ok dokes

 

as I have Super Oxides under oil here at the moment and have never experienced an ounce of problem with them, certainly non with regard to heating either

 

I`de like to see the refs, I`m either doing something right or I don`t know what!??? )

[jdurg]

Well, the sites I'm finding online have made me think. (Being at work it's tough to dig deep into the research). I've heard many times that old potassium should be cut in an inert atmosphere as well as under oil. I think the "under oil" part really depends on how old it is. Another thing I read which makes the "under oil" thing dangerous is that the organic oil, when in contact with the peroxide, can form organic peroxides which are really bad. I think I'm just going to have to stay "in the middle" on this. I think it's just safe to say that cutting up old chunks of potassium is not good period.

[YT2095]

hence using MINERAL OIL and not Olive or Sunflower oil ))

[Silencer]

What is an example of an organic peroxide, and why is it so dangerous?

[Gilded]

Organic peroxides are Unstable with a big U. A good (or bad) example is the infamous TCAP.

[budullewraagh]

TCAP is tricycloacetone peroxide btw

 

they are unstable because the oxygen is bonded to other oxygen, which is not too desirable. so, the excess oxygen is liberated upon decomposition.

 

with regard to kallium, have you ever dissolved it in liquid anhydrous ammonia? makes for a nifty reducing agent and looks cool, suppsedly...plus there's also the novelty of knowing you have reduced potassium...

i never have, for lack of anhydrous liquid ammonia and for fear that the feds would stop by thinking i was reducing ephedrine...which i dont do.

 

btw i think that's really cool that the old potassium metal forms peroxides and superoxides due to its electropositivity

[jdurg]

 

Hey there YT. Here's a picture of two of my sodium samples from that 'cheap' oil I have stored in. The picture comes from my article on sodium and potassium over at http://www.chemicalforums.com. The top piece is just how it looks when taken right out of the oil, and you can see the slight yellow tinge in areas and the overall shine of the metal. The bottom piece is one that I wiped all the oil off of, and you can see the dark red-brown color it has turned. I would love to take this to some place that could analyze it for me so I could figure out what the heck it is.

[YT2095]

nice pics!

 

and I must admit, If I didn`t know better I`de think it was the top one that you`de cleaned off, it lools shinier (but the wrong color).

the sodium I have is mostly coated in a white powdery looking layer, with the occasional tallow yellow substance on sharp (thin) corners.

 

perfectly silver/white when cut, but oxidises rapidly as you know yourself.

 

the bottom sample looks the strangest though? the Red/Brown lustre`s quite unusual, and I`ve no idea what it is either, it`s obviously some sort of contamination, what? I don`t know though?

[jdurg]

Thank you. It's remarkable how the top piece looks like platinum with its sheen. I think that happened when the hydroxide on the surface of the metal reacted with the cheap oil, thus saponifying it. This formed some soap and glycerin which adhered to the metal's surface thus keeping the shine. The soap is probably that yellow gunk on the edges. For the other piece, it's just strange. The reactivity of the metal sample didn't change at all, but it turned that funky color. I'm going to have to ask some friends of mine who work at a battery company. I know a couple of chemists there who work with alkali metals all the time. They may have an explanation for me.

[YT2095]

for sure!, maybe take a sample of the FRESH oil too, a breakdown of that would be cool.

 

the prob with some organic oils is that they WILL contain traces of unwanteds for chem purposes such as this, anything from Proteins to Metal ions.

 

it almost looks like your sodium`s gone Rusty LOL ))

[Guest gedtech]

I once came across a few bits of old Potassium that were a nice bright yellow colour and stored under what I assume was oil to start with was oil, it had all but the top cm or 2, converted into a slime like jelly. I did not feel the need to cut it up at the time. There was probably only a few grammes in the jar, so no BIG deal.

[Charles Sansom]

When I was in high school I was rummaging around in the chemical room in our science lab and found a jar of potassium chunks in mineral oil. That was in the middle seventies. Recently I had the opportunity to rummage around in there again and that same jar of potassium chunks is still there, never having been opened. I wonder just how stable the stuff is after all this time. It came from a reputable chemical supply house, but there's really no telling how long it was there when I found it the first time. I also found a jar of benzene that has probably been there since the sixties or so in that same chemical room. No telling what else lurks in there.

[Enthalpy]

From the participants of that one thread, I believe to have seen nobody recently.

[Hexogen]

I don't know,maybe...be careful with IMPROPER STORED Na?!?That peroxide/superoxide wasn't there only because it is a peroxide/superoxide and it's where it wants to be.I don't want to be rude but be careful how you store them.