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Zan Divine
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[*] posted on 16-5-2012 at 17:20
Cleaning and making lithium look presentable


Having prepared large, silvery ampoules of Na & K, I needed to face my nemesis, lithium, and try to prepare a comparably sized (1" x 6") ampoule for my best customer.

I've previously uploaded a pdf file describing the significant factors that effect the deterioration of fresh Li in air. The important lesson I took from this Naval study was that Li is inert to oxygen and nitrogen as long as H2O is less than 5 - 10 ppm.

My experience has been that when lithium is melted and poured in the air, it maintains a bright surface until it cools. I can only assume that the high temperature (such as it is) maintains a localized dry zone around it for a short time.

The metal needs to be cast in some sort of mold (or does it?).
Yet no container seems suitable. Molten lithium reacts with glass, Teflon, alumina, beryllia, carbon. Casting into metal has its own problems. If the metal is hot, Li welds to it. If it's too cold, the Li freezes too quickly and won't flow.

I melt the Li in a steel piston with a SS screen in the bottom and extrude it, once molten, into...what?
I finally decided that no mold was the best mold. I extrude the molten Li out the bottom of the piston and let it form a large teardrop shaped object (sometimes as large as 3/4"). It cools in a flood of argon and that's it. I just grab the hot chunk and pop it into vacuum.

Rinse. Repeat ad nauseum. The final product is shown below.
The sample is very nice, mostly silver with some light grey and no black nitride. Always room for improvement, though.

Has anyone else dealt with these problems? How did you address them? I've been toying with the idea of using a (water jacketed?) polyethylene tube as a mold....

This is not an original observation, but the most troubling thing about this group I metal is that it thinks it's a group II metal and insists on acting like it.









[Edited on 17-5-2012 by Zan Divine]

li44.jpg - 49kB

[Edited on 18-5-2012 by ScienceSquirrel]




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[*] posted on 17-5-2012 at 20:40


I don't know, lithium looking like that is hard to come by. I just have my ugly gray chunks with metallic edges (cut with scissors, and placed into mineral oil). Can I melt this on a stovetop under oil to get it to look better, or do I need to chemically clean it first? I heard from NurdRage that toluene (yay toluene!) works for potassium, so you might give that a go.



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[*] posted on 17-5-2012 at 23:26


Would Li react with RTV silicone rubber? If not you can make a mould with that, decontaminate and cast molten Li into that. It's flexibility would make it easy to de-mould too.



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[*] posted on 18-5-2012 at 04:32
Cleaning lithium


Hello! I have some lithium and no matter what i do, it gets coated with a tin layer of its oxides/peroxides. I've been looking for info. in the internet and found that toluene works great with cleaning potassium, so i've been thinking of using it with lithium too, but i dont know if it could react with it. So, should i use it with lithium, and it wont react?
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[*] posted on 18-5-2012 at 05:52


Quick question, there's already a thread just below this one entitled "Making lithium look presentable" on the subject of cleaning lithium metal. Why start a new thread on the same exact subject?

Robert




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18-5-2012 at 06:00
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[*] posted on 18-5-2012 at 09:44


Quote: Originally posted by elementcollector1  
I don't know, lithium looking like that is hard to come by. I just have my ugly gray chunks with metallic edges (cut with scissors, and placed into mineral oil). Can I melt this on a stovetop under oil to get it to look better, or do I need to chemically clean it first? I heard from NurdRage that toluene (yay toluene!) works for potassium, so you might give that a go.


Toluene and sodium can be upgraded by melting under toluene (see details in my topic "Shiny ampoules of Na and K") and stirring. This also removes that damned mineral oil.

With Li this isn't possible since Li melts 70+ degrees C higher than toluene boils (behaving more like a group II metal). Li can be melted in mineral oil but it floats on top and isn't very protected by the liquid.




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Zan Divine
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[*] posted on 18-5-2012 at 09:50


Quote: Originally posted by Arthur Dent  
Quick question, there's already a thread just below this one entitled "Making lithium look presentable" on the subject of cleaning lithium metal. Why start a new thread on the same exact subject?

Robert


That is, or was, my thread. I have no idea how the "Cleaning and" got tacked on to my title. I don't even see my original thread listed anymore.

[Edited on 18-5-2012 by Zan Divine]




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[*] posted on 18-5-2012 at 09:55


Quote: Originally posted by froot  
Would Li react with RTV silicone rubber? If not you can make a mould with that, decontaminate and cast molten Li into that. It's flexibility would make it easy to de-mould too.


RTV silicone is perfect on several counts, but on the reactivity issue, it falls flat. Molten Li will chew it up. Thanks for the suggestion, though. The reason I was leaning toward a polyethylene is that it just has C-C and C-H bonds and these are resistant.

[Edited on 18-5-2012 by Zan Divine]




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[*] posted on 18-5-2012 at 09:55


I have merged the two threads.
Your thread is most of it and I tacked cleaning on the title to cover vampirexevipex's query.
Nothing is gone.
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[*] posted on 18-5-2012 at 10:05


Quote: Originally posted by vampirexevipex  
Hello! I have some lithium and no matter what i do, it gets coated with a tin layer of its oxides/peroxides. I've been looking for info. in the internet and found that toluene works great with cleaning potassium, so i've been thinking of using it with lithium too, but i dont know if it could react with it. So, should i use it with lithium, and it wont react?


Sorry, I overlooked this question when answering a similar one.
The problem is moisture. It catalyzes the reactions with O2 & N2. The dark color on Li is Li3N, lithium nitride. One lone N2 molecule takes out 6 Li atoms in the process. I'm afraid that what works nicely for Na, K, etc. often fails miserably for Li.
Toluene won't react with Li but it won't melt it either.

The only method I have cleaned Li with (successfully) is mechanical.....melting it in a confined area and pushing the melt through a filter of SS mesh. The one improvement I envision is using SS wool to filter out the smaller detritus better than a fine mesh can.

In fact, I'm going to go take a picture of the crude piston to make its construction clearer in case others try this....brb....

There! Not pretty, but it's a disposable thing.


1.jpg - 97kB 2.jpg - 73kB

[Edited on 18-5-2012 by Zan Divine]




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[*] posted on 19-5-2012 at 19:45


Is there a solvent that is lighter than lithium?



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[*] posted on 20-5-2012 at 04:44


There is no solvent that is inert to molten lithium and that boils high enough to melt it. Even the lightest solvents, like pentane, still weigh 20% more than lithium (and boil way, way too low).

I'm fairly confident in saying there is no known solvent in which you can melt Li and have it sink to the bottom.

The d of Li is just slightly over 1/2 g per mL, most solvents fall into the range of ~0.6 to ~1.5 g per mL.

[Edited on 20-5-2012 by Zan Divine]




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[*] posted on 20-5-2012 at 06:01


Quote: Originally posted by Zan Divine  
In fact, I'm going to go take a picture of the crude piston to make its construction clearer in case others try this....brb....

There! Not pretty, but it's a disposable thing.


Cool apparatus! Is the piston a tight fit? I ask because I was wondering if upon heating, the metal expands and would seize the piston?

And when the apparatus is heated, in what vessel do you "squeeze out" the molten lithium?

As for solvents or mineral oils, it is indeed a damning thing that Lithium floats even the lightest inert solvent or oil. I tried to keep some in a jar but after some time, it just oxidizes to hell because it just won't stay down.

Robert




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[*] posted on 20-5-2012 at 06:06


Is it soldered all way around or is it held together with tack weld(s)?



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[*] posted on 20-5-2012 at 07:12


DMSO - density ~1g/cm<sup>3</sup>, BP 189°C, while Li's MP is 180°C



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[*] posted on 20-5-2012 at 09:42


DMSO would probably react with lithium. It has an oxygen atom, and as Nicodem mentioned in a thread recently, it can act as an oxidizing agent.
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[*] posted on 20-5-2012 at 10:49


What if you put a steel container over the lithium, under the oil? The container would catch the lithium without oxidising it, maybe.



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[*] posted on 20-5-2012 at 14:00


Q) Cool apparatus! Is the piston a tight fit?
A) The piston is not particularly tight.

Q) And when the apparatus is heated, in what vessel do you "squeeze out" the molten lithium?
A) "I finally decided that no mold was the best mold. I extrude the molten Li out the bottom of the piston and let it form a large teardrop shaped object (sometimes as large as 3/4"). It cools in a flood of argon and that's it. I just grab the hot chunk and pop it into vacuum." The Li just hangs there cooling. It looks like a punching bag.

Q) Is it soldered all way around or is it held together with tack weld(s)?
A) 2 tack welds. No solder. The cylinder had a nice, flat, smooth face. No leaks of molten Li since the Li is never under much pressure

Q) DMSO - density ~1g/cm3, BP 189°C, while Li's MP is 180°C.
A) There are lots of solvents with bp >180 C. None are less dense than lithium. Also, as noted, DMSO reacts with Li.

Q) What if you put a steel container over the lithium, under the oil? The container would catch the lithium without oxidising it, maybe.
A) You can let the Li splash into the mineral oil and it gets coated on all sides. The best alternative, if you want to use oil, is to fill the jar completely after adding the Li so that there are no air bubbles.

Also, if you do use oil, heating under vacuum and/or predrying by melting Na or K in it and stirring are good ideas. Do you have a feeling for exactly how low 5 ppm H2O is? Those are glovebox conditions. It's hard to dry things like oil that well.

Bubbling argon through the oil to sparge out the O2 and N2 helps too.


[Edited on 21-5-2012 by Zan Divine]




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[*] posted on 21-5-2012 at 19:12


Quote: Originally posted by Zan Divine  
There is no solvent that is inert to molten lithium and that boils high enough to melt it.


Jesus! Did I say that?!
Well, OK...but what I meant to say was "There is no solvent lighter than lithium that boils high enough to melt it."

[Edited on 22-5-2012 by Zan Divine]




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[*] posted on 21-5-2012 at 19:50


Really, something to trap the lithium under the mineral oil would be ideal. An inverted crucible, submerged in the oil? Just heat to melt, and when it's done, flip it over (still under the oil), take out the lithium (while holding it under oil), and transfer into container and environment of your choice.
Oil. :D




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[*] posted on 22-5-2012 at 20:11


The purification happens during the filtration. You can't omit that.



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[*] posted on 22-5-2012 at 20:33


What do you use for the filter again?



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[*] posted on 23-5-2012 at 04:40


I use stainless steel mesh. I plan to try stainless steel wool (the same filtering medium I used with Na & K) next because it will filter out finer particles.

[Edited on 23-5-2012 by Zan Divine]




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[*] posted on 25-5-2012 at 08:19


Quote: Originally posted by Zan Divine  
With Li this isn't possible since Li melts 70+ degrees C higher than toluene boils (behaving more like a group II metal). Li can be melted in mineral oil but it floats on top and isn't very protected by the liquid.


If you have a container that can hold enough pressure, toluene's boiling point would rise above the mp of lithium. I don't know how much pressure you need to handle and I imagine an explosion will spread lithium all over the place.

You could also try xylene (bp = about 138 °C), available at the hardware store, + some pressure.

[Edited on 25-5-2012 by vmelkon]
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[*] posted on 25-5-2012 at 08:28


Paraffin oil has a high boiling point. I'm not sure if it would react with lithium, though. Tetralin boils at over 200 degrees, but it's harder to procure. I doubt it would react with alkali metals in the same fashion as naphthalene, IIRC Nurdrage used tetralin in one of his potassium experiments.



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