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Author: Subject: Make Potassium (from versuchschemie.de)
NeonPulse
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[*] posted on 6-3-2016 at 15:32


So I did another test last night and found the fineness and shine of the Mg is really the key factor in my successes. I did a run using 50 ml lamp oil this time with 3.5g Mg 7g KOH and 1.2 ml tert butanol. Everything was added at the start and I let this run go for 6 hours. There was quite a lot of small to medium spheres sitting atop the reaction mixture by the end and I'm quite pleased with the results. I was also wondering if anybody has attempted to recover the used tetralin before? It's kind of expensive an if possible I'd like to recover it for further use. I have around 100 ml and was thinking about running it through a fine filter and dropping the temp to see if the un used catalyst will solidify for removal. Failing that I will just heat it to drive the alcohol off first and distill the tetralin that's left.

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[*] posted on 6-3-2016 at 17:53


Quote: Originally posted by NeonPulse  
So I did another test last night and found the fineness and shine of the Mg is really the key factor in my successes. I did a run using 50 ml lamp oil this time with 3.5g Mg 7g KOH and 1.2 ml tert butanol. Everything was added at the start and I let this run go for 6 hours. There was quite a lot of small to medium spheres sitting atop the reaction mixture by the end and I'm quite pleased with the results. I was also wondering if anybody has attempted to recover the used tetralin before? It's kind of expensive an if possible I'd like to recover it for further use. I have around 100 ml and was thinking about running it through a fine filter and dropping the temp to see if the un used catalyst will solidify for removal. Failing that I will just heat it to drive the alcohol off first and distill the tetralin that's left.





It's believed the catalyst is post-reaction present as K alkoxide (see proposed reaction mechanism, higher up).

I believe filtering after chilling might very well work. Considering the cost of tetralin, its worth trying.

There's some work done by me on recycling, reported higher up in the thread.


[Edited on 7-3-2016 by blogfast25]




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NeonPulse
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[*] posted on 20-3-2016 at 15:18


I wouldn't say I've discovered anything really new but I found that trying to coalesce all the small spheres of K in a beaker of oil is not easy. They seem to not want to join. So after thinking a bit about it a good approach is to put the K balls in a test tube with oil and heat. I pushed the balls together as much as possible but some were still stubbornly refusing to join so I waited to the oil was a bit cooler and pressed the still soft spheres together and re heated the tube and viola! The potassium welded itself together in a nice little ball.

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[*] posted on 22-12-2016 at 16:51



I think that some of the molten potassium handling techniques that I use may help.

Your molten metal won't coalesce because it's dirty.

To make my brilliant Na or K ampoules, I pre-process the metals for best results. My first step is to melt the metal in toluene or xylene in a what is essentially a large test tube. I get a mixture of molten metal and oxidation crud. Then I push a metal rod, fitted with several layers of stiff stainless steel screen, through this. The brilliant looking metal bubbles up through the screens. Being totally clean, it readily coalesces when I set the liquid inside rapidly spinning by swirling the tube. Leave the rod in place during cooling. Pull up and remove metal from rod.

The screens are a very close fit to the tube. Done using a belt sander on the very stiff screens.


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[Edited on 23-12-2016 by Dan Vizine]





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[*] posted on 24-12-2016 at 10:32


I can't seem to edit my last entry, so let me add this here instead.

The RHS picture may seem a little confusing due to shadows. The darker part, running down the apparent axis of the tube, is just a shadow of the tube on the wall behind it. This procedure really is as simple as just pushing a screen through the molten metal.

And, as someone has noted, higher viscosity liquids are not desirable.

Obviously, the re-solidified metal just slides off the pusher rod.

If your starting metal is visually "clean" (no particulates), but is just a bit dull looking, this is all it takes to inhibit coalescence. In this case, though, the remedy is often even easier than filtering it. You simply add one drop of DRY alcohol to the metal (in toluene, xylene) and the surfaces will brighten up. Repeat if the metal still isn't bright. The alcohol can be 2-PrOH or EtOH). Most of the product alkoxide sloughs off the metal surfaces and sinks to the bottom of the tube as green-gray flocculent material.

[Edited on 25-12-2016 by Dan Vizine]





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[*] posted on 28-12-2016 at 10:48


In case any of you do use the alcohol method of cleaning sodium or potassium there is a minor downside that I forgot to mention. You don't find details like this in the literature, at least I didn't, despite the fact that the alcohol cleaning trick has been known forever.

Obviously, not all of the alkoxide separates from the metal. There will be some left, but you can't see it. It's still enough to change the behavior of the molten metal toward dry, clean glass. The molten metal will now wet glass due to the powerful fluxing abilities of the alkoxide. It forms a sodium (or potassium) mirror.





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[*] posted on 29-12-2016 at 06:41


Quote: Originally posted by Dan Vizine  
(...)
If your starting metal is visually "clean" (no particulates), but is just a bit dull looking, this is all it takes to inhibit coalescence. In this case, though, the remedy is often even easier than filtering it. You simply add one drop of DRY alcohol to the metal (in toluene, xylene) and the surfaces will brighten up. Repeat if the metal still isn't bright. The alcohol can be 2-PrOH or EtOH). Most of the product alkoxide sloughs off the metal surfaces and sinks to the bottom of the tube as green-gray flocculent material.
[Edited on 25-12-2016 by Dan Vizine]

Quote: Originally posted by Dan Vizine  
(...)
Obviously, not all of the alkoxide separates from the metal. There will be some left, but you can't see it. It's still enough to change the behavior of the molten metal toward dry, clean glass. The molten metal will now wet glass due to the powerful fluxing abilities of the alkoxide. It forms a sodium (or potassium) mirror.

Thanks so much for posting this.

And would repeating the method with the long tube help the potassium get clean enough to make the balls look brilliant? Or is the dry alcohol method the only method you know of?
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[*] posted on 29-12-2016 at 21:22


I made an attempt at the reaction for the first time yesterday. Didn't work at all though because I couldn't get the sand bath hot enough. I think the old hotplate I was using is finally over the hill.

https://texium.wordpress.com/2016/12/29/failed-attempt-at-po...



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30-12-2016 at 06:04
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[*] posted on 30-12-2016 at 13:08


[/rquote]

And would repeating the method with the long tube help the potassium get clean enough to make the balls look brilliant? Or is the dry alcohol method the only method you know of?
[/rquote]

This depends on your goal. My goal is to make shiny metal samples without solvent.

I've never tried to make brilliant metal in any atmosphere except a vacuum. You can get nice silvery metal in solvents, but it dulls from shiny silver to "flat" silver kinda' quickly. Potassium, in my hands, always acquires a pale purple tint in solvents after some period of time.

I take this "flat" silvery metal, put it in a tube, remelt in under vacuum, filter through stainless steel wool and collect in another tube which is sealed under a vacuum. Here's a half pound potassium ampoule made this way:

7) half pound of Potassium.jpg - 43kB

[Edited on 30-12-2016 by Dan Vizine]





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[*] posted on 30-12-2016 at 22:51


I've tried making potassium several times now with no success what so ever. If someone could possibly give me some advice or tips, it would be greatly appreciated:). Here's a description of my latest attempt:

The magnesium was activated by leaving it to stand in a beaker of 5% acetic acid for about 20 seconds. This seemed to be effective at removing the oxide coating on the magnesium.

To a 500ml round-bottom flask, was added 3.5g of magnesium turnings and 7.3g of 95% potassium hydroxide flakes. Around 60ml of kerosene was then added in to act as the solvent. As a heating source, I used an oil bath (spent engine oil instead of cooking oil) heated by a hot plate. A liebig condenser, circulated with water and loosely sealed at the top with Al foil was then attached to the flask. The heat was set to maximum and pretty soon the kerosene began to reflux steadily in the flask. After 15 minutes of reflux, I added in 1.5ml of tert-butanol though the condenser.

After around 20 more minutes of reflux, another 1.5ml of alcohol were added. The mixture was refluxed for around 5 hours. Upon examining the contents of the flask, I found no potassium what so ever and the reaction mixture appeared almost completely unchanged. After removing the kerosene, a bit of water was added to the mixture resulting in no effect at all, confirming the complete absence of potassium:(.

It definitely got hot enough, the oil must have been well over 200 C.

Is there anything obviously wrong?
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[*] posted on 30-12-2016 at 23:06


Maybe too much water in your KOH, next time you can evaporate a part of your kerosine before adding magnesium and t-butyl alcohol to get rid of the water.
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[*] posted on 30-12-2016 at 23:25


Ok, I'll be sure to try that out next time. My KOH is 95% and I'm not sure if the residual 5% is water or some other junk, but hopefully as long as it is dry that shouldn't matter.

Thanks for the feedback:)
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[*] posted on 31-12-2016 at 01:50


KOH is quite often labelled as 95 or 99 % referring to everything but the water, which is usually 15%.
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[*] posted on 31-12-2016 at 07:30


Quote: Originally posted by Tsjerk  
Maybe too much water in your KOH, next time you can evaporate a part of your kerosine before adding magnesium and t-butyl alcohol to get rid of the water.


Ba(ClO3)2, did you understand the comment as written? What he meant was to distill a part of your solvent away first. Water will leave with this cut, due to its much lower bp.

The main solid impurity in this is K2CO3 from inevitable CO2 absorption from the air. And, of course, you can count on at least the 15% water that Tsjerk suggested.





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[*] posted on 31-12-2016 at 11:11


Ah right, I see. Thanks Tsjerk:). I'll try doing as you suggested next time. Boil off some of the kerosene and maybe even fuse the KOH before I use it.
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[*] posted on 31-12-2016 at 15:09


If you fuse it, before you use it, put it into a plastic sandwich bag. A thicker one if you have it. Then wrap with some additional bags, or similar, and try to pulverize it as best you can.

Boiling off a bit of solvent, with the KOH added, is still a good practice for a couple of reasons.





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[*] posted on 31-12-2016 at 18:36


Cool, looks like I'm back on track again. Thanks for your help.
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