Sciencemadness Discussion Board

Finally I got K metal from KOH + Mg

metalresearcher - 11-10-2011 at 11:14

Still tiny amounts but it is the beginning. I have to improve the shielding of the retort after cooling it down.


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Adas - 11-10-2011 at 11:49

Very nice. The only problem is, that the reaction is very fast. Next time you can try to purify the K by melting in inert gas.

cyanureeves - 11-10-2011 at 16:16

congrats! and boy you are stubborn,with as many attempts from the start with sodium and now potassium,you were bound for success. a taller oil can should trap more metal dont you think? the last video with the huge fireball would have scared me enough to stop further experimenting and so i have no kalium. i think kalium means balls.

AndersHoveland - 11-10-2011 at 16:46

I have always wondered why argon is always used as the "inert" atomsphere for storing potassium. Would not nitrogen work instead? I think perhaps since it is common knowledge that magnesium can burn in nitrogen, everyone just automatically assumed that potassium would also be reactive towards nitrogen, when in fact it is not.

Nitrogen actually can dissolve in molten sodium without reaction, even at 500degC. Na3N is only formed if the two elements are subject to electric discharge under low pressure.
Phase Diagram Evaluations, N-Na (Nitrogen-Sodium) System
James Sangster

[Edited on 12-10-2011 by AndersHoveland]

fledarmus - 12-10-2011 at 04:38

Mostly, argon is used because it is heavier than air and is a little better about staying put. Nitrogen is just a touch lighter than the average (air being 78% nitrogen and 21% oxygen), and is lighter than the oxygen in the air, so a small leak will allow oxygen to seep into your container. Helium as an inert gas is pretty much useless - it escapes rapidly through the tiniest spaces.

Chemistry Alchemist - 12-10-2011 at 05:12

alot of the K would of burned up in the flash when the reaction proceeded, there was a noticeable colour change when in the presents of Potassium... is there a way to hold it? and then once the reaction is done, let the pressure out and then open it up? im guessing that then the reaction goes off it releases some gas... so you could see if the reaction proceeded when then pressure in the vessel increased... or wouldn't this work well? just a guess

quicksilver - 12-10-2011 at 06:13

This thread doesn't belong in the Energetic Materials section of the Forum; therefore moved to General Chemistry.

blogfast25 - 12-10-2011 at 08:37

This method is like flogging a dead horse. Why make tiny amounts of basically irrecoverable potassium, good only for showing that there is some, when you can make appreciable quantities of neat, clean metal with a small conical flask, a primitive cooler (reflux), a sand bath and some (mostly) OTC chemicals? See the relevant potassium ‘synthesis’ thread…

But if you do want to improve things, try recovering the slag/metal mix and treat it with kerosene (or any inert hydrocarbon solvent). Some hours of jiggling the suspension at 100 C or more may yield some actual K nuggets. Recovering these you can merge them into larger ones, once you’ve separated them from the MgO.

blogfast25 - 12-10-2011 at 08:45

Quote: Originally posted by Chemistry Alchemist  
alot of the K would of burned up in the flash when the reaction proceeded, there was a noticeable colour change when in the presents of Potassium... is there a way to hold it? and then once the reaction is done, let the pressure out and then open it up? im guessing that then the reaction goes off it releases some gas... so you could see if the reaction proceeded when then pressure in the vessel increased... or wouldn't this work well? just a guess


KOH + Mg === > K + MgO + 1/2 H2

For each mol of K formed, 1/2 mol of H2 is formed. In standard conditions that's about 11 L of H2 (per mol of K), at higher temperatures, apply the Ideal Gas Laws. Hard to keep a lid on, except with a proper bomb (pressure resistant) reactor. Don't try this at home!

Containing the reaction products in a bomb type reactor would almost certainly lead to potassium hydride (KH) being formed: K +1/2 H2 === > KH

metalresearcher - 12-10-2011 at 10:04

On a German forum I posted the result as well and some advised me to 'moderate' the reaction by mixing it with MgO. I don't have MgO but I have silica sand normally used for a bird's cage (from a pet supply shop) which I can mix with the KOH + Mg. This mixture I will fill into the retort and heat to red hot and capture the K vapor to condense / freeze into lamp oil.

@cyanureeves : Thank you ! My first attempts a year ago with the 1200oC furnace were unsuccesful just because of the fact that the mild steel retorts burned out and the Na vapor leaked out.
The Mg methos requires a lot lower temps which do not damage the retort.

[Edited on 2011-10-12 by metalresearcher]

phlogiston - 12-10-2011 at 11:50

Heating Mg + SiO2 will give you magnesium silicide. An often performed demonstation experiment is to prepare this compound and drop chunks of it in hydrochloric acid, will will yield silane gas. Bubbles of this explode with audible pops when they come into contact with air.

I can tell you are Dutch. I don't have MgO, but I have a few kg of ZnO pigment that I was planning to discard anyway, if you think it could be of use to you, let me know. I am not sure if ZnO may perform a thermite-like reaction with Mg metal, though, and any K formed would probably react with the ZnO to Zn metal, so I suspect it is not a good choice for this purpose.

[Edited on 13-10-2011 by phlogiston]

[Edited on 13-10-2011 by phlogiston]

blogfast25 - 13-10-2011 at 05:12

Quote: Originally posted by metalresearcher  
On a German forum I posted the result as well and some advised me to 'moderate' the reaction by mixing it with MgO. I don't have MgO but I have silica sand normally used for a bird's cage (from a pet supply shop) which I can mix with the KOH + Mg. This mixture I will fill into the retort and heat to red hot and capture the K vapor to condense / freeze into lamp oil.

[Edited on 2011-10-12 by metalresearcher]


Phlogiston is entirely right: silica won’t do at all here, it’s simply not inert enough.

The only chemicals that realistically can be used here to temper the reaction are fluorite (CaF2) and cryolite (Na3AlF6). These are commonly used, especially CaF2, as adjuvants in commercial thermite reactions because they are totally inert in the conditions of the reaction: Mg cannot reduce either CaF2 or Na3AlF6.

[Edited on 13-10-2011 by blogfast25]