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Foeskes
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[*] posted on 8-7-2017 at 17:53
Making chromium metal?


I'm thinking of making chromium metal at some point.
According to Wikipedia chromium is made by alumothermic reduction of chromium oxide, however after seeing nurdrage's video on chromium thermite it doesn't look like its very viable. Maybe it will work if I add some kind of booster, but I'm not sure which booster to use, maybe sulfur and Aluminium? I also saw someone use potassium dichromate and Aluminium as a booster, not sure if it will form chromium nuggets though.
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JJay
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[*] posted on 8-7-2017 at 18:23


Schlessinger (in the SM library) suggested adding some potassium dichromate to the mix to raise the temperature of the reaction. He also suggested using a barium peroxide/aluminum mixture for ignition. I'm not sure if that's really necessary or if magnesium powder would work just as well.

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Foeskes
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[*] posted on 8-7-2017 at 20:09


Also what is a good way of producing chromium(III) oxide from Potassium dichromate?
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ninhydric1
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[*] posted on 8-7-2017 at 21:17


http://www.sciencemadness.org/talk/viewthread.php?tid=21562#...

Instead of sodium hydroxide, use potassium hydroxide.
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[*] posted on 9-7-2017 at 04:21


Quote: Originally posted by ninhydric1  
http://www.sciencemadness.org/talk/viewthread.php?tid=21562#...

Instead of sodium hydroxide, use potassium hydroxide.

I think you are heading in the wrong direction.

You can make Cr(OH)3 by dissolving chromate in dilute acid and reacting it with alcohol or sodium bisulphite to reduce it to Cr(III) and then add sodium hydroxide to ppt the Cr(OH)3

If you have ammonium dichromate you can do this
https://www.youtube.com/watch?v=Ula2NWi3Q34
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JJay
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[*] posted on 9-7-2017 at 05:22


I think you can convert chromium hydroxide to chromium oxide by heating it in a crucible. I haven't actually tried it and don't have a reference, but it seems reasonable to suppose that would work.

If not, you can react it with sulfuric acid and convert it to chromium sulfate and heat that to convert it to chromium oxide.




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Foeskes
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[*] posted on 9-7-2017 at 05:59


What if you mix chromate with sugar or charcoal and ignite?
Can sodium thiosulfate be used? Because sodium bisulfite is not sold anywhere here.
Or maybe glucose?

[Edited on 9-7-2017 by Foeskes]
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[*] posted on 10-7-2017 at 20:53


It is easy to make chromium (III) oxide from ammonium dichromate. Just set it in fire and watch the fireworks. The green ash will be the desired oxide. It will be unreactive and useless for wet chemistry, but good enough to use in a thermite.



Smells like ammonia....
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Foeskes
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[*] posted on 11-7-2017 at 05:19


What do you mean by "unreactive"?
Is it due to impurities or the structure?

[Edited on 11-7-2017 by Foeskes]
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elementcollector1
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[*] posted on 11-7-2017 at 07:22


I would imagine it's largely due to the structure - the elevated temperatures induce calcination in oxides, which renders them much less reactive than drying at lesser temperatures. However, in the molten state where thermite typically takes place, this doesn't matter at all.



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[*] posted on 11-7-2017 at 07:33


If you're looking for an element sample, aluminothermic reactions are not the way to go. You'll only end up with some rather ugly gray chromium nodules/powder.

You could try common Cr+6 or Cr+3 plating methods to electroplate chromium onto an electrode, then flake it off.

If you're just looking for chromium, you can chuck a mix of aluminum powder and chromium III oxide in an open-top steel pipe with a large (3x or more by stoicheometry) excess of aluminum. Place this in a bonfire and keep it at red heat for a while. The aluminum will melt and reduce the oxide to chromium, forming a sintered cake of aluminum oxides, aluminum, and chromium. Crush this up and stir it into hot HCl and everything except the chromium metal will dissolve.




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elementcollector1
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[*] posted on 11-7-2017 at 08:48


Quote: Originally posted by Praxichys  
If you're looking for an element sample, aluminothermic reactions are not the way to go. You'll only end up with some rather ugly gray chromium nodules/powder.


I wouldn't know about that, mine turned out lovely - a bit shinier than freshly broken metal.

I would think that purity is the main concern when going after element samples through thermite reduction, as too much aluminum or magnesium can dissolve in your metal sample, contaminating it. However, too little of your reducing agent can cause the mix to be much harder to ignite...




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Foeskes
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[*] posted on 12-7-2017 at 02:39


Quote: Originally posted by Praxichys  
If you're looking for an element sample, aluminothermic reactions are not the way to go. You'll only end up with some rather ugly gray chromium nodules/powder.

You could try common Cr+6 or Cr+3 plating methods to electroplate chromium onto an electrode, then flake it off.

If you're just looking for chromium, you can chuck a mix of aluminum powder and chromium III oxide in an open-top steel pipe with a large (3x or more by stoicheometry) excess of aluminum. Place this in a bonfire and keep it at red heat for a while. The aluminum will melt and reduce the oxide to chromium, forming a sintered cake of aluminum oxides, aluminum, and chromium. Crush this up and stir it into hot HCl and everything except the chromium metal will dissolve.


I thought HCl dissolves Cr quite well.
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