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Author: Subject: Cobalt oxide??
SAM4CH
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[*] posted on 22-4-2007 at 05:47
Cobalt oxide??


How can I prepare cobalt oxide "CoO" from cobalt II chloride??!!
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[*] posted on 22-4-2007 at 06:44


I think that you can first make a solution of cobalt II chloride and then precipitate cobalt hydroxide by addition of NaOH. Then heat the hydroxide until it dehydrates to CoO. I am not sure if this method works.



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[*] posted on 22-4-2007 at 07:10


make the carbonate or basic carbonate, using sodium carbonate or bicarbonate, filtter and wash well, heat to decompose. Overheating in air will result in the formation of some Co(III) oxide.
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[*] posted on 22-4-2007 at 12:44


The problem with all these precipitating alkaline methods is that contamination with cobalt (III) is very hard to avoid. In my experience, cobalt (II) is EXTREMELY easily oxidized by oxygen from air, as soon as a precipitate is made at high pH, and also in the presence of many ligands. E.g. a precipitate of Co(OH)2 is oxidized by air in a matter of seconds. Probably the same will happen with carbonate precipitates.

If you want to try the method of precipitating CoCO3, then try with bicarbonate, not with carbonate. But even then, you will have oxidized material. I once purchased some CoCO3. This was a nice purple powder. Now it is dark brown, and quite a lot of it is oxidized to cobalt (III).




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[*] posted on 22-4-2007 at 12:50


If O2 is such a problem then why not do it under inert conditions!?
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[*] posted on 22-4-2007 at 15:01


Tricky to heat stuff under inert gas. Perhaps try heating it (the carbonate) submerged in molten flux, so that the flux will form a molten layer protecting it from atmospheric oxygen while it's being heated. To do this, you must find a substance that suits the following criterias:

1. It must be intert
2. It must melt near RT
3. It must stay molten (not boil before 2KK or something)
4. It must be less dense than the carbonate (4.5 ish at least)

Magnesium chloride? Table salt?

Better melt the flux first then add the carbonate.




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[*] posted on 22-4-2007 at 20:57


Tricky finding a flux that isn't going to react with the cobalt carbonate of oxide.

The carbonate does require quite strong heating to effect decomposition. Might be able to heat it in a ceramic tube with a slow flow of N2

This all assumes that you care if you have CoO or some mixed oxide.
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[*] posted on 22-4-2007 at 21:27


Heat it with CO2, and maybe a dash of CO?

But all of this assumes Co(III) IS an intolerable impurity...which given the OP's brevity I would guess not...

Tim




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