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Author: Subject: Calcinated oxides "reactivation"
Mabus
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[*] posted on 19-3-2017 at 03:15
Calcinated oxides "reactivation"


As most people here know, majority of OTC oxides are calcinated which makes them very inert and practically useless as reagents. Now, I've seen some people claiming success with using either molten alkali or molten NaHSO4 to fuse the oxide into a more reactive mass, but the claims are scattered on the forum and there is no grand thread for these procedures. So I made this thread to ask people who have done this procedure to share their experience here or if they can post on the wiki to write about it on its article, as I think this is an important procedure that some of us might need at one point.

Link for the wiki article: http://www.sciencemadness.org/smwiki/index.php/Reactivation_...




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[*] posted on 30-8-2017 at 20:31
oxides as catalyst supports for anhydrides


Quote: Originally posted by Mabus  
As most people here know, majority of OTC oxides are calcinated which makes them very inert and practically useless as reagents. Now, I've seen some people claiming success with using either molten alkali or molten NaHSO4 to fuse the oxide into a more reactive mass, but the claims are scattered on the forum and there is no grand thread for these procedures. So I made this thread to ask people who have done this procedure to share their experience here or if they can post on the wiki to write about it on its article, as I think this is an important procedure that some of us might need at one point.

there are incredible amounts of "green chemistry' catalysts being explored that run the gamut of usefulness.

From safer, more economic room temperature, solvent free reactions for large scale industrial uses to the lab synthesis of psychoactive substances.
I have been researching these compounds recently an am amazed at their potential. Their usefulness is exponential. read up on sulfated, calcined, salts of Barium or Zirconium oxides especially. The trick is in the calcination step changing the crytal latice from a monoclinic form to a tetragononal one. Thus increasing the surface area and acid or base strength a thousand fold of concentrated sulfuric acid. Yes a thousand fold increase of acidity. And at ROOM TEMPs.



Link for the wiki article: http://www.sciencemadness.org/smwiki/index.php/Reactivation_...
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[*] posted on 24-1-2018 at 11:34


For Ta2O5, if dead burnt or overly calcined, it is very slow to react, even under pressure with 70% w/v HF.

In that instance, it can be fused with KHSO4, added to dilute sulfuric, filtered off and then rapidly redissolved in dilute HF. Same with Nb.




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Fulmen
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[*] posted on 24-1-2018 at 12:42


When I extracted cobalt from carbide tooling I started by heating it at appr 850°C to get the oxides. Acid digestion was still slow, so I ended up fusing it with NaOH. Worked like a charm, both cobalt and tungsten dissolved without problem.



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[*] posted on 24-1-2018 at 13:31


Currently I have a mix of elemental carbon and magnesium oxide, produced from the reaction between dry ice and magnesium ribbon. I'm trying to isolate the pure carbon. The MgO is incredibly resistant to dissolution in sulfuric acid, even hot 98% acid, so I suspect the high heat of the reaction has calcined it. Would hydroxide fusion help in this case? How does it work? Does it transform the oxide into another, more soluble, compound? And would it leave the carbon intact?
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Fulmen
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[*] posted on 24-1-2018 at 13:45


Basically it forms salts with acidic compounds (usually oxides). It probably won't work with MgO as it is basic.



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[*] posted on 24-1-2018 at 15:10


Hang on a second.

Isn't 'calcining' merely heating it up a lot for a long time ?

How does that cause certain substances to become chemically inert ?

Others become more active, others decompose, yet others explode in the same process.

Does anyone know what is happening at the electron level with this 'calcining' thing ?




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[*] posted on 24-1-2018 at 15:36


It seems to be related to surface area, porosity and possibly crystal structure. But I have to admit it doesn't make sense to me either. Dense, low surface materials would of course react slower, but in many cases they seem to turn completely inert.



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elementcollector1
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[*] posted on 24-1-2018 at 15:58


It might also be due to vitrification of the oxide - glasses, as we all know, are pretty resistant to attack.



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[*] posted on 4-6-2018 at 07:06


Yes, I have some Cr2O3 that has been calcined, but I'd rather just dissolve in acid. It's a shame that it requires alkali fusion



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