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crystal grower
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[*] posted on 31-1-2016 at 11:02
Bismuth oxide reduction


Hello,
I have been growing bismuth crystals a while ago and beside nice hopper crystals I also got some bismuth oxide from melting.
Is there a simplier way to reduce that oxide to elemental bismuth than reducing it with carbon under big temperatures without presence of oxygen?
Thakns for answer.



[Edited on 31-1-2016 by crystal grower]




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[*] posted on 31-1-2016 at 11:10


You can dissolve the bismuth oxide in hydrochloric acid, and then reduce it with aluminum foil, yielding a fine black powder of bismuth metal. This can then be dried and washed again with dilute HCl to remove excess aluminum, as bismuth will not dissolve in it.



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[*] posted on 31-1-2016 at 11:35


Quote: Originally posted by zts16  
You can dissolve the bismuth oxide in hydrochloric acid, and then reduce it with aluminum foil, yielding a fine black powder of bismuth metal. This can then be dried and washed again with dilute HCl to remove excess aluminum, as bismuth will not dissolve in it.

Thanks for answer, I will definitely try it;).




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[*] posted on 31-1-2016 at 17:28


Expect to run into serious difficulty when trying to melt bismuth powder back into a lump. Despite it seeming easy because of the low melting point, the powder has always oxidized before it melts for me.
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[*] posted on 31-1-2016 at 17:54


Quote: Originally posted by Tdep  
Expect to run into serious difficulty when trying to melt bismuth powder back into a lump. Despite it seeming easy because of the low melting point, the powder has always oxidized before it melts for me.

I guess you need either a suitable slag or an argon environment.
Suggestions for the former anyone?




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[*] posted on 31-1-2016 at 18:20


Sodium hydroxide worked when I was melting cadmium powder. The trick is to have a lot of metal powder and just enough flux to cover the surface, it seems.



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[*] posted on 31-1-2016 at 18:22


Quote: Originally posted by j_sum1  

I guess you need either a suitable slag or an argon environment.
Suggestions for the former anyone?


A low melting flux, like a soldering/brazing flux?

Teflon? MP = 327 C

[Edited on 1-2-2016 by blogfast25]




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[*] posted on 31-1-2016 at 18:37


Quote: Originally posted by elementcollector1  
Sodium hydroxide worked when I was melting cadmium powder. The trick is to have a lot of metal powder and just enough flux to cover the surface, it seems.


Bismuth is amphoteric: chances are there will be reaction between molten Bi and molten NaOH.

Paraffin wax? BP > 370 C. Melt wax, add Bi powder until wax solidifies. Re-melt wax, add more Bi-powder util wax re-solidifies. Repeat until all Bi-powder added and T > 280 C. Cool and find puddle of frozen Bi, neatly protected by paraffin. Live happy ever after. :D

See: https://books.google.co.uk/books?id=kaa2qeFRXmUC&pg=PA62...

Stearic acid: BP = 361 C.



[Edited on 1-2-2016 by blogfast25]




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[*] posted on 31-1-2016 at 23:39


Thanks everyone for answers.
I used to compress powders when I needed to melt them, but I will try to melt it with parafin as u said.
It seems to be simplier way.

[Edited on 1-2-2016 by crystal grower]




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[*] posted on 1-2-2016 at 00:15


Quote: Originally posted by crystal grower  
Hello,
I have been growing bismuth crystals a while ago and beside nice hopper crystals I also got some bismuth oxide from melting.
Is there a simplier way to reduce that oxide to elemental bismuth than reducing it with carbon under big temperatures without presence of oxygen?
Thakns for answer.



[Edited on 31-1-2016 by crystal grower]


According to Nile Red you can simply heat the bismuth oxide and it will decompose into oxygen and bismuth metal.
See this video, at around 4 minutes 45 seconds.
https://www.youtube.com/watch?v=grpSfjUImUs
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[*] posted on 1-2-2016 at 00:39


Quote: Originally posted by Deathunter88  

According to Nile Red you can simply heat the bismuth oxide and it will decompose into oxygen and bismuth metal.
See this video, at around 4 minutes 45 seconds.
https://www.youtube.com/watch?v=grpSfjUImUs

Of course but it must be in inert atmosphere as far as I know.
Or am I wrong ?




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[*] posted on 1-2-2016 at 06:03


I would consider hydrogen gas atmosphere, which you may more inexpensively and easily generate.

[Edit] Downside, H2/air presents an explosion hazard.

[Edited on 1-2-2016 by AJKOER]
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[*] posted on 1-2-2016 at 06:13


Quote: Originally posted by blogfast25  
]

Bismuth is amphoteric: chances are there will be reaction between molten Bi and molten NaOH.



It seems unlikely to me that the two would react. What would you believe the reaction would yield?

Also any gas tank for welding or a stream of dry hydrogen should work for an atmosphere. Heck, even CO2 might work, but I'm not sure about that one.




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[*] posted on 1-2-2016 at 07:56


Per Atomistry on Bi2O3 (link: http://bismuth.atomistry.com/bismuth_trioxide.html ) to quote:

"The trioxide does not decompose when heated to 1750° C. It is reduced, partially or completely, by a number of reducing agents, such as hydrogen, carbon, carbon monoxide, silicon, sodium, potassium, methane, ammonia, ammonium chloride, potassium cyanide, aluminium carbide, and an alkaline stannous solution. "

where the use of heated NH4Cl or an alkaline stannous solution seem interesting. Note, the result may just be a partial reduction to BiO.

If BiO is formed, to quote Atomistry on BiO:

"It is easily reduced to metal by heating on a charcoal block, or in a current of hydrogen or carbon monoxide; reduction in hydrogen takes place at 300° to 310° C., and in carbon monoxide begins at about 250° C."

Also:

"It is converted to metal by reaction with aqueous potassium hydroxide alone"

Link: http://bismuth.atomistry.com/bismuth_monoxide.html

[Edited on 1-2-2016 by AJKOER]
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