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Author: Subject: Crucible for NaOH fusion
RU_KLO
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[*] posted on 10-1-2025 at 11:35
Crucible for NaOH fusion


I need to perform fusion with NaOH + NaNO3 + Na2CO3.

the book asks for nickel crucible.

I read the wiki crucible:
https://www.sciencemadness.org/smwiki/index.php/Crucible

Getting a Nickel or magnesium oxide is difficult for me.

In another posts:

"The one time I melted NaOH in a porcelain crucible, I ended up destroying it by simply dissolving/weakening the ceramic to the point of failure. I've never had this problem with metal crucibles "
http://www.sciencemadness.org/talk/viewthread.php?tid=154253...

"But as mackolol said plain ceramic should be ok, I also did a lot with molten NaOH and KOH in them"
https://www.sciencemadness.org/whisper/viewthread.php?tid=15...


the procedure ask for a NaOH "bed" in the bottom of the crucible, the sample (fine ground) above this bed and in the middle, on top a layer of NaNO3 + Na2CO3.

heat (slowly) till everything dissolves. (no more that 15 sec in a nickel crucible)

Can this be "substituted" with a common porcelain crucible (which I can get)

I understand that alkaly (molten even more) attacks porcelain, but maybe not too hot (only until melting) and 10s there is no such attack or is minor.
(more important, not contaminating the sample - or trace contamination that will not invalidate the analysys)

Does anyone has experience with this?

Thanks






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[*] posted on 10-1-2025 at 15:34


So any type of ceramic material (ether Al or Si based) will dissolve is this mixture.
So will aluminum containers

You need nickel or platinum to prevent contamination of your product.
Cheap stainless, cast iron, etc will intorduce iron contamination turning your molten salt a black, then brown, then red
Good stainless will introduce crome turning first a light blue then a darker blue.

If this will effect your chemistry is unknown to me
I use these little cups with molten NaOH.
https://www.amazon.com/gp/aw/d/B06XZB1ZG2

[Edited on 10-1-2025 by Rainwater]




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[*] posted on 11-1-2025 at 03:22


Amazon does sell Ni crucibles.
https://www.amazon.com/s?k=nickel+crucible&crid=2HCLRQQR...
Ni is rather restistant to molten lye. NaOH with the other two salts dissolved in it is still very aggressive to most other materials.
Pt is the best but very $$$.
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RU_KLO
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[*] posted on 11-1-2025 at 03:23


Understand, thanks.

Could one made of graphite work? Or graphite will be corroded too?

I don't mind carbon contamination.




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[*] posted on 11-1-2025 at 03:30


Quote: Originally posted by RU_KLO  
Understand, thanks.
Could one made of graphite work? Or graphite will be corroded too?
I don't mind carbon contamination.

Graphite will be corroded I think, but it is an assumption. I have never tried.
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[*] posted on 11-1-2025 at 04:16


Silver works if you aren't getting too hot.
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