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Author: Subject: The trouble with neodymium...
elementcollector1
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[*] posted on 2-12-2016 at 20:28


Also, quick question about reducing NdF3: Wasn't calcium metal suggested at one point as a suitable alternative?

HoF (CaF2) = -1228 kJ/mol (Wolfram Alpha)

2 NdF3 + 3 Ca -> 2 Nd + 3 CaF2: -370 kJ/mol, more than the equivalent with lithium. Is there some reason this is not preferred that I missed? I read over the entire thread, but couldn't seem to find it. Is it due to calcium fluoride's high melting point?




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[*] posted on 6-12-2016 at 12:40


Update: Just got my sample of pure neodymium oxide from Snaucke Elements on EBay. It arrived as a white/gray powder, with distinct pink tinges under incandescent light.



Most of the sample was then mixed with diluted acetic acid and boiled, in the hopes that this would dissolve the oxide. To my surprise, this worked!



Once the bubblegum-pink neodymium acetate had crashed out, I then decided to test if it dissolved in ethanol. The results gave some important clues:

-The filtrate upon first coming out was the same dark pink as the concentrated aqueous solution. This is presumably due to residual water in the filtered acetate.

-As time went on, however, the filtered liquid became more dilute in coloration, and the drops coming out of the bottom of the filter paper were clear in coloration. The solid acetate on top retained mostly the same volume, though it had largely disintegrated into a paste. This indicates that the solid neodymium acetate is not soluble in ethanol, making separation of iron by selective dissolution in ethanol a viable procedure, provided the iron/neodymium acetates are boiled to dryness.



EDIT: Well, what do you know! The ethanol and water ended up separating just a few minutes after I made this post, and something cloudy has formed at the interface.



[Edited on 12-6-2016 by elementcollector1]




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[*] posted on 6-12-2016 at 12:49


Yay!





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Dan Vizine
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[*] posted on 23-5-2017 at 10:42


Quote: Originally posted by elementcollector1  
Also, quick question about reducing NdF3: Wasn't calcium metal suggested at one point as a suitable alternative?

HoF (CaF2) = -1228 kJ/mol (Wolfram Alpha)

2 NdF3 + 3 Ca -> 2 Nd + 3 CaF2: -370 kJ/mol, more than the equivalent with lithium. Is there some reason this is not preferred that I missed? I read over the entire thread, but couldn't seem to find it. Is it due to calcium fluoride's high melting point?


I'm confident that you're absolutely right and that it's superior to commercial lithium.





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[*] posted on 4-10-2017 at 10:44


The reason lithium is preferred is its fluoride's melting point. Ideally the reaction is run similar to a thermite, where all products are in the liquid phase. This affords good metal-slag separation.
Melting points:
Nd - 1021 C
LiF - 845 C
CaF2 - 1418 C

The reaction's target minimum running temperature is one where everything is molten, thus using LiF reduces this requirement to 1021C.

The other consideration is reaction enthalpy. Careful choice of reducing agent yields extra heat as part of the reaction, helping keep your external heating requirements low. Coincidentally I just yesterday found my calculations for reaction enthalpies for various reducing agents (the more negative the value, the greater the heat released):

Zn - deltaH = 1020.8
Ga - deltaH = 494
Mg - deltaH = -58.6
Na - deltaH = -72.8
Li - deltaH = -193.79
Ca - deltaH = -363.73



These were calculated by using the reaction equation for each:
A NdF3 + B M == C Nd + D MFx
where ABCD are the coefficients and M is the chosen metal. deltaH for elements is 0, so the calculation boils down to
dH = D*deltaH(MFx) - A*deltaH(NdF3)

In retrospect, I used the values for the solids but the products will be liquid. This changes the numbers a little, but preserves their order in the list.

Calcium produces the most heat but requires the highest temperature to melt, and I'm not sure if the tradeoff is favorable or not. If you have calcium metal, it might be worth a shot!

I've been thinking about this experiment again recently. God, I need to just try the last step already.
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[*] posted on 4-10-2017 at 11:35


Interesting.
"A binary eutectic composition of Formula and Formula was observed to melt at 769°C."
From
http://jes.ecsdl.org/content/104/11/661
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[*] posted on 5-10-2017 at 07:32


Formula and Formula you say? :P

From the link (in case it breaks): "A binary eutectic composition of 80.5 mole%LiF and 19.5 mole%CaF2 was observed to melt at 769°C."

Somewhat less than LiF alone, but the reaction still needs to achieve 1021C to melt the Nd.
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