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blogfast25
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MrHS:
I see now I've missed part of the action (your posts of 26/10).
Looks like a failure alright. Most likely explanation must indeed be oxygen.
I'm looking at that 'nested design' with argon blanket, with a small steel or iron crucible sitting inside a sealed off (bottom) copper piece of pipe
(1 1/2" to 2"). I don't have a furnace, so that means relying heavily on the anticipated exotherm and full blast propane from beneath.
Quote: Originally posted by MrHomeScientist  |
Come to think of it, now that I have this furnace setup, is magnesium reduction a possibility again? We scrapped that because it didn't produce enough
heat of reaction, but if I heat the whole thing externally that won't be a problem. Then I wouldn't need inert atmosphere either, which would simplify
greatly. In fact I think I still have the Mg + NdF3 mixture that failed from my first attempt... |
Remember that the low value of ΔG is related to the equilibrium constant of the reaction, via Nernst. For ΔG = 0 basically K = 1.
That means conversion will be very poor and you'll obtain a mix of metals, possibly an alloy.
It could be worth revisiting my reference to Brauer's methods for REEs. I had referenced them in the La thread before it got deleted by the spam
robot.
Brauer's part II suggests a method using anh. RECl<sub>3</sub> by reduction with calcium, boosted with sulphur, iodine or chlorate.
Magnesium seems generally useless for reduction of REE halides.
[Edited on 27-10-2014 by blogfast25]
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Brain&Force
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The reference to Brauer is in the new La thread. Download it if you haven't; it's a must read.
I'm wondering, if you flush out O2 with propane, will that work to prevent the lithium from reacting or will it just introduce side
reactions?
At the end of the day, simulating atoms doesn't beat working with the real things...
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blogfast25
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| Quote: Originally posted by Brain&Force | | I'm wondering, if you flush out O2 with propane, will that work to prevent the lithium from reacting or will it just introduce side
reactions? |
KA-BOOOOMMM!
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gdflp
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How about using strontium metal for the reduction of RE fluorides? It's a lot cheaper than calcium or lithium($80.75/5.5lbs, Free shipping from
GalliumSource), and it's more electronegative than calcium. According to WolframAlpha, it's exothermic, -335kJ/mol. In addition, it shouldn't have
the problem of reacting with the crucible. It's melting point is kind of high though at 777°C, that might cause problems.
[Edited on 10-28-2014 by gdflp]
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blogfast25
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Acc. Wolfram Alpha, what is exothermic? Nice number but what does it represent?
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Texium
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Perhaps he's referring to the reduction of neodymium fluoride with strontium?
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blogfast25
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If so, he's miscalculated, it's only about - 167 kJ/mol.
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Brain&Force
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http://www.sciencemadness.org/talk/viewthread.php?tid=32521&...
Strontium is definitely a cheaper choice, and it will probably work to reduce the Nd but it probably won't work without flushing out O2.
In Brauer there are references to reduction of anhydrous LnCl3 in alcoholic solution. It appears to be possible to make the anhydrous
chloride by heating with ammonium chloride, but the product will be contaminated with ammonium chloride afterwards. Will this affect the reduction in
any way?
At the end of the day, simulating atoms doesn't beat working with the real things...
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gdflp
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Sorry I wasn't more specific. Yes, I was talking about the reduction of neodymium fluoride with strontium, and my number was off because I calculated
using the equation 2NdF3 + 3Sr --> 2Nd + 3SrF2 and I didn't divide by 2.
Why would the product be contaminated with ammonium chloride, I thought the whole point of it was to allow it to decompose into NH3 and HCl,
effectively heating the RE chloride in a stream of HCl. Anhydrous RE chlorides should be stable to strong heating, so after the water has been
removed the mixture could be heated to sublime away any excess ammonium chloride.
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blogfast25
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I see no reason why it should. It should blow off nicely.
My own singular experience with NdCl3 hydrate/NH4Cl wasn't very positive even though previously I got it to work well for MnCl2 hydrate.
The mixture need to be very intimate (very finely ground) and starting from quite dry hydrate. I think partial vacuum probably helps things too.
Removing those very last traces of NH4Cl may be tricky, as indicated in the Brauer entry.
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Brain&Force
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I'm not entirely sure what would cause the explosion after re-reading this. Would the lithium react with the propane?
I specified that the oxygen would be flushed out, which should prevent an explosion from occurring (in theory).
At the end of the day, simulating atoms doesn't beat working with the real things...
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Dan Vizine
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Molten lithium will react with it at higher temperatures.
"All Your Children Are Poor Unfortunate Victims of Lies You Believe, a Plague Upon Your Ignorance that Keeps the Youth from the Truth They
Deserve"...F. Zappa
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Brain&Force
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Yeah, that's what I thought. Molten lithium doesn't particularly like concrete, either.
At the end of the day, simulating atoms doesn't beat working with the real things...
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Dan Vizine
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And yet it's stable in the molten state in pure dry oxygen.
I love the seeming contradictions in chemistry. Like this one:
A sample of Na at 200 C will spontaneously ignite in the air. A sample of K at 280 C won't. Yet we all know that K is more "reactive" than Na. So..??
[Edited on 29-10-2014 by Dan Vizine]
"All Your Children Are Poor Unfortunate Victims of Lies You Believe, a Plague Upon Your Ignorance that Keeps the Youth from the Truth They
Deserve"...F. Zappa
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blogfast25
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| Quote: Originally posted by Brain&Force |
I'm not entirely sure what would cause the explosion after re-reading this. Would the lithium react with the propane?
I specified that the oxygen would be flushed out, which should prevent an explosion from occurring (in theory). |
I was specifically referring to the flammability of propane as cause for great danger with open flames, nothing else.
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blogfast25
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| Quote: Originally posted by Dan Vizine | A sample of Na at 200 C will spontaneously ignite in the air. A sample of K at 280 C won't. Yet we all know that K is more "reactive" than Na. So..??
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Assuming these data points are factually correct then it may be related to volatility or activation energy.
You're right to use quote marks: "reactivity" is a poorly defined and elastic term.
Nature defies our simple models quite a lot.
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Praxichys
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| Quote: Originally posted by Dan Vizine | | A sample of Na at 200 C will spontaneously ignite in the air. A sample of K at 280 C won't. Yet we all know that K is more "reactive" than Na. So..??
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I wonder if this has something to do with passivation?
Aluminum is "more reactive" than iron, but iron reacts with the air faster. Perhaps the oxide properties of K are better suited to form a film on the
liquid than that of Na?
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blogfast25
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| Quote: Originally posted by Praxichys | | Quote: Originally posted by Dan Vizine | | A sample of Na at 200 C will spontaneously ignite in the air. A sample of K at 280 C won't. Yet we all know that K is more "reactive" than Na. So..??
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I wonder if this has something to do with passivation?
Aluminum is "more reactive" than iron, but iron reacts with the air faster. Perhaps the oxide properties of K are better suited to form a film on the
liquid than that of Na? |
It's possible but the comparison with Al/Fe is flawed because at these temperatures both Na and K are liquids, with constant surface renewal.
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Brain&Force
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| Quote: Originally posted by blogfast25 | | Brauer's part II suggests a method using anh. RECl<sub>3</sub> by reduction with calcium, boosted with sulphur, iodine or chlorate.
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Sulfur may not be a good idea for thermiting. The main reason is that many lanthanide monochalcogenides tend to be stable. With neodymium this may not
be a significant factor, as it's difficult to reduce to a 2+ state, but it will likely be signifiant if you intend to repeat the work with samarium,
ytterbium, or europium-containing mixtures.
At the end of the day, simulating atoms doesn't beat working with the real things...
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blogfast25
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| Quote: Originally posted by Brain&Force | | Sulfur may not be a good idea for thermiting. The main reason is that many lanthanide monochalcogenides tend to be stable. With neodymium this may not
be a significant factor, as it's difficult to reduce to a 2+ state, but it will likely be signifiant if you intend to repeat the work with samarium,
ytterbium, or europium-containing mixtures. |
CaS is likely to have a much more negative enthalpy of formation than REE sulphides. Properly formulated mixtures would then not lead to the latter
forming, only CaS.
Sulphur would not be my first choice of booster system though.
[Edited on 1-11-2014 by blogfast25]
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MrHomeScientist
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Yesterday I purchased a 40 cubic foot cylinder of pure argon, along with a regulator and some fittings, as step 1 in creating an inert atmosphere for
this reaction. Progress!
The graphic I posted on the previous page was intended as a 'nested crucible' which would be lowered into my small furnace and be heated externally
via propane torch. Instead of that, what about simply blowing a stream of argon over the mouth of the crucible containing the reaction? That would
provide a blanket of Ar over the reaction without needing to make any complex (for me) apparatus. I'd make the gas outlet into something like a wing
top attachment for bunsen burners, like this one: http://www.enasco.com/product/SB06947M
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The Volatile Chemist
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| Quote: Originally posted by MrHomeScientist | Yesterday I purchased a 40 cubic foot cylinder of pure argon, along with a regulator and some fittings, as step 1 in creating an inert atmosphere for
this reaction. Progress!
The graphic I posted on the previous page was intended as a 'nested crucible' which would be lowered into my small furnace and be heated externally
via propane torch. Instead of that, what about simply blowing a stream of argon over the mouth of the crucible containing the reaction? That would
provide a blanket of Ar over the reaction without needing to make any complex (for me) apparatus. I'd make the gas outlet into something like a wing
top attachment for Bunsen burners, like this one: http://www.enasco.com/product/SB06947M |
In my own uneducated opinion, it sounds good; It doesn't seem like you would be able to run the reaction for long, though, without running out of the
stuff (Argon)? also, wouldn't there be a pocket of air underneath the stream that wouldn't necessarily be replaced by the argon?
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blogfast25
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Mr HS:
My plan (if I ever get round to it) would be to hermetically seal the bottom of the outer crucible, then have a copper or steel pipe reach down into
it (to near the bottom), to pipe the Ar into the outer crucible. At first give it all a good flux, then switch to lower flow rate. Load the reactants
into the inner crucible while it's submersed into about half the depth of the outer crucible, then lower it to the bottom and start heating.
This should give a reasonably O2/N2 free atmosphere w/o the need to seal everything off perfectly.
Ar is denser than air, so that should help (a bit).
[Edited on 5-11-2014 by blogfast25]
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MrHomeScientist
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My progress on this experiment continues at glacial pace! I finally got around to ordering and fabricating my inert atmosphere crucible, made of black
iron pipe and fittings. Here it is, and I've dubbed it "The Gavel". Or if you prefer, "The Croquet Mallet".
Argon enters from the 1/4" pipe on the right. The 2" pipe on the left is the reaction chamber, inside which a small crucible which contains the
reactants will rest. A hole in the top of the chamber allows gas to exit, and the whole assembly will be heated from below (probably). Here's another
view:
You can see the exhaust hole in the lid, and the space inside where the small inner crucible will rest. I may need some sort of heat transfer media
inside to help heat the small crucible, something like stainless steel ball bearings.
The latest problem is that this whole thing just barely will not fit into my mini propane furnace. So I need to find a way to heat this thing up to
the requisite several hundred degrees. Maybe wrap the whole thing in insulating kaowool?
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blogfast25
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Looking good. Insulating will help, of course.
Remind me again which REE you're gunning for? REF<sub>3</sub> + 3 Li ?
[Edited on 1-3-2015 by blogfast25]
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