Dan Vizine
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Practical Techniques for Preparing Ampoules with Large Lanthanide Samples
Recently, I've had the opportunity to expand my element collection by doing some contract work for another collector. This collector happens to be
working his way through the lanthanides, and aside from the gas samples, this is the group of the periodic table which I needed most to acquire.
The samples that I've been working on for him recently include lanthanum, neodymium, protactinium and cerium.
Just judging from my cutting and cleaning operations, reactivity seems to increase in the same order.
The purpose of this entry is to explain how to make samples of lanthanide elements in glass ampoules under argon. Several of the samples weigh over
200 g and yet the requirement was that they be mailable without breakage. We achieved this.
The phases that need to be accomplished to duplicate my work are these:
1) you'll need to either glass blow rounded end tubes or, less desirably, use commercial test tubes. The reason they are less desirable is that they
typically have thinner walls.
2) you'll need to cut the bulk metal up.
3) you'll need to clean the metal and then finally ampoule it under argon in such a way that the metal sample contained within never has a chance to
slide easily during shipping, thus breaking open the ampoule.
These are not the only ways, but these are the ways that I used to prepare the samples:
Corresponding to requirement one, I made glass ampoules from three-quarter inch OD medium-wall borosilicate glass tubing. The typical length was about
8 inches.
Corresponding to requirement two, that depends on the equipment at hand. Lanthanum and neodymium were not particularly difficult to cut for any reason
having to do with reactivity. Protactinium was a slightly hidden danger and cerium was a flat-out hail of burning metal. What makes protactinium
somewhat of a hidden danger is its intermediate reactivity. Depending upon the thickness of the material, the blade pressure, and the blade speed, my
horizontal metal cutting bandsaw would sometimes accumulate a fair amount of protactinium sawdust, and this could ignite all at once if a flaming
particle hits it. Whereas I collected over 100 g of neodymium sawdust while preparing samples, I didn't accumulate any protactinium or cerium sawdust.
One way or another, it all was ignited eventually. Special precautions were taken for some of the more reactive ones.
This link is for a very short movie showing the cutting of cerium metal. Directly over the area where the sawdust burned, it was necessary to use a
trunk type ventilator.
https://www.dropbox.com/s/r7217wjanx6jnei/2015-09-07%2011.21...
that's one of the special precautions.
The other concerns sample temperature. Some researchers have noted ignition of bulk cerium. The pieces I had were several pounds and that would've
been a huge problem to deal with if it ignited. The first time I lowered the bandsaw blade onto the cerium, I was a little scared. SO much fire.... So
what I ended up doing was a slower but safer alternative. The cerium was stored in my refrigerator. I would take the metal downstairs and use the
bandsaw until I felt the bulk of the sample was warm to the touch. Then I'd throw the ingot back into a can under argon and back into the
refrigerator. This needed to be done multiple times as I had quite a few cuts to make. No other sample required cooling prior to cutting.
I cut the metal into long square sections about 11 mm on a side. This gave a metal slug that fitted fairly closely to the glass walls at the corners.
If you do not have access to a bandsaw, a hack saw will work especially if you aren't preparing multiple samples and you will simply have to file the
irregularities out of your crude forms.
It is particularly worthwhile to note that if you keep the filing speed low and the pressure moderate, you can even clean cerium in the atmosphere
with no special precautions. This is usually done to give a nice surface, but it isn't the final cleaning stage.
The final one needs to be done right next to your station with the argon. You need to arrange your sample tubes with a septum at the top so that you
can flush the entire tube out with argon gas. The needle supplying the gas should extend all the way to the bottom of the tube, while the connection
to the bubbler is at the top through a syringe needle. A stainless steel wire wheel was the final cleaning agent. Holding the bars in different
orientations to the wheel produces different surfaces. You have to only clean a little at a time so that the sample does not warm too much. So for a
sample with a total surface area of a few square inches it probably took about 4 to 5 minutes. That's a pretty conservative rate which gives a nice
metal surface and no discoloration due to inadvertent heating.
The next point addresses concern number 3. How are we going to immobilize the metal slugs in the glass tubes for shipping? When I was doing the
lanthanum samples in the first part of this project, I tried several methods. One method was very precise filing to allow the metal slug to need to be
pushed into the glass tube with a little force. Another method was to try to form the ampoule seal so close to the top of the metal sample that it
almost locked it in place. The last method that we tried, and the one that I have adopted for all others since, is the insertion of a thin, equally
well cleaned, shim of metal. Nearly all of the lanthanides can be cut into thin slices, say < 1 mm, without too much difficulty. Cerium is an
exception. You can still get the long thin slices you need, but you have to do it by hand with a hack saw. Cleaning thin sections, especially of
cerium, requires a very light touch on the wire wheel. A half dozen light touches are much better than one with more force. Once this sliver has been
formed and cleaned it's given a slight but continuous bend. This is inserted right alongside the main metal sample. The small amount of tension it
maintains with the glass walls prevents the metal samples from moving. You can see these in several of the samples, they are actually in all of them.
Once this is done, the tube is given a final flushing with argon, sealed with a rubber septum and then brought down to the torch for sealing. I purge
the glassblowing tube that goes to my mouth with argon before use and attempt to draw as little through the tube as humanly possible to get a good
ampoule seal.
Making and transporting large metallic samples inside glass ampoules has always been problematic. I believe that this technique of inserting a
miniature "leaf spring" of the same material along with your primary sample is the best that I have seen.
The picture below shows 4 Ce, 4 Pr and 5 Nd ampoules.
[Edited on 10-9-2015 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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aga
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Fabulous work Dan Vizine !
Thank you very much for sharing the techniques.
Edit:
Did you need any special torch or gas to melt/form the thicker walled glass tube ?
[Edited on 10-9-2015 by aga]
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Dan Vizine
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Not really, aga. A single orifice natural gas-oxygen torch is fine for work up to an inch in diameter. I use a Variflow type 3A blowpipe, as they like
to call it.
"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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gdflp
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I hope you weren't working with 200g of protactinium! Somehow, I think this is a typo
Those are some beautiful samples of the lanthanides though.
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Texium
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I'm gonna guess he meant to say praseodymium based on the fact that there are several tubes labeled Pr in the picture that he posted. But gee, it sure
would be cool to have some protactinium. Seems to be virtually nothing out there about its chemistry despite it having a very long lived isotope.
[Edited on 9-11-2015 by zts16]
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Dan Vizine
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Quote: Originally posted by zts16  | I'm gonna guess he meant to say praseodymium based on the fact that there are several tubes labeled Pr in the picture that he posted. But gee, it sure
would be cool to have some protactinium. Seems to be virtually nothing out there about its chemistry despite it having a very long lived isotope.
[Edited on 9-11-2015 by zts16] |
How embarrassing....yes, praseodymium.
Yes, I agree...no protactinium anywhere. I was rather surprised to learn that even promethium was once used in lighted dials.
[Edited on 11-9-2015 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
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chornedsnorkack
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| Quote: Originally posted by zts16 | it sure would be cool to have some protactinium. Seems to be virtually nothing out there about its chemistry despite it having a very long lived
isotope.
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Yes. 32 000 years. Longer than the 24 000 years of Pu-239... and no worries about going critical during handling.
Between the more stable actinides - Th, Pa, U, Np, Pu, Cm - which of them are more reactive and problematic when handling the metal in air?
But I suppose that preparing an ampoule with a large amount of alpha radioactive isotope of short half-life has problems of its own. How do you plan
to vent the buildup of helium?
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Dan Vizine
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There are many variables concerned in the word handling.
But as to the Pa, I think it has to do with an appropriate source. If it is extracted from uranium tailings, it will be a mixture of many harmful
isotopes and making it from Th-240 requires a true laboratory and a reason to make it.
As to the others, they are all very reactive metals. Thorium can be very pyrophoric and with its very high mp (~1800 C), it's hard to consolidate by
melting because of crucible contamination, etc. Uranium is also very reactive, can be pyrophoric and blackens in air quickly. It's easier (but not
easy) to work with due to a mp about equal to gold. Neptunium is less reactive (but still a better reducing agent than aluminum), blessed with a low
melting point. Pu isn't as reactive as some of the foregoing, and the mp is lower than aluminum. Overall, powdered Th and U seem to be some of the
harder to handle in air.
"All Your Children Are Poor Unfortunate Victims of Lies You Believe, a Plague Upon Your Ignorance that Keeps the Youth from the Truth They
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Oscilllator
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That's very interesting. In the past I hadn't paid much attention to the people going on about depleted uranium contamination from uranium munitions,
but this gives them a little more credibility. I imagine a slug travelling at a few km per second would spread around a lot of debris on impact, but
if that debris was pyrophoric then you could potentially get pretty serious contamination.
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chornedsnorkack
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| Quote: Originally posted by Dan Vizine | There are many variables concerned in the word handling.
But as to the Pa, I think it has to do with an appropriate source. If it is extracted from uranium tailings, it will be a mixture of many harmful
isotopes and making it from Th-240 requires a true laboratory and a reason to make it.
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How do you get Th-240? The heaviest Th isotope I could read of is Th-238.
But Pa has just 2 natural isotopes, and should be easy to extract at high purity:
Pa-234 is a daughter of U-238, but its longer lived isomer UZ has half-life of just 6,7 h (and is a minor decay branch).
So if you chemically separate U tailings from mother U, then all Pa-234 decays in a few days and you are left with pure Pa-231.
Compare with Pu, which, if you produce it by neutron irradiation, is liable to contain admixtures of Pu-240 (half-life 6500 years) and Pu-241
(half-life 14 years).
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sbreheny
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| Quote: Originally posted by Dan Vizine | Once this is done, the tube is given a final flushing with argon, sealed with a rubber septum and then brought down to the torch for sealing. I purge
the glassblowing tube that goes to my mouth with argon before use and attempt to draw as little through the tube as humanly possible to get a good
ampoule seal.
[Edited on 10-9-2015 by Dan Vizine] |
Nice work Dan. Can you please give more details on the sealing process - I don't understand what you are doing with the glassblowing tube. Is that
just the open end of the tube? I've never heard of an ampoule sealing technique involving one's mouth.
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