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Topic: Preparation of red allotrope of selenium  (Read 12435 times)

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Offline woelen

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Preparation of red allotrope of selenium
« on: June 11, 2005, 03:51:39 PM »
With some experimenting, I found out how to make the red allotrope of selenium from the black/grey allotrope. A nice experiment on its own, but it might also be interesting for people who collect elements. The grey allotrope can be obtained easily on eBay, while the red allotrope is much harder (and much more expensive) to obtain.

Today, I added the experiment to my site:

http://81.207.88.128/science/chem/exps/selenium/index.html

Have fun  :)

Isolation of the red powder is not hard. Simply rinse a few times with water, filter and dry. Yield is almost 100%.

Question: How stable is the red allotrope? If I store this, does it revert back to the grey/black allotrope, such that after a few months I end up with a black powder again?
Want to wonder? See http://www.oelen.net/science

Offline jdurg

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Re:Preparation of red allotrope of selenium
« Reply #1 on: June 12, 2005, 10:44:33 PM »
That is a very good question.  I am not sure about the stability of red selenium.  A while ago, I purchased an ampoule of red selenium from a supplier over in Austria.  In the photographs I was e-mailed, it had that nice bright red color to it.  When the ampoule arrived, it was still a deep red color but not nearly as bright.  It then looked a bit deeper like a fresh trickle of blood.  Over time, this selenium has gotten darker and darker and now looks like dried blood.  It's pretty similar in color to the brown amorphous allotrope of Boron.  I don't know what's happening with it, but it has definitely grown much, much darker over time.

Reading through the lengthy report in this link (http://aem.asm.org/cgi/content/full/65/11/4734), they mention that under some controlled conditions (anoxic) the red allotrope stayed stable for months, but under normal 'fresh' conditions, within a few days the red allotrope converted to the black one.  So it does appear that red selenium isn't all that stable.
« Last Edit: June 12, 2005, 10:48:53 PM by jdurg »
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Offline woelen

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Re:Preparation of red allotrope of selenium
« Reply #2 on: June 15, 2005, 05:28:45 PM »
That is a very good question.  I am not sure about the stability of red selenium.  A while ago, I purchased an ampoule of red selenium from a supplier over in Austria.  In the photographs I was e-mailed, it had that nice bright red color to it.  When the ampoule arrived, it was still a deep red color but not nearly as bright.  It then looked a bit deeper like a fresh trickle of blood.  Over time, this selenium has gotten darker and darker and now looks like dried blood.  It's pretty similar in color to the brown amorphous allotrope of Boron.  I don't know what's happening with it, but it has definitely grown much, much darker over time.

Reading through the lengthy report in this link (http://aem.asm.org/cgi/content/full/65/11/4734), they mention that under some controlled conditions (anoxic) the red allotrope stayed stable for months, but under normal 'fresh' conditions, within a few days the red allotrope converted to the black one.  So it does appear that red selenium isn't all that stable.
I kept the sample I prepared in a test tube, just as I prepared it some days ago. The precipitate is sitting there in the test tube under water. I'll keep it for several weeks and add a picture of it on my site at that time. Right now, it already has become a little darker. It still is nice red, but it lost some of its brilliance however. So, indeed, it appears that red selenium is not totally stable. In due time, I'll keep you informed.
Want to wonder? See http://www.oelen.net/science

Offline woelen

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Re:Preparation of red allotrope of selenium
« Reply #3 on: June 28, 2005, 04:39:17 PM »
I kept the sample I prepared in a test tube, just as I prepared it some days ago. The precipitate is sitting there in the test tube under water. I'll keep it for several weeks and add a picture of it on my site at that time. Right now, it already has become a little darker. It still is nice red, but it lost some of its brilliance however. So, indeed, it appears that red selenium is not totally stable. In due time, I'll keep you informed.
As promised, I would come back on this. I kept the sample for 17 days and made a picture of it. Just look at the original URL, I changed the page on my website.

Remarkably, the change of color, which I abserved in the first day did not continue at that rate. After 17 days, the sample of selenium still is quite bright red and it does not change noticeably. I kept the sample in a stoppered test tube, at ambient temperature (the last two weeks that was between 23 and 33 degrees centigrade).

I'll keep the sample for a much longer time and see what happens with it.
Want to wonder? See http://www.oelen.net/science

Offline jdurg

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Re:Preparation of red allotrope of selenium
« Reply #4 on: June 28, 2005, 11:13:26 PM »
Try taking some of the sample and removing the layer of water and chemicals above it.  (I.E. clean it and dry it and place it in its own container).  Perhaps the remaining acidic conditions and other chemicals in the water is helping to retard the transformation?
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Offline woelen

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Re:Preparation of red allotrope of selenium
« Reply #5 on: June 29, 2005, 07:44:32 AM »
Try taking some of the sample and removing the layer of water and chemicals above it.  (I.E. clean it and dry it and place it in its own container).  Perhaps the remaining acidic conditions and other chemicals in the water is helping to retard the transformation?
I'll repeat the experiment with a second corpuscle of selenium. I keep the current sample under water. The new sample I'll rinse with distilled water and dry. I'll keep the new sample in the dry state in a second small container. Then I can see the difference for the two methods of storage. Again, I'll keep you updated.
Want to wonder? See http://www.oelen.net/science

Offline woelen

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Re:Preparation of red allotrope of selenium
« Reply #6 on: July 25, 2005, 03:30:51 PM »
I finally found the time to do a new series of experiments with the red allotrope of selenium. I found the following:

Under the liquid, where it is prepared (containing SO2 as reductor), the selenium appears to remain red indefinitely (at least after so many weeks I do not see any change on my original sample, it still is nice red).
When the selenium is washed a few times with distilled water in order to remove the water-soluble chemicals, then it quickly turns darker. I let the sample dry, but after one day, the dry sample was even darker than red phosphorus, it was really dark brown.
When the selenium is washed with distilled water a few times and kept under distilled water, then it also turns dark quickly. After one day, the sample was almost black.

So, concluding, red selenium is not stable under ordinary storage conditions. Only, when stored in a reducing wet environment it appears to be stable. I have no explanation for this, maybe someone else has an explanation?
Want to wonder? See http://www.oelen.net/science

Offline Quaff

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Re: Preparation of red allotrope of selenium
« Reply #7 on: January 05, 2010, 09:10:50 PM »
With some experimenting, I found out how to make the red allotrope of selenium from the black/grey allotrope. A nice experiment on its own, but it might also be interesting for people who collect elements. The grey allotrope can be obtained easily on eBay, while the red allotrope is much harder (and much more expensive) to obtain.

Today, I added the experiment to my site:

http://81.207.88.128/science/chem/exps/selenium/index.html

Have fun  :)

Isolation of the red powder is not hard. Simply rinse a few times with water, filter and dry. Yield is almost 100%.

Question: How stable is the red allotrope? If I store this, does it revert back to the grey/black allotrope, such that after a few months I end up with a black powder again?

cool stuff.    Now you've got me wondering, whether it could be possible to use a tiny clump of the red amorphous selenium, and contact it to a larger piece of selenium, to maybe cause a change in the larger piece, to the red form.   Kind of how tin undergoes change when so nucleated:

http://www.youtube.com/watch?v=FUoVEmHuykM



Offline caveman

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Re: Preparation of red allotrope of selenium
« Reply #8 on: August 22, 2011, 05:17:26 PM »
would this experiment work with black selenium powder rather than black shot? ???

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