numos
Hazard to Others
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Registered: 22-2-2014
Location: Pasadena
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Strange flammable Chromium gas
So I just finished distilling a few hundred milligrams of Chromyl chloride and decided to seal it in an ampule, however as I did, a flame started
burning out of the ampule. I don't think Chromyl chloride is flammable, so I'm honestly stumped.
I know what a sodium flame looks like and the type of "second flame" that forms when heating glass, but this was definitely something different. the
flame even had some streaks in it, similar to when burning Zinc.
The flame only lasted a few seconds and then disappeared. It was made from Na-chloride, Sulfuric acid, and K-dichromate, although the distillation
should have removed those.
Any thoughts?
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woelen
Super Administrator
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Chromyl chloride is not flammable, but it may be that it decomposes quickly at elevated temperatures with appearance of heat and light. I cannot
conceive anything else which could lead to flames from an ampoule of CrO2Cl2.
Btw, I would be very reluctant to ampoule this chemical. As far as I know, it is not really stable and slowly decomposes, giving mainly Cr2O3, O2 and
Cl2. The gases build up pressure in an ampoule and this will lead to explosion of the ampoule after some time of storage. I am really sure about this,
but before you do so, be absolutely sure that it is safe to store the chemical in a completely sealed container.
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Praxichys
International Hazard
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I keep mine in the freezer at -20C. (Dedicated lab freezer only!) I think it has decomposed noticeably after a year, leaving ring of what I presume is
some oxide of chromium at the liquid level on the glass. I keep it in a round-bottomed flask with a greased stopper, which should blow out if there is
significant gas buildup.
I would not ampoule that either. It is one of those reagents that performs best when prepared fresh, anyway. At the very least, you would have to
redistill before use, at which point you could have just made a fresh batch with the same apparatus.
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