Stable Isotope Geochemistry


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Kim Baublys <[log in to unmask]>
Reply To:
Stable Isotope Geochemistry <[log in to unmask]>
Wed, 6 Jul 2005 08:43:17 +1000
text/plain (79 lines)
Hi Julie,

I have been using BrF5 in our manual extraction line for many years and we
have found that keeping things simple gives the best results.  We actually
found that the Hg diffusion pump was causing vacuum problems (lots of
grunge after many years of operation).  So then I changed to a silicon oil
diffusion pump but it didn't appear to make any difference to the ultimate

As a result I now run with a large liquid nitrogen trap just in front of
the rotary pump  plus another liquid nitrogen trap further up the line in
addition to the standard traps.  This system has been working very well for
the past year.  I just make sure that I freeze the residues from all traps
into the upper cold finger before daily disposal.  This minimizes any
rubbish going into the rotary pump.  My advice would be not to use the soda
lime at all. It will cause too many problems over time and as you have
found out it takes too long to pump down.  My current system takes only a
few minutes to recover between samples.   I am hoping that if I change the
rotary pump oil regularly that I should have many trouble free years of
operation.  Or until I have to source another cylinder of BrF5. :)


Kim Baublys
Stable Isotope Laboratories
Department Of Earth Sciences
University of Queensland 4072

Ph:   +61 7 3365 1131
Fax: +61 7 3365 1277

At 05:39 PM 5/07/2005 -0400, you wrote:
>BrF5 users:
>We have 2 vacuum lines that see bromine pentafluoride - a laser
>fluorination line plus a line used to distill and load BrF5 into a Kel-F
>container.  The fluorination line has Hg diffusion pumps for trapping
>residual BrF5 and protecting the mechanical pump downstream.  On the
>distillation line we were planning to use an in-line trap filled with
>granular soda lime.   However, I have been questioning how well the soda
>lime will work.  When we first put the trap in place, we could not pump
>the line down.  After taking the trap out and looking at the 60 micron
>filter on the downstream side, we saw the filter was at least partially
>clogged with tiny purple crystals.  Fluorite?  If so, that is surprising
>since the line had seen very little BrF5 so far.  After re-installing
>with a clean filter, we observe that the line is pumping down, but very
>slowly.  The soda lime is taking days (almost a week now) to degas.
>I'm interested in recommendations you have for protecting vac pumps from
>BrF5, and whether using soda lime is a practical solution.
>Thanks for any suggestions!
>Julia Cox
>Dept. of Geology
>University of Georgia
>Athens, GA  30602

Kim Baublys
Stable Isotope Laboratories
Department Of Earth Sciences
University of Queensland 4072

Ph:   +61 7 3365 1131
Fax: +61 7 3365 1277