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Stable Isotope Geochemistry

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Subject:
From:
Zachary Sharp <[log in to unmask]>
Reply To:
Stable Isotope Geochemistry <[log in to unmask]>
Date:
Wed, 18 Feb 2004 14:57:40 -0700
Content-Type:
text/plain
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Dear John,

Thanks for the advice.  To answer your questions.  1) Our F2 is high purity
and the first sample goes really fast.  It's only after the first two or
three times, as though the NaCl gets coated with NaF and no longer is reactive.

2) We have replaced the metal.  We've used Ni tubing and SS tubing.

Zach

At 02:30 PM 2/18/2004, you wrote:
>The next things I would check are:
>
>1) the purity of your F2.  If it contains a non-condensible gas, its rate
>of reaction will drop enormously at low pressures.  This will manifest
>itself as a persistent trace residue of F2, despite initially vigorous
>uptake (i.e., the first 99 % of reaction is rapid, but the last % takes
>forever).
>
>2) replace the metal of your NaCl/KCl trap.  You may have flourinated the
>metal close enough to the down-stream end of your trap that it can now
>slowly degas F2. Evidence in favor of this problem might include a trace F2
>blank when the trap is hot but only O2 or innert gas is passed through it.
>
>Good luck,
>
>John
>
>
> >Dear Isogeochemers,
> >
> >I am at wits end and need some help.  We are having terrible trouble
> >neutralizing excess F2 gas from our fluorination line.  Originally, we were
> >having wonderful success with NaCl.  Large amounts of F2 could be reacted
> >to NaF + Cl2 in a matter of seconds.  Things were great for months.  Then,
> >we replaced our used NaCl with a  new batach and the reaction no longer
> >proceeds.  After replacing the NaCl, we may get it to work one time, but if
> >we put in a new aliquot of F2, the rates of fluorination of the salt become
> >painfully slow.  We have tried different temperatures of reaction, used KBr
> >in place of NaCl and tried different grain sizes (melted the salts,
> >etc.).  No matter what we do, the reaction of F2 with our salt is so slow
> >as to be unusable.  I'm going crazy.  It used to work, but no longer.  I
> >understand that the Earth's magnetic field is weakening, but I don't think
> >that has anything to do with it!  We've even tried a different bottle of
> >NaCl.  Still no success.  Any ideas would be appreciated.
> >
> >Sincerely,
> >
> >Zachary Sharp

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