This is addressed to those in the Isogeochem community that use BrF5 for
laser-assisted fluorination of silicates:

We have experienced occasional difficulties purifying BrF5 from traces
of HF, prior to use. As regular practitioners of the art will recognise,
this has a detrimental effect on the barium fluoride window of the
reaction cell; it also results in a considerably longer pump-down time
being required to achieve baseline vacuum afterwards. Usually, repeated
cryogenic distillation is advocated to separate HF from BrF5, but this
is a tedious procedure at best; at worst, the relatively small
difference between the respective boiling points (41C at 1atm for BrF5,
20C for HF) renders the separation inefficient .

It is well established that NaF is effective in removing HF vapour,
through formation of NaHF2; a major benefit is that no gaseous products
are formed. We already this procedure here, to remove HF from a gas
stream consisting of O2 and HF. It occurred to me that maybe the same
reagent could be used to remove HF from BrF5. The NaF would need to be
in the form of pellets, rather than powder; however, such material is
commercially available for the purification of F2 from contamination by
HF. Presumably, the BrF5 vapour could be transferred from one reservoir
to another, by liquid nitrogen trapping, via a tube containing the NaF
pellets. This procedure seems sound in principle... but then why has it
not been adopted before? Or does no-one else have problems with their
BrF5?

Ultimately, switching to F2 as the fluorinating agent, rather than BrF5
is probably the best way forward. Those who are considering this route
may like to be aware that a small F2 generator, called the Fluorodec LT
and based on a replaceable electrolytic cartridge, was recently launched
onto the market by a UK company called Fluorogas. For anyone interested
in further information, the company may be contacted by e-mail at:
[log in to unmask]
There is also a website: www.fluorogas.co.uk


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Martin F Miller,
Planetary Sciences Research Institute,
The Open University,
Walton Hall,
Milton Keynes MK7 6AA

Tel (direct line): +44 1908 652011
Fax (departmental): + 44 1908 655910
E-mail: [log in to unmask]