Dear Francesca and others,

You better do not use Br-pentafluoride (BrF5) for recovering your Cr
metal. I understood you want to 'reactivate' (reduce) the Cr in the
reactor without removing it first, which in theory might be a good idea.
If you react with BrF5 the silica glass will be etched and eaten away -
rather slowly at room temperature and quickly if you heat up a bit -
besides the dangerous operation to carry out  and control the reaction.
Also, I expect the Cr2O3 to turn into CrF3 or other more complex
fluoride-compounds (also depending on any polution adsorbed on the
Cr-Cr2O3). You rather must think about reducing reactors instead of a
stronger oxidator than O2, such as H2 or CH4, if you want to remove the
oxygen from the metal - although this is just a rough idea - there will
be more (and probably better) reductors. However, I see still some other
problems in doing so - polutions from samples adsorbed on the Cr-Cr2O3
should be removed too, or else it will pile up and render the reactor
useless after a few 'reactivation' turns. I am wondering if reworking of
the Cr really pays off if considering the time and costs (salary of
analyst doing the job included) to get it right. The silica (or quartz)
glass reactor is another story, of course - if one can reload it with
fresh Cr it certainly will be economic to do so.

I hope 'my two pennies worth' is giving you a better idea about the
problems you face if reactivating/reducing the Cr in the reactor.

Pier.
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Dr. P.A. de Groot
University of the Witwatersrand
Economic Geology Research Unit
Department of Geology
Private Bag 3
2050 Johannesburg
South Africa
Tel. +27 11 7162564
Fax. +27 11 3391697
E-mail <[log in to unmask]>

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