Peter,

      I would suspect that the temperature isn't being regulated properly
in that furnace -- maybe the fault of the temperature controller or a bad
thermocouple, although I think they rarely go out.  You might fill a tube
with quartz chips and insert a temp probe down to the center and monitor it
for awhile.  I would leave the tube connected at the bottom so that helium
was still moving through it.   --  Steve

Steven Silva
U.S. Geological Survey
345 Middlefield Rd., Mailstop 434
Menlo Park, CA 94025
ph:  (650) 329-4558
fax: (650) 329-5590
email: [log in to unmask]






|---------+---------------------------------------------------->
|         |           Peter Ditchfield                         |
|         |           <[log in to unmask]
|         |           FORD.AC.UK>                              |
|         |           Sent by: Stable Isotope Geochemistry     |
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|         |           10/31/2003 03:12 AM                      |
|         |           Please respond to Stable Isotope         |
|         |           Geochemistry                             |
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  |       To:       [log in to unmask]                                                      |
  |       cc:                                                                                    |
  |       Subject:  reduction tube melt down                                                     |
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Dear Listmembers
We have had a recent spate of Cu reduction tubes becoming blocked by
some reaction taking place within the copper oxide which is forming as
the copper becomes oxidised. The system is a Carlo Erba EA attached to
a Europa geo 20/20 running in continuous flow mode. the reduction
furnace runs at 600 C.
Instead of the usual granular copper oxide replacing the granular
copper we get a black shiny (viterfied) plug of solid copper oxide
which blocks the He flow  and in bad cases fractures the silica tubing
of the reduction column.
There seems to be little pattern as to when it happens and is just as
likely towards the end of the life of a reduction column as a few hours
after a column change. The vast majority of samples that we process are
collagen.
Has anyone else had similar experiences? any thoughts on possible
causes such as excess water in the combustion products?


Dr. Peter Ditchfield
Stable Isotope Laboratory Manager
Research Laboratory for Archaeology
University of Oxford
6 Keble Road, Oxford, OX1 3QJ, UK
tel:01865-283647
fax:01865-273932