Hi Andy (and anyone else interested)

I have seen a similar problem to yours regarding crystals that nucleate and
grow in the silicate line (with the same result - no oxygen). We are
running a similar setup to the one that you describe - CLF3 in externally
heated Ni reaction vessels at ~500°C. Our problems usually stem from runs
where something goes amis (most noteably when the temperature got too high
due to the thermocouples being incorrectly placed) or occasionally when the
line needs cleaning or we inadvetently use too much reacgent. The crystals
are some type of metal chloride and are probably not soaking up the O - we
XRD'd them once and got Ni and Fe Chloride analyses - quite where the O
goes to I'm not sure.

Anyway, here is what we do. If we get a problem in one reaction vessel, we
try cleaning it out with a bottle brush + vacuum cleaner. That often solves
the problem for us. Otherwise, we take the reaction vessels off the line
and polish the inside using a lathe / glass paper - I have a theory that
the crystals will continue to grow once they have nucleated. Perodically
(6-12 months) we polish the inside of all the reaction vessels. 

My suggestions to reduce the problem are:

Check the temperarure of the heaters (our thermocouples measure the
temperatures at the bottom of the reaction vessel, whereas the max T is
about midway up - and that is the region where the crystals seem to grow).
Perodically polish the insides of the vessels if possible.
Try and use the minimum amount of reagent.

Hope that this helps

Cheers

Ian


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Ian Cartwright
Department of Earth Sciences
Monash University
Clayton, Vic 3168
AUSTRALIA

Tel  +61 (03) 9905 4887 / 4879
Fax  +61 (03) 9905 4903
e-mail: [log in to unmask]

May your peak tops be flat, may your isotopes be stable

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