Dear Marie

To get conversion of O2 to CO2 the graphite should show a dull red glow. I
would think that this would occur at temperatures higher than 650 to 700
degC, probably closer to 800-900 deg C. Try raising the temperature.
It is true too though, that the more porous the graphite gets the faster the
conversion will be. If raising the temperature does not do it, change the
graphite.

Good luck,

                Torsten.

>We are building a conventional fluorination line, and now testing the
>conversion chamber by introducing an aliquot of pure oxygen tank gas into
>our system, while heating a graphite rod up to 650-7000C. The furnace
>consists of a couple of IR lamps focussed on a graphite rod contained in a
>quartz tube (external heating), and the temperature of the graphite is
>checked by a thermocouple inserted inside the graphite. While heating the
>graphite and cooling down an U tube in a liquid nitrogen trap,  we
>introduce the oxygen in the previously pumped conversion chamber; at that
>moment what we should observe is first an increase of the pressure, as O2
>is introduced,  and then a progressive drop while the CO2 is condensed. We
>just see the O2 introduction and no CO2 seems to be trapped. We can't find
>out what is wrong.Two possible causes come to my mind :
>- we just form CO, but why?
>- the graphite quality we got is not compatible with an oxidation process?
>I am quite puzzled, as I used a similar device, not exactely the same but
>quite similar in principle in NIGL, few years ago, but it was no problem as
>Peter Greenwood and other friends there could attest. The major recognized
>difference about the quality of the graphite is that the one I bought here
>in France is far denser than the one currently used in UK; furthermore the
>shape of the graphite is different as we needed plane surfaces for the IR
>lamps heating....but I can't see any other major differences.
>
>If anybody can be of some help? Should I try another type of graphite?
>Which one? All ideas are really welcome, as we are quite novice in the
>business.
>

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Torsten W. Vennemann
Institute for Geochemistry
University of Tuebingen
Wilhelmstr. 56
72074 Tuebingen
Germany

Tel: (0)7071 29 74992
Fax: (0)7071 29 6870
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