Dear Janet,


I have been making my own reactor tubes ever since I've got my first
GC/C-IRMS (a Delta S) in 19xx, well longer ago than I care to remember.

My protocol for preparing reactor tubes slightly differs from yours in 2
points.

(1) For a variety of reasons, I aim for threading 2 of each Cu, Ni and
Pt wires into the ceramic tube. I don't twist them together but thread
them into the tube individually but that's just a matter of personal
preference, i.e. it works for me and my butter fingers; I never had much
luck with twisted or braided wires as in my hands they tend to get stuck
halfway up the tube and kink.

(2) More importantly, I oxidise a new reactor for 12-18 hours at 600-620
C, after which time I bring the furnace up to 940 C gradually while
shutting off the oxygen supply. Once at 940C, I leave the system to its
own devices for at least 6 hours (still in back-flush mode) and then run
a few dummies (simple alkane mix) to run in the furnace as the first few
runs tend to be c*r*a*p anyway, d13C-wise. However, after that the
reactor is good for say approx 200 runs (depending on complexity and
concentration of samples) before d13C-values start to get lighter.

What seems to happen in your case I suspect, is some sort of degradation
of the metals; I mean 12 hours in O2 at 940C is being a bit harsh on the
wires, don't you think?

Also, all the metal wires I use are Johnson Matthey products
(Puratronic), which are available from Alfa Aesar (
http://www.alfa.com/alf/index.htm ).


Hope this helps.


Best wishes,

Wolfram





> -----Original Message-----
> From: Stable Isotope Geochemistry
> [mailto:[log in to unmask]] On Behalf Of Janet Hope
> Sent: 30 July 2004 07:09
> To: [log in to unmask]
> Subject:
>
>
> I'm hoping someone can help with my home-made oxidation
> furnaces. We have run out of factory made Thermo Finnigan
> ones and am not getting reproducibility with the ones I make
> with 1X Cu 1X Ni 1X Pt as recommended by them. The only thing
> I notice is that even tho the wire OD's are 0.1mm for Cu and
> Pt the Nickel is 0.127mm. Could this be a problem?
>
> The 3 wires are twisted together before insertion  in the
> ceramic furnace , oxidised 12 hr 600C and 12 hr 940C- the
> first run is good for standards, but no's get progressively
> lighter. I never had this trouble with 2X Cu and 1X Pt and
> leaks are fine (16mV @ 20:1 split). With thanks
>
> Janet Hope
> Isotope and Organic Geochemistry
> Petroleum and Marine Division
>
> Geoscience Australia
> ABN: 80 091 799 039
>
> Tel: (02) 6249 9487 / 9594
> Fax: (02) 6249 9961
> email:   [log in to unmask]
> web site: http://www.ga.gov.au
>
>