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Cynthia, Greg and Joel,

We saw the same thing as Cyndi describes. We were using almost identical
parameters on a TC/EA DeltaPlusXL; reactor=1450 oC, GC=65 oC, He carrier=15
psi, aux= 17 psi, and we were running primarily pure BaSO4 at the time (~250
ug in silver cups).

In our case, the crystals grew only on the outside of the glassy carbon
tube. The inside surface remained largely unscathed. I also tried 'chipping'
the stuff off as best I could during repacking, but after several hundred
samples the O.D. of the glassy carbon tube reduced by ~4 mm.

The outside of the ceramic tube also "glazed" and cracked near the middle
and eventually broke during removal. In addition to the glazing, the whole
tube also developed a nice bend near the middle (where the glazing
appeared). The glazing showed diagonal striations which I suspected were
imprints from the oven heating coils as the tube bent and eventually touched
the walls of the element itself.

I don't know if the crystalline stuff is weakening the ceramic (looks
suspicious though doesn't it) or if the 1450+ oC and deep temperature cycles
are just wearing the tube (not to mention the oven) out ...

Anyone ever been told why silver cups are necessary? What would happen with
tin cups?

Cheers,
Steve
--------------------------------------------
Stephen W. Taylor
Lab Manager
Isotope Science Laboratory
University of Calgary
Dept. Physics & Astronomy
2500 University Dr. N.W.
Calgary, Alberta,
T2N-1N4
Tel   : 403 220 8268
Fax   : 403 220 7773
email : [log in to unmask]

> -----Original Message-----
> From: Stable Isotope Geochemistry [mailto:[log in to unmask]]On
> Behalf Of Cynthia Kester
> Sent: Wednesday, January 03, 2001 5:59 PM
> To: [log in to unmask]
> Subject: Re: Sulfate oxygen by on-line pyrolysis EA
>
>
> Greg and other sulfate-oxygen people,
>
> We are using a TC/EA set up with a Delta Plus XL for running d18O-SO4 with
> reasonable success.  I am interested if any other users of the same
> equipment have experienced any of the same problems we have
> though.  We have
> less memory problems when we run at higher temperatures (>1400C), but, it
> appears at higher temperatures we begin to damage the ceramic tube and/or
> the glassy carbon tube after a couple hundred samples.  We have not run
> enough other "stuff" to determine if the problem is just with SO4 or if
> water, NO3, etc. might also cause problems regardless of temperature.
> Anyhow, we start to accumulate a yellowish crystalline substance on the
> outside of the glassy carbon tube at approximately the level of the
> combustion.  We scrape this stuff off when we clean out the crucible (~200
> samples).  But eventually it gets thick in spots and then the
> ceramic starts
> to get a clear glaze on the outside at about the level of
> combustion.  We've
> had fine cracks then develop and then larger cracks until the ceramic tube
> ends up breaking.  We have thought that maybe the S is poisoning
> the tube at
> high temperatures??  Has anyone else seen this with or without
> SO4 samples?
> We've mainly run pure BaSO4 precipitates, some barite minerals, jarosite,
> alunite, etc.
>
> As far as how to actually do the analysis, we basically follow the TC/EA
> manual for recommended flow rates, temps, etc. we have the reactor set
> 1400-1450C and the GC at 90C.  We weigh about 0.3 mg BaSO4 into a silver
> cup.
>
> Does anyone have insight on the mystery crystalline-goo?
> thanks,
> Cyndi
>
> **************************************************************
> Cyndi Kester
> Ecologist--Stable Isotope Lab
> U.S. Geological Survey
> Denver Federal Center, Bldg. 21, MS 963
> Denver, Colorado 80225
>
> office:  303-236-0278
> lab:     303-236-7694
> fax:     303-236-4930
> email:   [log in to unmask]
>
>
> ----------
> >From: "Gregory A. Wandless" <[log in to unmask]>
> >To: [log in to unmask]
> >Subject: Sulfate oxygen by on-line pyrolysis EA
> >Date: Wed, Jan 3, 2001, 11:41 AM
> >
>
> > I am looking for references or any other information on doing sulfate
> > oxygen isotopic
> > analysis by on-line pyrolysis EA. Any suggestions?
> >
> > Thanks,
> > GAW
> >
> > --
> > =======================================
> > Gregory A. Wandless
> > Chemist
> > US Geological Survey
> > MS954
> > Reston, VA 20192
> >
> > Email:[log in to unmask]
> > Phone: (703) 648-6189
> > =======================================
>